Institution: Chancellor's Post Doctoral Research Fellow School of the Environment Faculty of Science University of Technology Sydney (UTS) Room: CB04.05.51A PO Box 123, Broadway NSW 2007, Australia
Dr M. Azizur Rahman is mainly interested in the contamination, ecotoxicology, biotransformation and bioremediation of heavy metals in aquatic (freshwater) environment. Other researches of Dr Aziz include i) bioaccumulation, biotransformation and trophic transfer of arsenic in aquatic food chain; ii) bioremediation and phytoremediation of heavy metals using aquatic macrophytes; iii) arsenic biogeochemistry and cycling in freshwater systems. The mechanism of iron acquisition in aquatic organisms under different iron nutrient conditions is also of great interest of Dr Aziz.
Dr Aziz has expertise in aquatic toxicology of environmental contaminants such as heavy metals, pesticides, insecticides. Dr Aziz also works on speciation studies of arsenic in freshwater systems in relation to the eutrophication and seasonal variation, and pollution studies with a reflection of remediation/restoration of contaminated aquatic systems. Outcomes of Dr Aziz’s researches contribute to the advancement of phytoremediation technology, impacts and health risks assessment of arsenic in freshwater systems.
Dr Aziz completed hi PhD in Environmental and Analytical Chemistry from Kanazawa University (Japan) in 2008. In PhD studies, Dr Aziz investigated arsenic uptake in aquatic macrophytes and their potential application in phytoremediation. Dr Aziz also studied arsenic speciation in freshwater systems in relation to the eutrophication and seasonal variation. Outcomes of his researches contribute to the understanding and advancement of phytoremediation technology, the roles of bioactivities of aquatic organisms on arsenic speciation in freshwater systems, and the impacts and health risks assessment of arsenic in freshwater systems and human health.
Dr Aziz’s outstanding achievements in PhD research was honoured with prestigious "President Award" of Kanazawa University as the best student of the year. Dr Aziz was also awarded the highly competitive JSPS (Japan Society for the Promotion of Science) postdoctoral research fellowship in 2008. In 2010, I received the Chancellor's postdoctoral research fellowship, University of Technology, Sydney (UTS).
Presently, Dr Aziz is working as a Chancellor's postdoctoral research fellow in the Centre of Environmental Sustainability (CEnS) at UTS. Presently, Dr Aziz’s current research is focused on arsenic bioavailability, biomagnification, detoxification in aquatic systems, and ecotoxicological validation of remediation technologies. In this project, Dr Aziz will investigate i) bioavailability and toxicity of arsenic species freshwater phytoplankton and macrophyte, ii) biotransformation and detoxification of inorganic arsenic species by freshwater phytoplankton, and iii) toxicological validation of arsenic remediation technologies.
Dr Aziz has been collaborating in a number of research projects with famous researchers around the world, including Prof. Hiroshi Hasegawa (Kanazawa University, Japan), Prof. Ravi Naidu (University of South Australia, Australia), Prof. Bill Maher (University of Canberra, Australia), Prof. M. Mahfuzur Rahman (Jahangirnagar University, Bangladesh), Prof. Saravanamuth Vigneswaran (University of Technology, Sydney, Australia), Dr Christel Hassler (University of Technology, Sydney, Australia), many others.
Dr Aziz is author/co-author of a significant number of book chapters, journal articles, conference papers. His professional and personal interests are closely related.
Abstract: Arsenic exists in a variety of chemical forms, and microbial metabolism results in the occurrence of thermodynamically unstable arsenite (AsIII) and methylarsenic compounds in freshwaters (rivers and lakes). The inorganic forms (AsV and AsIII) and the methylated forms (methylarsonic acid; MMAAV and dimethylarsinic acid; DMAAV) are the main species of As in freshwaters while the bulk of the total dissolved As is inorganic species. Although the predominant forms of methylarsenic compounds are consistently DMAAV followed by MMAAV, the DMAAIII and MMAAIII species have also been found in freshwaters. Several observations have revealed that phytoplankton activities are responsible for the seasonal variations of methylarsenic compounds in freshwaters. Although it was unclear if the occurrences of methylarsenic compounds were from the breakdown of larger molecules or the end-products of phytoplankton biosynthesis, recent studies have revealed that less toxic As–glutathione complexes are intermediates in the biosynthesis of organoarsenic compounds by phytoplankton. Recent studies have also revealed that eutrophication plays an important role in the production, distribution, and cycling of methylarsenic compounds in freshwaters. In this review, the recent reports on the influence of eutrophication on distribution, speciation, and bioaccumulation in freshwaters are discussed.
Abstract: Precious corals have been commercially exploited for many centuries around the world. The skeletons of these corals consist of calcium carbonate, and have been used as amulets or gemstones since ancient times. Different Corallium species of Coralidae family (e.g., Corallium rubrum, Corallium elatus, Corallium konojoi, and Paracorellium japonicum) were collected from different locations of the Mediterranean Sea (off Italy) and Pacific Ocean (off Japan and off Midway Island), and trace elements in their skeletons were analyzed. Results show that trace element concentrations in the skeletons of Corallium spp. were attributable to their habitat and origin. In particular, Mg/Ca and Ba/Ca ratios in the skeletons of Corallium spp. from the Mediterranean Sea and Japanese and the Midway Islands’ waters were found to be habitat-specific. This study also reveals that trace elements in the skeletons can be used as ecological indicator of the coral’s origin, and are expected to play an important part in the cultural study and sustainable management of precious corals. Findings of this study will also be of great relevance to the coral industry to authenticate and identify the habitat and origin of the corals.
Abstract: Straighthead is a physiological disorder of rice (Oryza sativa L.) that results in sterile florets with distorted lemma and palea, and the panicles or heads may not form at all in extreme cases. Heads remain upright at maturity, hence the name ‘straighthead’. The diseased panicles may not emerge from the flag leaf sheath when the disease is severe. Straighthead disease in rice results in poorly developed panicles and significant yield loss. Although other soil physicochemical factors involved, arsenic contamination in soil has also been reported to be closely associated with straighthead of rice. Monosodium methanearsonate has been a popular herbicide in cotton production in the USA, which has shown to cause injuries in rice that are similar to straighthead. Since toxicity of inorganic arsenic (iAs) is higher than other forms of arsenic, it may produce a more severe straighthead disorder in rice. The use of iAs-rich groundwater for irrigation, and the increase of iAs concentrations in agricultural soil in arsenic epidemic South and South-East Asia may cause a high incidence of straighthead in rice, resulting in a threat tosustainable rice production in this region.
Abstract: Arsenic (As) contamination is an important environmental consequence in some parts of salinity-affected South (S) and South-East (SE) Asia. In this study, we investigated the individual and combined phytotoxicity of arsenic (As) [arsenate; As(V)] and salinity (NaCl) on early seedling growth (ESG) of saline-tolerant and non-tolerant rice varieties. Germination percentage (GP), germination speed (GS) and vigor index (VI) of both saline-tolerant and non-tolerant rice varieties decreased significantly (p > 0.01) with increasing As(V) and NaCl concentrations. The highest GP (91%) was observed for saline non-tolerant BRRI dhan28 and BRRI dhan49, while the lowest (62%) was for saline-tolerant BRRI dhan47. The ESG parameters, such as weights and relative lengths of plumule and radicle, also decreased significantly (p < 0.01) with increasing As(V) and NaCl concentrations. Relative radicle length was more affected than plumule length by As(V) and NaCl. Although VI of saline-tolerant and non-tolerant rice seedlings showed significant variation (p < 0.05), weights and lengths of plumule and radicle of different rice varieties did not show significant variation for As(V) and NaCl treatments. Results reveal that the combined phytotoxicity of As(V) and NaCl on rice seed germination and ESG are greater than their individual toxicities, and some saline-tolerant rice varieties are more resistant to the combined phytotoxicity of As(V) and NaCl than the saline non-tolerant varieties.
Abstract: The occurrence, distribution, speciation, and biotransformation of arsenic in aquatic environment (marine- and freshwater) have been studied extensively by several research groups during last couple of decades. However, most of those studies have been conducted in marine waters, and the results are available in a number of reviews. Speciation, bioaccumulation, and biotransformation of arsenic in freshwaters have been studied in recent years. Although inorganic arsenic (iAs) species dominates in both marine- and freshwaters, it is biotransformed to methyl- and organoarsenic species by aquatic organisms. Phytoplankton is considered as a major food source for the organisms of higher trophic levels in the aquatic food chain, and this autotrophic organism plays important role in biotransformation and distribution of arsenic species in the aquatic environment. Bioaccumulation and biotransformation of arsenic by phytoplankton, and trophic transfer of arsenic in marine- and freshwater food chains have been important concerns because of possible human health effects of the toxic metalloid from dietary intake. To-date, most of the studies on arsenic biotransformation, speciation, and trophic transfer have focused on marine environments; little is known about these processes in freshwater systems. This article has been reviewed the bioaccumulation, biotransformation, and trophic transfer of arsenic in marine- and freshwater food chain.
Abstract: Arsenate (As(V)) transport into plant cells has been well studied. A study on rice (Oryza sativa L.) showed that arsenite is transported across the plasma membrane via glycerol transporting channels. Previous studies reported that the dimethylarsinic acid (DMAA) and monomethylarsonic acid (MMAA) uptake in duckweed (Spirodela polyrhiza L.) differed from that of As(V), and was unaffected by phosphate (H2PO4). This article reports the transport mechanisms of DMAA and MMAA in rice roots. Linear regression analysis showed that the DMAA and MMAA uptake in rice roots increased significantly (p ≤ 0.0002 and ≤0.0001 for DMAA and MMAA, respectively) with the increase of exposure time. Concentration-dependent influx of DMAA and MMAA showed that the uptake data were well described by Michaelis–Menten kinetics. The MMAA influx was higher than that of DMAA. The DMAA and MMAA uptake in rice roots were decreased significantly (p ≤ 0.0001 and ≤0.0077 for DMAA and MMAA, respectively) with the increase of glycerol concentration indicating that DMAA and MMAA were transported into rice roots using the same mechanisms of glycerol. Glycerol is transported into plant cells by aquaporins, and DMAA and MMAA are transported in a dose-dependent manner of glycerol which reveals that DMAA and MMAA are transported into rice roots through glycerol transporting channels. The DMAA and MMAA concentration in the solution did not affect the inhibition of their uptake rate by glycerol.
Abstract: The concern over ensuing fresh water scarcity has forced the developing countries to delve for alternative water resources. In this study we examined the potential of stagnant surface water bodies (SSWBs) as alternative fresh water resources in the densely populated Chittagong metropolitan area (CMPA) of Bangladesh – where there is an acute shortage of urban fresh water supply. Water samples, collected at one month intervals for a period of one year from 12 stations distributed over the whole metropolis. Samples were analyzed for pH, water temperature (WTemp), turbidity, electrical conductivity (EC), total dissolved solids, total solids, total hardness, dissolved oxygen (DO), chloride, orthophosphates, ammonia, total coliforms (TC) and trace metal (Cd, Cr, Cu, Pb, As and Fe) concentrations. Based on these parameters different types of water quality indices (WQIs) were deduced. WQIs showed most of CMPA-SSWBs as good or medium quality water bodies while none were categorized as bad. Moreover, it was observed that the minimal water quality index (WQIm), computed using five parameters: WTemp, pH, DO, EC and turbidity gave reliable estimate of water quality. The WQIm gave similar results in 72% of the cases compared with other WQIs which were based on larger set of parameters. Based on our finding, we suggest the wider use WQIm in developing countries for assessing health of SSWBs as it will minimize the analytical cost to overcome the budget constraints involved in this kind of evaluations. It was observed that except turbidity and TC content, all other quality parameters fluctuated within the limit of World Health Organization suggested standards for drinking water. From our findings we concluded that if the turbidity and TC content of water from SSWBs in CMPA are taken care of, they will become good candidates as alternative water resources all round the year.
Abstract: In this study, the effects of chelating ligands on iron movement in growth Medium, iron bioavailability, and growth of radish sprouts (Raphanus sativus) were investigated. Iron is an important nutrient for plant growth, yet the insoluble state of iron hydroxides in alkaline conditions decreases its bioavailability. Iron chelates increase iron uptake and have been used in agriculture to correct iron chlorosis. While previous studies have reported the effects of chelating ligands on iron solubility and bioavailability, the present study elucidates the pattern of iron movement by chelating ligands in plant growth Medium. The apparent mobility of iron in growth Medium was calculated using a ‘4-box’ model. Ethylenediaminedisuccinic acid (EDDS) and hydroxy-iminodisuccinic acid (HIDS) produced the highest apparent mobility of iron from the bottom layer of the medium (initially 10-4 M Fe(III)) to the upper layer (no iron), followed by glutamicdiacetic acid (GLDA), ethylenediaminetetraacetic acid (EDTA), methylglycinediacetic acid (MGDA), and iminodisuccinic acid (IDS). Iron movement in the growth Medium was influenced by the chelating ligand species, pH, and ligand exposure time. The iron uptake and growth of radish sprouts were related to the iron mobility produced by the chelating ligands. These results suggest that, in alkaline media, chelating ligands dissolve the hardly soluble iron hydroxide species, thus increasing iron mobility, iron uptake, and plant growth. HIDS, which is biodegradable, was one of the most effective ligands studied; therefore, this compound would be a good alternative to other environmentally persistent chelating ligands.
Abstract: Phytoremediation, a plant based green technology, has received increasing attention after the discovery of hyperaccumulating plants which are able to accumulate, translocate, and concentrate high amount of certain toxic elements in their above-ground/harvestable parts. Phytoremediation includes several processes namely, phytoextraction, phytodegradation, rhizofiltration, phytostabilization and phytovolatilization. Both terrestrial and aquatic plants have been tested to remediate contaminated soils and waters, respectively. A number of aquatic plant species have been investigated for the remediation of toxic contaminants such as As, Zn, Cd, Cu, Pb, Cr, Hg, etc. Arsenic, one of the deadly toxic elements, is widely distributed in the aquatic systems as a result of mineral dissolution from volcanic or sedimentary rocks as well as from the dilution of geothermal waters. In addition, the agricultural and industrial effluent discharges are also considered for arsenic contamination in natural waters. Some aquatic plants have been reported to accumulate high level of arsenic from contaminated water. Water hyacinth (Eichhornia crassipes), duckweeds (Lemna gibba, Lemna minor, Spirodela polyrhiza), water spinach (Ipomoea aquatica), water ferns (Azolla caroliniana, Azolla filiculoides, and Azolla pinnata), water cabbage (Pistia stratiotes), hydrilla (Hydrilla verticillata) and watercress (Lepidium sativum) have been studied to investigate their arsenic uptake ability and mechanisms, and to evaluate their potential in phytoremediation technology. It has been suggested that the aquatic macrophytes would be potential for arsenic phytoremediation, and this paper reviews up to date knowledge on arsenic phytoremediation by common aquatic macrophytes.
Abstract: This study was conducted to investigate the effect of external iron status and arsenic species on chelant-enhanced iron bioavailability and arsenic uptake. Rice seedlings (Oryza sativa L.) were used as model plant, and were grown in artificially contaminated sandy soils irrigated with Murashige and Skoog (MS) culture solution. Arsenate uptake in roots shoots of rice seedlings were affected significantly (p > 0.05) while dimethylarsinic acid (DMAA) was not by the additional iron and chelating ligand treatments. Regardless of iron concentrations in the soil solution, HIDS increased arsenic uptake for roots more than EDTA and EDDS. Chelating ligands and arsenic species also influenced iron uptake in rice roots. Irrespective of arsenic species, HIDS was found to be more effective in the increase of iron bioavailability and uptake in rice roots compared to other chelants. There was a significant positive correlation (r = 0.78, p < 0.05) between arsenate and iron concentrations in the roots of rice seedlings grown with or without additional iron indicating that arsenate inhibit iron uptake. In contrast, there was no correlation between iron and DMAA uptake in roots. Poor correlation between iron and arsenic in shoots indicated that iron uptake in shoots was neither affected by additional iron nor by arsenic species. Compared to the control, chelating ligands increased iron uptake in shoots of rice seedlings significantly (p < 0.05). Regardless of additional iron and arsenic species, iron uptake in rice shoots did not differed among EDTA, EDDS, and HIDS treatments.
Abstract: Aquatic arsenic cycles mainly depend on microbial activities that change the arsenic chemical forms and influence human health and organism activities. The microbial aggregates degrading organic matter are significantly related to the turnover between inorganic arsenic and organoarsenic compounds. We investigated the effects of microbial aggregates on organoarsenic mineralization in Lake Kahokugata using lake water samples spiked with dimethylarsinic acid (DMA). The lake water samples converted 1 μmol L−1 of DMA to inorganic arsenic for 28 d only under anaerobic and dark conditions in the presence of microbial activities. During the DMA mineralization process, organic aggregates >5.0 μm with bacterial colonization increased the densities. When the organic aggregates >5.0 μm were eliminated from the lake water samples using filters, the degradation activities were reduced. DMA in the lake water would be mineralized by the microbial aggregates under anaerobic and dark conditions. Moreover, DMA amendment enhanced the degradation activities in the lake water samples, which mineralized 50 μmol L−1 of DMA. The DMA-amended aggregates >5.0 μm completely degraded 1 μmol L−1 of DMA with a shorter incubation time of 7 d. The supplement of KNO3 and NaHCO3 to lake water samples also shortened the DMA-degradation period. Presumably, the bacterial aggregates involved in the chemical heterotrophic process would contribute to the DMA-biodegradation process in Lake Kahokugata, which is induced by the DMA amendment.
Abstract: Rice is the staple food for the people of arsenic endemic South (S) and South-East (SE) Asian countries. In this region, arsenic contaminated groundwater has been used not only for drinking and cooking purposes but also for rice cultivation during dry season. Irrigation of arsenic-contaminated groundwater for rice cultivation has resulted high deposition of arsenic in topsoil and uptake in rice grain posing a serious threat to the sustainable agriculture in this region. In addition, cooking rice with arsenic-contaminated water also increases arsenic burden in cooked rice. Inorganic arsenic is the main species of S and SE Asian rice (80 to 91% of the total arsenic), and the concentration of this toxic species is increased in cooked rice from inorganic arsenic-rich cooking water. The people of Bangladesh and West Bengal (India), the arsenic hot spots in the world, eat an average of 450 g rice a day. Therefore, in addition to drinking water, dietary intake of arsenic from rice is supposed to be another potential source of exposure, and to be a new disaster for the population of S and SE Asian countries. Arsenic speciation in raw and cooked rice, its bioavailability and the possible health hazard of inorganic arsenic in rice for the population of S and SE Asia have been discussed in this review.
Abstract: The effect of chelating ligands on iron (Fe) uptake and growth of radish (Raphanus sativus L.) was investigated. The ethylenediaminetetraacetic acid (EDTA) increased 55Fe uptake in roots of radish though its subsequent translocation from roots to shoots and leaves did not increase. About 70%—80% of the total 55Fe was distributed in the roots while about 5%—15% and 11%—17% were in shoots and leaves, respectively. The EDTA increased iron uptake into the roots of radish, but not in the above ground parts of the plant. The growth of radish (Raphanus sativus L.) decreased drastically in alkaline condition (pH > 9), even though the concentration of iron was sufficient in the growth medium. The growth of radish was enhanced successfully by the addition of hydroxyiminodisuccinic acid (HIDS) and EDTA. This might be because HIDS and EDTA solubilize iron from its precipitation with hydroxides at higher pH, and increase iron bioavailability. The influence of EDTA and HIDS on radish growth was comparable. Increase of radish growth by ethylenediaminedisuccinic acid (EDDS) and methylglicinediacetic acid (MGDA) was less than those by EDTA and HIDS. Considering the reproducibility of the radish growth (biomass production) at pH 10, HIDS is supposed to be more effective compared to EDTA.
Abstract: In this study, the influence of eutrophication on arsenic speciation in lake waters was investigated. Surface water samples (n = 1–10) were collected from 18 lakes in Japan during July 2007 and February 2008. The lakes were classified into mesotrophic (7 lakes) and eutrophic (11 lakes) based on the total phosphate (T-P) and chlorophyll-a (Chl-a) concentrations in water column. Inorganic, methylated and ultraviolet-labile fractions of arsenic species were determined by combining hydride generation atomic absorption spectrometry with ultraviolet irradiation. Organoarsenicals (mainly methylated and ultraviolet-labile fractions) comprised 30–60% of the total arsenic in most lakes during summer. On the other hand, inorganic arsenic species (As(III + V)) dominates (about 60–85%) during winter. The occurrence of ultraviolet-labile fractions of arsenic was higher in eutrophic lakes than those in mesotrophic lakes in both seasons. The concentration of dimethyl arsenic (DMAA) was high in eutrophic lakes during winter; and in mesotrophic lakes during summer. The results suggest that the conversion of As(III + V) to more complicated organoarsenicals occurred frequently in eutrophic lakes compared to that in mesotrophic lakes, which is thought to be the influence of biological activity in the water column. The distribution of arsenic species were well correlated with phosphate concentrations than those of Chl-a. This might be due to the competitive uptake of As(V) and phosphate by phytoplankton. The organoarsenicals (OrgAs)/As(V) ratio was higher at low phosphate concentration indicating that conversion of As(V) to OrgAs species was more active in phosphate-exhausted lakes with high phytoplankton density.
Abstract: Effects of eutrophication on arsenic speciation were studied in eutrophic Lake Kiba and mesotrophic Lake Biwa, Japan. By combining hydride generation atomic absorption spectrometry with ultraviolet irradiation, inorganic, methyl and ultraviolet-labile fractions of arsenic were determined. In both Lakes, inorganic species (As(V + III)) dominated over other forms of arsenic all the year round. Most of methylarsenic fraction was dimethylarsinic acid (DMAA), and the concentration of monomethylarsonic acid (MMAA) was below the detection limit. Measurements of size-fractioned arsenic concentrations in water column indicate that most of the DMAA was distributed in truly dissolved fraction (< 10 kDa), while ultraviolet-labile fractions were distributed in particulate (> 0.45 µm) and colloidal (10 kDa–0.45 µm) fractions. Arsenic speciation in eutrophic Lake Kiba fluctuated greatly with season. The ultraviolet-labile fractions were observed with the increase of DMAA from May to October, and they disappeared with the decrease of DMAA in January. In mesotrophic Lake Biwa, the ultraviolet-labile fractions of arsenic were not influenced as much as those in eutrophic Lake Kiba. On the other hand DMAA concentration was higher in Lake Biwa compared to that in Lake Kiba. The results suggest that the biosynthesis of complex organoarsenicals was enhanced by eutrophication, and the arsenic speciation would be influenced by the balance of biological processes in natural waters.
Abstract: Moringa oleifera Lam. seed oil of the indigenous-cultivar of Bangladesh was extracted using n-hexane (H), light petroleum ether (b.p. 40–60C) (LPE) and chloroform/methanol (50:50, v/v) mixture (CM). The oil content ranged from 37.50% (H) to 40.20% (CM). The moisture, protein, ash and crude fiber contents of seed residues, and the density, refractive index, color, acidity, saponification value, iodine value, unsaponifiable matter content, oxidative state, sterols, tocopherols and fatty acid composition of the extracted oil were determined. The oil contained a high amount of oleic acid (C18:1) of up to 74.41% and a high ratio of monounsaturated to saturated fatty acids with moderate oxidative stability. The results of the present study were compared with those reported in literature for different regional habitats, and species variants.
Abstract: The microbial activities in aquatic environments significantly influence arsenic cycles such as the turnover between inorganic arsenic and organoarsenic compounds. In Lake Kahokugata, inorganic arsenic was detected at concentrations ranging from 2.8 to 23 nM in all seasons, while the concentrations of dimethylarsinic acid (DMA) produced by microorganisms such as phytoplankton changed seasonally and showed a peak in winter. The changes in the concentrations of methylarsenic species did not correlate with the changes in phytoplankton abundance (chlorophyll a contents), suggesting that DMA-degradation is related to this inconsistency. DMA (1 μM) added into the lake water was converted to inorganic arsenic at 20 °C only under anaerobic and dark conditions, while DMA degradation was diminished under aerobic or light conditions. Moreover, DMA added to the lake water samples collected through four seasons was degraded at the same rates under anaerobic and dark conditions at 20 °C. However, at 30 °C, 1 μM of DMA in the summer lake water samples was rapidly degraded in 7 and 21 d. In contrast, DMA degradation was diminished in the winter lake water samples at 4 °C of incubation. Presumably, DMA-biodegradation activities are mainly controlled by changes in the water temperature in Lake Kahokugata, where the arsenic concentrations change seasonally.
Abstract: The influence of biodegradable chelating ligands on arsenic and iron uptake by hydroponically grown rice seedlings (Oryza sativa L.) was investigated. Even though the growth solution contained sufficient Fe, the growth of rice seedlings gradually decreased up to 76% with the increase of pH of the solution from 7 to 11. Iron forms insoluble ferric hydroxide complexes at neutral or alkaline pH in oxic condition. Chelating ligands produce soluble ‘Fe–ligand complex’ which assist Fe uptake in plants. The biodegradable chelating ligand hydroxyiminodisuccinic acid (HIDS) was more efficient then those of ethylenediaminetetraacetic acid (EDTA), ethylenediaminedisuccinic acid (EDDS), and iminodisuccinic acid (IDS) in the increase of Fe uptake and growth of rice seedling. A total of 79 ± 20, 87 ± 6, 116 ± 15, and 63 ± 18 mg dry biomass of rice seedlings were produced with the addition of 0.5 mM of EDDS, EDTA, HIDS, and IDS in the nutrient solution, respectively. The Fe concentrations in rice tissues were 117 ± 15, 82 ± 8, 167 ± 25, and 118 ± 22 μmol g−1 dry weights when 0.25 mM of EDDS, EDTA, HIDS, and IDS were added to the nutrient solution, respectively. Most of the Fe accumulated in rice tissues was stored in roots after the addition of chelating ligands in the solution. The results indicate that the HIDS would be a potential alternative to environmentally persistent EDTA for the increase of Fe uptake and plant growth. The HIDS also increased As uptake in rice root though its translocation from root to shoot was not augmented. This study reports HIDS for the first time as a promising chelating ligand for the enhancement of Fe bioavailability and As phytoextraction.
Abstract: The influence of ethylenediaminetetraacetic acid (EDTA) and chemical species on arsenic accumulation in aquatic floating macrophyte Spirodela polyrhiza L. (Duckweed) was investigated. The uptake of inorganic arsenic species (arsenate; As(V) and arsenite; As(III)) into the plant tissue and their adsorption on iron plaque of plant surfaces were significantly (p < 0.05) higher then those of organic species (monomethylarsonic acid (MMAA) and dimethylarsinic acid (DMAA)). The addition of EDTA to the culture media increased the uptake of As(V) and As(III) into the plant tissue though the MMAA and DMAA uptake were not affected. About 4-6% of the inorganic arsenic species were desorbed or mobilized from iron plaque by EDTA. Desorption of organic arsenic species was not affected by EDTA addition because the co-precipitation occurs only with inorganic species. Phosphate uptake was not affected by EDTA though its concentration in citrate-bicarbonate-EDTA (CBE)-extract was much higher than that of plant tissue. Iron uptake into the plant increased significantly (p > 0.05) by EDTA addition to the culture media while its concentration in CBE-extract decreased significantly (p < 0.05). The As(inorganic)/Fe ratios in plant were higher than those of CBE-extract which indicate the increased uptake of these arsenic species into the plant relative to the iron. The lower As(organic)/Fe ratios in plant and on CBE-extract suggest the reduction of accumulation of these arsenic species relative to the iron.
Abstract: Although human exposure to arsenic is thought to be caused mainly through arsenic-contaminated underground drinking water, the use of this water for irrigation enhances the possibility of arsenic uptake into crop plants. Rice is the staple food grain in Bangladesh. Arsenic content in straw, grain and husk of rice is especially important since paddy fields are extensively irrigated with underground water having high level of arsenic concentration. However, straw and husk are widely used as cattle feed. Arsenic concentration in rice grain was 0.570.02 mgkg1 with the highest concentrations being in grains grown on soil treated with 40mg As kg1 soil. With the average rice consumption between 400 and 650 g/day by typical adults in the arsenic-affected areas of Bangladesh, the intake of arsenic through rice stood at 0.20–0.35 mg/day. With a daily consumption of 4 L drinking water, arsenic intake through drinking water stands at 0.2 mg/day. Moreover, when the rice plant was grown in 60 mg of As kg1 soil, arsenic concentrations in rice straw were 20.670.52 at panicle initiation stage and 23.770.44 at maturity stage, whereas it was 1.670.20 mgkg1 in husk. Cattle drink a considerable amount of water. So alike human beings, arsenic gets deposited into cattle body through rice straw and husk as well as from drinking water which in turn finds a route into the human body. Arsenic intake in human body from rice and cattle could be potentially important and it exists in addition to that from drinking water. Therefore, a hypothesis has been put forward elucidating the possible food chain pathways through which arsenic may enter into human body.
Abstract: Although the main source of arsenic to human body is ground water, the use of arsenic contaminated ground water for irrigation gives rise to the question whether arsenic uptake in crop plants could also be another potential pathway of human exposure to arsenic. Arsenic content in straw, grain and husk of rice is especially important as rice is the staple food for man and straw and husk have been used as cattle feed. It was estimated that the daily intake of arsenic in human body from rice (containing 0.40 mg As/kg, the highest concentration of arsenic found in the present experiment in treatment containing 40 mg As/kg soil) is 0.20 to 0.32 mg/day (as the average consumption of rice by the people above five years old is between 400 and 650 gm/day) whereas it is 0.20 mg/day from drinking water (as the recommended safe level arsenic in drinking water is 0.05 mg As/l for Bangladesh and the average intake of water by an adult is about four litres). This finding suggests that arsenic intake in human body through rice could be a potential pathway in addition to drinking water. Therefore, a hypothesis have been put forward that the human beings have not been suffering from arsenicosis only from drinking water but also from "Plant-Animal-Man" and some other food chain pathways.
Abstract: In the present study, we investigated the arsenic uptake and biosorption by water fern (Salvinia natans L.) in relation to the phosphate concentrations in culture solution. The plants were grown for 5 days in aqueous culture solution and harvested. Compared to the control treatment, the plants accumulated highest amount of arsenate from phosphate deficient solutions and dimethylarsinic acid (DMAA) from phosphate-rich solutions. Both arsenate and DMAA accumulations in Salvinia natans L. increased significantly (p < 0.05) with the increase of their concentrations in the culture solutions. From culture solution having 100 µM of phosphate and 4.0 µM of arsenate and DMAA, Salvinia natans L. accumulated 0.15±0.02 and 0.04±0.00 µmol g-1 dry weight of arsenate and DMAA, respectively. In contrast, the plants accumulated 0.24±0.06 and 0.03 ±0.00 µmol g-1 dry weight of arsenate and DMAA from solution having 0.0 µM (control) of phosphate and 4.0 µM of arsenate and DMAA, respectively. The results indicate that increasing phosphate concentration in culture solutions decreases the accumulation of arsenate into the plant. This might be because of the suppression of arsenate by phosphate. Pearson correlation analysis showed that arsenate and phosphate concentrations in plant tissues were correlated significantly (r = -0.662; p < 0.05) though DMAA and phosphate concentrations were not correlated significantly (r = -0.076; p > 0.05). Thus, the arsenate uptake into the water fern (Salvinia natans L.) may occur through the phosphate uptake pathway. However, highly significant correlation was observed between arsenate and iron concentrations in the plant tissues (r = 0.662; p < 0.05) though the correlation between iron and DMAA was not significant. The results indicate the biosorption of arsenate on Fe-plaques of the plant surfaces which is also known as physico-chemical adsorption. The study demonstrates that the DMAA uptake mechanisms into the water fern (Salvinia natans L.) are deferent from that of arsenate. Between 32-62% of arsenate could be removed for a plant dry mass of 0.15 g within 5 days. Thus, Salvinia natans L. could be a good option for phytofiltration of arsenic.
Abstract: Straighthead disease is a physiological disorder of rice (Oryza sativa L.) characterized by sterility of the florates/spikelets leading to reduced grain yield. Though the exact cause of straighthead is unknown, a glass house experiment was conducted with rice (Oryza sativa L.) to investigate the effect of inorganic arsenic on straighthead disease. BRRI dhan 29, a popular Bangladeshi rice strain, was grown in soils spiked with arsenic (prepared from sodium arsenate, Na2HAsO4•7H2O) at the rate of 10, 20, 30, 40, 50, 60, 70, 80 and 90 mg of As kg-1 and one control treatment was also run to compare the results. Although there may be some other soil physico-chemical factors involved, arsenic concentration was found to be closely associated with straighthead of rice. With the increase of soil arsenic concentration, the severity of straighthead increased significantly. Up to the 50 mg of As kg-1 soil treatments, the severity of straighthead incidences were not prevalent. Straighthead resulted in sterile florets with distorted lemma and palea, reduced plant height, tillering, panicle length and grain yield. Straighthead caused approximately 17-100% sterile florates/spikelets formation and about 16-100% loss of grain yield. Straighthead also causes the reduction of panicle formation and panicle length significantly (p < 0.01). In the present study, panicle formation was found to be reduced by 21-95% by straighthead.
Abstract: Ferric (oxyhydro-)oxides (FeOx) precipitate in the rhizosphere at neutral or alkaline pH and are adsorbed on the plant root surfaces. Consequently, the higher binding affinity of arsenate to FeOx and the low iron phytoavailability of the precipitated FeOx make the phytoremediation of arsenic difficult. In the present study, the influence of chelating ligands on arsenic and iron uptake by hydroponically grown rice seedlings (Oryza sativa L.) was investigated. When chelating ligands were not treated to the growth medium, about 63 and 71% of the total arsenic and iron were distributed in the root extract (outer root surfaces) of rice, respectively. On the other hand, ethylenediaminetetraacetic acid (EDTA), ethylenediaminedisuccinic acid (EDDS) and hydroxyiminodisuccinic acid (HIDS) desorbed a significant amount of arsenic from FeOx of the outer root surfaces. Therefore, the uptake of arsenic and iron into the roots and their subsequent translocation to the shoots of the rice seedlings increased significantly. The order of increasing arsenic uptake by chelating ligands was HIDS > EDTA > EDDS. Methylglycinediacetic acid (MGDA) and iminodisuccinic acid (IDS) might not be effective in arsenic solubilization from FeOx. The results suggest that EDDS and HIDS would be a good and environmentally safe choice to accelerate arsenic phytoavailability in the phytoremediation process because of their biodegradability and would be a competent alternative to the widely used non-biodegradable and environmentally persistent EDTA.
Abstract: The uptake of arsenate (As(V)) and dimethylarsinic acid (DMAA) by aquatic macrophyte Spirodela polyrhiza L. was investigated to determine the influence of arsenic interaction with PO43− and Fe ions. Plants were grown hydroponically on standard Murashige and Skoog (MS) culture solutions. Arsenic concentrations in Fe-oxide (Fe-plaque) on plant surfaces were determined by citrate–bicarbonate–ethylenediaminetetraacetic acid (CBE) technique. S. polyrhiza L. accumulated 51-fold arsenic from arsenate solution compared to that from DMAA solution with initial concentrations of 4.0 and 0.02 μM of arsenic and phosphate, respectively. The arsenate uptake was negatively (p < 0.001) correlated with phosphate uptake and positively (p < 0.05) correlated with iron uptake. About 56% of the total arsenic was accumulated into the plant tissues while 44% was adsorbed on Fe-plaque (CBE-extract), when the plants were grown on arsenate solution. The DMAA uptake into the plant was neither affected by the phosphate concentrations nor correlated (p > 0.05) with iron accumulation. The results suggest that adsorption of arsenate on Fe-plaque of the surface of S. polyrhiza L. contributes to the arsenic uptake significantly. Thus, arsenate uptake in S. polyrhiza L. occurred through the phosphate uptake pathway and by physico-chemical adsorption on Fe-plaques of plant surfaces as well. The S. polyrhiza L. uses different mechanisms for DMAA uptake.
Abstract: A glass house study was conducted to investigate the accumulation of arsenic in tissues of five widely cultivated rice (Oryza sativa L.) varieties of Bangladesh namely BRRI dhan 28, BRRI dhan 29,
BRRI dhan 35, BRRI dhan 36, BRRI hybrid dhan 1. Arsenic concentrations were measured in straw, husk
and brown and polish rice grain to see the differential accumulation of arsenic among the rice varieties. The results showed that the concentrations of arsenic in different parts of all rice varieties increased significantly (p<0.05) with the increase of its concentrations in soil. The rice varieties did not showed significant differences in arsenic accumulation in straw, husk, brown and polish grain when the concentrations of arsenic in soil was low. However, at higher concentrations of arsenic in soil, different rice varieties showed significant differences in the accumulations of arsenic in straw, husk and grain. Significantly higher concentrations of arsenic in straw and husk of rice were observed in BRRI hybrid dhan 1 compared to those of other verities. The BRRI dhan 28 and 35 concentrated significantly higher amount of arsenic in brown and polish rice grain compared to those of other rice varieties. The results imply that arsenic translocation from root to shoot (straw) and husk was higher in hybrid variety compared to those of nonhybrid varieties. Arsenic concentrations in brown and polish rice grain of five rice varieties were found to follow the trend: BRRI dhan 28 > BRRI dhan 35 > BRRI dhan 36 > BRRI dhan 29 > BRRI hybrid dhan 1. The order of arsenic contents in tissues of rice was: straw > husk > brown rice grain > polish rice grain.
Abstract: A study was conducted to investigate the accumulation and distribution of arsenic in different fractions of rice grain (Oryza sativa L.) collected from arsenic affected area of Bangladesh. The agricultural soil of study area has become highly contaminated with arsenic due to the excessive use of arsenic-rich underground water (0.070 ± 0.006 mg l1, n = 6) for irrigation. Arsenic content in tissues of rice plant
and in fractions of rice grain of two widely cultivated rice varieties, namely BRRI dhan28 and BRRI hybrid dhan1, were determined. Regardless of rice varieties, arsenic content was about 28- and 75-folds higher in root than that of shoot and raw rice grain, respectively. In fractions of parboiled and non-parboiled rice grain of both varieties, the order of arsenic concentrations was; rice hull > branpolish > brown rice > raw rice > polish rice. Arsenic content was higher in non-parboiled rice grain than that of parboiled rice. Arsenic concentrations in parboiled and non-parboiled brown rice of BRRI dhan28 were 0.8 ± 0.1 and 0.5 ± 0.0 mg kg1 dry weight, respectively while those of BRRI hybrid dhan1 were 0.8 ± 0.2 and 0.6 ± 0.2 mg kg1 dry weight, respectively. However, parboiled and nonparboiled polish rice grain of BRRI dhan28 contained 0.4 ± 0.0 and 0.3 ± 0.1 mg kg1 dry weight of arsenic, respectively while those of BRRI hybrid dhan1 contained 0.43 ± 0.01 and 0.5 ± 0.0 mg kg1 dry weight, respectively. Both polish and brown rice are readily cooked for human consumption. The concentration of arsenic found in the present study is much lower than the permissible limit in rice (1.0 mg kg1) according to WHO recommendation. Thus, rice grown in soils of Bangladesh contaminated with arsenic of 14.5 ± 0.1 mg kg1 could be considered safe for human consumption.
Abstract: A glass house experiment was conducted to investigate the effect of soil arsenic on photosynthetic pigments, chlorophyll-a and -b, and their correlations with rice yield and growth. The experiment was designed with three replications of six arsenic treatments viz. control, 10, 20, 30, 60, 90 mg of As kg1 soil. Arsenic concentration in initial soil, to which the above mentioned concentrations of arsenic were added, was 6.44 ± 0.24 mg kg1. Both chlorophyll-a and -b contents in rice leaf decreased significantly (p < 0.05) with the increase of soil arsenic concentrations. No rice plant survived up to maturity stage in soil treated with 60 and 90 mg of As kg1. The highest chlorophyll-a and -b contents were observed in control treatment (2.62 ± 0.24 and 2.07 ± 0.14 mg g1 were the average values of chlorophyll-a and -b, respectively of the five rice varieties) while 1.50 ± 0.20 and 1.04 ± 0.08 mg g1 (average of five rice varieties) of chlorophyll-a and -b, respectively were the lowest. The content of photosynthetic pigments in these five rice varieties did not differ significantly (p > 0.05) from each other in control treatment though they differed significantly (p < 0.05) from each other in 30 mg of As kg1 soil treatment. Among the five rice varieties, chlorophyll content in BRRI dhan 35 was found to be mostly affected with the increase of soil arsenic concentration while BRRI hybrid dhan 1 was least affected. Well correlations were observed between chlorophyll content and rice growth and yield suggesting that arsenic toxicity affects the photosynthesis which ultimately results in the reduction of rice growth and yield.
Abstract: Some unavoidable drawbacks of traditional technologies have made phytoremediation a promising alternative for removal of arsenic from contaminated soil and water. In the present study, the potential of an aquatic macrophyte Spirodela polyrhiza L. for phytofiltration of arsenic, and the mechanism of the arsenic uptake were investigated. The S. polyrhiza L. were grown in three test concentrations of arsenate and dimethylarsinic acid (DMAA) (i.e. 1.0, 2.0 and 4.0 lM) with 0 (control), 100 or 500 lM of phosphate. One control treatment was also set for each test concentrations of arsenic. The PO3 4 concentration in control treatment was 0.02 lM. When S. polyrhiza L. was cultivated hydroponically for 6 d in culture solution containing 0.02 lM phosphate and 4.0 lM arsenate or DMAA, the arsenic uptake was 0.353 ± 0.003 lmol g1 and 7.65 ± 0.27 nmol g1, respectively. Arsenic uptake into S. polyrhiza L. was negatively (p < 0.05) correlated with phosphate uptake when arsenate was applied to the culture solutions owing to similar in the sorption mechanism between AsO3 4 and PO3 4 , and positively (p < 0.05) correlated with iron uptake due to adsorption of AsO3 4 onto iron oxides. Thus, the S. polyrhiza L. accumulates arsenic by physico-chemical adsorption and via the phosphate uptake pathway when arsenate was added to the solutions. These results indicate that S. polyrhiza L. would be a good arsenic phytofiltrator. In contrast, DMAA accumulation into S. polyrhiza L. was neither affected by the phosphate concentration in the culture nor correlated (p > 0.05) with iron accumulation in plant tissues, which indicates that S. polyrhiza L. uses different mechanisms for DMAA uptake.
Abstract: Arsenic concentration in raw rice is not only the determinant in actual dietary exposure. Though there have been many reports on arsenic content in raw rice and different tissues of rice plant, little is known about arsenic content retained in cooked rice after being cooked following the traditional cooking methods employed by the people of arsenic epidemic areas. A field level experiment was conducted in Bangladesh to investigate the influence of cooking methods on arsenic retention in cooked rice. Rice samples were collected directly from a severely arsenic affected area and also from an unaffected area, to compare the results. Rice was cooked according to the traditional methods employed by the population of subjected areas. Arsenic concentrations were 0.40+/-0.03 and 0.58+/-0.12 mg/kg in parboiled rice of arsenic affected area, cooked with excess water and 1.35+/-0.04 and 1.59+/-0.07 mg/kg in gruel for BRRI dhan28 and BRRI hybrid dhan1, respectively. In non-parboiled rice, arsenic concentrations were 0.39+/-0.04 and 0.44+/-0.03 mg/kg in rice cooked with excess water and 1.62+/-0.07 and 1.74+/-0.05 mg/kg in gruel for BRRI dhan28 and BRRI hybrid dhan1, respectively. Total arsenic content in rice, cooked with limited water (therefore gruel was absorbed completely by rice) were 0.89+/-0.07 and 1.08+/-0.06 mg/kg (parboiled) and 0.75+/-0.04 and 1.09+/-0.06 mg/kg (non-parboiled) for BRRI dhan28 and BRRI hybrid dhan1, respectively. Water used for cooking rice contained 0.13 and 0.01 mg of As/l for contaminated and non-contaminated areas, respectively. Arsenic concentrations in cooked parboiled and non-parboiled rice and gruel of non-contaminated area were significantly lower (p<0.01) than that of contaminated area. The results imply that cooking of arsenic contaminated rice with arsenic contaminated water increases its concentration in cooked rice.
Abstract: Arsenic is a known environmental toxicant and it occurs in the environment from natural and anthropogenic sources. Arsenic is one of the important environmental issues because of its occurrence, bioaccumulation, toxicity, and trophic transfer in the freshwater food chain. Aquatic organisms accumulate, retain, and transform arsenic when exposed to it through water, their diet, and other routes. Since arsenic toxicity mostly depends on its chemical forms, measurement of arsenic speciation in aquatic organisms is particularly important in assessing the ecological risks of the element. Arsenate (As(V)) comprises the major part of total arsenic in oxic waters, and phytoplankton take up As(V) and subsequently convert it to arsenite (As(III)) and then to less toxic dimethylarsinic acid (DMAA), monomethylarsonic acid (MMAA), and higher order organoarsenicals. Phytoplankton are supposed to convert inorganic arsenic species to methylarsenicals and to other organoarsenic compounds (lipids and arsenosugars) to reduce toxic effects of inorganic arsenicals. Since phytoplankton are considered to be a major food source for the organisms of higher trophic levels in the aquatic systems, biotransference of arsenic from lower to higher trophic levels is obvious, while biomagnification of the element in aquatic food chain is not consistent. Other important arsenic forms found in aquatic organisms include arsenocholine (AsC), arsenobetaine (AsB) and arsenosugars (AsS). This review discusses the bioaccumulation, biotransformation, and trophic transfer (biomagnification or diminution) of arsenic in the aquatic food chains in relation to its ecotoxicological risks in the freshwater environment.
Abstract: A large number of sites worldwide are contaminated by arsenic (As) as a result of human activities as well as from natural sources. Arsenic is a vital environmental and health concern due to its known chronic and epidemic toxicity. The main arsenic exposures to humans are through water pathway and food contamination originates from natural processes. Many of the available remediation technologies lost economic favor and public acceptance because of some unavoidable limitations of those technologies. Therefore, phytoremediation, a plant-based green technology, becomes an emerging and alternative technology that aims to extract or inactivate As in the environment. However, two approaches have been proposed in literature for the phytoremediation of arsenic: continuous or natural phytoremediation, and chemically enhanced phytoremediation. The first one is based on the use of natural hyperaccumulator plants having the ability to accumulate very high concentration of As in their shoots with exceptionally higher tolerance to As toxicity. On the other hand, As uptake in high biomass crop plants is increased using some chelating ligands in chemically enhanced phytoremediation technology.
Abstract: Humans are exposed to arsenic (As) from many sources including foods, water, and air. Although As contaminated drinking water is considered as the main source of dietary exposure, As has also been reported in many foods including agricultural, freshwater and seawater foods. Populations exposed to highly contaminated groundwater through drinking excrete higher levels of urinary As than they receive from drinking water alone, suggesting that they are exposed to As from sources other than drinking water. Therefore, dietary exposure from foods is supposed to be a significant source of As in human body. Bioavailability and form of As in foods are important from toxicological point of view. Inorganic species, As(III) and As(V), are the main constituents in foods, and are most toxic to humans. Cooking methods and ingredients used for cooking of foods affect greatly in the retention of As in cooked foods, and in the subsequent dietary intake. The basic diet of the rural population of the most As-prone Asian countries was mainly rice and vegetables which represents more than 50% of their total daily food intake. A substantial amount of As is absorbed or concentrated in cooked rice and vegetables from contaminated cooking water, and the inorganic fraction in cooking water, rice and vegetables represents over 80% of the total arsenic (T-As) content.
Abstract: Phytoremediation utilizes different plant species as a media of containment, destruction, or extraction of contaminant from different matrices including soil and water. Plants require essential metals i.e. Cu, Mn, Fe, Zn, Mo, etc. for growth and as such they are capable of accumulating these metals. Plants can also accumulate Cd, Cr, Pb, Co, Ag, Se, Hg etc., which are apparently non-essential for their growth and survival. This metal-accumulating property of plants has made them very popular in recent days in the remediation of metal-contaminated soil. This approach of remediation has the benefit of cost savings compared to the conventional treatment options. Plants capable of concentrating metal pollutants at enhanced rate - the hyperaccumulators - are commonly used for metal-polluted soil remediation. But, the bioavailability of the metals limits the performance of hyperaccumulators since a large proportion of metals in contaminated soils exist in ’non-labile’ state. There came the application of synthetic chelants to enhance the mobility and phytoavailability of metals to remediating plants. Various chelants are available which forms bioavailable and water-soluble stable metal complexes facilitating phytoextraction of these metals at enhanced rate by plants. While chelants are used because of their powerful metal solubilizing properties, it is the same characteristic which gives them the potential of becoming an eco-environmental threat. Environmental concerns are evoked due to the high persistency and poor photo-, chemo- and biodegradability of metal-chelant complexes. Different approaches have been proposed to combat the eco-environmental concerns raised by the use chelants in phytoremediation. Within the scope of this chapter, we will focus on the chelant assisted phytoremediation approaches for the removal of heavy metal contaminants from soil and eco-environmental consequences associated with it.
Abstract: Arsenic (As) is widely distributed in aquatic environments in various forms. In natural waters, the dominant inorganoarsenicals (iAs) are incorporated into microorganisms such as phytoplankton, and are converted to methylarsenicals and/or more high order organoarsenicals. In addition, the organoarsenicals are mineralized to iAs and methylarsenicals by bacteria. The cycling of As species would depend on the bioactivity of organisms. Microorganisms, such as phytoplankton and organisms of higher trophic levels, produce methylarsenicals in natural waters with maximum concentrations in summer. The degradation and mineralization of organoarsenic compounds are thought to depend mostly on bacterial activities, which influence the As cycling in aquatic environment. Arsenic metabolism in aquatic organisms results in the occurrence of thermodynamically unstable arsenite and methylarsenic compounds in natural waters. The inorganic forms (As(V) and As(III)) and the methylated forms (methylarsonic acid (CH3AsO(OH)2); MMAA(V) and dimethylarsinic acid ((CH3)2AsO(OH)); DMAA(V)) are the main arsenic species present in natural waters. Although the predominant form of methylarsenicals is consistently DMAA(V) followed by MMAA(V), the existence of trivalent methylarsenic species in the environment has also been reported.
Researchers reported the correlation between As(III)/methylarsenicals and chlorophyll-a concentrations and/or phytoplankton density, while others found that the seasonal changes of DMAA concentration is related to the temperature rather than the biological activity of phytoplankton. Eutrophication increases the concentration of nutrient salts and multiplies the primary producers, such as phytoplankton, in lake water. Lakes progress through the oligotrophic, mesotrophic and eutrophic process in the natural environment, and these transitions are very slow. Recently, the transition speed became faster because of discharged pollutants and nutrients from human activities, and the eutrophication affects the As circulation in lakes. Very recently, reports showed that the eutrophication influences As speciation in lake water too. In this chapter, the influence of eutrophication on arsenic speciation will be discussed.
Abstract: Toxic elements e.g. arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb), and zinc (Zn) are the chief environmental pollutants which can cause deleterious health effects in humans. Inhalation and consumption of metal-contaminated food are the major pathways of metal entrance into human body. Cultivation of crop plants in the metal-contaminated soils induces the bioaccumulation of toxic elements in the food chain. Among different food items, vegetables have major contribution in the daily diet, and the heavy metal contamination of vegetables poses a threat to human health with the prevalence of skin and gastrointerestinal cancer.
The uptake and bioaccumulation of toxic elements in vegetables are influenced by a number of factors such as atmospheric deposition, metal concentrations in soil, soil characteristics, and duration of cultivation. Cultivation areas near highways are exposed to atmospheric pollution in the form of metal containing aerosols which can be deposited on leaves of vegetables and then absorbed. The magnitude of heavy metal deposition on vegetable surfaces varied with morpho-physiological nature of the vegetables. Post-harvest activities, such as transportation, marketing, cooking, etc., may also influence the deposition of toxic elements in vegetables. Incorporation of toxic elements during transportation and marketing of vegetable can be occurred due to the use of contaminated water. Higher heavy metal content in vegetables from urban area then those from rural areas may be due to the contribution of urban activities which elevates heavy metal loads in atmospheric deposition and consequently in the edible part of the vegetables. Cooking has definite influence to the content of toxic elements in cooked items if the heavy metal concentrations in the cooking water are high.
Vegetable consumption varies with age group, food habit, as well as vegetable availability. For example the mean daily vegetable consumption among the European people is 153 g (ranged between 109-241 g) while it is around 250g among the South Asian people. Vegetables occupy a substantial proportion of the daily diet for the South-East Asian people, especially the Japanese, Korean and Chinese people. Thus, whatever the metal contents in vegetables are, their intake in human is, off course, dependent on the total vegetable consumption. In this review, the contribution of vegetables in dietary intake of toxic elements has been discussed from a common platform.
Abstract: The effect of iron plaque formation on plant surfaces and chemical species on arsenic uptake in Spirodela polyrhiza L. were investigated. Arsenate [As(V)] or arsenite [As(III)] concentration in S. polyrhiza L. was significantly (p < 0.05) higher than that of methyl arsenic species (MMAA or DMAA). In particular, the concentrations of As(V) and As(III) in CBE-extracts of plants with Fe-plaque were about 43% and 58% respectively higher then plants without Fe-plaque,. On the other hand, the As(V) and As(III) concentrations in tissues of plants with or without Fe-plaque remained almost unchanged. The results suggest that a significant amount of arsenate and arsenite were adsorbed on the Fe-plaque of S. polyrhiza L. surfaces. The concentrations of MMAA and DMAA in tissues and on CBE-extracts of S. polyrhiza L. were not significantly affected (p > 0.05) by the Fe-plaque on plant surfaces. These results indicate that methyl arsenic species might not be adsorbed on Fe-plaques. However, the significantly higher concentration of MMAA into the plant tissues than that of DMAA suggests that MMAA is more bioavailable to this plant. The ratios of As/P and As/Fe were significantly higher in tissues and CBE-extracts of plants exposed to inorganic arsenic species than plants exposed to methyl arsenic species. The results indicate enhanced uptake and adsorption of As(V) and As(III) than MMAA and DMAA in relation to phosphate and iron.
Abstract: Because of some unavoidable drawbacks of traditional technologies, phytoremediation has become promising to clean arsenic-contaminated soil and water. In the present study, we investigated the potential of duckweed (Spirodela polyrhiza L.), an aquatic macrophyte, for the phytofiltration of arsenic-contaminated water. When S. polyrhiza L. was cultivated hydroponically in culture containing 4.0 μM of arsenic species and 0.02 μM of phosphate, the accumulations were 0.353±0.003 and 0.58±0.01 μM g-1 for arsenate and 7.65±0.27 and 14.85±0.46 nM g-1 for dimethylarsinic acid (DMAA) after 6 and 12 days of incubation, respectively. With the increase of phosphate concentrations in the culture, arsenate accumulation decreased significantly, which suggests that arsenate and phosphate uptake is related. In contrast, the phosphate concentration in culture does not affect DMAA uptake significantly indicating that the aquatic plant may use different mechanism in DMAA uptake. The arsenate uptake efficiency was 0.195±0.001 and 0.30±0.01 μM g-1 L-1 after 6 and 12 days of incubation, respectively, from culture containing 4.0 μM of arsenate. Arsenate bioaccumulation was 78.8 – 98.8% higher than that of DMAA. These results reveal the potential of S. polyrhiza L. for phytofiltration of arsenate polluted water.
Abstract: The effect of iron plaque formation on plant surfaces and chemical species on arsenic uptake in Spirodela polyrhiza L. were investigated. Arsenate [As(V)] or arsenite [As(III)] concentration in S. polyrhiza L. was significantly (p < 0.05) higher than that of methyl arsenic species (MMAA or DMAA). In particular, the concentrations of As(V) and As(III) in CBE-extracts of plants with Fe-plaque were about 43% and 58% respectively higher then plants without Fe-plaque,. On the other hand, the As(V) and As(III) concentrations in tissues of plants with or without Fe-plaque remained almost unchanged. The results suggest that a significant amount of arsenate and arsenite were adsorbed on the Fe-plaque of S. polyrhiza L. surfaces. The concentrations of MMAA and DMAA in tissues and on CBE-extracts of S. polyrhiza L. were not significantly affected (p > 0.05) by the Fe-plaque on plant surfaces. These results indicate that methyl arsenic species might not be adsorbed on Fe-plaques. However, the significantly higher concentration of MMAA into the plant tissues than that of DMAA suggests that MMAA is more bioavailable to this plant. The ratios of As/P and As/Fe were significantly higher in tissues and CBE-extracts of plants exposed to inorganic arsenic species than plants exposed to methyl arsenic species. The results indicate enhanced uptake and adsorption of As(V) and As(III) than MMAA and DMAA in relation to phosphate and iron.
Abstract: Because of some unavoidable drawbacks of traditional technologies, phytoremediation has become promising to clean arsenic-contaminated soil and water. In the present study, we investigated the potential of duckweed (Spirodela polyrhiza L.), an aquatic macrophyte, for the phytofiltration of arsenic-contaminated water. When S. polyrhiza L. was cultivated hydroponically in culture containing 4.0 μM of arsenic species and 0.02 μM of phosphate, the accumulations were 0.353±0.003 and 0.58±0.01 μM g-1 for arsenate and 7.65±0.27 and 14.85±0.46 nM g-1 for dimethylarsinic acid (DMAA) after 6 and 12 days of incubation, respectively. With the increase of phosphate concentrations in the culture, arsenate accumulation decreased significantly, which suggests that arsenate and phosphate uptake is related. In contrast, the phosphate concentration in culture does not affect DMAA uptake significantly indicating that the aquatic plant may use different mechanism in DMAA uptake. The arsenate uptake efficiency was 0.195±0.001 and 0.30±0.01 μM g-1 L-1 after 6 and 12 days of incubation, respectively, from culture containing 4.0 μM of arsenate. Arsenate bioaccumulation was 78.8 – 98.8% higher than that of DMAA. These results reveal the potential of S. polyrhiza L. for phytofiltration of arsenate polluted water.
Abstract: Introduction: Arsenic contamination in water not only posses serious heath risks but also elevates its concentrations in agricultural soils which facilitates the entry of this toxic element into the food chain. Significant drawbacks of traditional technologies, phytoremediation has become promising to clean arsenic-contaminated soils and waters. As we know, no aquatic arsenic hyperaccumulating plant has been reported yet now. In the present study, we investigated the potentiality of an aquatic macrophyte (Spirodela polyrhiza) for the phytoremediation of arsenic-contaminated water and its uptake mechanism.
Experimental: Plants were grown in a batch culture under controlled environmental conditions [14/10 h light/dark schedule, 100-125 µ E m-2 s-1 light intensity, 22ºC and 20ºC (±2ºC) temperatures fro day and night, respectively, 75% humidity] on MS culture solution containing 0 (control), 1.0, 2.0 and 4.0 µML-1 of either arsenate or dimethylarsinic acid, modified with different PO43- [0.02 (control), 100 and 500 µML 1]. Plant samples were collected after 6 and 12 days of incubation and subjected to HNO3+H2O2 digestion on a heating block at 110ºC. Arsenic and Fe were analyzed by graphite-furnace atomic absorption spectrometer (GF-AAS). Total phosphate and nitrate were determined spectrophotometrically.
Results and Discussion: Among the two species, significant amount of arsenate was accumulated in this plant though DMAA uptake was negligible (Figure 1). Arsenate uptake was significantly (p<0.05) inversely correlated with that of phosphate suggests that arsenate uptake occurs through phosphate uptake pathway. However, high positive correlations (r = 0.828 and 0.945 for 6 and 12 days samples, respectively) between arsenate and Fe contents in this aquatic plant of PO43- deficient solution reviled that arsenate may also adsorbed physicochemically by iron oxides and accumulated in PO43- deficient condition. Very poor correlations between phosphate and DMAA and strong positive correlations between Fe and DMAA imply that, DMAA may bind to iron oxides and adsorbed on aquatic plants. However, arsenate uptake in aquatic macrophytes may occurs mainly through biochemical reaction while DMAA provably through physicochemical adsorption. The high arsenate uptake efficiency of this aquatic floating macrophyte reviled potential use for phytoremediation of arsenic-contaminated freshwater.
