Sorption and bioavailability of arsenic in selected Bangladesh soils

The bioavailability of arsenic (As) in the soil environment is largely governed by its adsorption–desorption reactions with soil constituents. We have investigated the sorption–desorption behaviour of As in four typical Bangladeshi soils subjected to irrigation with As-contaminated groundwater. The total As content of soils (160 samples) from the Laksham district ranged from <0.03 to approximately 43 mg kg⁻¹. Despite the low total soil As content, the concentration of As in the pore water of soils freshly irrigated with As-contaminated groundwater ranged from 0.01 to 0.1 mg l⁻¹. However, when these soils were allowed to dry, the concentration of As released in the pore water decreased to undetectable levels. Remoistening of soils to field moisture over a 10-day period resulted in a significant (up to 0.06 mg l⁻¹) release of As in the pore water of soils containing >10 mg As kg⁻¹ soil, indicating the potential availability of As. In soils containing <5 mg As kg⁻¹, As was not detected in the pore water. A comparison of Bangladeshi soils with strongly weathered long-term As-contaminated soils from Queensland, Australia showed a much greater release of As in water extracts from the Australian soils. However, this was attributed to the much higher loading of As in these Australian soils. The correlation of pore water As with other inorganic ions (P, S) showed a strongly significant (P < 0.001) relationship with P, although there was no significant relationship between As and other inorganic cations, such as Fe and Mn. Batch sorption studies showed an appreciable capacity for both As^V and As^III sorption, with As^V being retained in much greater concentrations than As^III.     

Field based speciation of arsenic in UK and Argentinean water samples

A field method is reported for the speciation of arsenic in water samples that is simple, rapid, safe to use beyond laboratory environments, and cost effective. The method utilises solid-phase extraction cartridges (SPE) in series for selective retention of arsenic species, followed by elution and measurement of eluted fractions by inductively coupled plasma mass spectrometry (ICP-MS) for “total” arsenic. The method is suitable for on-site separation and preservation of arsenic species from water. Mean percentage accuracies (n = 25) for synthetic solutions of arsenite (As^III), arsenate (As^V), monomethylarsonic acid (MA), and dimethylarsinic acid (DMA) containing 10 μg l⁻¹ As, were 98, 101, 94, and 105%, respectively. Data are presented to demonstrate the effect of pH and competing anions on the retention of the arsenic species. The cartridges were tested in the UK and Argentina at sites where arsenic was known to be present in surface and groundwaters, respectively, at elevated concentrations and under challenging matrix conditions. In Argentinean groundwater, 4–20% of speciated arsenic was present as MA and 20–73% as As^III. In UK surface waters, speciated arsenic was measured as 7–49% MA and 12–42% DMA. Comparative data from the field method using SPE cartridges and the laboratory method using liquid chromatography coupled to ICP-MS for all water samples provided a correlation of greater than 0.999 for As^III and DMA, 0.991 for MA, and 0.982 for As^V (P < 0.01).     

Arsenic uptake and speciation in vegetables grown under greenhouse conditions

The accumulation of arsenic (As) by vegetables is a potential human exposure pathway. The speciation of As in vegetables is an important consideration due to the varying toxicity of different As species. In this study, common Australian garden vegetables were hydroponically grown with As-contaminated irrigation water to determine the uptake and species of As present in vegetable tissue. The highest concentrations of total As were observed in the roots of all vegetables and declined in the aerial portions of the plants. Total As accumulation in the edible portions of the vegetables decreased in the order radish ≫ mung bean > lettuce = chard. Arsenic was present in the roots of radish, chard, and lettuce as arsenate (As^V) and comprised between 77 and 92% of the total As present, whereas in mung beans, arsenite (As^III) comprised 90% of the total As present. In aerial portions of the vegetables, As was distributed equally between both As^V and As^III in radish and chard but was present mainly as As^V in lettuce. The presence of elevated As in vegetable roots suggests that As species may be complexed by phytochelatins, which limits As translocation to aerial portions of the plant.     

Chemistry of inorganic arsenic in soils: kinetics of arsenic adsorption–desorption

The influence of ionic strength, index cations and competing anions on arsenate (As^V) adsorption–desorption kinetics was studied in an Alfisol soil. A flow-through reactor system similar to that developed by Carski and Sparks (Soil Sci Soc Am J 49:1114–1116, 1985) was constructed for the experiments. Arsenate adsorption kinetics for all the treatments were initially fast with 58–91% of As^V adsorbed in the first 15 min. Beyond 15 min, As^V adsorption continued at a slower rate for the observation period of the experiments. Changes in the solution composition had differing effects on the cumulative amount of As^V adsorbed by the soil. Ionic strength and different index cations had little effect on the amount of As^V adsorbed, while the presence of phosphate decreased the amount of As^V adsorbed from 169 to 89 and 177 to 115 g As^V μg⁻¹ in 0.03 M sodium nitrate and 0.01 M calcium nitrate, respectively. Considerably less As^V was desorbed than was adsorbed, with only between 2 to 17% of the adsorbed As^V desorbed. The presence of phosphate increased the amount of As^V desorbed by 17%, but other changes in the solution ionic strength or index cation had little effect on the amount of As^V desorbed.     

Arsenic contamination of natural waters in San Juan and La Pampa, Argentina

Arsenic (As) speciation in surface and groundwater from two provinces in Argentina (San Juan and La Pampa) was investigated using solid phase extraction (SPE) cartridge methodology with comparison to total arsenic concentrations. A third province, Río Negro, was used as a control to the study. Strong cation exchange (SCX) and strong anion exchange (SAX) cartridges were utilised in series for the separation and preservation of arsenite (As^III), arsenate (As^V), monomethylarsonic acid (MA^V) and dimethylarsinic acid (DMA^V). Samples were collected from a range of water outlets (rivers/streams, wells, untreated domestic taps, well water treatment works) to assess the relationship between total arsenic and arsenic species, water type and water parameters (pH, conductivity and total dissolved solids, TDS). Analysis of the waters for arsenic (total and species) was performed by inductively coupled plasma mass spectrometry (ICP-MS) in collision cell mode. Total arsenic concentrations in the surface and groundwater from Encon and the San José de Jáchal region of San Juan (north-west Argentina within the Cuyo region) ranged from 9 to 357 μg l^?1 As. Groundwater from Eduardo Castex (EC) and Ingeniero Luiggi (LU) in La Pampa (central Argentina within the Chaco-Pampean Plain) ranged from 3 to 1326 μg l^?1 As. The pH range for the provinces of San Juan (7.2–9.7) and La Pampa (7.0–9.9) are in agreement with other published literature. The highest total arsenic concentrations were found in La Pampa well waters (both rural farms and pre-treated urban sources), particularly where there was high pH (typically > 8.2), conductivity (>2,600 μS cm^?1) and TDS (>1,400 mg l^?1). Reverse osmosis (RO) treatment of well waters in La Pampa for domestic drinking water in EC and LU significantly reduced total arsenic concentrations from a range of 216–224 μg l^?1 As to 0.3–0.8 μg l^?1 As. Arsenic species for both provinces were predominantly As^III and As^V. As^III and As^V concentrations in San Juan ranged from 4–138 μg l^?1 to <0.02–22 μg l^?1 for surface waters (in the San José de Jáchal region) and 23–346 μg l^?1 and 0.04–76 μg l^?1 for groundwater, respectively. This translates to a relative As^III abundance of 69–100% of the total arsenic in surface waters and 32–100% in groundwater. This is unexpected because it is typically thought that in oxidising conditions (surface waters), the dominant arsenic species is As^V. However, data from the SPE methodology suggests that As^III is the prevalent species in San Juan, indicating a greater influence from reductive processes. La Pampa groundwater had As^III and As^V concentrations of 5–1,332 μg l^?1 and 0.09–592 μg l^?1 for EC and 32–242 μg l^?1 and 30–277 μg l^?1 As for LU, respectively. Detectable levels of MA^V were reported in both provinces up to a concentration of 79 μg l^?1 (equating to up to 33% of the total arsenic). Previously published literature has focused primarily on the inorganic arsenic species, however this study highlights the potentially significant concentrations of organoarsenicals present in natural waters. The potential for separating and preserving individual arsenic species in the field to avoid transformation during transport to the laboratory, enabling an accurate assessment of in situ arsenic speciation in water supplies is discussed.     

Arsenic speciation in polychaetes (Annelida) and sediments from the intertidal mudflat of Sundarban mangrove wetland, India

This paper documents the concentration of total arsenic and individual arsenic species in four soft-bottom benthic polychaetes (Perenereis cultifera, Ganganereis sootai, Lumbrinereis notocirrata and Dendronereis arborifera) along with host sediments from Sundarban mangrove wetland, India. An additional six sites were considered exclusively for surface sediments for this purpose. Polychaetes were collected along with the host sediments and measured for their total arsenic content using inductively coupled plasma mass spectrometry. Arsenic concentrations in polychaete body tissues varied greatly, suggesting species-specific characteristics and inherent peculiarities in arsenic metabolism. Arsenic was generally present in polychaetes as arsenate (As^V ranges from 0.16 to 0.50 mg kg^?1) or arsenite (As^III ranges from 0.10 to 0.41 mg kg^?1) (30–53 % as inorganic As) and dimethylarsinic acid (DMA^V <1–25 %). Arsenobetaine (AB < 16 %), and PO₄-arsenoriboside (8–48 %) were also detected as minor constituents, whilst monomethylarsonic acid (MA^V) was not detected in any of the polychaetes. The highest total As (14.7 mg kg^?1 dry wt) was observed in the polychaete D. arborifera collected from the vicinity of a sewage outfall in which the majority of As was present as an uncharacterised compound (10.3 mg kg^?1 dry wt) eluted prior to AB. Host sediments ranged from 2.5 to 10.4 mg kg^?1 of total As. This work supports the importance of speciation analysis of As, because of the ubiquitous occurrence of this metalloid in the environment, and its variable toxicity depending on chemical form. It is also the first work to report the composition of As species in polychaetes from the Indian Sundarban wetlands.     

Nitrogen uptake characteristics of Chordaria flagelliformis (Phaeophyta) in batch mode and continuous mode experiments

The uptake of NH ₄ ⁺ and urea by Chordaria flagelliformis was measured in a perturbed system (batch mode) and in an apparent steady-state system (continuous mode). The maximum uptake rates (V_max) measured in short-term depletion experiments greatly exceeded those determined under a steady nutrient supply. C. flagelliformis briefly exposed to high nutrient concentrations has an impressive capacity for rapid uptake (high V_max)_which is uncoupled from growth. In contrast, under continous, homogenous low N concentrations the alga appears well equipped (low half-saturation constant, K_m) to take up the available N. The results show that previous work based on batch mode uptake experiments probably overestimated the N requirements for the growth of many seaweeds.     

The influence of solid matrices on arsenic toxicity to Corophium orientale

In marine ecosystems, benthic organisms are really important because they are the first step in the transfer of contaminants from environment to biota. To this end, this study focused on biological assays with the amphipod Corophium orientale exposed to two different molecules of arsenic: arsenate (As^V), the most abundant form in sediments, and dimethyl-arsinate (DMA), expected to be moderately toxic as an intermediate in the process of detoxification. The toxicity of arsenic compounds was measured after exposure to three different matrices: water, spiked natural sediment and inert spiked quartz sand. LC₅₀ values were calculated for each exposure, and the results confirmed the highest toxicity of As^V, in addition to underlining the importance of matrix of exposure. Water exposure was the matrix which presented the highest toxicity for inorganic arsenic (As^V LC₅₀=3.51 mg L^?1 vs DMA LC₅₀=54.65 mg L^?1), spiked natural sediment demonstrated its capability to chelate arsenate toxicity (As^V LC₅₀=34.27 mg kg^?1 vs. DMA LC₅₀=52.19 mg kg^?1) and spiked quartz sand presented intermediate values for As^V (LC₅₀=25.26 mg kg^?1), whereas for DMA a lower toxicity was registered (LC₅₀=872.35 mg kg^?1). This study can provide some useful data linked with chemical speciation of arsenic and exposure matrix, for improving the correct management of contaminated sediment.     

A comparative study on arsenic and humic substances in alluvial aquifers of Bengal delta plain (NW Bangladesh), Chianan plain (SW Taiwan) and Lanyang plain (NE Taiwan): implication of arsenic mobilization mechanisms

Humic substances in groundwater and aquifer sediments from the arsenicosis and Blackfoot disease (BFD) affected areas in Bangladesh (Bengal delta plain) and Taiwan (Lanyang plain and Chianan plain) were characterized using fluorescence spectrophotometry and Fourier transform infrared (FT-IR) spectroscopy. The results demonstrate that the mean concentration of As and relative intensity of fluorescent humic substances are higher in the Chianan plain groundwater than those in the Lanyang plain and Bengal delta plain groundwater. The mean As concentrations in Bengal delta plain, Chianan plain, and Lanyang plain are 50.65 μg/l (2.8–170.8 μg/l, n = 20), 393 μg/l (9–704 μg/l, n = 5), and 104.5 μg/l (2.51–543 μg/l, n = 6), respectively. Average concentrations and relative fluorescent intensity of humic substances in groundwater are 25.381 QSU (quinine standard unit) and 17.78 in the Bengal delta plain, 184.032 QSU and 128.41 in the Chianan plain, and 77.56 QSU and 53.43 in the Lanyang plain. Moreover, FT-IR analysis shows that the humic substances extracted from the Chianan plain groundwater contain phenolic, alkanes, aromatic ring and amine groups, which tend to form metal carbon bonds with As and other trace elements. By contrast, the spectra show that humic substances are largely absent from sediments and groundwater in the Bengal delta plain and Lanyang plain. The data suggest that the reductive dissolution of As-adsorbed Mn oxyhydroxides is the most probable mechanism for mobilization of As in the Bengal delta plain. However, in the Chianan plain and Lanyang plain, microbially mediated reductive dissolution of As-adsorbed amorphous/crystalline Fe oxyhydroxides in organic-rich sediments is the primary mechanism for releasing As to groundwater. High levels of As and humic substances possibly play a critical role in causing the unique BFD in the Chianan plain of SW Taiwan.     

Marine diatoms grown in chemostats under silicate or ammonium limitation. IV. Transient response of Chaetoceros debilis,Skeletonema costatum,and Thalassiosira gravida to a single addition of the limiting nutrient

The kinetic response of ammonium- or silicate-limited and ammonium- or silicatestarved populations of Chaetoceros debilis, Skeletonema costatum, and Thalassiosira gravida was determined by a single addition of the limiting nutrient to a steady-state culture and subsequent monitoring of the nutrient disappearance of the limiting and non-limiting nutrients at frequent time intervals. The kinetic response of nonlimited (nutrient) populations of these three species was also determined. Three distinct modes of the uptake of the limiting nutrient were observed for ammonium-or silicate-limited populations of these three species, surge uptake (V _s ), internally (cellular) controlled uptake (V _i ), and externally (ambient limiting nutrient concentration) controlled uptake (V _e ). Non-limited populations did not exhibit the three distinct segments of uptake, V _s , V _i and V _e . Estimates of the maximal uptake rate (V _max) and the Michaelis constant (K _s ) were obtained from nutrient-limited populations during the V _e segment of the uptake curve. Pooled values of V _e for the three ammonium-limited populations yielded V _max and K _s estimates of 0.16 h^-1 and 0.5 g-at NH₄–N l^-1. Kinetic data derived from the V _e segment of the uptake curve for silicate-limited populations yielded different values of V _max and K _s for each of the three species. In a number of parameters that were measured, T. gravida was clearly different from C. debilis and S. costatum and its recovery from nutrient starvation was the slowest. Recovery of all species from silicate limitation or starvation was slower than from ammonium limitation or starvation. Ammonium-starved populations maintained a maximal uptake rate at a substrate concentration an order of magnitude lower (0.1 g-at NH₄–N l^-1) than that observed for NH₄-limited populations (1.0 g-at NH₄–N l^-1). Adaptation to the severity of the nutrient limitation occurred as changes in the magnitude of cellular characteristics, such as short-term uptake potential (V _s ) and affinity for the substrate (K _s ). The consequence of these results are discussed in terms of another possible mechanism to explain changes in species composition and succession in nutrient-depleted environments.Contribution No. 944 from the Department of Oceanography, University of Washington, Seattle, Washington 98195, USA.     

Effects of Cadmium on Nutrient Uptake and Translocation by Indian Mustard

Plants that hyperaccumulate metals are ideal subjects for studying the mechanisms of metal and mineral nutrient uptake in the plant kingdom. Indian Mustard (Brassica juncea) has been shown to accumulate moderate levels of Cd, Pb, Cr, Ni, Zn, and Cu. In this experiment, 10 levels of Cd concentration treatments were imposed by adding 10–190 mg Cd kg^–1 to the soils as cadmium nitrate [Cd(NO₃)₂]. The effect of Cd on phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and the micronutrients iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn) in B. juncea was studied. Plant growth was affected negatively by Cd, root biomass decreased significantly at 170 mg Cd kg^–1 dry weight soils treatment. Cadmium accumulation both in shoots and roots increased with increasing soil Cd treatments. The highest concentration of Cd was up to 300 mg kg^–1 d.w. in the roots and 160 mg kg^–1 d.w. in the shoots. The nutrients mainly affected by Cd were P, K, Ca, Fe, and Zn in the roots, and P, K, Ca, and Cu in the shoots. K and P concentrations in roots increased significantly when Cd was added at 170 mg kg^–1, and this was almost the same level at which root growth was inhibited. Zn concentrations in roots decreased significantly when added Cd concentration was increased from 50 to 110 mg kg^–1, then remained constant with Cd treatments from 110 to 190 mg kg^–1. However, Zn concentrations in the shoots seemed less affected by Cd. It is possible that Zn uptake was affected by the Cd but not the translocation of Zn within the plant. Ca and Mg accumulation in roots and shoots showed similar trends. This result indicates that Ca and Mg uptake is a non-specific process.     

Microbial activity and carbon, nitrogen, and phosphorus content in a subtropical seagrass estuary (Florida Bay): evidence for limited bacterial use of seagrass production

Bacterial abundance, production, and extracellular enzyme activity were determined in the shallow water column, in the epiphytic community of Thalassia testudinum, and at the sediment surface along with total carbon, nitrogen, and phosphorus in Florida Bay, a subtropical seagrass estuary. Data were statistically reduced by principle components analysis (PCA) and multidimensional scaling and related to T. testudinum leaf total phosphorus content and phytoplankton biomass. Each zone (i.e., pelagic, epiphytic, and surface sediment community) was significantly dissimilar to each other (Global R = 0.65). Pelagic aminopeptidase and sum of carbon hydrolytic enzyme (esterase, peptidase, and α- and β-glucosidase) activities ranged from 8 to 284 mg N m⁻² day⁻¹ and 113–1,671 mg C m⁻² day⁻¹, respectively, and were 1–3 orders of magnitude higher than epiphytic and sediment surface activities. Due to the phosphorus-limited nature of Florida Bay, alkaline phosphatase activity was similar between pelagic (51–710 mg P m⁻² day⁻¹) and sediment (77–224 mg P m⁻² day⁻¹) zones but lower in the epiphytes (1.1–5.2 mg P m⁻² day⁻¹). Total (and/or organic) C (111–311 g C m⁻²), N (9.4–27.2 g N m⁻²), and P (212–1,623 mg P m⁻²) content were the highest in the sediment surface and typically the lowest in the seagrass epiphytes, ranging from 0.6 to 8.7 g C m⁻², 0.02–0.99 g N m⁻², and 0.5–43.5 mg P m⁻². Unlike nutrient content and enzyme activities, bacterial production was highest in the epiphytes (8.0–235.1 mg C m⁻² day⁻¹) and sediment surface (11.5–233.2 mg C m⁻² day⁻¹) and low in the water column (1.6–85.6 mg C m⁻² day⁻¹). At an assumed 50% bacterial growth efficiency, for example, extracellular enzyme hydrolysis could supply 1.8 and 69% of epiphytic and sediment bacteria carbon demand, respectively, while pelagic bacteria could fulfill their carbon demand completely by enzyme-hydrolyzable organic matter. Similarly, previously measured T. testudinum extracellular photosynthetic carbon exudation rates could not satisfy epiphytic and sediment surface bacterial carbon demand, suggesting that epiphytic algae and microphytobenthos might provide usable substrates to support high benthic bacterial production rates. PCA revealed that T. testudinum nutrient content was related positively to epiphytic nutrient content and carbon hydrolase activity in the sediment, but unrelated to pelagic variables. Phytoplankton biomass correlated positively with all pelagic components and sediment aminopeptidase activity but negatively with epiphytic alkaline phosphatase activity. In conclusion, seagrass production and nutrient content was unrelated to pelagic bacteria activity, but did influence extracellular enzyme hydrolysis at the sediment surface and in the epiphytes. This study suggests that seagrass-derived organic matter is of secondary importance in Florida Bay and that bacteria rely primarily on algal/cyanobacteria production. Pelagic bacteria seem coupled to phytoplankton, while the benthic community appears supported by epiphytic and/or microphytobenthos production.     

Distribution of arsenic compounds in Plantaginaceae and Cyperaceae plants growing in contaminated soil

The ability of plant species to accumulate arsenic (As) species in the biomass from As-contaminated soils is variable. Among the plants widely grown at the As-contaminated locations, Plantaginaceae and Cyperaceae families belong to the frequent ones. In this study, the ability of Plantago lanceolata (Plantaginaceae) and three wetland plant species representing the family Cyperaceae (Carex praecox, Carex vesicaria, and Scirpus sylvaticus) naturally occurring in the soils with an elevated As in the Czech Republic were investigated. The plants were cultivated under controlled conditions in an As-contaminated soil reaching 735?mg?kg^?1 of the total As. The total As in plants reached up to 8.3?mg?kg^?1 in leaves, and up to 155?mg?kg^?1 in roots of C. praecox. Dominant As compounds were arsenite and arsenate with a small abundance of dimethylarsinic acid (DMA) in all the plant species. In Cyperaceae, small percentages of arsenobetaine (AB) and arsenocholine (AC) were detected, suggesting the ability of these plants to transform As into less toxic compounds. Moreover, the important role of As(V) sequestration on iron plaque on the root surface of Cyperaceae was confirmed. In this context, root washing with oxalic acid partially disrupted the iron plaque for the better release of arsenate.     

Nutrient uptake kinetics and growth of zooxanthellae maintained in laboratory culture

Growth characteristics and nutrient uptake kinetics were determined for zooxanthellae (Gymnodinium microadriaticum) in laboratory culture. The maximum specific growth rate (_max) was 0.35 d^-1 at 27 °C, 12 hL:12 hD cycle, 45 E m^-2 s^-1. Anmmonium and nitrate uptake by G. microadriaticum in distinct growth phases exhibited Michaelis-Menten kinetics. Ammonium half-saturation constants (K_s) ranged from 0.4 to 2.0 M; those for nitrate ranged from 0.5 to 0.8 M. Ammonium maximum specific uptake rates (V_max) (0.75 to 1.74 d^-1) exceeded those for nitrate (0.14 to 0.39 d^-1) and were much greater than the maximum specific growth rate (0.35 d^-1), suggesting that ammonium is the more significant N source for cultured zooxanthellae. Ammonium and nitrate V_max values compare with those reported from freshly isolated zooxanthellae. Light enhanced ammonium and nitrate uptake; ammonium inhibited nitrate uptake which was not reported for freshly isolated zooxanthellae, suggesting that physiological differences exist between the two. Knowledge of growth and nutrient uptake kinetics for cultured zooxanthellae can provide insight into the mechanisms whereby nutrients are taken up in coral-zooxanthelae symbioses.Contribution No. 1515 from the University of Maryland Center for Environmental and Estuarine Studies, Chesapeake Biological Laboratory, Solomons, Maryland 20688-0038, USA     

Temporal dynamics of arsenic uptake and distribution: food and water risks in the Bengal basin

Abstract

Contaminated food chain is a serious contender for arsenic (As) uptake around the globe. In Nadia, West Bengal, we trace possible means of transfer of As from multiple sources reaching different trophic levels, and associated seasonal variability leading to chronic As uptake. This work considers possible sources-pathways of As transfer through food chain in rural community. Arsenic concentration in groundwater, soil, rice, and vegetable-samples collected detected in different harvest seasons of 2014 and 2016. Arsenic level in shallow groundwater samples ranged from 0.1 to 354?µg/L, with 75% of the sites above the prescribed limit by WHO (10?µg/L) during the boro harvest season. High soil As content (～20.6?mg/kg), resulted in accumulation of As in food crops. A positive correlation in As conc. with increase over period in all sites indicating gradual As accumulation in topsoil. Unpolished rice samples showed high As content (～1.75?mg/kg), polishing reduced 80% of As. Among vegetables, the plant family Poaceae with high irrigation requirements and Solanaceae retaining high moisture, have the highest levels of As. Contaminated animal fodder (Poaceae) and turf water for cattle are shown to contaminate milk (0.06 to 0.24?µg/L) and behoves strategies, practices to minimize As exposure.     

Adsorption of arsenic (V) by iron (III)-modified natural zeolitic tuff

Adsorption of arsenic (V) by natural zeolitic tuff, modified with iron (III), was investigated. Also, the iron (III) adsorption characteristics by natural zeolitic tuff was evaluated. It was determined that iron (III) adsorption by starting zeolitic tuff was best represented by the Freundlich type of isotherm, having correlation coefficient (r ²) of 0.990. Arsenic (V) adsorption by iron (III)-modified zeolitic tuff followed a nonlinear type of isotherm. The best fit of the experimental data was obtained using the Langmuir–Freundlich model (r ² = 0.99), with the estimated maximum of arsenic (V) adsorption to iron (III)-modified zeolitic tuff of 1.55 mg/g.     

Morphological plasticity of submerged macrophyte Potamogeton wrightii Morong under different photoperiods and nutrient conditions

The morphological plasticity of the submerged macrophyte Potamogeton wrightii under different nutrient conditions and photoperiods was measured in a laboratory controlled experiment for 70 days in Japan. Six treatments were used in this experiment (3 × 2 factorial design with three replications) which consisted of three photoperiods and two nutrient conditions. Both photoperiod and nutrient condition had a pronounced effect on shoot and leaf morphology in P. wrightii. New shoot recruitment, and the length of main and new shoots gradually decreased with shortening photoperiod under both nutrient treatments. Plants under an 8 h photoperiod and high nutrient levels generated significantly more dead leaves (7.42 leaf·shoot^?1) and decomposed shoots (1.3 shoots·pot^?1) than plants under other treatments. Under short photoperiods (12 and 8 h) plants failed to produce flowering spikes in both nutrient conditions. In high nutrient conditions, P. wrightii produced shorter shoots, fewer leaves with shorter and narrower laminas, and smaller petioles compared with plants in the low nutrient condition. This may be adaptive under high nutrient conditions because it lowers foliar uptake and, thus, nutrient toxicity.     

Assessment of bioaccessibility and exposure risk of arsenic and lead in urban soils of Guangzhou City,China

Soil ingestion is an important human exposure pathway of heavy metals in urban environments with heavy metal contaminated soils. This study aims to assess potential health risks of heavy metals in soils sampled from an urban environment where high frequency of human exposure may be present. A bioaccessibility test is used, which is an in vitro gastrointestinal (IVG) test of soluble metals under simulated physiological conditions of the human digestion system. Soil samples for assessing the oral bioaccessibility of arsenic (As) and lead (Pb) were collected from a diverse range of different land uses, including urban parks, roadsides, industrial sites and residential areas in Guangzhou City, China. The soil samples contained a wide range of total As (10.2 to 61.0 mg kg⁻¹) and Pb (38.4 to 348 mg kg⁻¹) concentrations. The bioaccessibility of As and Pb in the soil samples were 11.3 and 39.1% in the stomach phase, and 1.9 and 6.9% in the intestinal phase, respectively. The As and Pb bioaccessibility in the small intestinal phase was significantly lower than those in the gastric phase. Arsenic bioaccessibility was closely influenced by soil pH and organic matter content (r ² = 0.451, p < 0.01) in the stomach phase, and by organic matter, silt and total As contents (r ² = 0.604, p < 0.001) in the intestinal phase. The general risk of As and Pb intake for children from incidental ingestion of soils is low, compared to their maximum doses, without causing negative human health effects. The exposure risk of Pb in the soils ranked in the order of: industrial area/urban parks > residential area/road side. Although the risk of heavy metal exposure from direct ingestion of urban soils is relatively low, the risk of inhalation of fine soil particulates in the air remains to be evaluated.     

Comparison of proton-specific ATPase activities in plume and root tissues of two co-occurring hydrocarbon seep tubeworm species Lamellibrachia luymesi and Seepiophila jonesi

Lamellibrachia luymesi and Seepiophila jonesi are co-occurring species of vestimentiferan tubeworms found at hydrocarbon seepage sites on the upper Louisiana slope of the Gulf of Mexico. Like all vestimentiferans, they rely on internal sulfide-oxidizing symbiotic bacteria for nutrition. These symbionts produce hydrogen ions as a byproduct of sulfide oxidation, which the host tubeworm needs to eliminate to prevent acidosis. The hydrothermal vent tubeworm Riftia pachyptila uses a high activity of P- and V-type H⁺-ATPases located in its plume epithelium to excrete protons. Unlike R. pachyptila, the seep species grow a posterior root, which they can use in addition to their plumes as a nutrient exchange surface. In this study we measured the ATPase activities of plume and root tissues collected from L. luymesi and S. jonesi, and used a combination of inhibitors to determine the relative activities of P- and V-type H⁺-ATPases. We found that the total H⁺-ATPase activity of their plumes was approximately 14 μmol h⁻¹ g⁻¹ wet weight, and that of their roots was between 5 and 7 μmol h⁻¹ g⁻¹ wet weight. These activities were more than ten times lower than those measured in R. pachyptila. We suggest that seep tubeworms might use passive channels to eliminate protons across their roots, in addition to ATP-dependant proton pumps located in their plumes and roots. In addition, we found strong differences between the types of ATPase activities in the plumes of L. luymesi and S. jonesi. While the H⁺-ATPase activity of L. luymesi plumes is dominated by P-type ATPases, S. jonesi has an unusually high activity of V-type H⁺-ATPases. We suggest that S. jonesi relies on its high V-type H⁺-ATPase activity to drive carbon dioxide uptake across its plume surface. L. luymesi, on the other hand, might rely partially on bicarbonate uptake across its root.