Assessing carcinogenic risks associated with ingesting arsenic in farmed smeltfish (Ayu, Plecoglossus altirelis) in aseniasis-endemic area of Taiwan

This study spatially analyzed potential carcinogenic risks associated with ingesting arsenic (As) contents in aquacultural smeltfish (Plecoglossus altirelis) from the Lanyang Plain of northeastern Taiwan. Sequential indicator simulation (SIS) was adopted to reproduce As exposure distributions in groundwater based on their three-dimensional variability. A target cancer risk (TR) associated with ingesting As in aquacultural smeltfish was employed to evaluate the potential risk to human health. The probabilistic risk assessment determined by Monte Carlo simulation and SIS is used to propagate properly the uncertainty of parameters. Safe and hazardous aquacultural regions were mapped to elucidate the safety of groundwater use. The TRs determined from the risks at the 95th percentiles exceed one millionth, indicating that ingesting smeltfish that are farmed in the highly As-affected regions represents a potential cancer threat to human health. The 95th percentile of TRs is considered in formulating a strategy for the aquacultural use of groundwater in the preliminary stage.     

Daily intake of TBT, Cu, Zn, Cd and As for fishermen in Taiwan

The consumption of contaminated seafood has been reported as an important route of human exposure to metals in Taiwan. We consider the concentrations of TBT, Cu, Zn, Cd, As, and the consumption of oysters of Taiwanese to be the important information related to public health in Taiwan. Therefore, the aim of this study was to evaluate the public health risks associated with TBT, Cu, Zn, Cd and As from shellfish for the general population and fishermen of Taiwan. In general, TBT concentrations in various oysters ranging from 0.32 to 1.51 microg/g dry wt. varied with sampling locations. The highest TBT, Cu, and Zn geometric mean (GM) concentrations in oysters of 1.51, 1180 and 1567 microg/g dry wt. were obtained from the Hsiangshan coastal area. The values of oyster consumption for fishermen were 94.1 and 250 g/day for typically and maximally exposed individuals, respectively. In particular, the highest intake (250 g/day) from fishermen was almost two times greater than that of the general population (139 g/day). The THQ (target hazard quotient) values of Hsiangshan's fishermen are 3.87 and 20.50 for TBT and Cu for maximally exposed individuals are higher than other oyster culture areas. It is interesting that those consuming oysters from Hsiangshan, Lukang, Taishi caused abnormally high THQs of TBT and other metals (100% over 1.0), and TBT was attributed to only 3-21% of the total THQs in different fishermen of Taiwan. Our results suggest that current environmental levels of TBT and other metals are associated with a significant potential threat to human health for fishermen resident in coastal areas of Taiwan.     

Evaluation of potential health risk of arsenic-affected groundwater using indicator kriging and dose response model

This study analyzed the potential health risk associated with the ingestion of arsenic-affected groundwater in the arseniasis-endemic Lanyang plain of northeastern Taiwan. Indicator kriging was used to estimate arsenic concentrations in groundwater. Target cancer risk (TR) and dose response functions were adopted to evaluate the potential health risk based on the estimated arsenic concentration distributions. The estimated arsenic concentrations in groundwater reveal that arsenic concentrations (>50 microg/L) in well water are high in six townships - JiaoSi, YiLan, JhungWei, WuJie, DonShan and LouDon. Highest arsenic concentrations (70.32 microg/L) are in the YiLan and the JhungWei townships. The estimated TR values at the arsenic-affected townships are ten times more than an acceptable standard (10(-6)). The largest TR values are 145.5 and 91.2 times higher than an acceptable standard for males and females, respectively. The estimated annual mortalities by arsenic-induced internal cancers occur in the YiLan township (ten cases), LouDon (five cases), WuJie (three cases), JhungWei (two cases) and DonShan (one case). The highest number of mortalities per year in the study area is 24. Residents of the six townships with high arsenic-affected groundwater should use tap water as drinking water and use groundwater only for other purpose. The well water in other townships in the Lanyang plain has no adverse effects on human health.     

Total and inorganic arsenic in the fauna of the Guadalquivir estuary: environmental and human health implications

To evaluate the impact on fauna of the release of toxic waste from the tailings dam operated by the Boliden Apirsa S.L company at Aznalcóllar, Seville (Spain) a study was carried out of total and inorganic arsenic contents in 164 samples from six different estuary species, including molluscs, crustaceans and fish, collected at six sampling stations distributed along the estuary and mouth of the River Guadalquivir. The contents found, expressed in micrograms per gram wet weight, were as follows. Total arsenic: Crassostrea angulata--giant cupped oyster (2.44 +/- 0.45); Scrobicularia plana--peppery furrow (2.50 +/- 0.73); Palaemon longirostris--delta prawn (1.33 +/- 0.54); Uca tangeri--AfroEuropean fiddler crab (1.76 +/- 0.08); Melicertus kerathurus--shrimp (3.60 +/- 1.92); and Liza ramada--mullet (0.65 +/- 0.38). Inorganic arsenic: C. angulata (0.09 +/- 0.02); S. plana (0.38 +/- 0.23); P. longirostris (0.04 +/- 0.01); U. tangeri (0.22 +/- 0.03); M. kerathurus (0.03 +/- 0.01); and L. ramada (0.03 +/- 0.03). The levels of total As are comparable to those obtained by other authors. With respect to inorganic arsenic, only S. plana and U. tangeri present high levels of inorganic arsenic. This may be due to the fact that these organisms live in estuary sediments, reservoirs of inorganic arsenic, and ingest particles of sediments during feeding. Because of the lack of information for this area concerning previous levels of total and inorganic arsenic in the species analysed, it was not possible to establish the impact on the fauna of the River Guadalquivir estuary of the toxic spill resulting from the failure of the mine tailings dam at Aznalcóllar. With respect to the implications to human health as a result of consumption of species from the Guadalquivir estuary, only with the species Scrobicularia plana, as a high consumption of this mollusc might, in some cases, exceed the maximum tolerable intake for inorganic arsenic indicated by the FAO/WHO. Consumption of the liver of L. ramada does not appear to present problems to human health.     

Exposure and risk assessment for aluminium and heavy metals in Puerh tea

As the consumption of Puerh tea is booming because of its multiple health-promoting effects, the possible health risks resulting from long-term exposure to metals contained in this tea need to be evaluated. To assess the human risk associated with drinking Puerh tea, concentrations of aluminium, lead, cadmium, mercury, zinc, copper and arsenic were determined in samples of Puerh tea, tea leaves from the plants, and planted soil collected from the Yunnan province, China. Site-specific exposure parameters such as body weight and consumption rate of Puerh tea were investigated in Kunming and Puer cities using face-to-face surveys. Health risks were evaluated for the inhabitants of Kunming and Puer cities by gender and by age groups. Although the Puerh tea plant easily absorbs aluminium from soil, the concentrations of Al and six other elements in Puerh tea were all far below the safety concentration limits of China. Both the HQ (Hazard Quotient) values for single elements and the HI (Hazard Index) value for all seven elements were far below one, indicating no non-carcinogenic risks from these seven elements for inhabitants of Kunming and Puer under the current consumption rates of Puerh tea. However, probabilistic estimation of carcinogenic risk shows that the 95th percentile carcinogenic rate of arsenic in Puerh tea approaches the accepted risk level of 10^− 4 for the highest exposure group. Therefore, the arsenic in Puerh tea is of concern.     

Role of dissolved and particulate cadmium in the accumulation of cadmium in cultured oysters (Crassostrea gigas)

Pacific oysters (Crassostrea gigas) collected on the coast of British Columbia, Canada have occasionally shown cadmium (Cd) concentrations at or above 2 microg g(-1) (wet weight), which has resulted in the loss of some international markets. This study investigated the source and transfer of Cd to oysters by focusing on the role of dissolved and particulate Cd in seawater. Parameters monitored for 1 year at two oyster farm sites on Vancouver Island included: oyster tissue mass and shell length, Cd in oysters, dissolved Cd, particulate Cd, temperature and salinity. Results show that dissolved Cd was the main source of Cd to the oysters and that Cd was mainly concentrated in the gut tissues. A seasonal trend was observed in Cd in oysters, in which levels were lowest during periods of higher temperatures. Results also indicate that the local oceanographic inputs and sediment diagenesis directly affect dissolved Cd and thereby influence the Cd levels in oysters. Particulate matter was not found to be a source of Cd in oysters, and was actually negatively correlated. This was likely due to the uptake of dissolved Cd by phytoplankton and the effect of phytoplankton on oyster tissue mass.     

Arsenic in coastal waters of South Australia

Surface seawater samples from South Australian coastal locations were analysed for dissolved inorganic arsenic [As(III) + As(V)], arsenite [As(III)] and particulate arsenic.Dissolved inorganic arsenic concentrations ranged from 1.10 to 1.61 μg As l^?1 (average 1.3 ± 0.1 μg As l^?1) with 1.2–4.3% (average 2.7%) present as arsenite. Particulate arsenic concentrations were below the limit of detection (0.0006 μg As l^?1) at most sampling stations.     

Pearl aquaculture-profitable environmental remediation?

Bivalve molluscs are filter feeders, with pearl oysters able to filter water at rates up to 25 lh(-1)g(-1) of dry wt. tissue. Since this process leads to rapid bioaccumulation of recalcitrant pollutants such as heavy metals, organochlorine pesticides and hydrocarbons from impacted sites, it has prompted the widespread use of molluscs as biomonitors to quantify levels of marine pollution. This paper proposes pearl oyster deployment as a novel bioremediation technology for impacted sites to remove toxic contaminants, reduce nutrient loads and lower concentrations of microbial pathogens. Estimates extrapolated from the literature suggest that a modest pearl oyster farm of 100 t oyster material per year could remove 300 kg heavy metals plus 24 kg of organic contaminants via deposition into the tissue and shell. Furthermore, it was estimated that up to 19 kg of nitrogen may be removed from the coastal ecosystem per tonne of pearl oyster harvested. Pearl oysters are also likely to filter substantial amounts of sewage associated microbial pathogens from the water column. Method of cultivation and site selection are the key to minimising negative environmental impacts of bivalve cultivation. Deployment of oysters at sites with high nutrient and contaminant loadings would be advantageous, as these compounds would be removed from the ecosystem whilst generating a value-added product. Future potential may exist for harvesting bio-concentrated elements for commercial production.     

Inorganic arsenic in cooked rice and vegetables from Bangladeshi households

Many Bangladeshi suffer from arsenic-related health concerns. Most mitigation activities focus on identifying contaminated wells and reducing the amount of arsenic ingested from well water. Food as a source of arsenic exposure has been recently documented. The objectives of this study were to measure the main types of arsenic in commonly consumed foods in Bangladesh and estimate the average daily intake (ADI) of arsenic from food and water. Total, organic and inorganic, arsenic were measured in drinking water and in cooked rice and vegetables from Bangladeshi households. The mean total arsenic level in 46 rice samples was 358 microg/kg (range: 46 to 1,110 microg/kg dry weight) and 333 microg/kg (range: 19 to 2,334 microg/kg dry weight) in 39 vegetable samples. Inorganic arsenic calculated as arsenite and arsenate made up 87% of the total arsenic measured in rice, and 96% of the total arsenic in vegetables. Total arsenic in water ranged from 200 to 500 microg/L. Using individual, self-reported data on daily consumption of rice and drinking water the total arsenic ADI was 1,176 microg (range: 419 to 2,053 microg), 14% attributable to inorganic arsenic in cooked rice. The ADI is a conservative estimate; vegetable arsenic was not included due to limitations in self-reported daily consumption amounts. Given the arsenic levels measured in food and water and consumption of these items, cooked rice and vegetables are a substantial exposure pathway for inorganic arsenic. Intervention strategies must consider all sources of dietary arsenic intake.     

Urinary arsenic methylation capability and carotid atherosclerosis risk in subjects living in arsenicosis-hyperendemic areas in southwestern Taiwan

Long-term exposure to inorganic arsenic from artesian drinking well water is associated with carotid atherosclerosis in the Blackfoot Disease (BFD)-hyperendemic area in Taiwan. The current study examined the arsenic methylation capacity and its risk on carotid atherosclerosis. A total of 304 adults (158 men and 146 women) residing in the BFD-hyperendemic area were included. The extent of carotid atherosclerosis was assessed by duplex ultrasonography. Chronic arsenic exposure was estimated by an index of cumulative arsenic exposure (CAE) and the duration of artesian well water consumption. Urinary levels of inorganic arsenite [As(III)], arsenate [As(V)], monomethylarsonic acid [MMA(V)] and dimethylarsinic acid [DMA(V)] were determined by high performance liquid chromatography linked on-line to a hydride generator and atomic absorption spectrometry (HPLC-HG-AAS). The percentage of arsenic species, primary methylation index [PMI = MMA(V) / (As(III) + As(V)] and secondary methylation index [SMI = DMA(V) / MMA(V)] were calculated and employed as indicators of arsenic methylation capacity. Results showed that women and younger subjects had a more efficient arsenic methylation capacity than did men and the elderly. Carotid atherosclerosis cases had a significantly greater percentage of MMA(V) [%MMA(V)] and a lower percentage of DMA [%DMA (V)] compared to controls. Subjects in the highest two tertiles of PMI with a median of CAE > 0 mg/L-year had an odds ratio (OR) and a 95% confidence interval (CI) of carotid atherosclerosis of 2.61 and 0.98-6.90 compared to those in the highest two tertiles of PMI with a CAE = 0 mg/L-year. We conclude that individuals with greater exposure to arsenic and lower capacity to methylate inorganic arsenic may be at a higher risk to carotid atherosclerosis.     

Detection of adenoviruses in shellfish by means of conventional-PCR, nested-PCR, and integrated cell culture PCR (ICC/PCR)

We tested three PCR based methodologies to detect adenoviruses associated with cultivated oysters. Conventional-PCR, nested-PCR, and integrated cell culture-PCR (ICC/PCR) were first optimized using oysters seeded with know amounts of Adenovirus serotype 5 (Ad5). The maximum sensitivity for Ad5 detection was determined for each method, and then used to detect natural adenovirus contamination in oysters from three aquiculture farms in Florianopolis, Santa Catarina State, Brazil, over a period of 6 months. The results showed that the nested-PCR was more sensitive (limit of detection: 1.2 PFU/g of tissue) than conventional-PCR and ICC-PCR (limit of detection for both: 1.2 x 10(2)PFU/g of tissue) for detection of Ad5 in oyster extracts. Nested-PCR was able to detect 90% of Ad5 contamination in harvested oyster samples, while conventional-PCR was unable to detect Ad5 in any of the samples. The present work suggests that detection of human adenoviruses can be used as a tool to monitor the presence of human viruses in marine environments where shellfish grow, and that nested-PCR is the method of choice.     

Arsenic biogeochemistry and human health risk assessment in organo-arsenical pesticide-applied acidic and alkaline soils: an incubation study

Organo-arsenical compounds are considered non-carcinogenic, and hence, are still allowed by the regulatory agencies for use in agriculture as pesticides. Due to rapid encroachment of suburban areas into former agricultural lands, the potential for human exposure to soil-arsenic has increased tremendously in recent years. However, insufficient data is available on the stability of organo-arsenicals in soils; as to whether they remain in an organic form, or are converted over time to potentially carcinogenic inorganic forms. A static incubation study was conducted to estimate soil speciation and in-vitro bioavailability (i.e., bioaccessibility) of arsenic as a function of soil properties. Two chemically variant soil types were chosen, based on their potential differences with respect to arsenic reactivity: an acid sand with minimal arsenic retention capacity and an alkaline clay loam with relatively high concentrations of Fe/Al and Ca/Mg. The soils were amended with dimethylarsenic acid (DMA) at three rates, 45, 225 and 450 mg/kg, and incubated for 1 year. A sequential extraction scheme was employed to identify the geochemical forms of arsenic in soils, which were correlated with the in-vitro bioavailable fractions of arsenic. Human health risk calculated in terms of excess cancer risk (ECR) showed that risk assessment based on bioaccessible arsenic concentrations instead of the traditional total soil arsenic is a more realistic approach. Results showed that soil properties (such as pH, Fe/Al content and soil texture) of the two soils dictated the geochemical speciation, and hence, bioaccessibility of arsenic from DMA, indicating that the use of organic arsenicals as pesticides in mineral soils may not be a safe practice from a human health risk perspective.     

Arsenic binding mechanisms on natural red earth: a potential substrate for pollution control

Natural red earth (hereafter NRE) was used as a novel adsorbent to examine its retention behaviour in different inorganic arsenic species (As (III) and As (V)) that are abundant in natural water. Adsorption isotherms were constructed at pH approximately 5.5 for As(III) and As(V) in 0.01 M NaNO(3) at 298K for 5 g/L NRE system. The initial arsenic [As(III) or As(V)] concentrations varied between approximately 10(-5) and approximately 10(-4) M. The experimental data were quantified using single site or stepwise Langmuir models. Sorption maximum, was observed at approximately 0.173 mM of As(V). To reach the maximum surface coverage of red earth at pH approximately 5.5 As(III) requires approximately 0.308 mM of initial loading. When compared to As (III), As(V) shows strong affinity for NRE surface sites. This study suggests the potential of NRE as a starting material in decontaminating water polluted with As species.     

Health risks of heavy metals to the general public in Tianjin, China via consumption of vegetables and fish

Consumption of vegetables and fish contaminated with the heavy metals Cu, Zn, Pb, Cd, Hg, and Cr is the most likely route for human exposure in Tianjin, China. Health risks associated with these heavy metals were assessed based on the target hazard quotients (THQs), which can be derived from concentrations of heavy metals in vegetables and fish consumed in four districts (Dong Li, Xi Qing, Jin Nan, and Bei Chen) and the urban area of Tianjin, China. Individual metal THQ (<1) values indicate the relative absence of health risks associated with intake of a single heavy metal through consumption of either contaminated vegetables or fish only. However, consumption of both vegetables and fish would lead to potential health risks especially for children, since individual THQs for vegetables and fish would sum up to almost 1. If individual THQs resulting from crops consumption are considered, the health risks would be greater for children since the THQ values will always be >1. Risk contribution from Cr is minimal compared to the other elements. Hg is the major risk contributor for children in Bei Chen since the THQ contribution amounts to about 45% of the total THQ values due to vegetables and fish consumption. The health risk to adults in Ding Li is ascribed mainly to the intake of Cd by vegetables and fish consumption, which contributes a substantial fraction to the total THQ (about 51%).     

Field and laboratory arsenic speciation methods and their application to natural-water analysis

The toxic and carcinogenic properties of inorganic and organic arsenic species make their determination in natural water vitally important. Determination of individual inorganic and organic arsenic species is critical because the toxicology, mobility, and adsorptivity vary substantially. Several methods for the speciation of arsenic in groundwater, surface-water, and acid mine drainage sample matrices using field and laboratory techniques are presented. The methods provide quantitative determination of arsenite [As(III)], arsenate [As(V)], monomethylarsonate (MMA), dimethylarsinate (DMA), and roxarsone in 2-8 min at detection limits of less than 1 microg arsenic per liter (microg As L(-1)). All the methods use anion exchange chromatography to separate the arsenic species and inductively coupled plasma-mass spectrometry as an arsenic-specific detector. Different methods were needed because some sample matrices did not have all arsenic species present or were incompatible with particular high-performance liquid chromatography (HPLC) mobile phases. The bias and variability of the methods were evaluated using total arsenic, As(III), As(V), DMA, and MMA results from more than 100 surface-water, groundwater, and acid mine drainage samples, and reference materials. Concentrations in test samples were as much as 13,000 microg As L(-1) for As(III) and 3700 microg As L(-1) for As(V). Methylated arsenic species were less than 100 microg As L(-1) and were found only in certain surface-water samples, and roxarsone was not detected in any of the water samples tested. The distribution of inorganic arsenic species in the test samples ranged from 0% to 90% As(III). Laboratory-speciation method variability for As(III), As(V), MMA, and DMA in reagent water at 0.5 microg As L(-1) was 8-13% (n=7). Field-speciation method variability for As(III) and As(V) at 1 microg As L(-1) in reagent water was 3-4% (n=3).     

Detection of hepatitis A virus (HAV) in oysters (Crassostrea gigas)

Because shellfish (oysters, clams, and mussels) are filter-feeders, pathogens become concentrated within them, and human consumption of raw, or under-cooked shellfish can result in disease outbreaks. Identification of hepatitis A virus (HAV) in shellfish has been difficult for several reasons: the concentration of virions in shellfish tissues are very low, detection methods based on in vitro propagation are unreliable, recovery of virions from shellfish tissues is inefficient, and PCR inhibitors in shellfish tissues limit the success of RT-PCR. These facts underlie difficulties in determining cause and effect relationships between hepatitis A outbreaks and detection of HAV contamination in shellfish samples. We have developed a reliable and highly sensitive method for detection of HAV in oyster tissues at low levels (0.001 FFU/ml-fluorescent focus units per milliliter). Our method combines dissection of the gastrointestinal oyster tract, organic extraction before PEG precipitation, and RNA extraction with Trizol LS, followed by RT-PCR and hybridization using a digoxigenin-labeled HAV cDNA probe. Our results will benefit both public health officials concerned about hepatitis A infections caused by consumption of HAV-contaminated oysters and shellfish producers who require reliable methods for quality control of commercial oyster production.     

Preparation and evaluation of iron–chitosan composites for removal of As(III) and As(V) from arsenic contaminated real life groundwater

A study on the removal of arsenic from real life groundwater using iron–chitosan composites is presented. Removal of arsenic(III) and arsenic(V) was studied through adsorption at pH 7.0 under equilibrium and dynamic conditions. The equilibrium data were fitted to Langmuir adsorption models and the various model parameters were evaluated. The monolayer adsorption capacity from the Langmuir model for iron chitosan flakes (ICF) (22.47 ± 0.56 mg/g for As(V) and 16.15 ± 0.32 mg/g for As(III)) was found to be considerably higher than that obtained for iron chitosan granules (ICB) (2.24 ± 0.04 mg/g for As(V); 2.32 ± 0.05 mg/g for As(III)). Anions including sulfate, phosphate and silicate at the levels present in groundwater did not cause serious interference in the adsorption behavior of arsenate/arsenite. The column regeneration studies were carried out for two sorption–desorption cycles for both As(III) and As(V) using ICF and ICB as sorbents. One hundred and forty-seven bed volumes of As(III) and 112 bed volumes of As(V) spiked groundwater were treated in column experiments using ICB, reducing arsenic concentration from 500 to <10 μg/l. The eluent used for the regeneration of the spent sorbent was 0.1 M NaOH. The adsorbent was also successfully applied for the removal of total inorganic arsenic down to <10 μg/l from real life arsenic contaminated groundwater samples.     

Biomonitoring of trace metal contamination in the Potengi estuary, Natal (Brazil), using the oyster Crassostrea rhizophorae, a local food source.

The oyster Crassostrea rhizophorae was collected in September 1997 from 10 stations along the Potengi estuary, Natal, Brazil, a mangrove-lined estuary receiving anthropogenic inputs of trace metals. C. rhizophorae is a net accumulator of trace metals and can be used as a biomonitor, the accumulated soft tissue concentrations representing integrated records of bioavailable metal fractions over the life of the oyster. Significant differences in oyster accumulated concentrations (and hence bioavailabilities) of Fe, Zn, Cu, Cr, Pb, Cd, Ni and Ag (but not Mn) were found between stations, and attributed to anthropogenic inputs including discharges of sewage and industrial effluent. The oysters are also a local food source, and concentrations of zinc, copper and lead in some of the oysters are above typical public health recommended limits.     

Environmental exposure to lead and arsenic among children living near a glassworks

Concentrations of lead (Pb) in blood (B-Pb, geometric mean 34.6 micrograms l-1, n = 127) and inorganic arsenic (As) and its metabolites in urine (U-As, mean 5.1 micrograms/g creatinine, n = 35) did not differ between children living in a village close to a glassworks emitting both Pb and As and children living in a reference area. There was no significant effect on B-Pb and U-As related to parents working at the glassworks or consumption of domestically grown vegetables. Neither was there any significant effect upon B-Pb of sex, age, potentially lead-exposing hobbies, or consumption of canned foods. Boys had higher U-As than girls (5.8 vs 4.2 micrograms/g creatinine, p = 0.005), and there was a decrease with age (range 8.4-10.4 years, 27% per year, p = 0.01). Further, parental smoking habits had a significant effect on both B-Pb and U-As. In children of non-smoking parents the B-Pb was 30 micrograms l-1, in children with one parent who smoked 39 micrograms l-1 (smoking father 37, smoking mother 41 micrograms l-1) and in children with two parents who smoked 47 micrograms l-1 (p less than 0.001). The corresponding values for U-As were 4.2, 5.5, and 13 micrograms/g creatinine, respectively (p = 0.01).     

Arsenic oxidation and bioaccumulation by the acidophilic protozoan, Euglena mutabilis, in acid mine drainage (Carnoulès, France)

In the acid stream (pH 2.5-4.7) originating from the Carnoulès mine tailings, the acidophilic protozoan Euglena mutabilis grows with extremely high sulfate (1.9-4.9 g/l), iron (0.7-1.7 g/l) and arsenic concentrations (0.08-0.26 g/l). Strong variations in flow rate and high sulfate concentrations (up to 4.9 g/l) have been registered in early winter and might be the reason for the reduction in cell number of the protozoan from October to December 2001. No relation was established between arsenic concentration and/or speciation and abundance of the protozoan in the stream. Arsenite, which is the most toxic form, predominates in water. The oxidation of arsenite to arsenate occurred within a few days in laboratory experiments when E. mutabilis was present in Reigous Creek water and synthetic As(III)-rich culture medium. Methylated compounds (MMA, DMA) were not identified in the culture media. The protozoan bioaccumulated As in the cell (336 +/- 112 microg As/g dry wt.) as inorganic arsenite (105 +/- 52 microg As/g dry wt.) and arsenate (231 +/- 112 microg As/g dry wt.). Adsorption of As at the cell surface reached 57 mg/g dry wt. in the As(V) form for E. mutabilis grown in 250 mg/l As(III) synthetic medium. Both intracellular accumulation and adsorption at the cell surface increased for increasing As(III) concentration in the medium but the concentration factor in the cell relative to soluble As decreased.