Arsenic drinking water exposure and urinary excretion among adults in the Yaqui Valley, Sonora, Mexico

The objective of this study was to determine arsenic exposure via drinking water and to characterize urinary arsenic excretion among adults in the Yaqui Valley, Sonora, Mexico. A cross-sectional study was conducted from July 2001 to May 2002. Study subjects were from the Yaqui Valley, Sonora, Mexico, residents of four towns with different arsenic concentrations in their drinking water. Arsenic exposure was estimated through water intake over 24 h. Arsenic excretion was assessed in the first morning void urine. Total arsenic concentrations and their species arsenate (As V), arsenite (As III), monomethyl arsenic (MMA), and dimethyl arsenic (DMA) were determined by HPLC/ICP-MS. The town of Esperanza with the highest arsenic concentration in water had the highest daily mean intake of arsenic through drinking water, the mean value was 65.5 microg/day. Positive correlation between total arsenic intake by drinking water/day and the total arsenic concentration in urine (r = 0.50, P < 0.001) was found. Arsenic excreted in urine ranged from 18.9 to 93.8 microg/L. The people from Esperanza had the highest geometric mean value of arsenic in urine, 65.1 microg/L, and it was statistically significantly different from those of the other towns (P < 0.005). DMA was the major arsenic species in urine (47.7-67.1%), followed by inorganic arsenic (16.4-25.4%), and MMA (7.5-15%). In comparison with other reports the DMA and MMA distribution was low, 47.7-55.6% and 7.5-9.7%, respectively, in the urine from the Yaqui Valley population (except the town of Cocorit). The difference in the proportion of urinary arsenic metabolites in those towns may be due to genetic polymorphisms in the As methylating enzymes of these populations.     

Effects of arsenic speciation and low dissolved oxygen condition on the toxicity of arsenic to a lotic mayfly

The influence of site-specific conditions on contaminant bioavailability and toxicity to benthic invertebrates is a key consideration in the environmental risk assessment process. This is particularly relevant for contaminants with complex speciation chemistries, such as arsenic. The present study addressed uncertainties regarding arsenic toxicity to a mayfly (Baetis tricaudatus) under low dissolved oxygen (DO) conditions characteristic of many contaminated sites. Arsenic toxicity (arsenite, As(III); arsenate, As(V)) to mayfly nymphs was assessed under two DO scenarios (68 and 84% saturation). Arsenic speciation ratios were determined during testing to confirm the nature of arsenic exposure. The present study found that As(III) was more lethal and bioaccumulated to a greater degree in B. tricaudatus compared to As(V), but the sublethal toxicities of the two arsenic species were similar. Nymph growth and development were significantly inhibited after 12 d of exposure to both 1 mg/L of As(III) and As(V). Exposure to arsenic under low DO conditions (6.5 mg/L, 68% saturation) did not significantly affect As(III) or As(V) toxicity and bioaccumulation over 12 d. The DO level of 6.5 mg/L, however, appeared to be marginally lethal to B. tricaudatus. Results indicate that the Canadian arsenic criterion for the protection of aquatic life (5 microg/L) is protective of B. tricaudatus and is low enough to accommodate differences in arsenic toxicity because of the interconversions between As(III) and As(V). These findings provide insight regarding the toxicity and speciation of arsenic under DO conditions considered to be low for this lotic mayfly species and representative of existing conditions at mine sites in northern Canada.     

Modification of risk of arsenic-induced skin lesions by sunlight exposure, smoking, and occupational exposures in Bangladesh

BACKGROUND: The risk of skin lesions associated with arsenic exposure from drinking water in Bangladesh is considerably greater in men than in women. METHODS: Using baseline data from 11,062 cohort members in the Health Effects of Arsenic Longitudinal Study in Araihazar, Bangladesh, we performed a cross-sectional analysis to evaluate whether the association between arsenic exposure from drinking water and the risk of skin lesions is modified by tobacco smoking, excessive sunlight, the use of fertilizer, and the use of pesticides. A time-weighted well arsenic concentration was estimated for each participant by incorporating history of well use. Relative excess risk for interaction (RERI) and its 95% confidence intervals (CIs) were estimated using adjusted prevalence odds ratios. RESULTS: We observed a synergistic effect between the highest level of arsenic exposure (> 113 microg/L) and tobacco smoking on risk of skin lesions in men (RERI = 1.5 [95% CI = 0.3 to 2.7] overall and 1.7 [0.2 to 3.4] for the subpopulation with longer-term arsenic exposure). We also observed suggestive synergistic effects between higher levels (28.1-113.0 microg/L and 113.1-864.0 microg/L) of arsenic exposure and fertilizer use in men (RERI = 1.0 [-0.2 to 2.2] and 1.3 [-0.2 to 2.9] respectively). Furthermore, the risk of skin lesions associated with any given level of arsenic exposure was greater in men with excessive sun exposure. The patterns of effect estimates in women indicate similar-but-weaker interaction effects of arsenic exposure with tobacco smoking and fertilizer use. CONCLUSIONS: These findings help explain why the risk of arsenic-related skin lesions was much greater in men than in women in Bangladesh. Because most arsenic-induced skin cancers arise from these skin lesions, treatment and remediation plans should take into consideration these etiologic cofactors.     

Effectiveness of arsenic mitigation program in Bangladesh--relationship between arsenic concentrations in well water and urine

BACKGROUND: Arsenic in drinking water remains a major public problem in Bangladesh, although arsenic mitigation programs began there a decade ago. The purpose of this study was to examine the effectiveness of this program by determining the relationship between current arsenic levels in well water and the high level of urinary arsenic excretion. METHODS: A community-based cross-sectional study was conducted in the Pabna district of Bangladesh between May and July 2005. We included 174 married couples and collected their drinking water from 138 wells. The allowable limit for arsenic in drinking water is 50 microg/L in Bangladesh, while the normal level of urinary arsenic is < or =40 microg x 1.5 L(-1) x day(-1) by Dhaka Community Hospital. RESULTS: Of 348 subjects, 304 exceeded the urinary arsenic level of 40 microg x 1.5 L(-1) x day(-1). Of all wells, 44.2% had arsenic levels >50 microg/L. Multiple-adjusted odds ratios of urinary arsenic level >40 microg x 1.5 L(-1) x day(-1) were 8.90 (95% CI: 3.31-23.93) for the arsenic level in well water of 11-50 microg/L, and 53.07 (11.91-236.46) for that of 51-332 microg/L, compared with < or =10 microg/L. When the Bangladeshi standard arsenic level in drinking water of 50 microg/L was used, the sensitivity in detecting subjects with a urinary arsenic level >40 microg x 1.5 L(-1) x day(-1) was 50%, although when the World Health Organization (WHO) guideline value of 10 microg/L was used, it was 76.3%. CONCLUSIONS: Green marked wells, which the Bangladesh government regards as safe, are not always safe. The mitigation programs should use the WHO guideline arsenic level to determine the safety of well water for drinking.     

氢化物发生—原子荧光光谱法(HG-AFS)测定食品中不同价态的无机砷

应用氢化物发生——原子荧光分析技术建立了食品中总无机砷、三价砷［Ａｓ（Ⅲ）］和五价砷［Ａｓ（Ⅴ）］的测定方法。用６ｍ ｏｌ／ＬＨＣｌ提取食品中无机砷,在２ｍ ｏｌ／ＬＨＣｌ条件下测定总无机砷,再利用三价砷、五价砷氢化物发生酸度条件的不同对三价砷进行选择测定。本方法标准曲线线性范围：总无机砷为０～４００μｇ／Ｌ,Ａｓ（Ⅲ）为０～３００μｇ／Ｌ;检出限：总无机砷１．６μｇ／Ｌ,Ａｓ（Ⅲ）１．１μｇ／Ｌ;相对标准偏差：总无机砷为１．９３％ ,Ａｓ（Ⅲ）为２．４９％ ;样品回收率：总无机砷为８５％ ～１０５％ ,Ａｓ（Ⅲ）为８０％ ～１１５％ ;一般食品样品的测定无干扰。     

Inorganic arsenic speciation in soil and groundwater near in-service chromated copper arsenate-treated wood poles

The environmental impact of chromated copper arsenate (CCA)-treated utility poles is linked to the possible soil and groundwater contamination with arsenic. The objective of the present study was to determine the arsenic speciation in soil and groundwater near in-service CCA-treated poles. Arsenite (As[III]) and arsenate (As[V]) concentrations were determined in 29 surface and subsurface soil samples collected near eight CCA-treated wood poles. Temporal variability of total arsenic concentrations and inorganic arsenic speciation was also assessed in groundwater at two sites through four sampling events over a 19-month period. Arsenic speciation was carried out by a solvent extraction method using ammonium pyrrolidine dithiocarbamate-methyl isobutyl ketone, and total arsenic was quantified by inductively coupled plasma/atomic emission spectrometry/hydride generation. Average arsenic concentrations in surface soils immediately adjacent to utility poles ranged from 153+/-49 to 410+/-150 mg/kg but approached background levels (below 5 mg/kg) within 0.50 m from the poles. A positive correlation was found between surface soil As concentration and total Fe content. In subsurface samples (0.50 m), arsenic levels were generally high in sandy soils (up to 223+/-32 mg/kg), moderate in clayey soils (up to 126+/-26 mg/kg), and relatively lower in organic soils (up to 56+/-24 mg/ kg). Arsenic(V) was the predominant arsenic species in surface (>78%) and subsurface soils (>66%). Total arsenic concentrations in groundwater below the clayey site were high and varied widely over time (79-390 microg/L), with 30 to 68% as As(III). Below the utility pole located on the organic site with a high Fe content, lower total arsenic levels (12-33 microg/L) were found, with As(III) ranging from 0 to 100%.     

Unventilated indoor coal-fired stoves in Guizhou province, China: cellular and genetic damage in villagers exposed to arsenic in food and air

BACKGROUND: Inorganic arsenic (iAs) is a well-known human carcinogen recognized by the World Health Organization and the International Agency for Research on Cancer. Currently, most iAs studies in populations are concerned with drinking water and occupational arsenicosis. In Guizhou province, arsenicosis caused by the burning of coal in unventilated indoor stoves is an unusual type of exposure. Because the poisoning mechanism involved in arsenicosis is as yet unknown and no effective therapy exists, progress has been slow on the prevention and therapy of arsenicosis. OBJECTIVES: We examined the relationship between arsenic (As) exposure from the burning of coal in unventilated indoor stoves and genetic damage in humans, using cellular and molecular indices. We selected villagers from Jiaole township, Guizhou province, China, who had been exposed to milligram levels of As daily via food and air contaminated by the burning of As-containing coal in unventilated indoor stoves. RESULTS: The As-exposed subjects from Jiaole were divided into four groups according to skin lesion symptoms: nonpatients, mild, intermediate, and severe arsenicosis. Another 53 villagers from a town 12 km from Jiaole were recruited as the external control group. In the four groups of exposed subjects, As concentrations in urine and hair were 76-145 microg/L and 5.4-7.9 microg/g, respectively. These values were higher than those in the external control group, which had As concentrations of 46 microg/L for urine and 1.6 microg/g for hair. We measured sister chromatid exchange and chromosomal aberrations to determine human chromosome damage, and for DNA damage, we measured DNA single-strand breaks and DNA-protein cross-links. All measurements were higher in the four exposed groups compared with the external control group. DNA repair was impaired by As exposure, as indicated by the mRNA of O-6-methylguanine-DNA methyltransferase (MGMT), X-ray repair complementing defective repair in Chinese hamster cells 1 (XRCC1), and, to a lesser extent, by the mismatch repair gene hMSH2 mRNA. The expression of mutant-type p53 increased with aggravation of arsenicosis symptoms, whereas the expression of p16-INK4(p16) decreased. p53 mutated at a frequency of 30-17% in the carcinoma (n = 10) and precarcinoma (n = 12) groups. No mutation was found in p16, although deletion was evident. Deletion rates were 8.7% (n = 23) and 38.9% (n = 18) in noncarcinoma and carcinoma groups, respectively. CONCLUSIONS: The results showed that long-term As exposure may be associated with damage of chromosomes and DNA, gene mutations, gene deletions, and alterations of DNA synthesis and repair ability.     

Arsenic species in solutions for parenteral nutrition

BACKGROUND: In spite of its high toxicity, arsenic is a common contaminant in pharmaceuticals. This is stated by pharmacopoeias' monographs where it is not generically included with other heavy metals, but has its own specifications. Arsenic should not exceed 0.1 mg/L in most pharmaceutical products for IV administration. This limit, however, was established without taking into consideration the specific arsenic species which contribute to this amount. In this work, the presence of arsenite and arsenate species in solutions of amino acids, salts, vitamins, and lipids commercialized for IV administration was investigated. METHODS: The measurements were done by hydride generation atomic absorption spectrometry. RESULTS: The results showed that all commercial formulations contain both arsenic species in some level; however, the total arsenic content exceeded the allowed limit in only a few samples. Calcium gluconate, sodium bicarbonate, heparin, and vitamin solutions were the most contaminated, presenting total arsenic concentration ranging from 62 to 249 microg/L. The most important finding, however, was the different ratios As(V)/As(III) among the formulations. Whereas practically only As(V) was found in ampoules containing water for injection and salt solutions (NaCl, KC1, phosphates), As(III) predominated in solutions of vitamins, gluconate, and glucose. As these are reducing substances, we investigated the possibility of their reaction with As(V) and its conversion into As(III). The heating of As(V) in the presence of gluconate, glucose, ascorbic acid, methionine, isoleucine, sodium chloride, and pure water, in autoclave for 15 minutes, showed that, whereas no As(III) was found in pure water and sodium chloride solution, approximately 50% of As(V) was converted into As(III) in the remainder of the solutions. Conclusions: The results showed that As(V), the main species in these formulations, may be converted into As(III), depending on the presence of reducing substances among the formulation constituents.     

Risk of arsenic-related skin lesions in Bangladeshi villages at relatively low exposure: a report from Gonoshasthaya Kendra

OBJECTIVE: Arsenic concentrations in 25% of tube wells in Bangladesh exceed 50 microg/L, a level known to be hazardous. Levels in individual wells vary widely. We gathered data on arsenic exposure levels and skin lesion prevalence to address the lack of knowledge about risks where the average arsenic concentrations was lower. METHODS: The nongovernmental organization Gonoshasthaya Kendra did three related studies of keratotic skin lesions since 2004: (1) an ecological prevalence survey among 13 705 women aged > 18 in a random sample of 53 villages; (2) a case-control study of 176 cases and age- and village-matched referents; and (3) a prevalence survey of the entire population of 11,670 in two additional villages. We calculated prevalence as a function of average arsenic concentrations as reported in the National Hydrochemical Survey, and measured arsenic concentrations in wells used by subjects in the case-control study. FINDINGS: The prevalence of skin lesions was 0.37% in people exposed to arsenic concentrations below 5 microg/L, 0.63% at 6-50 microg/L, and 6.84% at 81 microg/L. In the case-control analysis, relative risk of skin lesions increased threefold at concentrations above 50 microg/L (P < 0.05). CONCLUSION: Little serious skin disease is likely to occur if the arsenic concentration in drinking water is kept below 50 microg/L, but ensuring this water quality will require systematic surveillance and reliable testing of all wells, which may be impractical. More research is needed on feasible prevention of toxic effects from arsenic exposure in Bangladesh.     

Prevalence of arsenic exposure and skin lesions. A population based survey in Matlab, Bangladesh

STUDY OBJECTIVE: To assess prevalence of arsenic exposure through drinking water and skin lesions, and their variation by geographical area, age, sex, and socioeconomic conditions. DESIGN, SETTING, AND PARTICIPANTS: Skin lesion cases were identified by screening the entire population above 4 years of age (n = 166,934) living in Matlab, a rural area in Bangladesh, during January 2002 and August 2003. The process of case identification involved initial skin examinations in the field, followed by verification by physicians in a clinic, and final confirmation by two independent experts reviewing photographs. The tubewell water arsenic concentrations (n = 13,286) were analysed by atomic absorption spectrometry. Drinking water history since 1970 was obtained for each person. Exposure information was constructed using drinking water histories and data on water arsenic concentrations. MAIN RESULTS: The arsenic concentrations ranged from <1 to 3644 microg/l, and more than 70% of functioning tubewells exceeded the World Health Organisation guideline of 10 microg/l. Arsenic exposure had increased steadily from 1970s to the late 1990s, afterwards a decrease could be noted. In total, 504 skin lesions cases were identified, and the overall crude prevalence was 3/1000. Women had significantly higher cumulative exposure to arsenic, while men had significantly higher prevalence of skin lesions (SMR 158, 95% CI 133 to 188). The highest prevalence occurred in 35-44 age groups for both sexes. Arsenic exposure and skin lesions had a positive association with socioeconomic groups and achieved educational level. CONCLUSIONS: The result showed sex, age, and socioeconomic differentials in both exposure and skin lesions. Findings clearly showed the urgency of effective arsenic mitigation activities.     

Total arsenic accumulation in yabbies (Cherax destructor Clark) exposed to elevated arsenic levels in Victorian gold mining areas, Australia

Arsenic is a proven carcinogen often found at high concentrations in association with gold and other heavy metals. The freshwater yabby, Cherax destructor Clark (Decapoda, Parastacidae), is a ubiquitous species native to Australia's central and eastern regions, with a growing international commercial market. However, in this region of Australia, yabby farmers often harvest organisms from old mine tailings dams with elevated environmental arsenic levels. Yabbies exposed to elevated environmental arsenic were found to accumulate and store as much as 100 microg/g arsenic in their tissues. The accumulation is proportional to the concentration of arsenic in the sediment and is high enough to be of concern for people who eat the yabbies. A comparison of arsenic levels in wild and lab-fed animals also was performed. Although there was no significant difference in the level of arsenic in the various organs of the wild animals, the animals purchased from a yabby farm showed a significantly higher arsenic concentration in their hepatopancreas (3.7 +/- 0.9 microg/g) compared to other organs (0.6-1.8 microg/g). Furthermore, after a 40-d exposure to food containing 200 to 300 microg/g inorganic arsenic, arsenate (As[V])-exposed animals showed a significant increase in tissue-specific arsenic accumulation, whereas arsenite (As[III])-exposed animals showed a lower, nonsignificant increase in As uptake, primarily in the hepatopancreas. These results have important implications for yabby growers and consumers alike.     

Metabolism of 74As-labeled trivalent and pentavalent inorganic arsenic in mice

Man is exposed to different forms of arsenic in the environment but differences in metabolism and toxicity are poorly understood. The differences in metabolism between pentavalent and trivalent inorganic arsenic in mice following single oral administration of ⁷⁴As-labeled arsenate or arsenite (0.4 and 4 mg As/kg body wt) was studied. Valence state of the administered arsenic was strictly controlled, which has not always been the case in previous studies. In mice given the high dose, whole body retention was two to three times higher after exposure to As(III) compared to As(V). Retention was also dose dependent. Five weeks after administration, high dose/low dose retention ratios were 6 and 11 for As(V) and As(III). Differences found in most organs studied (blood, kidney, liver, bile, brain, skeleton, and skin) were most obvious in liver and bile with concentrations 2 to 10 times higher in the As(III) groups. Red cell/plasma ratios were 2–3 for As(III) and close to unity for As(V). It is suggested that the observed differences between As(V) and As(III) are due to differences in degree of methylation and subsequent elimination primarily via the kidneys.     

Reduction in urinary arsenic levels in response to arsenic mitigation efforts in Araihazar, Bangladesh

BACKGROUND: There is a need to identify and evaluate an effective mitigation program for arsenic exposure from drinking water in Bangladesh. OBJECTIVE: We evaluated the effectiveness of a multifaceted mitigation program to reduce As exposure among 11,746 individuals in a prospective cohort study initiated in 2000 in Araihazar, Bangladesh, by interviewing participants and measuring changes in urinary As levels. METHODS: The interventions included a) person-to-person reporting of well test results and health education; b) well labeling and village-level health education; and c) installations of 50 deep, low-As community wells in villages with the highest As exposure. RESULTS: Two years after these interventions, 58% of the 6,512 participants with unsafe wells (As >/=50 microg) at baseline had responded by switching to other wells. Well labeling and village-level health education was positively related to switching to safe wells (As < 50 mug/L) among participants with unsafe wells [rate ratio (RR) = 1.84; 95% confidence interval (CI), 1.60-2.11] and inversely related to any well switching among those with safe wells (RR = 0.80; 95% CI, 0.66-0.98). The urinary As level in participants who switched to a well identified as safe (< 50 microg As/L) dropped from an average of 375 microg As/g creatinine to 200 microg As/g creatinine, a 46% reduction toward the average urinary As content of 136 microg As/g creatinine for participants that used safe wells throughout. Urinary As reduction was positively related to educational attainment, body mass index, never-smoking, absence of skin lesions, and time since switching (p for trend < 0.05). CONCLUSIONS: Our study shows that testing of wells and informing households of the consequences of As exposure, combined with installation of deep community wells where most needed, can effectively address the continuing public health emergency from arsenic in drinking water in Bangladesh.     

Breast-feeding protects against arsenic exposure in Bangladeshi infants

BACKGROUND: Chronic arsenic exposure causes a wide range of health effects, but little is known about critical windows of exposure. Arsenic readily crosses the placenta, but the few available data on postnatal exposure to arsenic via breast milk are not conclusive. AIM: Our goal was to assess the arsenic exposure through breast milk in Bangladeshi infants, living in an area with high prevalence of arsenic-rich tube-well water. METHODS: We analyzed metabolites of inorganic arsenic in breast milk and infant urine at 3 months of age and compared them with detailed information on breast-feeding practices and maternal arsenic exposure, as measured by concentrations in blood, urine, and saliva. RESULTS: Arsenic concentrations in breast-milk samples were low (median, 1 microg/kg; range, 0.25-19 microg/kg), despite high arsenic exposures via drinking water (10-1,100 microg/L in urine and 2-40 microg/L in red blood cells). Accordingly, the arsenic concentrations in urine of infants whose mothers reported exclusive breast-feeding were low (median, 1.1 microg/L; range, 0.3-29 microg/L), whereas concentrations for those whose mothers reported partial breast-feeding ranged from 0.4 to 1,520 microg/L (median 1.9 microg/L). The major part of arsenic in milk was inorganic. Still, the infants had a high fraction (median, 87%) of the dimethylated arsenic metabolite in urine. Arsenic in breast milk was associated with arsenic in maternal blood, urine, and saliva. CONCLUSION: Very little arsenic is excreted in breast milk, even in women with high exposure from drinking water. Thus, exclusive breast-feeding protects the infant from exposure to arsenic.     

Arsenic biotransformation by the brown macroalga, Fucus serratus

The brown alga Fucus serratus was maintained in aquaria with added arsenate (0, 20, 50, and 100 microg As/L, four individuals per treatment) for up to 19 weeks. Biotransformation of arsenic by Fucus was monitored by high-performance liquid chromatography/inductively coupled plasma mass spectrometry and liquid chromatography/electrospray mass spectrometry analysis of aqueous extracts of algal frond tips removed periodically throughout the experiment. Major arsenic species monitored were arsenate, arsenite, methylarsonate, dimethylarsinate, and the four arsenosugars 1 to 4 found naturally in Fucus. Algae accumulated arsenate readily and transformed it into several arsenic compounds depending on the exposure concentration. At 100 microg As/L, the major metabolite was arsenite with smaller quantities of methylarsonate and dimethylarsinate, but only traces of arsenosugars were formed. In contrast, the 20-microg-As/L group accumulated only small quantities of arsenite and methylarsonate, while dimethylarsinate and arsenosugars were major arsenic metabolites. At 50 microg As/L exposure, algae had significant quantities of all arsenic metabolites monitored. Arsenate was toxic to the algae at 100 microg As/L but had no obvious detrimental effect at 20 microg As/L. The data are consistent with a process of arsenate detoxification by reduction and alkylation; at higher exposures, however, the alkylation processes become saturated, leading to an accumulation of arsenite and subsequent toxicity.     

The development and use of an innovative laboratory method for measuring arsenic in drinking water from western Bangladesh

All of Bangladesh's approximately 10 million drinking-water tube wells must be periodically tested for arsenic. The magnitude of this task and the limited resources of Bangladesh have led to the use of low-cost, semiquantitative field kits that measure As to a relatively high 50 microg/L national drinking water standard. However, there is an urgent need to supplement and ultimately replace these field kits with an inexpensive laboratory method that can measure As to the more protective 10 microg/L World Health Organization (WHO) health-based drinking water guideline. Unfortunately, Bangladesh has limited access to atomic absorption spectrometers or other expensive instruments that can measure As to the WHO guideline of 10 microg/L. In response to this need, an inexpensive and highly sensitive laboratory method for measuring As has been developed. This new method is the only accurate, precise, and safe way to quantify As < 10 microg/L without expensive or highly specialized laboratory equipment. In this method, As is removed from the sample by reduction to arsine gas, collected in an absorber by oxidation to arsenic acid, colorized by a sequential reaction to arsenomolybdate, and quantified by spectrophotometry. We compared this method with the silver diethyldithiocarbamate [AgSCSN(CH2CH3)2] and graphite furnace atomic absorption spectroscopy (GFAAS) methods for measuring As. Our method is more accurate, precise, and environmentally safe than the AgSCSN(CH2CH3)2 method, and it is more accurate and affordable than GFAAS. Finally, this study suggests that Bangladeshis will readily share drinking water with their neighbors to meet the more protective WHO guideline for As of 10 microg/L.     

Toxicity, biotransformation, and mode of action of arsenic in two freshwater microalgae (Chlorella sp. and Monoraphidium arcuatum)

The toxicity of As(V) and As(III) to two axenic tropical freshwater microalgae, Chlorella sp. and Monoraphidium arcuatum, was determined using 72-h growth rate-inhibition bioassays. Both organisms were tolerant to As(III) (72-h concentration to cause 50% inhibition of growth rate [IC50], of 25 and 15 mg As[III]/L, respectively). Chlorella sp. also was tolerant to As(V) with no effect on growth rate over 72 h at concentrations up to 0.8 mg/L (72-h IC50 of 25 mg As[V]/L). Monoraphidium arcuatum was more sensitive to As(V) (72-h IC50 of 0.25 mg As[V]/L). An increase in phosphate in the growth medium (0.15-1.5 mg PO4(3-)/L) decreased toxicity, i.e., the 72-h IC50 value for M. arcuatum increased from 0.25 mg As(V)/L to 4.5 mg As(V)/L, while extracellular As and intracellular As decreased, indicating competition between arsenate and phosphate for cellular uptake. Both microalgae reduced As(V) to As(III) in the cell, with further biological transformation to methylated species (monomethyl arsonic acid and dimethyl arsinic acid) and phosphate arsenoriboside. Less than 0.01% of added As(V) was incorporated into algal cells, suggesting that bioaccumulation and subsequent methylation was not the primary mode of detoxification. When exposed to As(V), both species reduced As(V) to As(III); however, only M. arcuatum excreted As(III) into solution. Intracellular arsenic reduction may be coupled to thiol oxidation in both species. Arsenic toxicity most likely was due to arsenite accumulation in the cell, when the ability to excrete and/or methylate arsenite was overwhelmed at high arsenic concentrations. Arsenite may bind to intracellular thiols, such as glutathione, potentially disrupting the ratio of reduced to oxidized glutathione and, consequently, inhibiting cell division.     

Arsenic in drinking-water and risk for cancer in Denmark

BACKGROUND: Arsenic is a well-known carcinogen, which is often found in drinking-water. Epidemiologic studies have shown increased cancer risks among individuals exposed to high concentrations of arsenic in drinking-water, whereas studies of the carcinogenic effect of low doses have had inconsistent results. OBJECTIVE: Our aim was to determine if exposure to low levels of arsenic in drinking-water in Denmark is associated with an increased risk for cancer. METHODS: The study was based on a prospective Danish cohort of 57,053 persons in the Copenhagen and Aarhus areas. Cancer cases were identified in the Danish Cancer Registry, and the Danish civil registration system was used to trace and geocode residential addresses of the cohort members. We used a geographic information system to link addresses with water supply areas, then estimated individual exposure to arsenic using residential addresses back to 1970. Average exposure for the cohort ranged between 0.05 and 25.3 microg/L (mean = 1.2 microg/L). Cox's regression models were used to analyze possible relationships between arsenic and cancer. RESULTS: We found no significant association between exposure to arsenic and risk for cancers of the lung, bladder, liver, kidney, prostate, or colorectum, or melanoma skin cancer; however, the risk for non-melanoma skin cancer decreased with increasing exposure (incidence rate ratio = 0.88/microg/L average exposure; 95% confidence interval, 0.84-0.94). Results adjusted for enrollment area showed no association with non-melanoma skin cancer. CONCLUSIONS: The results indicate that exposure to low doses of arsenic might be associated with a reduced risk for skin cancer.     

Arsenic in drinking water and skin lesions: dose-response data from West Bengal,India

BACKGROUND: Over 6 million people live in areas of West Bengal, India, where groundwater sources are contaminated with naturally occurring arsenic. The key objective of this nested case-control study was to characterize the dose-response relation between low arsenic concentrations in drinking water and arsenic-induced skin keratoses and hyperpigmentation. METHODS: We selected cases (persons with arsenic-induced skin lesions) and age- and sex-matched controls from participants in a 1995-1996 cross-sectional survey in West Bengal. We used a detailed assessment of arsenic exposure that covered at least 20 years. Participants were reexamined between 1998 and 2000. Consensus agreement by four physicians reviewing the skin lesion photographs confirmed the diagnosis in 87% of cases clinically diagnosed in the field. RESULTS: The average peak arsenic concentration in drinking water was 325 microg/liter for cases and 180 microg/liter for controls. The average latency for skin lesions was 23 years from first exposure. We found strong dose-response gradients with both peak and average arsenic water concentrations. CONCLUSIONS: The lowest peak arsenic ingested by a confirmed case was 115 microg/liter. Confirmation of case diagnosis and intensive longitudinal exposure assessment provide the basis for a detailed dose-response evaluation of arsenic-caused skin lesions.