Human exposures to arsenic from consumption of well water in West Bengal, India

Arsenic affects on cerebellar development of mice

To evaluate arsenic affects on the development of cerebellum, the mother mice received drinking water containing arsenic trioxide (As2O3) 4 ppm during gestation and lactation period. The cytogenesis was observed by immunohistochemical technique using 5'-bromo-2'-deoxyuridine (BrdU) antibody. To characterize the arsenic neurotoxicity, 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), an oxidative DNA lesion marker, and 8-nitroguanine, a nitrative DNA lesion marker were used to verify DNA damage. Arsenic-exposed litters showed neuron necrosis. The mitosis of granule cells decreased dramatically in arsenic-exposed mice as compared with arsenic unexposed mice. 8-OxodG was formed in neurons of all the layers, especially in the granular layer in cerebellum of arsenic-exposed mice. There is no significant difference, however, in the expression of 8-nitroguanine between arsenic-exposed and -unexposed mice. These results indicate that arsenic can disturb the mitosis of granule cells and interfere with the normal development of mice cerebellum. Arsenic-induced pathological changes in vivo may be caused by oxidative DNA damage other than nitrative DNA damage.

In utero arsenic exposure induces early onset of atherosclerosis in ApoE-/- mice

Consumption of arsenic contaminated drinking water has been linked to higher rates of coronary disease, stroke, and peripheral arterial disease. Recent evidence suggests that early life exposures may play a significant role in the onset of chronic adult diseases. To investigate the potential for in utero arsenic exposure to accelerate the onset of cardiovascular disease we exposed pregnant ApoE-knockout (ApoE(-/-)) mice to arsenic in their drinking water and examined the aortic trees of their male offspring for evidence of early disease 10 and 16 weeks after birth. Mice were maintained on normal chow after weaning. ApoE(-/-) mice are a commonly used model for atherogenesis and spontaneously develop atherosclerotic disease. Mice exposed to arsenic in utero showed a >2-fold increase in lesion formation in the aortic roots as well as the aortic arch compared to control mice at both 10 and 16 weeks of age. The mice exposed to arsenic also had a 20-40% decrease in total triglycerides, but no change in total cholesterol, phospholipids and total abundance of VLDL or HDL particles. Subfractionation of VLDL particles showed a decrease in large VLDL particles. In addition, the arsenic-exposed mice showed a vasorelaxation defect in response to acetylcholine suggesting disturbance of endothelial cell signalling. These results indicate that in utero arsenic exposure induces an early onset of atherosclerosis in ApoE(-/-) mice without a hyperlipidemic diet and support the hypothesis that in utero arsenic exposure may be atherogenic in humans.

Heavy Metal Poisoning: Clinical Presentations and Pathophysiology

Humans have had a long and tumultuous relationship with heavy metals. Their ubiquitous nature and our reliance on them for manufacturing have resulted at times in exposures sufficient to cause systemic toxicity. Their easy acquisition and potent toxicity have also made them popular choices for criminal poisonings. This article examines the clinical manifestation and pathophysiology of poisoning from lead, mercury, arsenic, and thallium.

Metal ions and carcinogenesis

Metals are essential for the normal functioning of living organisms. Their uses in biological systems are varied, but are frequently associated with sites of critical protein function, such as zinc finger motifs and electron or oxygen carriers. These functions only require essential metals in minute amounts, hence they are termed trace metals. Other metals are, however, less beneficial, owing to their ability to promote a wide variety of deleterious health effects, including cancer. Metals such as arsenic, for example, can produce a variety of diseases ranging from keratosis of the palms and feet to cancers in multiple target organs. The nature and type of metal-induced pathologies appear to be dependent on the concentration, speciation, and length of exposure. Unfortunately, human contact with metals is an inescapable consequence of human life, with exposures occurring from both occupational and environmental sources. A uniform mechanism of action for all harmful metals is unlikely, if not implausible, given the diverse chemical properties of each metal. In this chapter we will review the mechanisms of carcinogenesis of arsenic, cadmium, chromium, and nickel, the four known carcinogenic metals that are best understood. The key areas of speciation, bioavailability, and mechanisms of action are discussed with particular reference to the role of metals in alteration of gene expression and maintenance of genomic integrity.

Evaluation of DNA damage in patients with arsenic poisoning: urinary 8-hydroxydeoxyguanine

The relationship between arsenic exposure and DNA damage in patients with acute or chronic arsenic poisoning was analyzed. Urinary 8-hydroxydeoxyguanine (8-OHdG) concentrations were measured as an indication of oxidative DNA damage. A remarkable increase in 8-OHdG in the urine was observed in 60% of 52 patients with acute arsenic poisoning from the accidental oral intake of the arsenic trioxide. This was two- to threefold higher than levels in normal healthy subjects (n = 248). There was a clear relationship between arsenic concentrations in urine after acute poisoning and elevated levels of 8-OHdG. Levels of urinary 8-OHdG returned to normal within 180 days after the acute arsenic poisoning event. In patients chronically poisoned by the consumption of well water with elevated levels of arsenate [As(V)], elevated 8-OHdG concentrations in urine were also observed. A significant correlation between the 8-OHdG levels and arsenic levels in the urine was observed in 82 patients with chronic poisoning. Thus, evidence of oxidative DNA damage occurred in acute arsenic poisoning by arsenite [As(III)] and in chronic arsenic poisoning by As(V). In chronic poisoning patients provided low-arsenic drinking water, evidence of DNA damage subsided between 9 months and 1 year after the high levels of arsenic intake were reduced. The initial level of arsenic exposure appeared to dictate the length of this recovery period. These data indicate that some aspects of chronic and acute arsenic poisoning may be reversible with the cessation of exposure. This knowledge may contribute to our understanding of the risk elevation from arsenic carcinogenesis and perhaps be used in a prospective fashion to assess individual risk.

Health effect levels for risk assessment of childhood exposure to arsenic

Health risks to children from chemicals in soil and consumer products have become a regulatory focus in the U.S. This study reviews short-term health effect levels for arsenic exposure in young children (i.e., 0-6 years old). Acute health effects are described mostly in adults in case reports of arsenic poisoning from water or food and in studies of medicinal arsenic treatment. Several epidemiological studies report health effects from subchronic arsenic exposure in children primarily from drinking water in developing countries. Acute health effects typically include gastrointestinal, neurological, and skin effects, and in a few cases facial edema and cardiac arrhythmia. Dermatoses are most consistently reported in both adults and children with subchronic exposure. With low exposure, the prevalence and severity of disease generally increases with age (i.e., length of exposure) and arsenic dose. The available data collectively indicate a lowest-observed-adverse-effect level around 0.05mg/kg-day for both acute and subchronic exposure. At low doses, children do not appear to be more sensitive than adults on a dose-per-body-weight basis, although data for acute exposures are limited and uncertainties exist for quantifying potential neurological or vascular effects at low-level subchronic exposures. Based on these data, possible reference levels for acute and subchronic exposure in young children are 0.015 and 0.005mg/kg-day, respectively.

Insertional mutagenesis in a homologue of a Pi transporter gene confers arsenate resistance on chlamydomonas

An arsenate-resistant mutant AR3 of Chlamydomonas reinhardtii is a recessive mutant generated by random insertional mutagenesis using the ARG7 gene. AR3 shows about 10-fold resistance against arsenate toxicity compared with the wild type. By using a flanking region of an inserted tag as a probe, we cloned the corresponding wild-type allele (PTB1) of a mutated gene, which could completely complement the arsenate-resistance phenotype of AR3. The size of PTB1 cDNA is about 6.0 kb and it encodes a putative protein comprising 1666 amino acid residues. This protein exhibits significant sequence similarity with the yeast Pho89 protein, which is known to be a Na(+)/Pi co-transporter, although the PTB1 protein carries an additional Gln- and Gly-rich large hydrophilic region in the middle of its primary structure. Analyses of arsenic accumulation and release revealed that PTB1-disrupted cells show arsenate resistance due to low arsenate uptake. These results suggest that the PTB1 protein is a factor involved in arsenate (or Pi) uptake. Kinetics of Pi uptake revealed that the activity of high-affinity Pi transport component in AR3 is more activated than that in the wild type.

A dugwell program to provide arsenic-safe water in West Bengal, India: preliminary results

In 1982, Dr. K. C. Saha, a dermatologist of Calcutta, West Bengal, identified patients with skin lesions from the district of 24 Parganas, leading him and others to search for a cause. The cause was soon identified to be arsenic in drinking water, but even today, 20 years later, large number of people continue to drink arsenic contaminated water and patients are increasing in number. Project Well is a program chosen for implementation in some villages of North 24 Parganas. Arsenic safe drinking water is provided for adopted villages by constructing shallow, concrete dugwells designed to tap the water of the unconfined aquifer, 20-30 feet below ground level, that contains low levels (< 0.05 mg/L) of arsenic in the target region. The traditional dugwell design is modified by use of tube well hand pumps to withdraw water. The project includes community involvement, programs to increase awareness of the need to drink arsenic safe water, and training in monitoring of dugwell water for arsenic and harmful pathogens. Disinfecting of the water and regulating the water hazard diagram are also included in the training program. The plan is to make the system sustainable at the village level using indigenous labor and materials.

Chronic arsenic poisoning

Symptomatic arsenic poisoning is not often seen in occupational exposure settings. Attempted homicide and deliberate long-term poisoning have resulted in chronic toxicity. Skin pigmentation changes, palmar and plantar hyperkeratoses, gastrointestinal symptoms, anemia, and liver disease are common. Noncirrhotic portal hypertension with bleeding esophageal varices, splenomegaly, and hypersplenism may occur. A metallic taste, gastrointestinal disturbances, and Mee's lines may be seen. Bone marrow depression is common. 'Blackfoot disease' has been associated with arsenic-contaminated drinking water in Taiwan; Raynaud's phenomenon and acrocyanosis also may occur. Large numbers of persons in areas of India, Pakistan, and several other countries have been chronically poisoned from naturally occurring arsenic in ground water. Toxic delirium and encephalopathy can be present. CCA-treated wood (chromated copper arsenate) is not a health risk unless burned in fireplaces or woodstoves. Peripheral neuropathy may also occur. Workplace exposure or chronic ingestion of arsenic-contaminated water or arsenical medications is associated with development of skin, lung, and other cancers. Treatment may incklude the use of chelating agents such as dimercaprol (BAL), dimercaptosuccinic acid (DMSA), and dimercaptopanesulfonic acid (DMPS).

Element concentrations in urine of patients suffering from chronic arsenic poisoning

In order to know the element levels in the urine of patients with chronic arsenic poisoning caused by arsenic assimilated from burning coal via air and food, we investigated various elements in the urine of 16 patients with this disease and 16 controls living in the same county in Guizhou Province of China. Concentrations of 25 elements (Al, As, Ba, Be, Bi, Ca, Cd, Cr, Cu, Fe, Ga, Mg, Mn, Mo, Ni, P, Pb, Rb, Sb, Se, Sn, Sr, Ti, V and Zn) were determined by an inductively coupled plasma mass spectrometer or an inductively coupled plasma atomic emission spectrometer. The average concentrations of Cu, Ga and Sn as well as As in the patients were significantly higher, and those of Cr, Rb, Sr and Ti in the patients were significantly lower than the control values. Al, Ba, Mn, Ni and Se were under detection limit in the patients, though they could be detected in the controls. There were no positive correlations between the concentration of As and the concentrations of other elements, including Cu, Ga and Sn in the patients. The results of this study suggest that As from burning coal might influence the urinary excretion of some elements.

Effect on water resources from upstream water diversion in the Ganges basin

Bangladesh faces at least 30 upstream water diversion constructions of which Farakka Barrage is the major one. The effects of Farakka Barrage on water resources, socioeconomy, and culture have been investigated downstream in the basins of the Ganges and its distributaries. A diversion of up to 60% of the Ganges water over 25 yr has caused (i) reduction of water in surface water resources, (ii) increased dependence on ground water, (iii) destruction of the breeding and raising grounds for 109 species of Gangetic fishes and other aquatic species and amphibians, (iv) increased malnutrition, (v) deficiency in soil organic matter content, (vi) change in the agricultural practices, (vii) eradication of inland navigable routes, (viii) outbreak of waterborne diseases, (ix) loss of professions, and (x) obstruction to religious observances and pastimes. Further, arsenopyrites buried in the prebarrage water table have come in contact with air and formed water-soluble compounds of arsenic. Inadequate recharging of ground water hinders the natural cleansing of arsenic, and threatens about 75,000,000 lives who are likely to use water contaminated with up to 2 mg/L of arsenic. Furthermore, the depletion of surface water resources has caused environmental heating and cooling effects. Apart from these effects, sudden releases of water by the barrage during the flood season cause devestating floods. In consideration of such a heavy toll for the areas downstream, strict international rules have to be laid down to preserve the riparian ecosystems.

Pharmacokinetics, metabolism, and carcinogenicity of arsenic

The carcinogenicity of arsenic in humans has been unambiguously demonstrated in a variety of epidemiological studies encompassing geographically diverse study populations and multiple exposure scenarios. Despite the abundance of human data, our knowledge of the mechanism(s) responsible for the carcinogenic effects of arsenic remains incomplete. A deeper understanding of these mechanisms is highly dependent on the development of appropriate experimental models, both in vitro and in vivo, for future mechanistic investigations. Suitable in vitro models would facilitate further investigation of the critical chemical species (arsenate/arsenite/MMA/DMA) involved in the carcinogenic process, as well as the evaluation of the generation and role of ROS. Mechanisms underlying the clastogenic effects of arsenic, its role in modulating DNA methylation, and the phenomenon of inducible tolerance could all be more completely investigated using in vitro models. The mechanisms involved in arsenic's inhibition of ubiquitin-mediated proteolysis demand further attention, particularly with respect to its effects on cell proliferation and DNA repair. Exploration of the mechanisms responsible for the protective or anticarcinogenic effects of arsenic could also enhance our understanding of the cellular and molecular interactions that influence its carcinogenicity. In addition, appropriate in vivo models must be developed that consider the action of arsenic as a promoter and/or progressor. In vivo models that allow further investigation of the comutagenic effects of arsenic are also especially necessary. Such models may employ initiation-promotion-progression bioassays or transgenic animals. Both in vitro and in vivo models have the potential to greatly enhance our current understanding of the cellular and molecular interactions of arsenic and its metabolites in target tissues. However, refinement of our knowledge of the mechanistic aspects of arsenic carcinogenicity is not alone sufficient; an understanding of the pharmacokinetics and target tissue doses of the critical chemical species is essential. Additionally, a more thorough characterization of species differences in the tissue kinetics of arsenic and its methylated metabolites would facilitate the development of more accurate and relevant PBPK models. Improved models could be used to further investigate the existence of a methylation threshold for arsenic and its relevance to arsenic carcinogenicity in humans. The significance of alterations in relative tissue concentrations of SAM and SAH deserves further attention, particularly with respect to their role in modulating methyltransferases involved in arsenic metabolism and DNA methylation. The importance of genetic polymorphisms and nutrition in influencing methyltransferase activities must not be overlooked. In vivo models are necessary to evaluate these factors; transgenic or knockout models would be particularly useful in the investigation of methylation polymorphisms. Further evaluation of methylation polymorphisms in human populations is also warranted. Other in vivo models incorporating dietary manipulation could provide valuable insight into the role of nutrition in the carcinogenicity of arsenic. With more complete knowledge of the pharmacokinetics of arsenic metabolism and the mechanisms associated with its carcinogenic effects, development of more reliable risk assessment strategies are possible. Integration of data, both pharmacokinetic and mechanistic in nature, will lead to more accurate descriptions of the interactions that occur between the active chemical species and cellular constituents which lead to the development of cancer. This knowledge, in turn, will facilitate the development of more accurate and reliable risk assessment strategies for arsenic.

Folic acid protects SWV/Fnn embryo fibroblasts against arsenic toxicity

It has been proposed that arsenic exerts its toxic effects, in part, by perturbing cellular methyl metabolism. Based on the hypothesis that folic acid treatment will attenuate the cytotoxic and growth inhibitory effects of arsenic, SWV/Fnn embryo fibroblasts were cultured in media supplemented with various concentrations of folic acid during treatment with sodium arsenite or dimethylarsinic acid (DMA). It was found that folic acid protects SWV/Fnn embryo fibroblasts from sodium arsenite and DMA cytotoxicity in a dose-dependent manner. In contrast, folic acid supplementation has no effect on toxicity resulting from treatment with ethanol or staurosporine, suggesting that folic acid is not generally protective against necrosis and apoptosis. Although folic acid protects against acute arsenic toxicity, this agent shows a modest and delayed ability to attenuate the growth inhibitory effect of arsenic on these cells. These results support a model in which perturbations of methyl metabolism contribute to the acute cytotoxicity of arsenic.