ReviewA global health problem caused by arsenic from natural sources
Introduction
Arsenic is a ubiquitous element in the environment. It is produced commercially by reduction of arsenic trioxide with charcoal. Arsenic trioxide is a by-product of metal smelting operations and also present in flue dust from the roasting of ores, especially those produced in copper smelting. Because of its prevalence in nature and its toxicity, the potential for arsenic contamination of water, air, and soil from both geological and anthropogenic sources is a significant environmental health concern.
Inorganic arsenicals have been classified as Group I carcinogens based on human epidemiological data (IARC, 1987). The evidence for arsenic carcinogenicity in animals was very limited until sodium arsenate was found to cause tumours in mice (Ng et al., 1999).
The clinical manifestations of chronic arsenicosis in humans include non-cancer effects of hyper- and hypo-pigmentation, keratosis, hypertension, cardiovascular diseases and diabetes; and cancer end point typically skin, lung and bladder cancers. Cancers involving other organs have also been implicated (IPCS, 2001).
Inorganic arsenic was regarded as the number one toxin in the USEPA list of prioritised pollutants. It has been generally accepted that arsenic contamination in the environment is causing a significant global health problem. It has been estimated that about 60–100 million people in India and Bangladesh are currently at risk as a result of drinking arsenic-contaminated waters (Ahmad, 2001; Chakraborti et al., 2001). Arsenicosis is also prevalent in certain areas of PR China (e.g. Shanxi, Xinjiang, and Inner Mongolia) (Wang et al., 2000; Guo et al., 2001), Taiwan (Chen et al., 1999), Vietnam (Berg et al., 2001) and recently Nepal (Tandukar and Neku, 2002). For these endemic areas, the major arsenic exposure pathway is believed to be from drinking contaminated groundwater whereas the contribution of arsenic from food is relatively low.
Guizhou Province of PR China has a rich resource of coal. Unfortunately, in this province elevated natural arsenic concentrations are found in coal and arsenicosis is prevalent among the residents. For this area, the major exposure pathway has been linked to ingestion of food that is contaminated by arsenic deposition during the burning of coal for cooking, drying of crops, and heating purposes (Liu et al., 2002).
A summary of the global health problems caused by chronic exposure poisoning from natural sources is reported. Possible intervention strategies to minimise the adverse health effects caused by arsenic are also discussed.
Section snippets
Chronic arsenic toxicity in animals
There is a noticeable absence of two-year carcinogenicity studies in animals for either the inhalation or oral route of exposure (ATSDR, 1998). Results so far published in the literature provide very limited supportive evidence of arsenic carcinogenicity in animals (IARC, 1987). In light of the ongoing controversy over that arsenic has been classified as a carcinogen based essentially on human epidemiological data, we established a two-year mouse model successfully to demonstrate arsenic
Chronic arsenic toxicity in humans
There are numerous epidemiological studies in humans that have demonstrated the carcinogenic effects of inorganic arsenic from inhalation exposure (Ferreccio et al., 1996) and oral exposure (Tseng, 1977).
Long-term exposure to arsenic results in chronic arsenic poisoning (arsenicosis). This has been reported to occur in people who live in endemic areas with high arsenic concentrations in drinking water or in burning coal (Hopenhayn-Rich et al., 2000; Pi et al., 2000; Berg et al., 2001; Liu et
Drinking water containing naturally high levels of arsenic
Globally, arsenic contamination in drinking water is a major public health issue. Groundwater is a major source of drinking water in many part of the world, especially the South East Asia Region Countries (SEAR). Arsenic contamination of groundwater has been reported in many SEAR countries including Bangladesh and India (Chatterjee et al., 1995; Ahmad, 2001; Shraim et al., 2002), Vietnam (Berg et al., 2001), Nepal (Tandukar and Neku, 2002), Taiwan (Chen et al., 1999), and PR China (Wang et al.,
Coal containing naturally high levels of arsenic
Generally coal contains low arsenic concentration that poses no health risks to humans, as the arsenic content in most coals is less than 5 mg kg−1. However, some coals may contain up to 35 000 mg kg−1 (Ding et al., 2001). Power plants using high arsenic-containing coal as a fuel, especially in India and Czechoslovakia, could be a major source of pollution in the environment. The wastewater discharged from such power plants is also highly contaminated with arsenic (Wang, 1997). Using high
Urinary arsenic concentrations
Urinary arsenic is widely used as a biomarker for arsenic exposure in humans. Total arsenic concentrations were reported to correlate with increases in arsenic exposure (Valentine et al., 1979; Hopenhayn-Rich et al., 1996a; Ng et al., 1998; Mandal et al., 2001).
Human bodies methylate the ingested inorganic arsenic [InAs=As(III) + As(V)] to monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA), which are less reactive with the tissue constituents than the parent InAs and therefore are more
Possible intervention
Currently there are some countries where arsenic contamination in the groundwater has reached a very alarming level and requires immediate attention, especially in Bangladesh and India. The present situation in Bangladesh demands a thorough screening of tubewells to assess the arsenic concentrations, identify hot spots, and implement suitable intervention programs. Intervention options may include dug wells and deep tubewells, where low arsenic concentrations are usually present. Other
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