The presence of arsenic in drinking water in Latin America and its effect on public health

In various Latin American countries such as Argentina, Chile, Mexico, El Salvador; Nicaragua, Peru and Bolivia, at least four million people drink water containing arsenic at levels which pose a risk to their health to such an extent that in certain areas this has become a public health problem. This is a compilation of work carried out on the problem of arsenic in drinking water and its effects on the health of those exposed to it. This situation must be addressed in order to minimize its effects and reduce arsenicism in the affected areas. The presence of arsenic in the environment and in water sources for human consumption is due to natural geological factors (Mexico, Argentina, Chile, Peru, Nicaragua), anthropogenic activities, including mining and metal smelting (Chile, Bolivia and Peru), electrolytic processes for the production of high quality metals such as cadmium and zinc (Brazil) and, to a lesser extent, the use of organic arsenic-based pesticides in agriculture (Mexico). It is well known that in most cases the presence of arsenic in surface water and groundwater in Latin America is associated with Tertiary and Quaternary volcanism in the Andes Mountains. It derives from dissolved minerals, erosion and disintegration of rocks and from atmospheric deposition (aerosols). In water it can be found in its trivalent and pentavalent forms. Arsenic in drinking water is generally found in the form of arsenate and 40% to 100% can be absorbed easily in the gastrointestinal tract (Frederick et al. 1994). Ingested inorganic arsenic is absorbed by the tissues and gradually eliminated by methylation in the kidneys, into the urine. When ingestion is greater than excretion it tends to accumulate in the hair and nails. The principal means of exposure to arsenic are ingestion and inhalation. It can accumulate in the body after chronic exposure and at certain concentrations causes changes to the skin with secondary effects on the nervous system, respiratory and gastrointestinal tracts, as well as hematopoiesis; it can also build up in the bones, muscles and skin and, to a lesser extent, in the liver and kidneys. Toxicological and epidemiological studies confirm this information and indicate that chronic ingestion of arsenic in drinking water results in skin lesions, hyperpigmentation and hyperkeratosis of the palms of the hands and soles of the feet; it also causes nervous system disorders, diabetes mellitus, anemia, liver disorders, vascular illnesses and skin, lung and bladder cancer. Consumption of water containing arsenic over the long term leads to chronic effects and arsenicism. The treatment involves providing patients with drinking water that is free from arsenic. The next step is to monitor the patient and ensure that he is no longer exposed to the element. Other proposed treatments are chelation and improved nutrition. Its toxicity depends on oxidation, chemical structure and solubility in the biological medium. The scale of arsenic toxicity declines in the following order: arsine > As inorganic > As organic > As inorganic > As organic > arsenic compounds and elemental arsenic. The toxicity of As is 10 times higher than that of As and the lethal dose for adults is 1-4 mg As/kg. For the more common forms such as AsH3, As2O3, As2O5 this dosage varies between 1.5 mg/kg and 500 mg/kg of body mass (The National Academy of Sciences 1999). It has been shown that children are more sensitive than adults to arsenic poisoning and are the most affected by arsenicism, because of malnutrition and lack of sanitation in scattered (poor) rural areas. Those most at risk are people living in scattered rural areas, who drink untreated water and are unaware of the risk to which they are exposed. Health, environmental and sanitation authorities must plan water supplies and promote and implement risk prevention and control programs where drinking water contains higher than the recommended levels of arsenic. The programs should involve the authorities, community and local health systems.