11. The History of Organic Arsenical Pesticides and Health Risks Related to the Use of Agent Blue

Arsenicals in agriculture: Beginning in the 1970s, the use of arsenic compounds, such as for wood preservatives, began to grow. By 1980, in the USA, 70 % of arsenic had been consumed for production of wood preservatives. This practice was later stopped, due to the US Environmental Protection Agency (EPA) ban of the arsenic-and chromium-based wood preservative chromated copper arsenate. In the past, arsenical herbicides containing cacodylic acid as an active ingredient have been used extensively in the USA from golf courses to cotton fields, drying out the plants before harvesting. The original commercial form of Agent Blue was among ten toxic insecticides, fungicides and herbicides partially deregulated by the US Environmental Protection Agency (EPA) in February 2004, and specific limits on toxic residues in meat, milk, poultry, and eggs were removed. Today, however, they are not used as weed-killers anymore, with one exception of monosodium methanearsonate (MSMA), a broadleaf weed herbicide for use on cotton. Severe poisonings from cacodylic acid caused headache, dizziness, vomiting, profuse and watery diarrhea, followed by dehydration, gradual fall in blood pressure, stupor, convulsions, general paralysis and possible risk of death within 3–14 days. The relatively frequent use of arsenic and its compounds, in both industry and agriculture, points to a wide spectrum of opportunities for human exposure; this exposure can be via inhalation of airborne arsenic, contaminated drinking water, beverages, or from food and drugs. Today, acute organic arsenical poisonings are mostly accidental. Considerable concern has developed surrounding its delayed effects, for its genotoxic and carcinogenic potential, which has been demonstrated in epidemiological studies and subsequent animal experiments. The Conclusion is that there is substantial epidemiological evidence for an excessive risk, mostly for skin and lung cancer, among humans exposed to organic arsenicals in occupational and environmental settings. Furthermore, the genotoxic and carcinogenic effects have only been observed at relatively high exposure rates. Current epidemiological and experimental studies are trying to elucidate the mechanism of this action, pointing to the question of whether arsenic is actually the true genotoxic or rather an epigenetic carcinogen. Due to the complexity of its effects both options remain plausible. Its interactions with other toxic substances still represent another important field of interest.