RESUMO
Evaluates the risks to human health and the environment posed by exposure to amitrole, a herbicide with a very wide spectrum of activity against annual and perennial broad leaf and grass type weeds. Amitrole, which appears to act by inhibiting the formation of chlorophyll, is widely used around orchard trees, on fallow land prior to sowing, along roadsides and railway lines, and for weed control in ponds. The herbicide is not approved for direct application to food crops. A review of studies on the environmental fate of amitrole concludes that the compound is relatively rapidly degraded in the environment, with no evidence of either bioaccumulation or entry into the food chain. Exposure of the general public is expected to be minimal. Studies in both humans and animals show that amitrole is rapidly absorbed and rapidly excreted in urine in an unchanged form. The most extensive section evaluates the large number of experimental studies that have demonstrated toxic effects on the thyroid. These findings support the conclusion that amitrole is goitrogenic, causing thyroid hypertrophy and hyperplasia, depletion of colloid, and increased vascularity. Experiments indicate that these changes precede the development of thyroid neoplasia; the precise mechanism triggering the change from hyperplasia to neoplasia remains to be elucidated. Although studies of occupationally-exposed workers are largely reassuring, the book recommends annual monitoring of thyroid function in workers regularly handling amitrole at either the formulation or application stage. The book further concludes that amitrole poses no significant threat to the environment, that levels in food and drinking-water should be extremely low, and that the herbicide poses no threat to the health of workers or the general population when manufactured and used as recommended
