Residue Reviews

We have made a survey of the published literature on the mutagenicity in procaryotes of herbicides. The importance of the study of the possible mutagenic or genotoxic effects of pesticides is evident: the great majority of people all over the world are exposed daily to minute amounts of pesticides present in their food, and a smaller number of people (agricultural workers and workers in pesticide plants) are exposed to even higher doses of these substances.

For many decades the widespread use of synthetic pesticides was indiscriminate. Scientists have found that not only are the insects building up tolerances to certain common pesticides, but that pesticides residues are also accumulating in the environment at an alarming rate. Pesticides like DDT and aldrin are being replaced by malathion and temephos and others which are less persistent in the environment. It is important to know the environmental fate of pesticides of public health importance especially when used repeatedly for many years. The objective of this paper is to review the work that has been done on temephos, an insecticide which is being used extensively in several parts of the world and particularly in the Volta Basin, West Africa, to control the vectors of onchocerciasis (river blindness).

The harvest-aid herbicides DEF (S,S,S-tributylphosphorotrithioate) and merphos(S,S,S-tributylphosphorotrithioite) have been employed for defoliation of cotton for over 20 years. These compounds are readily taken up by the plant leaf and induce and accelerate abscission. There is little information available on the chemical characteristics of these compounds or on their environmental fate. DEF, however, appears to have very low vapor pressure and is also apparently quite stable. For the most part, environmental fate and human exposure estimates for these compounds have been based on data derived from parathion studies. While these estimates may prevail to some degree, the compounds are not completely comparative, as for example, the fact that parathion hydrolyzes readily under alkaline conditions while DEF reportedly does not.

The U.S. Environmental Protection Agency (EPA) is responsible for establishing Water Quality Criteria which are protective of fresh water and marine life as well as human health. In 1980 the EPA announced the availability of criteria for 65 priority toxic pollutants listed under section 307 (a)(1) of the 1977 amendments of the Clean Water Act. Stara et al. (1980) have reviewed the processes and problems involved in establishing such criteria. They list four levels of toxic effects: (1) acute, subchronic and chronic, (2) mutagenic, (3) teratogenic, and (4) carcinogenic. The latter three are all potentially genotoxic in action. Chemicals causing genetic aberrations theoretically have no threshold (Albert et al. 1977) and therefore a zero-incidence is desirable. Chemicals causing toxic action other than genotoxicity are subject to the establishment of a “No Observable Affect Exposure Level” (NOAEL) (Stara et al. 1980) and therefore have a definable threshold. Often the establishment of zero incidence levels is not feasible for genotoxic materials so risk models must be developed. The “one-hit” model recommended in the EPA’s Interim Cancer Procedures and Guidelines for Health Risk… (1976) has been used for non-threshold risk assessment in the establishment of Water Quality Criteria (EPA 1980), and a modified version was used for chemicals with determinable thresholds. In both models the accuracy of the eventual predicted measure is highly dependent on the reliability of the bioconcentration data which are available in the literature.