Case Study in Environmental Chemistry....

Authors: Sarunya Hengpraprom and Cindy Lee, Environmental Engineering and Science, Clemson University.

Abstract : This case study considers the rate at which exposure to sunlight can transform a pesticide known as terbufos. Transformation of a contaminant by photolysis will change its behavior in a given situation. In some cases, a product of photolysis is just as toxic or more toxic than the parent compound. In other cases, the products of photolysis are rendered nontoxic and the transformation can be considered beneficial. The experiment described in this case study produced some of the first basic kinetics data available to evaluate the importance of photolysis as a process to remove terbufos from the environment. For more detailed information about this research, see Lee, C. M.; Anderson, B.; and Elzerman, A. W. 1999. Photochemical oxidation of terbufos. Environmental Toxicology and Chemistry. 18(7):1349-1353.

Introduction

Pesticides are used on a regular basis for agricultural, commercial, and domestic protection of plants, woods, and soils, and to control the growth of certain vegetation. Even though there are many positive features associated with pesticides, some can adversely affect the environment and human health (1). Many pesticides move from targeted areas to nontargeted areas by volatilization, by transport to surface water and sediment or by penetration through the soil profile. Elevated levels of pesticides in water system can render the quality of water unfit for human consumption (1).

The primary transformation processes (e.g., hydrolysis, photolysis, oxidation, and biodegradation) are responsible for reducing persistence and/or diminishing toxicity of pesticides in the environment. For certain pesticides, some processes do not necessarily diminish toxicity but generate products of equal or greater toxicity than parent compounds. Terbufos is an example of several pesticides that undergo oxidation-reduction reaction which results in products (e.g./ terbufos sulfoxide and terbufops sulfone) of greater toxicity and more persistence in the environment than the parent compound (2).

Terbufos (S- (((1,1-dimethylethyl) thio) methyl) O, O-diethyl-phosphorodithionate) is a widely used, organophosphothionate insecticide that works against a broad range of insects and has been extensively used in the Midwestern United States to control corn rootworms, seedcorn maggots, white grubs, and other pests (3). Due to its widespread use, considerable research has focused on the environmental fate of terbufos. The purpose of the research described in this case study was to study the transformation processes, especially photolytic degradation reaction, of terbufos in the aquatic system.