Case Study in Environmental Chemistry....

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

Chemical and Physical Properties of Endosulfan: Endosulfan (1,2,3,4,7,7-hexachlorobicyclo- (2,2,1)-hepten-2-3-bisixymethylene 5, 6-sulfite) is a broad-spectrum cyclodiene insecticide that is markedly different than other cyclodienes, for example, chlordane, dieldrin, and heptachlor, in its physical, chemical, and physiological properties and behavior in organisms (9) (See Table 2). Endosulfan is an unsaturated cyclic organic sulfite (10). This insecticide was synthesized by Frensch and Goebel (11) and brought to the market under the trade name "Thiodan". This pesticide is synthesized by the action of thionylchloride on the addition product from hexachlorocyclopentadiene and cis-butene-1,4-diol (11). Technical endosulfan consists of two isomers, a - and b -endosulfan, in the ratio of 70:30. Both of these isomers have quite different physical properties such as melting point, aqueous solubility, and vapor pressure. The structural formula of endosulfan and its metabolites are shown in Figure 3.

Question 1: Why does technical endosulfan contain both isomers? Check your answer.

Question 2: According to the Table 2, which isomer would you expect to be more mobile in the environment, why? (Hint: check vapor pressure and water solubility). Check your answer.

Question 3: Based on Figure 3, would you expect the water solubility of endosulfan diol to be greater or less than the parent compounds? Check your answer.

Transport and Partition of Endosulfan: Endosulfan is a moderately hydrophobic (log Kow ~3.98) compound. Therefore, sorption is considered to be the major route of disappearance from a water body, with volatilization, hydrolysis and biodegradation as minor routes by comparison (11). The two isomers of endosulfan express different degradation times in a soil system. The different values of half-life of each isomer under different laboratory conditions were demonstrated by many researchers. For example, Miles and Moy (13) reported the half-life under neutral pH condition (pH 7) of the a-isomer as 88 days, and as 40 days for the b -isomer. These two isomers will persist longer under more acidic conditions. Endosulfan sulfate, a metabolite of endosulfan, will also be associated with colloids or particulates, leaving very little freely dissolved in the water. Because endosulfan and its metabolite are hydrophobic, they will partition to adipose (fatty) tissues of organisms. Subsequently, endosulfan will bioaccumulate and be transported in the environment by the organism itself and through the food chain from organism to organism. The bioaccumulation of endosulfan has been observed in animals as well as humans (14).