Case Study in Environmental Chemistry

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

Answers:

1: Why does technical endosulfan contain both isomers?

Answer: The technical endosulfan consists of two isomers (alpha- and beta-isomer) because synthesis and purification of a single isomer is expensive and both isomers are effective for the target organisms. Other examples of pesticides containing several isomers are lindane and chlordane.

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).

Answer : The a -endosulfan is expected to be more volatile and less water-soluble than b -endosulfan. The higher volatilization rate of the a -isomer is due to its low water solubility and relatively high vapor pressure and Henry's Law constant. The a -endosulfan has a Henry's Law constant approximately 27 times that of b -endosulfan, which correlates well with the greater rate of disappearance. The slightly higher water solubility of b -endosulfan as compared to that of a -endosulfan is a consequence of the difference in the polarity of compounds. The dipole moment is 1.02 and 3.18 Debye unit for a -and b -endosulfan, respectively.

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

Answer : According to Figure 3, endosulfan diol should have higher water solubility than the parent isomers because the two hydroxyl groups attached to C-H bond allow endosulfan diol to form hydrogen bonds. In addition, the molecular weight of endosulfan diol is lower than the parent compounds, leading it to have the higher water solubility. We would expect the Kow of endosulfan diol to be lower as well.

4: Why do you think the endosulfan diol is less toxic?

Answer : Endosulfan diol is less toxic than the parent compounds because of its higher water solubility, leading it to favor the aqueous phase rather than organic phases.

5: Express the relationship of the kinetic rate (k) versus temperature. Is it inversely or directly proportional?

Answer : The kinetic rate is inversely proportional to the negative value of temperature: k µ (-1/T)

6: Use data from Table 3 calculate the half-life of both isomers under a given condition.

Answer : See Table 4

7: Use data from Table 3 plot the Arrhenius curve of each isomer at pH 8 under autoclave and non-autoclaved conditions.

Answer : See Figure 4 and Figure 5

8: Calculate the activation energy (Ea) of each isomer based on the results obtained from question 4 and also report the frequency factor (ln A).

Answer : See Table 5

9: Would the hypotheses been accepted or ejected based on your results?

Answer : See Hengpraprom S, Lee, CM, Coates JT, Elzerman AW. 1998. The Hydrolysis of endosulfan