Evaluation of the environmental fate of thymol and phenethyl propionate in the laboratory.

BACKGROUND: The natural monoterpenoid pesticides thymol and phenethyl propionate (PEP) are used indoors and outdoors, but their fate in the environment has not been reported. In order better to understand their impact on the environment, water metabolism and soil metabolism studies were conducted with thymol and PEP at a concentration of 10 microg g(-1) in water and in soil under laboratory conditions.
RESULTS: Dissipation half-lives of thymol and PEP were 16 and 5 days in water and 5 and 4 days in soil. 2-Phenylethanol and 2-(4-hydroxyphenyl)ethanol were detected as primary degradation products of PEP. Over time, a considerable volatilization loss of thymol, but not of phenethyl propionate, was found in the 1 month study under the experimental conditions used. Less than 6% of thymol and PEP were detected as bound residues, and less than 3% were mineralized during the 30 day study.
CONCLUSION: In order to maximize the pesticidal effect, more attention should be paid to the temperature for thymol than for PEP when they are being applied, owing to the high volatility of the former. Thymol and PEP pose low risks to the ecosystem because of their rapid dissipation and low bound residues in the environment.