Enantioselective toxicity and degradation of chiral herbicide fenoxaprop-ethyl in earthworm Eisenia fetida

• Published in: Ecological indicators 2017-04, Vol.75, p.126-131
• Main Authors: Jing, Xu, Yao, Guojun, Liu, Donghui, Qu, Han, Zhou, Qian, Zhou, Zhiqiang, Wang, Peng
• Format: Article
• Language: English
• Subjects: Chiral; Degradation; Earthworm; Fenoxaprop-ethyl; Toxicity
• ISSN: 1470-160X; 1872-7034
• DOI: 10.1016/j.ecolind.2016.12.006

[Display omitted] •Acute toxicity of fenoxaprop-ethyl and its four metabolites was conducted.•Enantioselective toxicity of fenoxaprop-ethyl and its chiral metabolites was found.•Enantioselective degradation of fenoxaprop-ethyl in earthworms was investigated. The enantioselective degradation of fenoxaprop-ethyl in ecological indicator earthworm was studied and the main metabolites (fenoxaprop, 6-chloro-2,3-dihydrobenzoxazol-2-one, ethyl-2-(4-hydroxyphenoxy)propanoate, 2-(4-hydroxyphenoxy)propanoic acid) were also monitored on an enantiomeric level. The individual enantiomers of fenoxaprop-ethyl and its three chiral metabolites were prepared to study the acute toxicity to earthworm. Chiral analysis methods were set up based on HPLC–MS/MS with chiralpak IC chiral column. Fenoxaprop-ethyl was not found in earthworms, while the primary metabolite fenoxaprop was in relatively high levels indicating a quick hydrolysis degradation. Fenoxaprop was accumulated almost exclusively with R-enantiomer in earthworms and the bio-concentration factors of R-fenoxaprop and S-fenoxaprop were 1.39 and 0.17 respectively with the enantiomer fraction (EF) values about 0.99. The degradation of R-fenoxaprop in earthworms followed first-order kinetics with half-life of 1.82day. The other metabolites could not be detected in earthworms. The calculated LC50 values showed ecological indicator earthworm was more sensitive to the four metabolites than fenoxaprop-ethyl. Furthermore, earthworm was more sensitive to the R-form of the chiral metabolites than the S-form and rac-form. The results suggested metabolites and enantioselectivity should be taken into consideration to better predict the exposure concentration and apply ecological indicators in toxicological studies.