Evolution of toxicity upon hydrolysis of fenoxaprop-p-ethyl.
Hydrolysis of fenoxaprop-p-ethyl (FE), a widely used herbicide, was studied in aqueous buffer solutions at pH ranging from 4.0 to 10.0. The degradation kinetics, strongly dependent on pH values, followed first-order kinetics. FE was relatively stable in neutral media, whereas it degraded rapidly with decreasing or increasing pH. In acidic conditions (pH = 4, 5), the benzoxazolyl-oxy-phenyl ether linkage of FE was cleaved to form ethyl 2-(4-hydroxyphenoxy)propanoate (EHPP) and 6-chloro-2,3-dihydrobenzoxazol-2-one (CDHB). While in basic conditions (pH = 8, 9, 10), herbicidal activity fenoxaprop-p (FA) was formed via breakdown of the ester bond of the herbicide. Both the two pathways were concurrent in neutral conditions (pH = 6, 7). Toxicity studies on Daphnia magna showed that FE was most toxic to D. magna with 48 h EC(50) of 14.3 micromol/L, followed by FA (43.8 micromol/L), CDHB (49.8 micromol/L), and EHPP (333.1 micromol/L). Mode of toxic action analysis indicated that EHPP exhibited toxicity via polar narcosis, whereas CDHB belonged to reactive acing compound. The mixture toxicity of CDHB and EHPP was nonadditive and can be predicted by a response addition model. Therefore, the evaluation of overall FE toxicity to D. magna in the aquatic systems needs to consider the degradation of FE.
Lin
Jing
J
Department of Environmental Science and Technology, Dalian University of Technology, Linggong Road 2, Dalian 116024, People's Republic of China.
Chen
Jingwen
J
Cai
Xiyun
X
Qiao
Xianliang
X
Huang
Liping
L
Wang
Degao
D
Wang
Zhuang
Z
D000818:Animals; D003621:Daphnia / Q000187:drug effects; D006540:Herbicides / Q000737:chemistry* / Q000633:toxicity*; D006868:Hydrolysis; D010080:Oxazoles / Q000737:chemistry* / Q000633:toxicity*; D011422:Propionates / Q000737:chemistry* / Q000633:toxicity*; D013997:Time Factors; D014874:Water Pollutants, Chemical / Q000633:toxicity
D006540:Herbicides; D010080:Oxazoles; D011422:Propionates; D014874:Water Pollutants, Chemical; C416661:fenoxaprop ethyl