Bioconcentration and metabolism of pyriproxyfen uniformly labeled with C at the phenoxyphenyl ring were studied using tadpoles of African clawed frog, Xenopus laevis, exposed to water at the nominal concentrations of 3 and 300 ppb for 22 days under the flow-through conditions, with a following 3 day depuration phase. Neither meaningful mortality nor abnormal behavior was observed in control and exposure groups throughout the study. After the rapid uptake to tadpoles, pyriproxyfen was extensively metabolized and excreted, and as a result, steady-state bioconcentration factors and depuration half-lives ranged from 550 to 610 and from 0.34 to 0.54 days, respectively. The metabolites were mostly distributed in the liver or gastrointestinal tract. The major metabolic reactions were hydroxylation at the 4' position of the phenoxyphenyl group and cleavage of the ether linkage, followed by sulfate conjugation.

No abstract

IntroductionPyridalyl (I) [2,6-dichloro-4-(3,3-dichloroallyloxy)phenyl 3-[5-(trifluoromethyl)-2-pyridyloxy]propyl ether] is a new insecticide controlling Lepidoptera and Thysanoptera on cotton, fruits and vegetables. [1][2][3] Aquatic invertebrates are more susceptible to I than fish and algae, based on standard ecotoxicological data: common carp (Cyprinus carpio) 96-hr LC 50 , Ͼ10 mg/l; Daphnia magna 48-hr EC 50 , 0.0038 mg/l; green alga (Pseudokirchneriella subcapitata) 72-hr EbC 50 , Ͼ10 mg/l. 2,3) Aquatic invertebrates are one of the most diverse taxonomic classes in terms of ecology and physiology 4,5) and are known to exhibit species-dependent susceptibility to chemicals, including pesticides. 6) Although Daphnia magna is the typical species used to assess the impact of a chemical on aquatic invertebrates due to the ease of handling and availability of a large ecotoxicological database, 7) cladocerans have been found to be less susceptible to certain insecticides than other invertebrates, such as midges. 8) Midges and amphipods are the other important classes from their ecology in the aquatic environment and are known to show different susceptibility to chemicals, including pesticides. 9) Recently, ecotoxicological testing methods have been recommended by the Organization for Economic Cooperation and Development (OECD), the Office of Chemical Safety and Pollution Prevention Substances, United States Environmental Protection Agency (OPPTS), the American Society for Testing and Materials (ASTM) and Ministry of Agriculture, Forestry and Fisheries, Japan (JMAFF) 9-12) for both species as a standard species. From these viewpoints, the acute toxicity of I to larval midge Chironomus yoshimatsui and adult amphipod Hyalella azteca was investigated in the present study. Furthermore, the metabolism of I in these invertebrates as well as its body residues was briefly examined to explain the apparent difference in its acute toxicity. Materials and Methods Chemicals[ 14 C]-I uniformly labeled at dichlorophenyl ring ( Fig. 4; specific activity, 9.70 and 9.87 MBq/mg; radiochemical purity, 95.7-97.1%) as well as non-radiolabeled I were prepared in our laboratory. The following authentic standards of potential metabolites were also prepared in our laboratory 13,14) with chemical purities of 98.0 to 98.8%: 3,5-dichloro-4-(3-(5-trifluoromethyl-2-pyridyloxy)propoxy)phenol (II) and 2-{3,5-dichloro-4-[3-(5-trifluoromethyl-2-pyridyloxy)propoxy]phenoxy}acetic acid (III). Hydrogenated caster oil (HCO-40) was purchased from Nikko Chemicals and used without treatment. Acute toxicity and related metabolism of pyridalyl inChironomus yoshimatsui and Hyalella azteca Mitsugu MIYAMOTO* and Toshiyuki KATAGI Environmental Health Science Laboratory, Sumitomo Chemical Co., Ltd., 2-1, Takatsukasa 4-chome, Takarazuka, Hyogo 665-8555, Japan (Received April 12, 2010; Accepted June 22, 2010) Acute toxicity and metabolism of a new insecticide pyridalyl were examined in the larval midge Chironomus yoshimatsui and adult amphipod Hyalella aztec...