Bioaccumulation, Biotransformation, and Metabolite Formation of Fipronil and Chiral Legacy Pesticides in Rainbow Trout

Abstract

To assess the fate of current-use pesticides, it is important to understand their bioaccumulation and biotransformation by aquatic biota. We examined the dietary accumulation and enantioselective biotransformation of the chiral current-use pesticide fipronil, along with a mixture of selected chiral [alpha-hexachlorocyclohexane (alpha-HCH), heptachlor epoxide (HEPX), polychlorinated biphenyls (PCBs) 84, 132, 174, o,p'-DDT, and o,p'-DDD] and nonchiral (p,p'-DDT, p,p'-DDD) organochlorine compounds in juvenile rainbow trout (Oncorhynchus mykiss). Fish rapidly accumulated all compounds, as measured in the carcass (whole body minus liver and GI tract) during the 32 d uptake phase, which was followed by varying elimination rates of the chemicals (half-lives (t1/2s) ranging from 0.6 d for fipronil to 77.0 d for PCB 174) during the 96 d depuration period. No biotransformation was observed for alpha-HCH, HEPX, PCB 174, o,p'-DDT, or o,p'-DDD based on consistent enantiomeric fractions (EFs) in the fish and their t1/2s falling on a log K(ow)--log t1/2 relationship established for recalcitrant contaminants in fish. p,p'-DDT and PCBs 84 and 132 were biotransformed based on the former's t1/2 position below the log K(ow)--log t1/2 relationship, and the PCBs change in EF. Fipronil was rapidly biotransformed, based on a change in EF, a t1/2 that fell below the log K(ow)--log t1//2 relationship, which accounted for 88% of its elimination, and the rapid formation of fipronil sulfone, a known metabolite. Fipronil sulfone was found to persist longer (t1/2 approximately 2 d) than its parent compound fipronil (t1/2 approximately 0.6 d) and needs to be considered in fate studies of fipronil. This research demonstrates the utilities of the log K(ow)--log t1/2 relationship as a mechanistic tool for quantifying biotransformation and of chiral analysis to measure biotransformation in fish.

Bioconcentration and metabolism of pesticides and industrial chemicals in the frog

“…However, the bioaccumulation factor can be also estimated from the equation "α·F/k D " by using absorption efficiency (α) and feeding rate (F, in g food/g of frog/day). 53) However, much less information on α and F in frogs 5) with a large variance in these values, as compared with fish and birds, presently makes it difficult to correctly estimate the bioaccumulation factor. Recently, the fugacity concept was used to examine the relationship between the metamorphosis of Rana clamitans tadpoles and the elimination of orally dosed polychlorinated biphenyls.…”

“…Although its behavior in the frog was not examined, a slower depuration of the sulfone, by a factor of 3 to 4, than of fipronil (log K ow =4.0 and 3.7, respectively) was reported in the dietary exposure of rainbow trout to fipronil. 53) The slower depuration is likely to originate from its less metabolic transformation than the parent. This information on the metabolites of DDT and fipronil strongly suggests the necessity of more investigation on the bioconcentration and bioaccumulation profiles of hydrophobic metabolites resistant to metabolism.…”

Enantioselective interaction with acetylcholinesterase of an organophosphate insecticide fenamiphos

“…1)], cetylthiocholine iodide (ATCh-I), 5,5 0 -dithio-bis-2-nitrobenzoic acid (DNTB) and bovine serum albumin (BSA) were purchased from Sigma (St. Louis, MO), Other solvents or chemicals were of HPLC or analytical grade. Test solutions of the enzymes were made in 0.01 mol L 21 potassium phosphate buffer (pH 7.4).…”

Chirality as an Environmental Forensics Tool

“…Wiberg et al [230] suggested that the difference in degradation of these two congeners could be attributed to changes in chemical assimilation across the gastrointestinal tract from hydrophobicity and steric hindrance. Enrichment of (À)-PCB 84 and (þ)-PCB 132 was observed in subsequent dietary exposures for rainbow trout [231]. A follow-up study exposed jouvenile trout to mixtures of PCBs similar in congener composition to that found in the Great Lakes, and found similar results for PCBs 95 and 136 along with production of several identified OH-PCBs as well as a number of unidentified OH-PCBs [232].…”