Influence of Dietary Coexposure to Benzo(a)pyrene on the Biotransformation and Distribution of 14C-Methoxychlor in the Channel Catfish (Ictalurus punctatus)

Abstract

Methoxychlor (MXC) is an organochlorine pesticide whose mono- and bis-demethylated metabolites, 2-(4-hydroxyphenyl)-2-(4-methoxyphenyl)-1,1,1-trichloroethane (OH-MXC) and 2,2-bis(4-hydroxyphenyl)-1,1,1-trichloroethane (HPTE), respectively, are estrogenic and antiandrogenic. Studies in vitro showed that treatment of channel catfish with a polycyclic aromatic hydrocarbon increased phase I and phase II metabolism of MXC. To determine the in vivo significance, groups of four channel catfish were treated by gavage for 6 days with 2 mg/kg (14)C-MXC alone or 2 mg/kg (14)C-MXC and 2 mg/kg benzo(a)pyrene (BaP). On day 7, blood and tissue samples were taken for analysis. Hepatic ethoxyresorufin O-deethylase activity was 10-fold higher in the BaP-treated catfish, indicating CYP1A induction. More MXC-derived radioactivity remained in control (42.8 +/- 4.1%) than BaP-induced catfish (28.5 +/- 3.2%), mean percent total dose +/- SE. Bile, muscle and fat contained approximately 90% of the radioactivity remaining in control and induced catfish. Extraction and chromatographic analysis showed that liver contained MXC, OH-MXC, HPTE, and glucuronide but not sulfate conjugates of OH-MXC and HPTE. Liver mitochondria contained more MXC, OH-MXC, and HPTE than other subcellular fractions. Bile contained glucuronides of OH-MXC and HPTE, and hydrolysis of bile gave HPTE and both enantiomers of OH-MXC. The muscle, visceral fat, brain and gonads contained MXC, OH-MXC, and HPTE in varying proportions, but no conjugates. This study showed that catfish coexposed to BaP and MXC retained less MXC and metabolites in tissues than those exposed to MXC alone, suggesting that induction enhanced the elimination of MXC, and further showed that potentially toxic metabolites of MXC were present in the edible tissues.

Organochlorine pesticides (OCPs) in wetland soils under different land uses along a 100-year chronosequence of reclamation in a Chinese estuary

“…Both the MXC and ∑ENDs concentrations were also higher in the D30 and D20 surface soils. This implies that more MXC and endosulfan might have been used and accumulated in these regions because MXC is an insecticide that was developed to replace DDT and was widely used all over the world because of its lower toxicity to mammals and lower persistence in the environment relative to DDT 26 32 . Meanwhile, endosulfan is still in use in China 12 .…”

<i>In vitro</i> metabolism of pesticides and industrial chemicals in fish

“…In vitro studies using the hepatic microsomes (+ UDPGA) and cytosol (+ PAPS) of I. punctatus showed a formation rate of glucuronide conjugate ten-times higher than the sulfate one from the Odemethylated metabolite, 85) which partly explains the detection of glucuronides as dominant components in the bile and liver of the force-fed fish. 138) 3.1.3. Pyrethroids The main biliary metabolites of cis-cypermethrin with the static water exposure of O. mykiss were a 4′-OH derivative and its glucuronide, representing 80-90% of the residue in total.…”