Toxicological Sciences, Vol 52, 168-177, Copyright © 1999 by Society of Toxicology
JA Steevens and WH Benson
The mechanism of interaction between chlorpyrifos, an organophosphate
insecticide, and methyl mercury, an organometal, was assessed utilizing the
amphipod, Hyalella azteca. Previous studies have demonstrated that
chlorpyrifos and methyl mercury interact additively, with survival as the
endpoint. In addition, exposure to chlorpyrifos and methyl mercury
increased the accumulation and decreased the elimination of methyl mercury.
To elucidate the mechanism responsible for these interactions, biochemical
mechanisms indicative of chlorpyrifos and methyl mercury toxicity were
assessed in H. azteca. Biochemical endpoints that were evaluated include
the inhibition of acetylcholinesterase enzyme and indicators of oxidative
stress such as glutathione-S-transferase activity, lipid peroxidation,
protein oxidation, and glutathione content. Methyl mercury antagonized the
effects of chlorpyrifos in vivo on acetylcholinesterase inhibition. Methyl
mercury did not induce oxidative damage; however, chlorpyrifos decreased
glutathione-S- transferase activity. Additional studies demonstrated that
methyl mercury did not affect the in vitro bioactivation of chlorpyrifos or
the subsequent inhibition of acetylcholinesterase enzyme activity.
Chemical-chemical interactions were examined utilizing chromatographic
techniques. Results of thin layer chromatography suggested the formation of
a chlorpyrifos-methyl mercury complex. The formation of this complex may
result in increased accumulation of methyl mercury, apparent additive
toxicity, and protection against chlorpyrifos mediated acetylcholinesterase
inhibition.
ARTICLES
Toxicological interactions of chlorpyrifos and methyl mercury in the amphipod, Hyalella azteca
Department of Pharmacology, School of Pharmacy, The University of Mississippi, University 38677, USA.
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