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Genetic Toxicology

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Mutation Research 342 (1995) 25-36

Evaluation of the genetic toxicity of the organophosphate insecticide chlorpyrifos
B. Bhaskar Gollapudi *, Alan L. Mendrala, V. Ann Linscombe
The Toxicology Research Laboratory, 1803 Building, The Dow Chemical Company, Midland, MI 48674, USA
Received 21 December 1993; revised 21 September 1994; accepted 8 November 1994Abstract

The genetic toxicity of chlorpyrifos [O, O,-diethyl-O-(3,5,6-trichloro-2-pyridinyl)phosphorothioate,C.A.S. Number: 2921-88-2)], an organophosphate insecticide, was examined by employing several end points such as gene mutations in bacteria (Ames test) and mammalian cell cultures ( C H O / H G P R T assay), cytogenetic abnormalities in mammalian cells both in vitro (rat lymphocytechromosomal aberration test, RLCAT) and in vivo (mouse bone marrow micronucleus test) and induction of DNA damage and repair in rat hepatocytes in vitro. There was no indication of genotoxic activity for chlorpyrifos in any of these assays. These results are consistent with the reported lack of carcinogenic potential for chlorpyrifos in both mice and rats.

Keywords: Chlorpyrifos; Genetic toxicity;Clastogenicity; Mutagenicity; DNA damage and repair

1. Introduction

Chlorpyrifos (C.A.S. Number: 2921-88-2) is a widely used insecticide through- out the world. It belongs to the class of chemicals collectively known as organophosphates. It is the active ingredient in D U R S B A N ®, L O R S B A N ®, and P R E D A T O R ® brand of insecticides. For a general introduction of theorganophosphate insecticides, the reader is referred to an expert report published by W H O (1986). Chlorpyrifos and other organophosphates inhibit the acetylcholinesterase enzyme in the nervous system of a number of

species including humans. The insecticidal activity of organophosphate pesticides is due to the accumulation of toxic levels of acetylcholine in the targeted species. Chlorpyrifos (O, O,-diethyl-O-(3,5,6-trichloro2-pyridinyl)phosphorothioate) is a solid at room temperature with the following structure: CI--~C1 C1 -_t...'~./t__ O - - P - - (OCH 2CH 3)2 S The studies reported here are a part of the total safety evaluation of chlorpyrifos and deal with the assessment of the genotoxic potential. A variety of end points were employed in assessing the genotoxic potential of chlorpyrifosduring the period of 1985-1991.

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* Corresponding author. Tel.: 517-636-7179; Fax: 517-6389863. Elsevier Science B.V. SSDI 0 1 6 5 - 1 2 1 8 ( 9 4 ) 0 0 0 7 7 - 8

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B.B. Gollapudi et al. / Mutation Research 342 (1995) 25-36

2. Materials and methods

2.1. Test material Chlorpyrifos samples used in these studies were obtained from Dow Chemical/DowElanco, Midland, MI. All assaysexcept the in vitro cytogenetics were conducted using a lot of chlorpyrifos with a purity of 95.7-97.9%. The in vitro cytogenetic assay which was conducted more recently employed a different lot having a purity of 98.6%. Chlorpyrifos was dissolved in dimethyl sulfoxide (DMSO) and added to the in vitro systems. Chlorpyrifos was determined to be stable in DMSO for at least 4 h. Genetic toxicity assaysThe Salmonella typhimurium bacterial reverse mutation assay was conducted using the pre-incubation procedure of Maron and Ames (1983). A list of the tester strains and the corresponding positive control chemicals are shown in Table 1. Liver homogenates ($9) prepared from male Sprague-Dawley rats ( A R O C L O R 1254-induced, Ames et al., 1975) were purchased from SITEK Research Laboratories,Rockville, MD). The assay involved incubating the bacterial culture with the test material and, where applicable, $9 mix (containing 20% liver homogenate) for 30 min at 30°C in a gyrotory incubator (300 rpm). This mixture was then supplemented with top agar, poured on minimal glucose agar petri plates and the his + revertants were counted after incubating the plates at 37°C for 2 days. The criteria for...
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