In vivo studies on genotoxicity of pure and commercial linuron

The ureic herbicide linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea] (CAS 330-55-2) was investigated for genotoxicity in a series of in vivo experiments. Since human exposure to herbicides is not only to the active principles, but also to all the chemicals present in the commercial formulation, we tested both pure and commercial linuron. Groups of rats were treated with gavage containing different doses of the herbicide (pure compound or commercial formulation) for 14 days. The doses were 150, 300 and 450 mg/kg b.wt. for the pure compound and 315.8, 631.6 and 947.4 mg/kg b.wt. for the commercial formulation (47.5% of linuron). Faeces and urine were collected at regular intervals. Urine specimens were analysed for their mutagenic metabolites, thioethers and d-glucaric acid content. Faeces extracts were tested for mutagenicity. Linuron's ability to cause DNA damage and cytogenetic effects was also investigated after treating groups of rats once with different doses of pure or commercial linuron. DNA single-strand breaks were assessed in rat liver using the alkaline elution technique and the single-cell microgel electrophoresis assay (SCGE: `comet' assay), and in rat testes cells with the SCGE assay. Micronuclei induction was analysed in rat bone marrow erythrocytes. Results obtained were mainly negative when the excretion of mutagenic metabolites in urine and faeces of animals treated with the pure compound or with the linuron-based commercial formulation were monitored, whereas an increase in the urinary excretion of thioethers and d-glucaric acid was observed in rats treated with the commercial formulation. No increase in the frequency of micronucleated polychromatic erythrocytes was observed in the treated animals. However, linuron affected the viability of hepatocytes isolated from animals treated with higher doses. This cytotoxicity was accompanied by the induction of DNA single-strand breaks in the liver, as seen by the alkaline elution assay. The potential of pure linuron to induce in vivo DNA damage was confirmed with the microgel electrophoresis technique (`comet' assay). Cytotoxicity was also seen in rat testes cells. However, no indication of DNA damage was visible.