A comparison of biomarkers in assessing the combined effects of pesticide mixtures on non-target soil invertebrates

[摘要] ENGLISH ABSTRACT: Agricultural environments are usually contaminated with mixtures of antropogenicallyintroduced chemicals as a result of pesticide spraying, which can affect beneficial, nontargetsoil invertebrates, such as earthworms negatively. Most studies on mixture toxicityhave focused on interactions of chemicals with similar structures and mechanisms.However, chemical mixtures may occur as conglomerates of diverse structures andtoxicological mechanisms in the environment.This study was aimed at assessing the effects of pesticides singly, and in a mixture, onearthworms, using lifecycle parameters (growth and reproduction) and biomarkers(neutral red retention (NRR) assay and acetylcholinesterase (AChE) inhibition) asendpoints. Thus, to determine whether any interactions occurred between the pesticidesas shown by the measured endpoints. Another aim was to validate the use of the chosenbiomarkers for assessing mixture toxicity.The pesticides used were from three groups: organophosphates, heavy metal-containingpesticides and pyrethroids. From these three groups, four of the most commonly usedpesticides in the orchards and vineyards of the Western Cape, South Africa, were chosen,namely chlorpyrifos (organophosphate), azinphos-methyl (organophosphate), copperoxychloride (heavy metal-containing fungicide) and cypermethrin (pyrethroid).Earthworms were exposed in the laboratory to a range of concentrations of chlorpyrifosand copper oxychloride singly, and in 1:1 mixtures of these pesticides in artificial soil, forfour weeks. After the exposure period, the biomass change was determined as measureof growth, and cocoon production, hatching success and number of hatchlings per cocoonwere determined as measures of reproduction.Growth (biomass change) and reproduction (cocoon production) were affected by thehighest concentration treatment (20mg/kg) of chlorpyrifos, but copper oxychloride andthe mixture of the two pesticides showed no observable effects on lifecycle parameters.Dose related effects on NRR times were however determined for both pesticides and themixture. Dose related effects on AChE activity were found for chlopyrifos and themixture of the two pesticides, but not for copper oxychloride. Short-term exposures (48hours) of earthworms to the following pesticides in artificial groundwater: chlorpyrifos, copper oxychloride, azinphos-methyl, cypermethrin, chlorpyrifos-copper oxychloride,chlorpyrifos -azinphos-methyl and chlorpyrifos-cypermethrin, were done followed by thedetermination of AChE inhibition. Dose related effects were exhibited on the AChEactivity of earthworms exposed to chlorpyrifos, a mixture of chlorpyrifos and copperoxychloride, azinphos-methyl, and a mixture of azinphos-methyl and chlorpyrifos.Copper oxychloride, cypermethrin and the mixture of chlorpyrifos and cypermethrin hadno effect on AChE activity. Earthworms died at the highest exposure concentration ofthe mixture of chlopyrifos and cypermethrin.Results have shown that although the pesticides did not cause observable effects onlifecycle parameters, there were effects at subcellular and biochemical level, as shown bythe biomarkers. Mixtures of pesticides, in some instances, affected earthwormsdifferently from their single components, indicating interactions between the pesticides inmixtures, as shown by the measured endpoints. The NRR assay proved to be a goodgeneral biomarker of soil contamination, and the AChE activity could also be a valuabletool in assessing the effects of organophosphate mixtures and mixtures oforganophosphates and pesticides from other groups.

[发布机构] Stellenbosch University