Assessing the effects of L-cyhalothrin and rain events on soil microarthropod community using a terrestrial model ecosystem

Abstract

To identify potential risks derived from changing climatic regimes has become a major concern worldwide. Alterations of rain patterns are expected to modify the environmental responses of biological communities in soil, often due to alterations in moisture levels, a key factor for soil microarthropods. Pesticide use imposes great disturbances to soil, altering its functional dynamics. Since environmental conditions such as rain and temperature regimes can interfere with chemical speciation and/or chemical’s persistence in soil, soil organisms might be affected in a different way in contaminated soil under different climatic scenarios. Lambda-cyalothrin is a pyrethroid insecticide widely used to control insect pests for public health and cultivated lands. Annual agricultural use of L-cyalothrin has increased over the last years, while insecticide residuals have been detected in irrigation and storm-runoff water, and associated sediments as well. The potential risk of this pesticide to aquatic organisms is known to be high, but its effects on terrestrial communities remain practically unknown. Moreover, to date, the combined effect of changes on rain patterns and L-cyhalothrin application has not been investigated. Aiming to fill this gap, a semi-field experiment was performed using Terrestrial Model Ecosystems (TMEs). The effect of different doses of the commercial formulation of Judo® insecticide, containing L-cyalothrin as active ingredient (a.i.), was evaluated in soil fauna communities of a pasture field free of pesticide applications for more than 5 years. Doses of 0, 7.5 and 37.5 g of a.i./ha were investigated, equivalent to 0, 1 and 5 times the recommended dose, respectively. Three replicates per test dose were exposed to different rain regimes to reach moistures corresponding to 30, 50 and 70% of the water-holding capacity of the field soil. After 2 and 8 weeks of insecticide application, soil samples were collected to characterize soil fauna communities (microarthropods, nematodes, enchytraeids and earthworms). In this study only the results of mites and Collembola are shown. These data, although with high variability, suggest that toxicity levels derived from L-cyalothrin applications may be influenced by rain regime and that composition of soil mesofauna communities may be a good indicator of the influence of pesticides along time under changing climatic conditions