Use of earthworms as a pesticide exposure indicator in soils under conventional and organic management

Abstract

The intensive use of agricultural soils reveals the massive application of agrochemicals. There is no follow-up of the presence of pesticide residues in soil or their toxic effects on organisms that are beneficial for agrosystems, such as earthworms (Lumbricus terrestris L.) The objective of this study was to evaluate the effect of pesticides used in horticultural orchards on earthworms, and the use of earthworms as an indicator through carboxylesterase (CbE) activity, which is an enzyme involved in the detoxification metabolism of organophosphorus, carbamates, and pyrethroids. Eight individuals were place in each polyethylene container and the container were buried under the soil surface in two apple orchards, one under organic management and the other under conventional management. The experiment was carried out in triplicate. A control treatment was conducted in the laboratory. The experiment was repeated in autumn, winter, spring, and summer of the 2014-2015 study period. Three internal gut tissues of the earthworm were measured for CbE activity in the laboratory. Results showed higher CbE activity in the crop-gizzard of the control treatment with 14.22 ± 1.00 µmol min-1 mg-1 in winter; the lowest activity was recorded in soil under conventional management in summer with 6.15 ± 2.77 µmol min-1 mg-1 (p ≤ 0.05). There was a seasonal difference in enzymatic activity that was higher in winter and autumn with 14.22 and 13.93 µmol min-1 mg-1, respectively, and lower in summer and spring with 6.15 and 6.31 µmol min-1 mg-1 (p ≤ 0.05), respectively; enzymatic activity was associated with higher pesticide application. It can be concluded that CbE activity is sensitive to the inhibitory action of pesticides and can therefore be used as a biological indicator of agrochemicals.