Survival, morphology and reproduction of Eisenia andrei (Annelida, Oligochaeta) as affected by Vertimec® 18 EC (a.i. abamectin) in tests performed under tropical conditions

Abstract

The effects of abamectin (Vertimec® 18 EC) on Eisenia andrei were evaluated under tropical conditions through acute and chronic tests. Tests were performed using a Tropical Artificial Soil (TAS), aiming to deliver tropical ecotoxicological data, and a natural soil (NS) contaminated in situ, aiming to simulate realistic exposure scenarios for Brazilian strawberry crop fields. To these ends, adaptations of the standard international protocols were performed: coconut shell residue was used as a source of organic matter in replacement for sphagnum peat moss in TAS and all tests were conducted under a temperature of 25±2°C. In the acute and chronic tests with TAS, the pesticide was incorporated in concentrations of 0–14 and 0–10.5mg abamectin/kg soil, respectively. In the NS tests, the organisms were exposed to samples of soil sprayed in situ with water (Control), the recommended field dose of 0.9L Vertimec® 18 EC/ha (RD); twice this dosage (2DR); and 2DR:control soil dilutions (12.5; 25; 50; and 75%). The TAS tests indicated LC50 values of 7.64mg a.i./kg (14 days) and 8.65mg a.i./kg (28 days) and chronic NOEC<0.88mg a.i./kg. The organisms exposed to the pesticide also presented morphological alterations (thinning, discoloration of the posterior region; constriction in different regions of the body; fragmentation, and loss of segments, mainly in the posterior region), behavioral alterations (lethargy or slowed response to mechanical stimuli), and weight loss. The average number of juveniles produced decreased from 33 (Control) to 3 in the lowest pesticide treatment (0.875mg a.i./kg TAS), and no reproduction was observed at higher pesticide concentrations. There was no significant response to any parameter analyzed in the tests performed with NS, even for the worst-case scenario (2DR). Results suggest low risk of Vertimec® 18 EC to earthworms if the recommended dosage for strawberry crop and good agricultural practices are followed. It is important to consider, however, that only one application of the product was evaluated in the NS tests, whereas multiple applications as well as inadequate use of pesticides are common in the main Brazilian strawberry region.