Sublethal toxicity of chlorpyrifos on Octolasion cyaneum (Annelida: Oligochaeta, Lumbricidae)

Abstract

The aim of this study was to evaluate the survival, biomass, reproductive
parameters and morphological changes of Octolasion cyaneum (Annelida:
Oligochaeta, Lumbricidae) exposed to different concentrations of chlorpyrifos. The experimental unit consisted of a container with 750 g of soil mixed with the concentration of the insecticide and 10 adult individuals (weight range: 300-600 mg). The treatments were: 0, 120, 240, 480 (recommended application concentration), 960 and 1440 g of chlorpyrifos ha-1. The design was completely randomized with four replications and was conducted under controlled conditions (20±2ºC, 14L: 10O). O. cyaneum biomass differed between treatments at 7, 14 and 28 days after application (DAA) (p<0.05), and showed the highest biomass in the control. The number of cocoons and juveniles at 56 DAA was higher in the control compared to the other treatments (p<0.05). In the bioassay 235 individuals were alive and 5 were dead, nevertheless the 35% of organisms showed morphological changes. It was noted that the percentage of damage varied depending on the concentration of the insecticide (p = 0.0046). Chlorpyrifos did not affect the survival of O. cyaneum but caused morphological changes and a reduction in biomass and reproductive parameters.