Combined effects of salinity and chlorpyrifos on the earthworm Eisenia andrei

Soil salinization could represent a threat for earthworms, affecting their general health status, reproduction and survival. This stressing condition could be worsened by the presence of further anthropic factors, like pesticides, whose effect may be exacerbated in a climate change scenario. Hence the goal of this study was to evaluate the effects of salinity (SAL), chlorpyrifos (CP) and their combination on the earthworm Eisenia andrei. Five different SAL conditions (0.1 ÷ 12 g/L), and five different CP concentrations (3.16 ÷ 316 mg/kg) were tested in “single stressor” experiments. Seventeen different combinations (SAL 2.5 ÷ 10 g/L; CP 5 ÷ 80 mg/kg) were tested in the following “combination” experiment. The endpoints considered were mortality, growth, reproduction and acetylcholinesterase (AChE) activity. Exposure to SAL decreased growth, survival and reproduction of earthworms, especially at the highest salt concentrations, where no cocoons were found at the end of the experiment. CP affected survival and growth only at the highest concentration, where 100% mortality was observed. Contrariwise, reproduction was affected also at lower concentrations of CP. AChE activity was drastically inhibited by increasing CP concentrations. In the combination experiment, neither SAL nor CP affected worm survival. Growth and number of laid cocoons were reduced by both stress factors, with no interactive effects. Number of juveniles showed a hormetic response to CP in the absence of SAL. Interestingly, SAL eliminated the hormesis. AChE activity was affected only by CP, and not by SAL. In conclusion, combination experiments showed that E. andrei life cycle traits were negatively affected by soil SAL, and also by CP at high concentrations. AChE activity was very sensitive to CP, while it was not affected by SAL. The number of juveniles was the only endpoint showing interactive effects between the two stress factors.