Synergistic and Sublethal Effects of Agrochemical Mixtures on Porcellio laevis: A Chronic and Acute Toxicity Assessment

Abstract

Contamination of terrestrial habitats by pesticides presents an ecological issue of significance due to an impact on non-target terrestrial invertebrates. The terrestrial isopod, Porcellio laevis, as a cosmopolitan species, is significant as a bioindicator due to its functions in decay and nutrient cycling. Since lethal endpoints continue to be of the most significance in most studies, sublethal impacts in relation to changes in growth, breeding, and behavior offer earlier and ecologically relevant indicators of distress. This study estimated acute and chronic toxic impacts of common pesticides, Cyperkill (an insecticide), Garlon (an herbicide), and Benlate (a fungicide), individually and in combination in binomial mixtures. Adult Porcellio laevis were treated with treated leaves and soil amended with Cyperkill (0.15, 0.30, 0.60 ppm), Garlon and Benlate (300, 600, 900 ppm), and three binary mixtures (Cyperkill + Garlon, Cyperkill + Benlate, and Garlon + Benlate) for 8 weeks. Changes in body weight, food consumption, juvenile production, and rates of mortality. LC₅₀ of Cyperkill was estimated in an acute toxicological bioassay after 24 h and 48 h through Probit regression analysis. The juvenile output and body weight dropped considerably under all pest control treatments, most notably under multiple exposures, indicating evidence of synergistic toxicity. Food consumption was not significantly different under treatment, however, there was an overall trend of a drop under pest control treatment. Percentage mortality increased with an increase in the concentration of pest control, and maximum lethality was caused by the treatment combination of Cyperkill + Garlon. The LC₅₀ value of Cyperkill decreased from 24 h to 48 h, indicating increased toxicity after prolonged exposure durations. These findings confirmed that both single and mixed exposures to pesticides have adverse effects on the main physiological and reproductive indices of Porcellio laevis. The combination of sublethal criteria, in correlation with mortality indicators, provides a more comprehensive characterization of ecological risk. This validates the significance of mixture research and behavior-based biomarkers in ecotoxicological assessments of soils.