This study assessed the chronic toxicity of polystyrene nanoplastics (PSNP) and clothianidin (CLO), individually and as a binary mixture, on enchytraeids Enchytraeus crypticus and collembolans Folsomia candida. The assays were performed according to ISO protocols, using a tropical soil (Entisol) as the test substrate. The mixture assays were performed using equitoxic concentration, standardized according to the preliminary EC50 values for each contaminant (1 Toxic Unit = reproductive EC50 average), and the toxicological interactions were assessed through the Abbott model. Individually, CLO was much more toxic than PSNP (LOEC-based) to both enchytraeids (CLO = 2.67 mg kg-1, PSNP = 128 mg kg-1) and collembolans (CLO = 0.02 mg kg-1, PSNP = 56.25 mg kg-1). Collembolans were more sensitive to both contaminants compared to enchytraeids, but the difference in sensitivity was higher for CLO (> 100 times) than for PSNP (2.3 times). The binary mixtures showed additive effects of PSNP + CLO for both species at all mixture concentrations. For collembolans, concentrations that caused no significant effects individually (18.75 mg PSNP kg-1 and 0.01 mg CLO kg-1) induced significant negative effects when in mixture, indicating that the co-occurrence of individually non-toxic concentrations might not be safe for collembolans.
Bandeira et al. (2026) studied this question.