Is nano ZnO/chlorpyrifos mixture more harmful to earthworms than bulk ZnO? A multigeneration approach

As chlorpyrifos is one of the most widely used organophosphorus insecticides and ZnO-NPs are identified as NPs of the highest concern due to their negative effects on aquatic and soil organisms the objective of this study was to evaluate mixture toxicity of CHP and ZnO (bulk and nanoparticles (20 nm)) on two types of soil, artificial (AS) and natural (NS), and over two generations of earthworms. Primary endpoint measured was reproduction inhibition and biochemical biomarkers (acetylcholinesterase, catalase, glutathione-S transferase and malondialdehyde content). Results showed that mixture toxicity differs in respects to all tested factors: soil type, ZnO particle size and earthworm generation. CHP/ZnO mixtures had synergistic effects and significantly reduced a number of juveniles in both generations in AS, while the effects were additive or even antagonistic in NS. There was no difference in reproduction inhibition in respect to particle size of ZnO used in the mixtures. Negative effects could also be detected on growth dynamics of juvenile earthworms (2nd generation) as they had lower initial body mas, reduced growth rate and lower body mass as adults. Measured enzymes responded differently in respect to ZnO particle size used in the mixtures, with CHP/bZnO producing stronger effects. Measured concentrations of the bioavailable Zn in the soils showed no difference in the concentration of bioavailable Zn²⁺ between mixtures, but significantly more Zn²⁺ was retrieved from AS. General biomarker response indicated that 2nd generation of earthworms had lower capability to cope with oxidative stress.