Impacts of organic matter content on toxicity of phenanthrene to the collembolan, Folsomia candida.

Returning straw to soil can increase the soil organic matter (OM) content, thus lowering the bioavailability of lipophilic compounds. However, the effects of OM content and its fractions (particulate organic carbon (POC) and mineral-associated organic carbon (MAOC)) on the toxicity of soil polycyclic aromatic hydrocarbons (PAHs) to soil invertebrates remain poorly understood. In this study, collembolan Folsomia candida was exposed to a range of phenanthrene (PHE) concentrations (0, 5, 10, 20, 30, 40 mg kg-1 dry soil) at four different OM addition rates (0%, 0.25%, 0.35%, 0.5%) for 28 days. At the end of the experiment, the life-history traits (survival and juvenile production), and the internal PHE concentration of F. candida and the fractions of OM (POC and MAOC) were determined. The results showed that increasing OM content reduced the internal PHE concentration at higher soil PHE concentrations. The survival and juvenile production was significantly increased by increasing OM content under PHE contamination (p < 0.05). Further, the concentration causing 50% inhibition of juvenile production (EC50) value for the effect of PHE on juvenile production was significantly increased by adding OM (p < 0.05). Partial least squares structural equation modeling demonstrated that different soil organic matter fractions differed in their ability to immobilize PHE, and MAOC showed a capacity to reduce the bioavailability and toxicity of PHE better than POC. These results show that the addition of OM could alleviate the toxicity of PHE to F. candida. Our findings highlight the potential of exogenous organic matter to reduce PAH toxicity to soil invertebrates and provide a theoretical basis for the ecological remediation of PAH-contaminated soils.