Effects of nano- and microplastics on the bioaccumulation and distribution of phenanthrene in the soil feeding earthworm Metaphire guillelmi

Microplastics (MPs) and nanoplastics (NPs), are collectively referred to as fine plastic particles (FPs), have been reported for both the "vector" effect and "dilution" effect which alters the bioaccumulation of organic contaminants. However, which effect plays a dominant role, especially in terrestrial ecosystems, remains unknown. In the present study, we used C-14-radioactive labeling tracing technique to assess the sorption of a typical polycyclic aromatic hydrocarbon, phenanthrene on soil particles and FPs, as well as the contribution of vector effects of FPs on the bioaccumulation and distribution of phenanthrene by the geophagous earthworm Metaphire guillelmi. The results showed that the presence of FPs in soil decreased the bioaccumulation of C-14-Phenanthrene in M. guillelmi by decreasing the bioavailable fraction of phenanthrene in soil, and the decreasing effect was more dramatic for NPs treatments. In all cases, bioaccumulation of C-14-Phenanthrene in M. guillelmi was still determined by the free concentration of C-14-Phenanthrene in soil and limited vector effects was observed. Moreover, the different correlation coefficients between the free concentration of C-14-Phe in two soils and bioaccumulated C-14-Phenanthrene in earthworms indicated that soil properties remained a dominant factor that determines the bioaccumulation efficiency of C-14-Phenanthrene in the FPs-soil system. Although the total C-14-Phenanthrene bioaccumulation in earthworms did not increase, vector effects may be responsible for the increased relative distribution of C-14-phenanthrene in the organ region, compared with skin and gut regions, leading to unknown risks to organs that are sensitive to these contaminants.