Aging Changes the Vector Effects of Various Microplastics on the Bioaccumulation of Decabromodiphenyl Ethane in Earthworms

The widespread use and nonstandard disposal of plastic products led to inevitable copollution of microplastics (MPs) and novel brominated flame retardants (NBFRs). However, gaps remain in understanding the influence of aged MPs on the bioaccumulation and biotoxicity of NBFRs in terrestrial environments. We assessed the effects of UV-aged MPs derived from poly(lactic acid) (PLA) and polyethylene (PE) on the bioaccumulation of decabromodiphenyl ethane (DBDPE) in a soil-earthworm system. After 28-d exposure, DBDPE bioaccumulation in the intestine of earthworms under coexposure (0.1% or 1% MPs in 10 mg kg^-1 DBDPE soil) exhibited better impacts of MPs than that in the whole tissue. Overall, the aging of biodegradable PLA-MPs promoted DBDPE bioaccumulation in the intestine of earthworms through ingestion and thus reduced DBDPE attachment on the aged PLA-MPs in soil, which relied on their increased adsorption to DBDPE. Similarly, the aging of PE-MPs reduced DBDPE bioaccumulation in the intestine due to the decreased adsorption ability to DBDPE. Specifically, aged PLA-MPs increased DBDPE in the intestine by 15%, while aged PE-MPs decreased it by 21%. Aged PE-MPs formed stable biofilms in soil with strong binding to DBDPE, thereby reducing DBDPE bioaccumulation in earthworms but exacerbating its migration risks. This reflected the "vector effect" of aged MPs on DBDPE bioaccumulation in earthworms with ingestion. Furthermore, SR-FTIR confirmed that MPs remained in tissues and DBDPE was loaded on the MPs' surface in the intestine, indirectly verifying the vector effect of MPs. This work highlights discrepant risks between biobased degradable and fuel-based hydrocarbon MPs in HOC-contaminated soil in realistic environmental scenarios.