Fate of Bisphenol AF (BPAF) in Soil-Earthworm System: Dual Role of Bioaccumulation and Biotransformation

Bisphenol AF (BPAF) contamination in soil from plastic and rubber use is widespread, yet its bioaccumulation and biotransformation in terrestrial invertebrates and its effects on the fate of BPAF in soil remain unknown. Here, we used ¹⁴C-radiotracer to study the accumulation, distribution, metabolism, and excretion of BPAF in the geophagous earthworm Metaphire guillelmi. Earthworms significantly promoted the formation of nonextractable BPAF residues in soil, accelerating BPAF dissipation. After 21 days of exposure, bioaccumulation of total BPAF-derived residues was 6.3-fold higher than that of extractable parent BPAF in earthworms, primarily located in the gut (73.6%), followed by skin (14.7%), body fluid (7.0%), and organs (4.7%), with 47.4% overall existing as tissue-bound residues (TBRs). TBRs showed limited elimination from earthworms but might release BPAF and its transformation products (TPs), predominantly BPAF, into the soil upon earthworm death, increasing BPAF persistence. The dominant TP in earthworms was the monosulfate conjugate of BPAF, the first such conjugate reported in soil animals. Both the TBR formation and excretion of BPAF monosulfate could contribute to the detoxification of BPAF in M. guillelmi. The results underscore a dual role of earthworms in the fate of BPAF in soil (accelerating dissipation vs. increasing persistence) and highlight risks associated with BPAF conjugation and TBR formation.