Mechanisms for tissue-specific accumulation and phase I/II transformation of 6:2 fluorotelomer phosphate diester in earthworm (M. guillelmi)

By Yumin Zhu, Yibo Jia, Menglin Liu, Liping Yang, Shujun Yi, Xuemin Feng, and Lingyan Zhu
Environ Int
March 9, 2021
DOI: 10.1016/j.envint.2021.106451

Polyfluoroalkyl phosphate esters (PAPs) are high production volume surfactants used in the food contact paper and packaging industries. They are prone to partition to soil due to their strong hydrophobicity and may biotransform into recalcitrant perfluoroalkyl carboxylic acids (PFCAs); little is known about their fate and behaviors in terrestrial organisms. Here, geophagous earthworms (M. guillelmi) were exposed to 6:2 fluorotelomer phosphate diester (6:2 diPAP)-contaminated soil to examine tissue-specific accumulation and biotransformation. 6:2 diPAP quickly accumulated in M. guillelmi with the highest biota-soil-accumulation factor (BSAF) in the gut, followed by the organs, skin, and body fluid. The total amount of 6:2 diPAP accumulated in the skin was the highest due to its high mass content. These results indicated that skin absorption and gut processes were two major pathways for earthworms to accumulate 6:2 diPAP from soil. In vitro desorption experiments indicated that the gut digestion fluid greatly promoted the desorption of 6:2 diPAP from the soil and enhanced its bioavailability. Degradation of 6:2 diPAP in the soil was stimulated when the earthworm appeared. In contrast to the soil, a more extensive transformation occurred in the earthworm. Perfluorohexanoic acid (PFHxA) was the primary phase Ⅰ product, followed by perfluoropentyl propanoic acid (FPePA), perfluoropentanoic acid (PFPeA), 2-perfluorohexyl ethanoic acid (FHEA), and perfluoroheptanoic acid (PFHpA), which confirmed the occurrence of α- and β-oxidation in earthworms. For the first time, a new phase II product, namely, a 6:2 fluorotelomer alcohol sulfate conjugate, was identified in earthworms at unexpectedly high levels, which might be the primary way earthworms eliminate 6:2 diPAP. Both in vivo and in vitro experiments suggested that 6:2 diPAP experienced faster and more extensive biotransformation in the gut than in the organs. This work sheds light on the bioaccumulation and biotransformation of 6:2 diPAP in terrestrial invertebrates, providing strong evidence of indirect sources of PFCAs in the environment.

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