Isomer-Specific Accumulation of Perfluorooctanesulfonate from (N-Ethyl perfluorooctanesulfonamido)ethanol-based Phosphate Diester in Japanese Medaka (Oryzias latipes)

Abstract

While (N-ethyl perfluorooctanesulfonamido)ethanol (FOSE) -based phosphate diester (diSPAP) has been proposed as a candidate precursor of perfluorooctanesulfonate (PFOS), its potential biotransformation to PFOS has not been verified. Metabolism of diSPAP was investigated in Japanese medaka ( Oryzias latipes ) after exposure in water for 10 days, followed by 10 days of depuration. Branched isomers of diSPAP (B-diSPAP) were preferentially enriched in medaka exposed to diSPAP, with the proportion of branched isomers (BF) ranging from 0.56 to 0.80, which was significantly greater than that in the water to which the medaka were exposed (0.36) (p < 0.001). This enrichment was due primarily to preferential uptake of B-diSPAP. PFOS together with perfluorooctanesulfonamide (PFOSA), N-ethyl perfluorooctanesulfonamide (NEtFOSA), 2-(perfluorooctanesulfonamido)acetic acid (FOSAA), NEtFOSAA, FOSE, and NEtFOSE were detected in medaka exposed to diSPAP, which indicated the potential for biotransformation of diSPAP to PFOS via multiple intermediates. Due to preferential metabolism of branched isomers, FOSAA and PFOSA exhibited greater BF values (>0.5) than those of NEtFOSA, NEtFOSAA, and NEtFOSE (<0.2). Such preferential metabolism of branched isomers along the primary pathway of metabolism and preferential accumulation of B-diSPAP led to enrichment of branched PFOS (B-PFOS) in medaka. Enrichment of B-PFOS was greater for 3-, 4-, and 5-perfluoromethyl PFOS (P3MPFOS, P4MPFOS, and P5MPFOS), for which values of BF were 0.58 ± 0.07, 0.62 ± 0.06, and 0.61 ± 0.05 (day 6), respectively; these values are 5.8-, 7.8-, and 6.4-fold greater than those of technical PFOS. This work provides evidence on the isomer-specific accumulation of PFOS from diSPAP and will be helpful to track indirect sources of PFOS in the future.

Perfluoroalkyl Acids (PFAAs) and Selected Precursors in the Baltic Sea Environment: Do Precursors Play a Role in Food Web Accumulation of PFAAs?

“…The present study included selected precursors; however, other PFOS or PFCA precursors or intermediates have been shown to form PFAAs. 3,35 Future use of more generic analytical methods, such as the total oxidizable precursor method, 36 alongside targeted analyses would provide further information on the importance of precursors compared to PFAAs in food web accumulation. …”

“…Identified perfluoro-octane sulfonic acid (PFOS) precursors include methyl and ethyl perfluorooctane sulfonamidoethanols (Me-and EtFOSE) and sulfonamides (Me-and EtFOSA). 2,3 On the other hand, fluorotelomer-based chemicals can be degraded to PFCAs, and these precursors include polyfluoroalkyl phosphoric acid esters (PAPs). 4 PFAAs are found globally in fish and wildlife, including different trophic levels within food webs.…”

Temporal changes (1997–2012) of perfluoroalkyl acids and selected precursors (including isomers) in Swedish human serum

“…Dust and food ingestion have been identified as direct exposure pathways for Meand EtFOSAA (Beesoon et al, 2011;Gebbink et al, 2015b;Ullah et al, 2014), but also intake of Me-and EtFOSE (e.g., through inhalation of air and ingestion of dust ) and subsequent transformation is a potential exposure source to Meand EtFOSAA (Peng et al, 2014). FOSAA has been reported in chicken eggs obtained in Sweden (Gebbink et al, 2015b), however, degradation of FOSEs could also be an indirect exposure pathway for this fluorinated chemical (Xu et al, 2004).…”

“…FOSAA has been reported in chicken eggs obtained in Sweden (Gebbink et al, 2015b), however, degradation of FOSEs could also be an indirect exposure pathway for this fluorinated chemical (Xu et al, 2004). FOSA detected in human serum could originate from direct exposure through one or more exposure pathways (diet, dust, drinking water, and air) (Gebbink et al, 2015a) or from intakes of fluorinated chemicals such as Me-and EtFOSE, Me-and EtFOSAA, and/or Me-and EtFOSA followed by biotransformation to FOSA (Peng et al, 2014).…”

“…There are, however, also PFASs that are less persistent and that can undergo transformation. Methyl and ethyl perfluorooctane sulfonamidoethanols (Me-and EtFOSE) and perfluorooctane sulfonamides (Me-and EtFOSA) are PFASs that have been identified as precursors to perfluorooctane sulfonic acid (PFOS) (Benskin et al, 2009;Peng et al, 2014;Xie et al, 2009). The manufacturing of PFOS and its precursors resulted in a mixture of linear and branched isomers (Martin et al, 2010), and production was phased out by the main manufacturer between 2000 and 2002 in North America and Europe.…”