Multi-target analyses of persistent organic pollutants, halogenated natural products, and organophosphate esters in bivalves from Seto Inland Sea, Japan: Residue levels, profiles, and spatial trends

Comprehensive monitoring studies on the multiple exposure status to persistent organic pollutants (POPs), halogenated natural products (HNPs), and organophosphate esters (OPEs) of coastal biota are quite limited worldwide, especially for wild sessile bivalves. The present study performed multi-target analyses of POPs, HNPs, and OPEs in mussel and oyster samples collected in 2017 and 2019 from the coastal areas of Seto Inland Sea, the largest semi-enclosed sea in Japan. For OPEs, we established a highly accurate analytical method applicable for bivalve soft tissue samples, with minimal blank contamination. Multi-target analyses based on gas and liquid chromatography/mass spectrometry revealed the ubiquity of not only legacy but also emerging compounds in the coastal areas of Seto Inland Sea. However, clear differences in the spatial distribution patterns of POPs, HNPs, and OPEs were observed, indicating the presence of compound-specific local emission sources in the coastal environment. Interestingly, several aryl- and chlorinated-OPEs, including triphenyl phosphate (TPHP), tricresyl phosphate (TMPP), tris(2-chloroisopropyl) phosphate (TCIPP), and tris(1,3-dichloroisopropyl) phosphate (TDCIPP), were found in the bivalve samples with detection frequencies >50 %, and the residue levels of these OPE compounds were higher than those of the major hexabromocyclododecanes and polybrominated diphenyl ethers at almost all the sampling points. These results might be attributed to the increasing demand of OPEs as alternatives after the regulation of such hazardous brominated flame retardants (BFRs). Especially, considering that TCIPP has the lowest log octanol/water partition coefficient (log Kow) and thus the lowest bioaccumulation potential among the above OPEs and BFRs, but still accumulate at relatively higher concentrations in the bivalves, substantial amount of TCIPP input into the coastal areas of Seto Inland Sea and subsequent exposure for organisms can be suggested.