Gene biomarkers in estuarine oysters indicate pollution profiles of metals, brominated flame retardants, and poly- and perfluoroalkyl substances in and near the Laizhou Bay.

The Laizhou Bay (LZB) is of ecological and fishery importance. The discharge of effluents containing numerous pollutants into the LZB via rivers poses significant risks to ecosystem and human health. Estuarine biomonitoring is therefore crucial for assessing the contribution of rivers to coastal pollution and their impacts on species. Estuarine oyster Crassostrea gigas is a preferable bioindicator to pollution conditions. This study measured accumulation of contaminants and expression levels of gene biomarkers in the LZB and Northern Shandong Peninsula (NSP) oysters. The LZB oysters accumulated higher levels of brominated flame retardants (BFRs) and poly- and perfluoroalkyl substances (PFAS), while NSP oysters exhibited greater accumulation of heavy metals. Decabromodiphenyl ethane was the dominant BFR, while perfluorooctanoic acid and perfluoro-2-methoxyacetic acid were the dominant PFASs in oysters. The expression of gene biomarkers effectively distinguished the LZB and NSP oysters, with CYP2 subfamilies expression correlating with BFRs and PFASs and metallothionein expression indicating heavy metals. The reproductive endocrine and neuroendocrine-immune systems in oysters might be the targets of BFRs and heavy metal pollution, respectively. The negative correlation between contaminant accumulation and gene expression might be explained by adaptive evolution, emphasizing the need to consider genetic diversity in ecological risk assessments.