| Perfluorooctanoic acid (PFOA) is a synthetic organic chemical characterized by its unique hydrophobic and oleophobic properties. It is extensively utilized in the production of a wide range of industrial and consumer products essential for human life, including aqueous film-forming foams, medical devices and textiles. PFOA is widespread in the aquatic environment, and poses serious ecological risks, which has garnered global attention. Consequently, several countries and organizations have implemented strict restrictions or controls on its use. Notably, in 2019, PFOA and its salts were included in Annex A of the Stockholm Convention on Persistent Organic Pollutants. Further, in 2023, the Ministry of Ecology and Environment of the People's Republic of China and other six departments issued the "Key Regulated New Pollutant List 2023", which proposed environmental risk control measures for PFOA, its salts, and related compounds. With the increase in regulatory measures, the production and usage of PFOA have declined, resulting in the rapid development and use of alternatives. Hexafluoropropylene oxide dimer acid (HFPO-DA), Hexafluoropropylene oxide trimer acid (HFPO-TA), and Hexafluoropropylene oxide tetramer acid (HFPO-TeA) have emerged as principal alternatives. These alternatives, composed of CF2 or CF2O repeating units, maintain chemical properties similar to PFOA and are predominantly used in the manufacture of fluoropolymers and their processing aids.
Bivalves, as filter-feeding organisms, are prolific and have a broad geographic distribution. They possess a significant capacity to accumulate organic contaminants, making them ideal indicators for monitoring pollution in marine environments and assessing the status of various marine ecosystems. In this study, the Manila clams (Ruditapes philippinarum) were utilized as test organisms. These clams were exposed to two concentrations (2 ng·mL-1 and 200 ng·mL-1) of PFOA and its alternatives (HFPO-DA, HFPO-TA, HFPO-TeA) within a mariculture setting.
The purpose of this study was to analyze the tissue distribution, accumulation, elimination patterns of these compounds in clams, and to evaluate differences in the accumulation ability of organisms to enrich for PFOA and its ether carboxylic acid alternatives in clams by calculating kinetic parameters. Additionally, water-soluble proteins were extracted from visceral masses and gills of clams and incubated in vitro to explore the differences of binding rates between the target compounds and clams proteins. The binding modes between target molecules and proteins was investigated using molecular docking techniques to further elucidate the relationship between molecular-protein interactions and the bioaccumulation properties of clams.
It was found that that PFOA and its ether carboxylic acid alternatives were rapidly enriched in Manila clams. The enrichment rate of targets increased according to HFPO-DAgill>mantle>adductor muscle. After a 21-day depuration period, the levels of these contaminants in Manila clams approached those of the control group. Furthermore, Accumulation capacity of PFOA and its ether carboxylic acid alternatives in the Manila clams, and binding rates of different target molecules to clam body proteins are strongly correlated with target concentrations. The lower concentrations of the targets leaded to the greater the absorption rate constants (Ku) and bioconcentration factors (BCF) in Manila clams and lower the binding rates of the targets to the protein. The content and protein binding of the targets in each tissue were HFPO-DA |
