;In marine species of the food web
Bioaccumulation controls internal concentrations of pollutants, including PFAS, in individual organisms. When bioaccumulation is looked at in the perspective of the entire food web, it is called biomagnification, which is incredibly important to track because lower concentrations of pollutants in environmental matrices such as seawater or sediments, can very quickly grow to harmful concentrations in organisms at higher trophic levels, including humans. Notably, concentrations in biota can even by >5000 times those present in water for PFOS and C10-C14 PFCAs. PFAS can enter an organism by ingestion of sediment, through the water, or directly via their diet. It accumulates namely in areas with high protein content, in the blood and liver, but its also found to a lesser extent in tissues.
Biomagnification can be described using the estimation of the trophic magnification factor (TMF), this describes the relationship between the contamination levels in a species and their trophic level in the food web. TMFs are determined by graphing the log transformed concentrations of PFAS against the assigned trophic level, and taking the antilog of the regression slope (10).
In a study done on a macrotidal estuary in Gironde, SW France, TMFs were >1 for nearly all 19 PFAS compounds considered in the study and were particularly high for PFOA and PFNA (6.0 and 3.1 respectively). A TMF> 1 means that accumulation in the organism is greater than that of the medium, in this case the medium being sea water.
PFOS, a long chain sulfonic acid, was found at the highest concentrations relative to other PFASs measured in fish and birds in Northern seas such as the Barents Sea and the Canadian Arctic. A study and an interactive map by the EWG using its results showed freshwater fish in the U.S. ubiquitously contain high levels of harmful PFAS, with a single serving typically significantly increasing the blood PFOS level.
Bioaccumulation and biomagnification of PFASs in marine species throughout the food web, particularly frequently consumed fish and shellfish, can have important impacts on human populations.  PFASs have been frequently documented in both fish and shellfish that are commonly consumed by human populations, which poses health risks to humans and studies on the bioaccumulation in certain species are important to determine daily tolerable limits for human consumption, and where those limits may be exceeded causing potential health risks. This has particular implications for populations that consume larger numbers of wild fish and shellfish species. In addition to health risks, populations may be impacted by advisories, limits of fishing closures for certain species that are put in place to help mitigate health risks from potential consumption of species with higher levels of accumulated PFASs, but result in a loss of food sources and important subsistence species depended on by local communities. There is research being done in this area, including into spatial patterns of PFAS bioaccumulation in fish and crustaceans.