Apex predators, such as sharks and tuna are particularly susceptible to the biomagnification and bioaccumulation of toxic metals within their tissues. (1−5) These naturally occurring, toxic metal elements are becoming increasingly common in marine ecosystems as human activities (e.g., the burning of fossil fuels, the refining of metal ores, or through their use in electrical components) release ever more emissions directly into the atmosphere, terrestrial, aquatic, or marine ecosystems. (6) Shark products, especially the dried fins used in shark fin soup throughout Asia, are frequently consumed as luxury goods (7) and are reputed to have numerous health benefits and life extending qualities. (2) However, previous studies performed in Hong Kong, (2) the Galapagos Islands, (1) the Caribbean, (3) and Australian coastal waters (8) have all shown that consumers of shark fin and shark products are frequently exposed to levels of pollutants that are deemed unsafe for human consumption. In some instances, the consumption of shark products has exposed humans to more than three times the recommended toxic metal allowance. (9) Human exposure to toxic metals such as mercury, arsenic, cadmium, and lead have all been linked with adverse health risks such as central nervous system and brain damage, (6,10) numerous types of cancer, (11) fetal cognitive development complications, (12) hearing loss, (13) and increased incidence of cardiovascular disease. (14,15) These effects can be particularly severe and acute when exposure takes place in utero during pregnancy or in early childhood development. (11,12,15−17)

As a consequence of overfishing to supply increasing demand, shark populations have declined significantly throughout the world, with some populations declining by more than 70% since 1970. (18−21) Much of this overfishing supplies the global demand for shark products that are consumed by humans; this consumption is a significant pathway that can expose humans to unsafe levels of toxic metals. (22,23) As a consequence of the high trophic levels sharks occupy as apex predators, and the recognized bioaccumulation of toxic metals that occurs at higher tropic levels, (24,25) we hypothesize that shark fins purchased in Singapore will contain levels of arsenic, mercury, cadmium, and lead above the prescribed safe maximum limits. More specifically, because of their closer proximity to industry and other polluting human activities, we expect to find higher concentrations of toxic metals in coastal habitat-associated sharks in comparison to those that are predominantly pelagic species.

This work shows that shark fin purchased in Singapore does contain concentrations of toxic metals that exceed the permissible concentrations detailed by the Singapore government and world health authorities. These results suggest that the consumption of shark fin can be a significant source of exposure to elements that have an adverse effect on human health. Our work here shows that there are significant differences in the concentrations of toxic metals between shark species, and significant differences in the concentration of toxic metals from species that live in different environments (e.g., pelagic vs coastal) can be detected. With this information, we advocate for a universal shark fin labelling system, indicating the species of shark from which a fin was removed and where it was caught. This is beneficial from a human health and conservation perspective. It allows for the avoidance of specific species, or species that live in environments where levels of toxic metals can be elevated to such concentrations that are harmful to human health. This labelling also gives the consumer material to make an informed decision on purchasing fins that come from endangered or vulnerable species, or from unsustainably managed stocks.

Given the continued availability and consumption of shark products, especially shark fins in Asian countries; it would be wise for governments in the region to prepare safe consumption guidelines for these products. Particularly, as shark fin soup frequently contains multiple fins from various species, (7) the consumption of more than one fin greatly increases the possibility that safe exposure limits will be exceeded. Our research shows that fins from several species of sharks have concentrations of toxic metals that exceed international and nationally determined safe consumption levels, given this information, we suggest that the tradition of consuming shark fins at celebratory events is not a wise or healthy practice; safe alternatives such as artificial shark fin should be sought as a replacement.