Over the last half-century, the booming global trade of fish and fish products has created a unique challenge—how to identify and quantify human exposure to contaminants from imported marine products. With marine fish consumption surpassing that of meat and international fish exports skyrocketing, concerns about the global transfer of contaminants through food trade have come to the forefront.
The increased trade in fish raises worries about the potential transfer of contaminants through food exports and imports, surpassing the traditional routes of long-range transport through the atmosphere or ocean currents. Contamination from distant sources can lead to higher dietary exposures than locally sourced products, particularly concerning for species like herring, Atlantic cod, and tuna that may accumulate bioaccumulative contaminants such as polychlorinated biphenyls (PCBs) and mercury.
Despite bans on substances like PCBs, they persist in marine fish, especially in coastal areas of Western Europe and the eastern USA. Additionally, fish raised in seawater mariculture systems, fed on wild-caught fish-meal, also face exposure to PCBs and other persistent organic pollutants (POPs) from multiple sources. The complex landscape of global fish production and trade makes it challenging to quantify the toxic chemical exposure faced by consumers who include fish in their diets.
In a groundbreaking study published in Nature Food, Huang and colleagues sought to quantify consumer exposure to POPs, using PCB-153 as a representative contaminant, due to its resistance to biodegradation and extensive monitoring data availability. To estimate concentrations of PCB-153 in marine fish globally, the researchers employed chemical fate and bioaccumulation models. These models used global PCB emission data and atmospheric transport models to estimate concentrations in air, water, and sediment. Bioaccumulation models were then used to estimate POP concentrations in 38 species of coastal marine fish. The study focused on seven broad categories of fish: anchovies, herring-like, cod-like, flatfish, salmon, tuna and billfish, and all other fish.
The results were illuminating. They revealed that a significant proportion (84%) of PCB exposure in sub-Saharan fish consumers could be attributed to fish imported from Western and Northern Europe, as opposed to less than 2% from local fish. On the flip side, European fish consumers had reduced exposure due to consumption of fish imported from regions with low PCB-153 contamination.
The study also included a case study on Atlantic salmon trade, showcasing that PCB-153 accumulation in wild-caught and farmed salmon could be estimated within a factor of two of measured concentrations. Importantly, the study highlighted the lower PCB-153 estimated daily intake from salmon raised with plant-based feeds compared to traditional fish-based feed.
Huang and colleagues have developed a valuable tool for estimating exposure to specific chemicals from the global trade of marine fish and fish products on a per-country basis. This approach could potentially be expanded to other sectors, including freshwater aquaculture and coastal crustacean fisheries. As aquaculture continues to grow and fish becomes an increasingly vital dietary protein source, this information may prove invaluable for stakeholders, policymakers, and trade-related agencies in shaping sustainable and safe practices in the fishing and aquaculture industries.
Source: Nature
