A groundbreaking international study published in the prestigious journal Science has revealed alarming levels of toxic “forever chemicals” in popular seafood species, including salmon, tuna, and four locally-caught fish varieties in Hong Kong. Led by researchers from City University of Hong Kong (CityU), the comprehensive analysis of 212 edible fish species across two decades of global data warns that imported seafood may transfer contamination risks across borders, potentially increasing consumers’ exposure to cancer-causing substances.
The Invisible Threat: PFAS in Our Seafood
Perfluoroalkyl and polyfluoroalkyl substances, commonly known as PFAS, are synthetic chemicals prized for their resistance to heat, water, and oil. Found in non-stick cookware, waterproof clothing, food packaging, and firefighting foam, these compounds have earned the nickname “forever chemicals” due to their extraordinary persistence in the environment. Once released, they do not break down naturally but instead accumulate in water systems, enter the food chain, and build up in human tissue over time.
Professor Kenneth Leung Mei-yee, Director of CityU’s State Key Laboratory of Marine Environmental Health, collaborated with an international team to analyse seawater monitoring data and fish samples spanning the past 20 years. Their findings paint a concerning picture for seafood lovers worldwide.
Global Findings: Imported Fish, Local Risks
The study highlights a phenomenon the researchers call “cross-border transfer” of PFAS contamination. Even nations with relatively clean coastal waters are not immune, as their reliance on imported fish exposes populations to elevated levels of these pollutants.
Consider Italy as a case study: although the country imports only 11.7% of its fish from Sweden, that single source accounts for a staggering 35.8% of Italians’ total PFAS intake. This disproportionality underscores how global trade networks can circumvent local environmental protections.
In Asia, the situation appears particularly acute. The median PFAS concentration in Asian marine fish stands at 1.03 nanograms per gram, nearly three times higher than the global average of 0.34 ng/g. Waters off Saudi Arabia and certain regions of Thailand show especially severe contamination.
Hong Kong’s Local Suspects
While Hong Kong’s overall PFAS exposure from local seafood remains low, CityU’s targeted testing identified four indigenous species with notably elevated concentrations:
- Six-fingered threadfin (locally known as ma yau or ngau yu)
- Green eel (ching mun sin)
- Yellow croaker (wong gu yu)
- Red snapper (hung taan yu), a bottom-dwelling fish that feeds on sediment
These findings align with broader patterns observed globally. The research team categorised three high-risk fish types that tend to accumulate PFAS most readily:
- Top predatory species: Six-fingered threadfin, swordfish, and tuna, due to biomagnification up the food chain
- High-fat fish: Salmon and herring, as PFAS have an affinity for fatty tissues
- Bottom-dwellers: Red snapper and goby species, which come into direct contact with contaminated sediment
Three Major Health Concerns
Excessive PFAS consumption poses several documented health risks, according to the research:
Cancer risk: Studies link elevated PFAS levels to increased likelihood of prostate, kidney, and testicular cancers.
Reproductive and developmental harm: The chemicals may reduce fertility, raise the risk of hypertension during pregnancy, and contribute to delayed development in children.
Immune system disruption: PFAS can weaken the body’s natural defences and interfere with endocrine function.
Expert Guidance for Vulnerable Groups
Professor Leung urges the public to remain vigilant without succumbing to panic. Those most at risk—including the elderly, pregnant women, young children, and individuals with chronic illnesses—should take particular care.
Practical Recommendations
- Limit imported high-risk fish: Reduce consumption of fatty or top-predator species known to carry higher PFAS loads
- Diversify your diet: Rotate protein sources to prevent any single contaminant from accumulating in the body
- Make informed choices: Refer to the study’s list of high-risk species when shopping for seafood
Broader Implications and Next Steps
This research serves as a wake-up call for food safety regulators worldwide. As global seafood trade continues to expand, national monitoring systems must evolve to account for transboundary chemical contamination. For consumers, the message is clear: awareness and moderation are key.
The study’s findings have already sparked discussions among public health authorities in Hong Kong about potential dietary guidelines. Meanwhile, international calls for stricter PFAS regulation in manufacturing and waste management are gaining momentum.
For those seeking to reduce their exposure without eliminating seafood entirely, experts suggest choosing smaller, lower-fat fish from local waters, and varying protein sources across meals. Sustainable fishing practices and consumer advocacy can also drive industry change over time.
As Professor Leung notes, “We are not asking people to stop eating fish—seafood remains a valuable source of nutrition. But informed choices can help minimise unnecessary risks.”
This article is based on research published in Science (December 2025) by City University of Hong Kong and international partners.