Excessive amounts of heavy metal have been detected in over half of tuna samples, some of which exceeded the Hong Kong statutory limit for mercury content by nearly twofold, the Consumer Council said on Monday.

Methylmercury – an organic compound of mercury – was found in 49 out of 50 sashimi samples, of which, 10 out of 19 sashimi tuna samples contained “excessive” amounts of the toxicant, the statutory body said. Additionally, one tuna and one salmon sample were found to have parasites, with the tuna sample containing worm eggs. All 19 tuna and 31 salmon samples were sourced from local restaurants, supermarkets, and takeaway outlets.

Tuna sashimi
Tuna sashimi. Photo: Wikicommons.

Mercury is an element that occurs naturally in the environment but can enter the food chain from industrial sources. Overconsumption of the heavy metal can have an adverse effect on the nervous system, particularly among unborn foetuses, the Hong Kong Centre for Food Safety says.

If a pregnant woman consumes six pieces of fish with the highest mercury sample she will exceed her tolerable intake limit of methylmercury recommended by the Joint FAO/WHO Expert Committee on Food Additives, the Council warned.

“As it is impossible for the naked eye to identify whether parasites are present in fish, and excessive heavy metals could only be detected via laboratory tests,” the authority said. “The Council urges traders to strictly comply with the statutory requirements to ensure food safety, while also calls for the respective authorities to step up their efforts in enforcement and inspection to better protect public health.”

No solid food in Hong Kong should contain a mercury level higher than 0.5ppm (parts per million used to measure concentration), according to the Food Adulteration (Metallic Contamination) Regulations. However, 10 of the 19 tuna samples contained mercury levels 6 to 196 per cent higher than the standard, while only one of the 31 salmon samples exceeded the limit.

‘Small’ parasite presence

The parasite roundworm and its eggs found in two samples were not moving at the time of the test, the Council said, adding that both had a “small” presence in the fish and had been chemically treated.

Sheung Shui fish market
A fish market in Sheung Shui. Photo: Wikicommons.

Eating raw marine fish can expose consumers to Anisakis infection, caused by a type of roundworm, which can result in abdominal pain, nausea and vomiting within an hour to 12 hours of ingestion, the authority cautioned.

‘Authenticity of the fish’

The tests also revealed that one of the 31 salmon samples were identified as rainbow trout – a fresh-water species – while the others were Atlantic salmon – a marine species. The restaurant that sold the trout sample allegedly advertised the fish as “silver salmon,” which the Council said was “a questionable description that does not correspond with the actual species.”

All of the 19 tuna samples were found to belong to five tuna species: five bigeyes, four yellowfin, four Atlantic bluefins, four Southern bluefins, and two Northern bluefins.

The Hong Kong Free Press #PressForFreedom 2019 Funding Drive seeks to raise HK$1.2m to support our non-profit newsroom and dedicated team of multi-media, multi-lingual reporters. HKFP is backed by readers, run by journalists and is immune to political and commercial pressure. This year’s critical fundraiser will provide us with the essential funds to continue our work into next year.

funding drive press for freedom

Jennifer Creery is a Hong Kong-born British journalist, interested in minority rights and urban planning. She holds a BA in English at King's College London and has studied Mandarin at National Taiwan University.