Mercury contamination in canned tuna sold across major European markets has reached worrying levels, with some samples containing four times the legal limit, French environmental groups said on Tuesday.

According to a new report from the Paris-based NGO Bloom, which focuses on preserving the marine environment, and consumer rights organization Foodwatch, tests revealed mercury contamination in all 148 canned tuna samples purchased in France, Germany, England, Spain and Italy.

More than half of the samples exceeded the mercury safety limit of 0.3 milligrams per kilogram, the standard typically applied to other fish, they warned.

The two organizations are urging retailers and governments to take immediate action, including reducing the permitted levels of mercury in tuna products, Agence France-Presse reported.

"What we end up with on our dinner plates is a colossal risk to public health that's not considered seriously," Karine Jacquemart, CEO of Foodwatch France, said at a news briefing this week.

Europeans consume an average of 2.8 kg of tuna annually, primarily in canned form, which according to Bloom contains two to three times more mercury than fresh tuna. The European standard currently allows a maximum mercury level of one part per million, Euronews reported.

"We won't give up until we have a more protective European standard," Jacquemart said.

Bloom claimed that the current mercury threshold was established to ensure 95 percent of caught tuna could be marketed. That is the reason why tuna, among the most contaminated species, is given maximum tolerance in mercury three times higher than less-contaminated species, it said.

'No health reason'

The two organizations argued that there is no health reason to justify different mercury standards between tuna and other fish species. "Mercury is not less toxic if it's ingested through tuna, only the concentration of mercury counts," they said.

The European Food Safety Authority permits a weekly intake of 1.3 micrograms of methylmercury per kg of body weight — significantly higher than the United States threshold of 0.7, the organizations said.

Methylmercury is the most common mercury form when it comes to food and it is classified as "possibly carcinogenic to humans", meaning it could have the potential to cause cancer, Euronews reported.

Julie Guterman, who headed the 18-month study for Bloom, challenged the existing standards, saying: "If we apply the maximum threshold set out in European regulations, anyone weighing more than 79 kg is at risk after consuming one portion. So what's the point of these standards?"