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From: Food Quality & Safety magazine, December/January 2011

Heavy Metals in Seafood

Interlaboratory comparison in EU yields good results

European Union (EU) researchers conducting an experiment in which 57 laboratories from 29 countries volunteered to test for the presence of heavy metals in seafood found that most of the labs came up with similar results, thus underscoring the efficacy of the tests.

The results should enhance consumer confidence, as maximum levels of lead, cadmium, and total mercury in seafood are regulated by EU law, and it has been proven that most participants are able to correctly measure them. In addition, this comparison has highlighted other issues, such as the apparent dependency of the measurements of inorganic arsenic on the type of food tested.

Each laboratory received a sample without knowing the levels of heavy metals present, and was asked to measure and report the values back to the European Commissions Joint Research Centre (JRC).

Excessive intake of heavy metals may lead to a decline in mental, cognitive, and physical health. A particular concern is potential developmental defects in children exposed in utero. From a toxicological point of view, the chemical form in which the metal is ingested plays a significant role. For example, methylmercury is much more toxic than inorganic mercury compounds, while inorganic arsenic is more toxic than the organic species of arsenic, according to a news release from the JRC.

Labs Compare Results

The interlaboratory comparison was organized in support of the European Co-operation for Accreditation, the Asia Pacific Laboratory Accreditation Cooperation, and the national reference laboratories associated to the European Union Reference Laboratory for Heavy Metals in Feed and Food.

Participants were asked to report both the measured value of each heavy metal in question in the sample and the uncertainties associated with those measurements. The results were scored according to international standards.

The outcome of the exercise was generally positive. All of the 57 laboratories that registered reported results. The share of satisfactory scores ranged between 80% and 96%. Participants tended to underestimate the content of total arsenic, and to a lesser extent total cadmium.

Contrary to a previous exercise (IMEP-107 on total and inorganic arsenic in rice), the values reported for inorganic arsenic showed a large spread. Interestingly, this indicates that the matrix (in this case, seafood), has a major influence on the analytical determination of inorganic arsenic. This is a crucial consideration for legislators, because specifying a single maximum level of arsenic in food would appear to not be feasible.

Legislative Situation

In Europe, maximum levels for lead, cadmium, and total mercury in food are laid down in legislation, varying from 0.5 to 1.0 mg per kg for different seafood. No maximum level exists for the methylmercury form of mercury, as its measurement requires specific analytical equipment not routinely present in testing laboratories. However, methylmercury is the main source of human intake of mercury in fish and fishery products, and is important due to its high toxicity compared to inorganic mercury.

No maximum levels for arsenic have been laid down in European legislation either, due to a lack of information about reliable analytical methods for determining inorganic arsenic in different food commodities. In addition, measurement values of inorganic arsenic are generally believed to be method-dependent.

The interlaboratory comparison was, therefore, extended to include methyl- mercury and inorganic arsenic in order to investigate the issues that laboratories encounter in measuring these substances.

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