Mercury in fish
9 July 2003
Mercury (in the form of methylmercury) is a contaminant commonly found in fish, particularly in long-living or predatory fish. Mercury occurs naturally in ocean sediment and is transformed by bacteria into methylmercury, which accumulates in aquatic organisms. The concentration in particular fish species is determined by the lifespan of the species and by its feeding habits. While mercury contamination can occur as a result of human activities, in most parts of the world the mercury in ocean sediment is of natural origin.
Public health concerns in relation to methylmercury in food are related to its potential to affect the nervous system, particularly in the developing foetus. Some epidemiological studies have suggested an association between increased maternal dietary exposure to methylmercury and delayed neurodevelopment in children.
Recent developments
Recent developments have raised the awareness of both the public and regulatory authorities about mercury in fish:
First, in June 2003, the World Health Organisation (WHO) revised its recommendation for the amount of methylmercury which can be safety consumed. A recent meeting of the Joint FAO/WHO Expert Committee on Food Additives (JECFA) established a new stricter health standard for methylmercury - a tolerable intake level of 1.6 microgram per kilogram bodyweight per week. This is approximately half the previous health standard used by FSANZ in its risk assessment.
Second, new analytical data have become available on the mercury content of fish from the 2001-2002 National Residue Survey, the 2000 Victorian survey, the 1999 NSW Department of Health survey, and from recently published New Zealand data. These surveys indicate that the current maximum permitted level for total mercury in fish (1 mg/kg) in the Australia New Zealand Food Standards Code is exceeded in some individual samples of large fish species such as shark and swordfish.
Previous consideration of methylmercury by FSANZ
FSANZ last examined data on the safety of methylmercury during the review of the Food Standards Code (1998-2000). At that time, no revisions were made to the permitted Maximum Levels (MLs) for mercury in fish, however, it was noted that women of childbearing age who were high consumers of fish could exceed a level of intake considered safe for the developing foetus. As a consequence, in January 2001, FSANZ prepared a fact sheet entitled Mercury in Fish: Advisory Statement for Pregnant Women. This fact sheet provided information for pregnant women and those women considering pregnancy on the appropriate level of consumption of fish, particularly the larger predatory fish. It was distributed to relevant organisations and was made available on the FSANZ website.
Current initiatives by FSANZ
In response to the WHO revised recommended weekly intake for methylmercury, FSANZ will re-examine the risks associated with consumption of fish for the general population as well as for women of childbearing age. Current data on the safety of methylmercury will be reviewed. Dietary modelling will also be undertaken using the new survey data to assess dietary exposure to methylmercury for all sectors of the Australian and New Zealand population.
FSANZ will revise the advisory statement on mercury in fish on the basis of the new dietary modelling. A possible outcome may be a reduction in the amount of certain fish that can be safely consumed, both for the general population as well as for women of childbearing age. This work will be done in consultation with representatives from Commonwealth and State governments and from the fishing industry.
FSANZ is also working with State, Territory and New Zealand governments and industry to assess management options for large fish with high mercury content. This may include revisions to the sampling plan for mercury in fish in Standard 1.4.1 - Contaminants and Natural Toxicants - to clarify sampling and analytical procedures.
Is there a public health concern?
There is no reason for the general public to be overly concerned about the safety of fish available on the Australian and New Zealand markets. The level of mercury in most fish species is low and when a variety of fish are consumed as part of a balanced diet the intake of methylmercury is small and should not be a cause for concern. While mercury can accumulate in the body over time, it is also readily excreted and, therefore, health problems can only occur following relatively high-level exposure over an extended period – for the vast majority of the population, this is an unlikely scenario.
FSANZ will continue to monitor developments in relation to mercury in fish and to assess the potential risks for all sectors of the population. Appropriate dietary advice will be provided where necessary. Fish continues to be an important source of nutrients for the whole population but should be eaten as part of a varied and balanced diet.
Further information