Academic journal article Canadian Journal of Public Health

Methylmercury Blood Guidance Values for Canada

Academic journal article Canadian Journal of Public Health

Methylmercury Blood Guidance Values for Canada

Article excerpt

ABSTRACT

Exposure to methylmercury (MeHg) from fish and marine mammal consumption continues to present a public health concern. To date, developmental neurotoxicity is the most sensitive health outcome, forming the basis for health-risk assessments and the derivation of biomonitoring guidance values. This article summarizes existing Health Canada MeHg blood guidance values for general population and expands them to include a harmonized provisional interim blood guidance value of 8 µg/L based on the existing provisional Tolerable Daily Intake for children, pregnant women and women of childbearing age. Associated public health actions, according to age, sex, and level of exposure are recommended.

Key words: Methylmercury; biomonitoring; guidance

La traduction du résumé se trouve à la fin de l'article. Can J Public Health 2010;101(1):28-31.

Mots clés : méthylmercure; biosurveillance; valeur guide

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Exposure to methylmercury (MeHg) from fish and marine mammal consumption continues to present a public health concern in Canada and elsewhere.1,2 Extensive toxicological and epidemiological evidence have indicated that neurotoxicity resulting from in utero exposure is the most sensitive health outcome. 2-6 This evidence has formed the basis of health-risk assessments and biomonitoring guidance values that allow researchers and clinicians to evaluate individual and population risk and guide public health actions when necessary. This article summarizes Health Canada MeHg blood guidance values and their associated public health recommendations, according to age, sex, and level of exposure. Included are existing guidance values for the general adult population and provisional interim guidance values for children, pregnant women and women of childbearing age for the protection of the developing nervous system.

Health Canada methylmercury biomonitoring guidance values

In the 1970s, the Medical Services Branch (currently First Nations and Inuit Health Branch of Health Canada, hereafter FNIHB) was involved in the initial investigations of blood and hair mercury levels among First Nations residents in Ontario and Quebec.3 In 1973, a Task Force on Organic Mercury in the Environment was established by the Minister of National Health and Welfare (currently Health Canada) "in order to respond to the problem of high and unusual mercury levels in relation to the health and well-being of residents of Grassy Narrows and Whitedog, Ontario".3

On the recommendation of the Task Force, FNIHB implemented a systematic mercury biomonitoring program among First Nations and Inuit in the early 1970s. Between 1970 and December 1992, 71,842 hair and blood tests for MeHg on 38,571 individuals were carried out in 514 indigenous communities across Canada.7

To identify "at risk" individuals and provide appropriate preventive action, FNIHB established a set of biomonitoring guidance values applicable to the general population of high fish consumers (e.g., First Nations and Inuit).3 The guidance values were based on the recommendations of the 1971 Swedish Expert Group report,8 which concluded that the lowest blood concentration associated with adverse clinical effects was approximately 200 µg/L. This analysis was based on the findings from investigations of large outbreaks of organic mercury poisoning - in Japan in the 1950s-60s and in Iraq in the 1970s. The Expert group recommended applying a safety factor of 10 to derive "safe" levels in human populations.8 This analysis became the basis for the World Health Organization (WHO)'s Joint Expert Committee on Food Additives (JECFA) 1972 derivation of the Tolerable Weekly Intake (TWI) for MeHg of 3.3 µg/kg bw (body weight)/week.9 This TWI was adopted by Health Canada's Food Directorate, and expressed as the Provisional Tolerable Daily Intake (pTDI) of 0.47 µg MeHg/kg bw/day.10

In 1976, a WHO Expert Group also concluded, based on the Japan and Iraq data, that the earliest effects (paraesthesia) in the most sensitive 5% of exposed adults could be expected at blood levels of 200-500 µg/L with corresponding hair concentration of 50-125 mg/kg and that the lower values could be reached by a daily mercury intake of 3-7 µg/kg bw/day. …

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