Mercury Exposure, Fish Consumption and Provisional Tolerable Weekly Intake

Mercury (Hg) is recognised as a pollutant of high importance due to its high degree of toxicity, persistence and bioaccumulative properties. Fish consumption is an essential component of a healthy diet for the human population, however, it is also the major source of Hg mainly from ingestion of contaminated seafood, including from available commercialised fish species. By virtue of human health risks associated with Hg exposure, reference doses (RfD) or “Provisional Tolerable Weekly Intake” (PTWI) have been established by the Food and Agriculture Organization (FAO)/World Health Organization (WHO), Joint Expert Committee on Food Additives (JECFA) and also by the United States Environmental Protection Agency (USEPA). JECFA established a PTWI for MeHg of 1.6 μg kg bw⁻¹ week⁻¹, whereas USEPA pointed a lower value of MeHg intake, setting the RfD at 0.1μg kg bw⁻¹ day⁻¹ (equivalent to 0.7μg kg bw⁻¹ week⁻¹). Recently (2012), PTWI suggested by JECFA for MeHg was revised by the European Food Safety Authority (EFSA) to 1.3 µg MeHg kg bw⁻¹ week⁻¹

Human exposure to Hg is overviewed in this chapter, relating food consumption levels and RfDs worldwide established by FAO/WHO and USEPA, and reporting a case study near the Mid-Atlantic Ridge (Azores). The study (i) develops a brief review of Hg concentration in the muscle of commercial fish species caught in the Azores archipelago and compares the measured Hg concentration with the maximum levels of Hg for certain contaminants in foodstuffs established by European Community, (ii) evaluates the human exposure to Hg, through fish consumption using a food frequency questionnaire, (iii) assesses Hg exposure using the Hg concentration quantified in scalp hair, (iv) evaluates the Hg intake levels, through the application of formulas established by the WHO and (v) establishes isocurves indicating the maximum number of fishmeal per week without exceeding the MeHg RfD (USEPA RfD), by combining number of meals (per week), amount of fish ingested (by meal) and levels of MeHg in fish.

Finally, in order to obtain an average of 250 mg day⁻¹ of the omega-3 fatty acids EPA and DHA, USA dietary guidelines of 2010 recommend a consumption of 227g of seafood per week. However, only fish with MeHg concentrations below 0.34 µg g⁻¹ can be selected to be consumed so that the PTWI established by JECFA would not be exceeded, despite the concentration of 0.5 µg g⁻¹ (for most of the fish species) or the concentration of 1.0 µg g⁻¹ (“exception list”) allowed for fish consumption.