Application of hair-mercury analysis to determine the impact of a seafood advisory

Abstract

Following an official recommendation in the Faroe Islands that women should abstain from eating mercury-contaminated pilot whale meat, a survey was carried out to obtain information on dietary habits and hair samples for mercury analysis. A letter was sent to all 1180 women aged 26–30 years who resided within the Faroes, and the women were contacted again 1 year later. A total of 415 women responded to the first letter; the second letter resulted in 145 repeat hair samples and 125 new responses. Questionnaire results showed that Faroese women, on average, consumed whale meat for dinner only once every second month, but the frequency and meal size depended on the availability of whale in the community. The geometric mean hair-mercury concentration at the first survey was higher in districts with available whale than in those without (3.03 vs. 1.88 μg/g; P=0.001). The mercury concentration also depended on the frequency of whale meat dinners and on the consumption of dried whale meat. The 36 women who did not eat whale meat at all had a geometric mean hair-mercury concentration of 1.28 μg/g. At the time of the second survey, the geometric mean had decreased to 1.77 μg/g (P<0.001), although whale was now available in all districts. In comparison with previously published data on hair-mercury concentrations in pregnant Faroese women, these results document substantially lower exposures as well as a further decrease temporally associated with the issue of a stricter dietary advisory.

Introduction

Dietary recommendations are usually issued without any subsequent assessment of their impact. Therefore, little information is available on factors that affect compliance. In regard to some food contaminants, exposure markers constitute an objective and powerful instrument to assess individual intake levels (Grandjean et al., 1994a). For example, exposure biomarker data have been critical for public policy decisions on the abatement of contamination with lead (Annest et al., 1983) and methylmercury (Schober et al., 2003). In addition, knowledge of one's own exposure to a dietary contaminant could be an important incentive to changing food habits. Methylmercury exposure is almost always exclusively dietary and originates from certain types of freshwater fish and seafood (UNEP, 2002). For the assessment of dietary intakes of this food contaminant, hair-mercury analysis has been found to be highly suitable, albeit somewhat imprecise (Grandjean et al., 2002). Hair sampling does not require any expertise, the sample can be sent by regular mail and may be stored at room temperature, and the relatively high mercury concentration allows a simple and rapid analysis by well-documented technology (Cernichiari et al., 1995; Grandjean et al., 1994b).

In the Faroe Islands, the main single source of increased methylmercury exposure is whale meat (Andersen et al., 1987). Within this small fishing community in the North Atlantic, a new dietary recommendation was dispersed through news media and thereby reached all residents. To examine the impact of this advisory and to assess whether knowledge of one's own exposure might lead to changes in dietary habits, we contacted twice by mail an age-stratified group of the female population. Table 1 shows the time schedule of the main events of the study.

The North Atlantic pilot whale (Globicephala melas) has been hunted in several communities in the North Atlantic and is still harvested in the Faroes (Johansen and Olafsson, 1999). The Faroese pilot whale catch is a traditional, communal, environmentally sustainable, and noncommercial hunt. The authorities distribute the meat and blubber according to traditional rules, the main rule being equal shares for all inhabitants of the district.

The pilot whale catch proceeds as follows: a school of pilot whales, being observed near the coast, is driven into a fiord and beached, preferably on a gently sloping seashore. The whales are then killed by stabbing the neck with a special knife that severs the carotid arteries. Acknowledging the animal welfare issues, the Faroese authorities have updated the age-old rules laid down for the pilot whale hunt by banning the harpoon and the whale spear and by regulating the use of hooks from boats (Bloch et al (1990a), Bloch et al. (1990b)).

The pilot whale is a small whale that occurs in large schools in the North Atlantic and the Mediterranean and (as a closely related species) in the Pacific Ocean. As a small cetacean, this whale is not covered by regulations decided by the International Whaling Commission (IWC). Working jointly with the IWC, the International Council for the Exploration of the Sea, the North Atlantic Marine Mammal Co-operation Organization, and other authorities, Faroese and international scientists keep a close watch on the size of the whale population. The most recent estimate is that there are approximately 780,000 animals in the Northeast Atlantic (Bloch et al (1990a), Bloch et al. (1990b)).

Since 1584, Faroese civil servants have secured detailed reports on the pilot whale harvest, including the date of the catch, the location, the number of whales, the amount of meat and blubber of each whale, and the distribution of the catch to members of the local communities. The amount of meat and blubber is measured in skinn units, each consisting of 38 kg meat and 34 kg blubber. The statistics are incomplete before 1709, but subsequent reports show that the annual catch fluctuates around a long-term average catch of approximately 1000 animals, or 6000 skinn (Bloch et al (1990a), Bloch et al. (1990b)). The Faroese authorities consider this harvest of pilot whales in the waters around the Faroe Islands both sustainable and legitimate. Should the scientists so recommend, the authorities will be prepared to limit the catches (Bloch et al (1990a), Bloch et al. (1990b)). So far, catches have been limited only in order to avoid waste when the need for whale meat and blubber is considered to be met in a particular district.

The distribution of the catch is administrated by the local head of police (Bloch et al (1990a), Bloch et al. (1990b)). The meat and blubber are salted, frozen, or cut in strips for drying. By these preservation procedures, the catch can be kept for many months, thereby ensuring a steady supply over time. Normally, storage time is expected to last up to 1 year, since pilot whale catches are seasonal and mostly occur in the late summer months. While fresh meat and blubber may be cooked hours or days after the catch, feasting ceremonies with unusual big consumption do not occur.

Since 1980, pregnant women have been advised to limit their consumption of pilot whale meat and blubber to avoid methylmercury exposure. A large study of women who gave birth at the Faroese hospitals in 1986–1987 showed that about 15% had hair-mercury concentrations above 10 μg/g (Grandjean et al., 1992), a level then considered the upper limit of safe exposure (IPCS, 1990). A subsequent recommendation in 1989 extended the advice to indicate that adults should not eat more than 150–200 g of pilot whale meat (and 100–200 g of blubber) per month. With a mercury concentration of about 2.1 μg/g whale meat, this intake would correspond to an average daily dose of 0.2 μg/kg body weight for a 60-kg woman.

The children born in 1986–1987 were examined by sophisticated neuropsychological and neurophysiological methods at age 7 years, and the results showed significant exposure-associated decrements in several brain functions (Grandjean et al., 1997; Weihe et al., 1996). These results were presented and discussed at an international conference in 1998. In August 1998, the following diet recommendations were issued by the Faroese authorities, based on the demonstrated effects of mercury exposure and on a general assessment of PCBs: “The mercury content of pilot whale meat is high and is one of our main mercury sources. Therefore, we recommend that adults eat no more than one to two meals a month. Women who plan to become pregnant within 3 months, pregnant women, and nursing women should abstain from eating pilot whale meat. High PCB contents in blubber lead us to recommend that adults, at the maximum, eat pilot whale blubber once to twice a month. However, the best way to protect fetuses against the potential harmful effects of PCBs is if girls and women do not eat blubber until they have given birth to their children. Pilot whale liver and kidneys should not be eaten at all”.