revised final - Agency for Toxic Substances and Disease Registry ...

MERCURY 445
5. POTENTIAL FOR HUMAN EXPOSURE
women living in interior (3.2±0.8 ppb) or urban areas (3.3±0.5 ppb) of Alaska and less than one-seventh the
mean value for coastal Alaskan Inuit women (7.6±2.7 ppb) known to consume seal meat and oil, as well as
marine fish (Galster 1976). The latter breast milk total mercury level is comparable to the median (2.45 ppb)
and maximum (8.7 ppb) values reported for women in the Faroe Islands that consume large amounts of fish
and pilot whale meat (Grandjean et al. 1995a).
Levels of total mercury in breast milk have been monitored in several foreign countries over the past three
decades. A mean breast milk mercury concentration of 3.6±2.2 ppb (range, non-detected to 9.8 ppb) was
reported for an urban population in Tokyo, Japan (Fujita and Takabatake 1977). In a study of urban women
residing in Madrid, Spain, the mean breast milk mercury concentration was 9.5±5.5 ppb (range, 0.9–19 ppb)
(Baluja et al. 1982). These authors did not provide any information (i.e., whether females were fish
consumers, the number of dental amalgams they had, or their occupations) that would explain the relatively
high mercury levels. Skerfving (1988) reported mercury concentrations ranged from 0.2 to 6.3 ppb in breast
milk of Swedish women that consumed fish; however, this author did not provide specific information on the
fish consumption rate or the number of dental amalgams of the study population. Most recently, Oskarsson
et al. (1996) reported a mean total breast milk concentration of 0.6±0.4 ppb (range, 0.1–2.0 ppb) for a group
of Swedish women that consumed freshwater fish and had an average of 12 amalgam fillings. This was a
smaller range in mercury concentrations than that reported by Skerfving (1988).
All of these general population breast milk mercury concentrations are in sharp contrast to those reported for
samples collected from women in Minamata, Japan, where industrial effluents containing methylmercury
caused widespread contamination of local seafood. Breast milk total mercury concentrations were on the
order of 63 ppb in individuals who lived in the vicinity of Minamata, Japan and had consumed highly
mercury-contaminated fish (Fujita and Takabatake 1977). Similarly, in Iraq, where consumption of bread
made from seed grain treated with methylmercury as a fungicide caused a similar mercury poisoning
outbreak, breast milk concentrations as high as 200 ppb were reported (Bakir et al. 1973). Breast milk
containing total mercury levels of >4 ppb would exceed the safe level (2 µg methylmercury/day for an
average 5-kg infant) (Wolff 1983). It is important to emphasize, however, that in general, the beneficial
effects associated with breast feeding seem to override or at least compensate for any neurotoxic effects on
milestone development that could be due to the presence of contaminants, such as mercury, in human milk
(Egeland et al. 1997).