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

MERCURY 249
2. HEALTH EFFECTS
The accumulation of mercury is greater in larger fish and in fish higher in the food chain. The tendency for
increased mercury concentration with increasing fish body weight is particularly noticeable in carnivorous
fish species. Malm et al. (1995) analyzed mercury concentrations in 16 species of carnivorous fish from the
Tapajos River basin in Brazil and hair samples from local populations who regularly ate such fish. Mercury
levels in the fish averaged 0.55 ppm (range, 0.04–3.77 ppm), and the mercury levels in the hair of the
affected fish-eating populations averaged approximately 25 ppm. In one population that consumed higher
quantities of large carnivorous fish at the end of the local rainy season, 8 of 29 persons evaluated had hair
mercury levels above 40 ppm, and one individual had a hair mercury concentration of 151 ppm. Some
villages along the river can have per capita daily fish consumption rates around 200 g or more, which would
greatly impact the human body burden and hair levels of mercury in such populations.
Hair-to-Blood Concentration Ratio
The hair:blood concentration ratio for total mercury is frequently cited as 250. However, a precise basis for
this particular value is unclear. Ratios reported in the literature range from 140 to 416, a difference of more
than a factor of 2.5 (see Table 2-9). Differences in the location of hair sampled (head versus chest, distance
of sample from head or skin) may contribute to differences in observed ratios between studies. For
example, as much as a 3-fold seasonal variation in mercury levels was observed in average hair levels for a
group of individuals with moderate-to-high fish consumption rates, with yearly highs occurring in the fall
and early winter (Phelps et al. 1980; Suzuki et al. 1992). Thus, it is important to obtain hair samples as
close to the follicle as possible to obtain an estimate of recent blood levels. Large errors (the direction of
which depends on whether samples were taken while blood levels were falling or rising) could result if hair
samples are not taken close to the scalp. Several studies did not report the distance to the scalp for the hair
samples taken. The high slope reported by Tsubaki (1971a) may have reflected the fact that mercury levels
were declining at the time of sampling (Berglund et al. 1971), so the hair levels may reflect earlier, higher
blood levels. Hair taken from different parts of the body also may yield different ratios. In 26 subjects with
moderate-to-high fish consumption, axillary hair (i.e., from the armpit area) was found to contain an
average of 23% less mercury than head hair (Skerfving et al. 1974).
Phelps et al. (1980) obtained multiple blood samples and sequentially analyzed lengths of hair from
339 individuals in Northwestern Ontario. The large sample size and the attention to sampling and analysis
with regard to the hair:blood relationship make the results from this study the most appropriate to use for
estimating the mercury blood levels of the Seychellois women during pregnancy. The actual ratio Phelps et