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

MERCURY A-18
APPENDIX A
Seychelles population using the neuropsychological test that showed positive results in the Faroe Islands
population will also allow a more direct comparison of results.
The diet in the two studies was also considerably different. The majority of the mercury exposure to the
Faroe Island population came from whale meat (estimated at about 3 ppm in muscle tissue) with a relatively
small portion coming from fish. Some of the mercury in whale meat is in the form of inorganic mercury.
In the Seychelles study, all of the mercury came from fish as methylmercury with concentrations of around
0.3 ppm. Whale meat blubber is widely consumed in the Faroe Islands and also contains polychlorinated
biphenyls (PCBs). Grandjean et al. (1995b) estimated a daily intake of 200 µg of PCB. This value can be
compared to the Tolerable Daily Intake of PCBs established by the FDA, of 60–70 µg/day for an adult.
Further statistical analysis of the possible influence of PCBs on the observed study results needs to be
conducted (see the discussion below on Peer Panel 1Review of Key Studies for additional comments).
The primary biomarker used to estimate mercury exposure was also different between the two studies. The
Faroe Island analysis used cord blood, and the Seychelles study used maternal hair level. The use of
mercury in cord blood has the advantage of being a more direct measure of exposure to the fetus, but the
levels at term may not reflect exposures at earlier developmental stages. While Grandjean et al. (1997) did
report maternal hair mercury levels, the mean hair level for the interquartile range of 2.6–7.7 ppm was
reported only as a geometric average (4.27 ppm). In contrast, the Seychellois study reported only an
arithmetic mean level for the entire study population (6.8 ppm). While both are valid measures, a direct
comparison of “average” values for the two studies is not possible without further statistical analysis of both
data sets.
In the case of the Faroe study, there were no data presented in the peer-reviewed publications to address
variability of food/whale meat or blubber intake among the Faroe Islanders, making it difficult to evaluate
the possibility of peak intake levels during critical development phases. Consumption data was reported
only as