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

MERCURY A-20
APPENDIX A
panel that addressed the issue of concurrent PCB exposures, the Statistics/Design Panel, noted that only 3 of
208 PCB congeners were measured in the Faroe study, and stated that it “seems likely that mercury was
measured more accurately than the biologically relevant PCB exposure. Consequently even if the
neurological effects seen in this study were caused entirely by PCBs, it is possible that mercury would still
be more highly correlated with these effects than PCBs.” The Statistics/Design Panel also said that “the
best method to deal with this problem would be to study a population where exposure to PCBs is not an
issue.” This statement points directly to the Seychelles study as the study most appropriate for MRL
derivation.
Another issue raised at Raleigh workshop concerned the taking of hair samples for determining pre-natal
exposure. In the Seychelles, hair samples were collected 6 months post-partum, and segments
corresponding to pregnancy were selected for analysis. In the case of the Faroese, hair samples were taken
at the scalp. Regarding that, the Confounders and Variables (Epidemiology) panel stated that “Given the
time it takes the Hg to be excreted into the hair, we can assume that samples collected at parturition do not
cover the last 6 weeks of gestation, during which critically important neuronal proliferation and
differentiation is taking place.”
Regarding both the Seychelles and Faroe studies, the Neurobehavioral Endpoints Panel found “no specific
neurobehavioral signature injury from MeHg” in the data from either study (Seychelles or Faroe). The
same panel also noted that episodic exposure in the Faroe Islands (1–2 fish meals/week and