Which prenatal biomarker is most appropriate for methylmercury dose-response for neurodevelopmental effects?
Developmental neurotoxicity (DNT) is a well-established hazard of methylmercury (MeHg) exposure. This evidence base primarily includes studies that measured biomarkers of MeHg exposure in samples of maternal hair, maternal blood, and cord blood. We used a comprehensive literature review (1998-2022) to investigate which of these prenatal biomarkers is more appropriate for detecting neurodevelopmental effects of MeHg. Seven studies were identified that measured both maternal hair and cord blood Hg levels. In these studies, several DNT test results covering most domains of DNT were modeled. Cord blood Hg was found to produce larger effect estimates than maternal hair Hg across most domains of DNT with cord blood Hg being more sensitive in more than 90% of cases. When comparing sensitivity of results from cord blood Hg to from maternal hair Hg there was a 75% increase (range: 4-583%). In the two domains where results for maternal hair Hg were more sensitive, the increase was only 18% (Range: 7-29%). There were only two studies that compared maternal blood with maternal hair biomarkers (maternal blood Hg was more sensitive (mean 320% and range 43-855%) and cord blood biomarkers (maternal blood Hg was more sensitive by about 30%). Maternal hair Hg remains an appropriate biomarker for population exposure monitoring purposes, but these data suggest that cord blood Hg is more appropriate for modeling of MeHg DNT effects. Future work may benefit from simultaneous collection of MeHg content of maternal blood, hair and cord blood biomarker samples and using all of them for DNT modeling.