Which prenatal biomarker is most appropriate for methylmercury dose-response for neurodevelopmental effects?

Developmental neurotoxicity (DNT) is a well-established hazard attributed to methylmercury (MeHg) exposure. This evidence is based primarily upon includes studies that measured biomarkers of MeHg exposure in samples of maternal hair and blood, and cord blood. The aim of this review was to investigate which of these prenatal biomarkers is most appropriate for quantifying the DNT effects attributed to MeHg. A comprehensive literature search covered MeHg dose-response literature published 1998-2022. Studies were evaluated for risk of bias and study sensitivity using IRIS approach. Quantitative results of investigations were extracted and statistically compared. Seven studies were identified that measured both maternal hair and cord blood Hg levels. In these investigations, several DNT umbrella tests and their sub-tests results were modeled. Cord blood MeHg was more sensitive, producing larger estimates of MeHg potency, in most of the comparisons (91%) with maternal hair MeHg estimates for the same sub-tests in the same study. When comparing results from cord blood Hg to maternal hair Hg there was a 75% increase in sensitivity (range: 4-583%). In the two domains where results for maternal hair Hg were more sensitive, the rise was only 18% (Range: 7-29%). There were limited data (two studies) that compared maternal blood and 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 approximately 30%). Maternal hair Hg remains an appropriate biomarker for exposure monitoring in many populations, but these data suggest that cord blood Hg is more appropriate for dose-response modeling of MeHg DNT effects.