Relationship of prenatal methylmercury exposure and language/verbal function: a meta-analysis

Developmental neurotoxicity (DNT) is a well-established hazard of methylmercury (MeHg) exposure. Past research on MeHg has highlighted DNT tests of language/verbal function (in particular the Boston naming test (BNT)) as an important aspect of MeHg toxicity.

We conducted a meta-analysis based on a recent systematic review of MeHg neurodevelopmental dose-response cohort studies published 1998-2025 that reported similarly normed tests of language/verbal function. Meta-analyses were based on recent studies using maternal blood biomarkers or cord blood biomarkers converted into maternal blood biomarkers.

For the BNT with or without cues, analysis (based on 2 studies (3 populations)) results were adverse, but not statistically significant. For the similarly normed language/verbal tests, decrements were statistically significant [-0.0085 95% (-0.0167; -0.0003) per MeHg µg/L maternal blood (based on eight studies)]. Results of a fill and trim sensitivity analysis were similar in the size of the effect to the original results. The two studies with sex-specific results indicated that boys appeared to be more sensitive to MeHg-related language/verbal function decrements when compared with girls.

Although most of the individual study results of language/verbal function were not statistically significant, the meta-estimate showed a statistically significant decrement in language/verbal function in children due to prenatal MeHg exposure.