Cognitive Deficit in 7-Year-Old Children with Prenatal Exposure to Methylmercury

TLDR

A cohort of 1,022 Faroese children was followed, with prenatal methylmercury exposure assessed via cord blood and maternal hair mercury, and at age 7 they underwent comprehensive neuropsychological testing covering motor, attention, memory, language, and visuospatial tasks. Despite no obvious clinical abnormalities, prenatal methylmercury exposure was linked to deficits in language, attention, memory, and to a lesser extent visuospatial and motor functions, with these effects persisting after adjustment and even at exposure levels deemed safe.

Abstract

A cohort of 1022 consecutive singleton births was generated during 1986–1987 in the Faroe Islands. Increased methylmercury exposure from maternal consumption of pilot whale meat was indicated by mercury concentrations in cord blood and maternal hair. At approximately 7 years of age, 917 of the children underwent detailed neurobehavioral examination. Neuropsychological tests included Finger Tapping; Hand–Eye Coordination; reaction time on a Continuous Performance Test; Wechsler Intelligence Scale for Children—Revised Digit Spans, Similarities, and Block Designs; Bender Visual Motor Gestalt Test; Boston Naming Test; and California Verbal Learning Test (Children). Clinical examination and neurophysiological testing did not reveal any clear-cut mercury-related abnormalities. However, mercury-related neuropsychological dysfunctions were most pronounced in the domains of language, attention, and memory, and to a lesser extent in visuospatial and motor functions. These associations remained after adjustment for covariates and after exclusion of children with maternal hair mercury concentrations above 10 μg/g (50 nmol/g). The effects on brain function associated with prenatal methylmercury exposure therefore appear widespread, and early dysfunction is detectable at exposure levels currently considered safe.