Domain specific effects of postnatal toenail methylmercury exposure on child behaviour

Very little is known about the relationship between postnatal methylmercury concentrations (via toenails as bioindicator) and behavioural characteristics of Pacific Island children living in New Zealand. The aim of this study was to explore the association between total mercury exposure and different domains of behavioural problems in Pacific children.

A sample of nine-year-old Pacific Island children resident in Auckland, New Zealand participated in this study. Total mercury was determined in biological samples (toenail clippings) on behavioural problems as identified by mothers (using the child behaviour checklist). Specific behavioural domains, particularly aggression, rule breaking, attention and social problems were studied in relation to mercury exposure using toenails. The determination of mercury concentration in toenail clippings, after acid digestion was carried out using inductively coupled plasma mass spectrometry.

The observational study was conducted between July 2010 and July 2011 in which 278 eligible nine-year-old Pacific Island children were enrolled (Girls n=58%; boys n=42%).

showed that 21% of the children had total toenail mercury concentrations (1.5μg/g to 6μg/g) higher than the United State Environmental Protection Agency recommended levels (RfD; 1μg/g Hg) for optimal health in children. Aggressive behaviour was associated with total toenail mercury exposure after adjusting for gender, ethnicity and income levels (OR: 2.15 95% CI 1.45, 3.18 p-value <0.05; OR 1.38 95% CI 0.83, 1.2 p value <0.05, respectively).

Overall, this research contributes to the understanding of total toenail mercury concentrations for Pacific people in New Zealand using toenail clippings as biomarkers in terms of associations with child behavioural problems. Mercury in toenails demonstrated a moderate association with a specific behavioural domain - aggressive behaviour.