Lead and mercury exposure in pregnant women in the UK: a cross-sectional observational study (The PEAR Study)

Objectives 
Lead and mercury are recognised as critical determinants of population health, especially for children and pregnant women. Few UK cohorts have measured lead or mercury in pregnant women since 1990. The aims of this study are to: (1) quantify lead and mercury exposures in a sample of pregnant women in the UK; (2) document concentrations over time in pregnant women in Bristol, UK; (3) compare concentrations with international data.

Design 
Whole blood samples were obtained from pregnant women in a quantitative arm of the Pregnancy, the Environment And nutRition (PEAR) Study in a cross-sectional observational study design. The samples were analysed by ICP-MS (Health and Safety Executive, Buxton, UK).

Setting 
Community-based with recruitment through a hospital antenatal clinic in south-west England.

Participants 
Women ≥18 years old and ≥11 weeks pregnant by last menstrual period.
Primary outcome measures: Whole blood lead and speciated mercury concentrations.

Results 
The whole blood lead concentration was: mean 5.8 (SD 6.2), median 4.6 (IQR 3.5, 5.9), range 1.7–78.1 μg/l (n=262; gestational age range by scan 8.3-15.9 weeks). These values are about 84% lower than in pregnant women in the UK Avon Longitudinal Study of Parents and Children (ALSPAC; 1991–1992), about 47% lower than in the UK Born in Bradford (BiB) study (2007–2010), and about 57% lower than in White women in the UK MaBEL study (2011). Blood total mercury concentration was: mean 0.83 (SD 0.64), median 0.69 (IQR 0.34, 1.19), range 0.07-3.40 (about 60% lower than in pregnant women in ALSPAC and about 37% lower than in BiB). These results are similar to contemporary concentrations found in Europe and USA.

Conclusion 
Blood concentrations of lead and mercury in pregnant women in the UK have declined considerably since the early 1990s. However, no safe levels have previously been identified for adverse effects on cognition, preterm birth rate or coronary heart disease prevalence. These data will contribute to the ongoing development of public health advice.