External lead contamination of women's nails by surma in Pakistan: Is the biomarker reliable?

Adverse health effects of heavy metals are a public health concern, especially lead may cause negative health impacts to human fetal and infantile development. The lead concentrations in Pakistani pregnant women's nails, used as a biomarker, were measured to estimate the lead exposure. Thirteen nail samples out of 84 nails analyzed contained lead higher than the concentration (13.6 μg/g) of the fatal lead poisoning case, raising the possibility of an external contamination. Eye cosmetics such as surma are recognized as one of the important sources of lead exposure in Pakistan. We collected in Pakistan 30 eye cosmetics made in Pakistan, Saudi Arabia and western countries. As the metal composition analysis by energy dispersive X-ray fluorescence spectrometry revealed that some surma samples contained lead more than 96%, the surma might contaminate the nail specimen. Scanning electron microscopy observations showed that lead-containing surma consists of fine particle of galena (ore of lead sulfide) in respirable dust range (less than 10 μm). In addition, relative in vitro bioavailability of lead in the surma was determined as 5.2%. Thus, lead-containing surma consists of inhalable and bioavailable particles, and it contributes an increased risk of lead exposure. Moreover, the relationship between the surma and the lead-contaminated nails by lead isotope ratios analysis indicated the potential of lead contamination in nails by surma. These results suggest that lead in the nails was derived both from body burden of lead and external contamination by lead-containing surma. Therefore, nail is not suited as a biomarker for lead exposure in the countries where surma used, because we may overestimate lead exposure by surface lead contamination in the nail by surma.