Lead and mercury in breast milk

Heavy metals are potentially toxic substances, especially for the susceptible infant. Exposure to mercury (Hg) and lead (Pb) may result in neurotoxic and nephrotoxic impairment and in anemia. Previous data on breast milk Pb and Hg contents are sparse or missing for the Austrian population. No evaluations of the influence of mothers' lifestyles on Pb and Hg levels in breast milk are available.

Five- to 10-mL individual samples of breast milk were provided from healthy mothers in Vienna (urban; n = 59), Linz (industrial; n = 47), and Tulln (rural; n = 59). A questionnaire about area of residence, maternal nutrition, smoking habits, and dental fillings was filled out by the lactating mothers. Milk samples and infant formulas were lyophilized, wet-ashed with nitric acid (65%), and analyzed with atomic absorption spectrophotometry. Spiked skim milk powder was used as reference material. Statistical analysis included the Kruskal-Wallis test and multiple robust regression analysis.

Breast milk showed low Hg and Pb concentrations (Hg: 1.59 +/- 1.21 1g/l, n = 116; Pb: 1.63 +/- 1.66 6g/l, n = 138). Eight percent of the breast milk samples marginally exceeded the screening level of 3.5 micro g/L for Hg. Austrian Pb values declined strongly during the last 20 years. Bivariate comparison revealed that the factors significantly related to metal levels in breast milk were area of residence (Hg, Pb), prematurity (Hg), consumption of fish (Pb) and cereals (Hg), vitamin supplementation (Hg), and smoking (Pb). The Hg and Pb contents of cow milk and infant formulas were far below respective guideline values.

Neither Hg nor Pb concentrations exceeded critical levels. There are no reports on infants harmed by the intake of milk from unexposed mothers. We conclude that even theoretical risks from current Hg or Pb levels for the breastfed infant of a healthy mother can be ruled out.