Violation of lead and cadmium standards are often used in litigation under California's Proposition 65 because the threshold warning level, based on "reproductive toxicity", requires the potential ingestion of very small amounts. The general toxicity of lead and cadmium are well known; see for example http://toxnet.nlm.nih.gov/cgi-bin/sis/search/f?./temp/~CGoBJV:1:human and http://toxnet.nlm.nih.gov/cgi-bin/sis/search/f?./temp/~OGv2YK:1:human.
Now researchers have identified a link between relatively low levels of these metals and hormone markers of delayed onset of puberty in girls. Researchers took blood samples from young girls and measured concentrations of two reproductive hormones (inhibin B and luteinizing hormone) that serve as markers of hypothalamic, pituitary, and gonadal functioning. The researchers found no significant associations between blood lead and cadmium and luteinizing hormone.
However, girls aged 10 or 11 with blood lead levels of 5 μg/dL or higher were 75% less likely than girls with blood lead under 1 µg/dL to have levels of inhibin B greater than 35 pg/mL, a level typically deemed consistent with puberty by the limited research in this area. The researchers also found proportionately lower levels of inhibin B in girls who had relatively high levels of both cadmium and lead, compared with girls who had only high lead. Moreover, after adjusting for age, inhibin B levels were lowest for iron-deficient girls with blood lead levels of 1 µg/dL or higher, suggesting that lead may be particularly toxic for girls with iron deficiency.
The researchers conclude that lead may suppress the production of hormones associated with puberty, especially in concert with cadmium. They stress that, on a national scale, changes in the timing of onset and/or progression of puberty can have considerable public health and social implications for both boys and girls. For instance, relatively late-maturing girls are at risk for diminished bone strength and fragility fractures later in life. The researchers also noted that the hormone alterations linked to lead and cadmium exposure in the study could have other as-yet unknown effects.
The study can be found at http://ehp03.niehs.nih.gov/article/fetchArticle.action?articleURI=info%3Adoi%2F10.1289%2Fehp.1001943.