Occupational lead exposures population studies

Taken together, the results of both the occupational and general population studies do not provide conclusive evidence that lead exposure, as assessed by PbB levels, is positively associated with hyper-... 

Epidemiologic, experimental, and in vitro mechanistic data indicate that lead exposure elevates blood pressure in susceptible individuals. In populations with environmental or occupational lead exposure, blood lead concentration is linked with increases in systolic and diastolic blood pressure. Studies of middle-aged and elderly men and women have identified relatively low levels of lead exposure sustained by the general population to be an independent risk factor for hypertension. In addition, epidemiologic studies suggest that low to moderate levels of lead exposure are risk factors for increased cardiovascular mortality. Lead can also elevate blood pressure in experimental animals. The pressor effect of lead may be mediated by an interaction with calcium mediated contraction of vascular smooth muscle, as well as generation of oxidative stress and an associated interference in nitric oxide signaling pathways. 

Cardiovascular Effects. There is currently considerable scientific debate as to whether there is a causal relationship between lead exposure and hypertension. Another area of controversy is whether African Americans are more susceptible to the cardiovascular effects of lead than are whites or Hispanics. The evidence from both occupational studies and large-scale general population studies (i.e., National Health and Nutrition Examination Survey [NHANES II], British Regional Heart Study [BRHS]) is not sufficient to conclude that such a causal relationship exists between PbB levels and increases in blood pressure. The database on lead-induced effects on cardiovascular function in humans will be discussed by presenting a summary of several representative occupational studies followed by a discussion of the findings from the large-scale general population studies. 

M.B. Schenker of Institute of Toxicology, University of California Davis in Davis, California is leading a multidisciplinary study supported by National Cancer Institute (NCI). This study will examine whether environmental asbestos deposits in California are associated with increased rates of mesothelioma. The study will address geological occurrence of asbestos and potential human exposure based on population patterns and known occupational exposure, and epidemiological characteristics of the disease in the state. The project will plan a case-control study to rigorously test the hypothesis that mesothelioma in California is independently associated with environmental asbestos exposure. 

Navas-Acien et al. (2007) conducted a qualitative systematic review of lead exposure and cardiovascular end points except blood pressure and hypertension. They identified 12 studies of clinical cardiovasctrlar end points in general populations and 18 studies of cardiovascular mortality in occupational cohorts. They concluded that the evidence was suggestive but not sufficient to infer causal relationships between lead exposure and clinical cardiovasctrlar outcomes because of the small number of prospective studies, the lack of standardized assessment and information on outcomes, and methodologic limitations, such as exposure and outcome misclassification. 

Cardiovascular effects of Pb in humans are the subject of Chapter 13, particularly with respect to effect potency in older exposure subjects but with inclusion of other risk groups. Cardiovascular effects, while inconsistently quantified across human populations, have been identified in multiple epidemiological studies, supported by a number of experimental data sets appearing in the global literature. Chapter 14 on human reproductive and developmental impacts of lead exposures presents the more useful data across several risk groups within human populations. Chapter 15 discusses adverse effects of lead on the renal system as nephrotoxicity is considered to occur across both occupational and nonoccupational subsets of human populations and subsets within nonoccupational categories. Discussions in Chapter 15, much like those in Chapter 18 on immunotoxicity, have benefited from quite recent findings. 

The efficacy of urinary porphyrin profiles as a biomarker of exposures to metals other than lead in human populations is less well established. Studies on dentists with occupational mercury exposure have provided preliminary evidence of the potential utility of urinary porphyrin changes as a biomarker of low-level mercury exposure in human subjects (Woods et al. 1993), and further studies have demonstrated their efficacy as a measure of cumulative effects of mercury on specific tests of neurobehavioral function (Echeverria... 

Winneke, G., Kraemer, U., Brockhaus, A., Ewers, U., Kujanek, G., Lechner, H. and Janke, W. (1983) Neuropsychological studies in children with elevated tooth-lead concentrations. II. Extended study. Int. Arch. Occup. Env. Health, 51, 231-252 Winneke, G., Beginn, U., Ewert, T., Havestadt, C., Kraemer, U., Krause, C., Thon, H.L. and Wagner, H.M. (1985) Comparing the effects of perinatal and later childhood lead exposure on neuropsychological outcome. Env. Res., 38, 155-167 Yule, W., Lansdown, R., Millar, I. and Urbanowicz, M.A. (1981). The relationship between blood lead concentrations, intelligence and attainment in a school population a pilot study. Dev. Med. Child Neurol, 23, 567-576... 

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