Blood lead levels general population studies

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. 

Basing their views upon an examination of the biochemical evidence for adverse effects of lead rather than upon studies of child brain development, the US Environmental Protection Agency (EPA) [4] and the World Health Organization (WHO) [5] have recommended upper limits to the population median blood lead level. In consequence, the US EPA has promulgated an ambient air quality standard designed to limit the exposure of the general population to airborne lead [4]. This standard will necessitate tight control over emission of lead into the atmosphere. 

Figure 1 General pattern of results from clinic, smelter, and general population studies of lead exposure effects on cognitive function, as reflected by deficits in IQ scores on various standardized tests. The magnitude of IQ decrements associated with a broad range of blood lead levels is estimated here based on evaluation of studies noted in figure key and discussed in text. Note that latest results from certain newer studies point toward lead effects on IQ across a broad range of PbB levels, down to as low as 10-15 fig/d or perhaps lower (as illustrated in Figure 2). Key R = Rummo studies D = de la Burde studies N = Needleman studies W = Winneke studies UK = Recent British studies by Smith, Lansdown, Yule, Harvey, etc.

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. 

Despite the importance of activities related to lead for the economy of these cities, the large population potentially exposed and the fact that the Torreon refinery is generally considered one of the largest in Latin America, no studies have been carried out on air lead levels in the areas surrounding the smelters, only one study has been carried out on lead levels in blood and dust at Ciudad Juarez and two on lead in hair in Torreon. Their results will be presented in the relevant sections. In both cases, the need for further studies and the urgency for the strengthening of regulations to control lead emissions by these sources is evident from the data. 

For the general population, the presence of lead in blood results from exposure to a range of environmental influences (water, air, soil) or is derived directly from other specific sources (food cans, paint, etc). Lead in blood levels have been falling in most countries for a number of years now, as the most obvious sources of exposure have been more tightly controlled. Lead levels are now down to lOpg/lOOml or less in most of the industrialised countries. However various clinical studies continue to suggest that child behaviour and intelligence may be adversely affected by even very low concentrations of lead in blood, and this area has become the focus of attention in recent years. 

From the outset of studies in Glasgow it was clear that potential problems existed with respect to the levels of environmental lead exposure (Goldberg, 1984). Our experience of this suggested that the problem was linked to soft plumbosolvent water supplies and lead plumbing, and consequent increases in blood lead concentration in the general population of the West of Scotland... 

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