Lead, toxicity

Reviews on the occurrence, biochemical basis, and treatment of lead toxicity in children (11) and workers (3,12,13) have been pubhshed. Approximately 17% of all preschool children in the United States have blood lead levels >10 //g/dL. In inner city, low income minority children the prevalence of blood lead levels >10 //g/dL is 68%. It has been estimated that over two million American workers are at risk of exposure to lead as a result of their work. PubHc health surveillance data document that each year thousands of American workers occupationally exposed to lead develop signs and symptoms indicative of... 

Workers in the metals treatment industry are exposed to fumes, dusts, and mists containing metals and metal compounds, as well as to various chemicals from sources such as grinding wheels and lubricants. Exposure can be by inhalation, ingestion, or skin contact. Historically, metal toxicology was concerned with overt effects such as abdominal coHc from lead toxicity. Because of the occupational health and safety standards of the 1990s such effects are rare. Subtie, chronic, or long-term effects of metals treatment exposure are under study. An index to safety precautions for various metal treatment processes is available (6). As additional information is gained, standards are adjusted. 

There are no children In the reference area who had lead toxicity or whose blood lead level exceeded 29 pg/dl (Table XIII). The term "lead toxicity" Is defined here as a child with a blood-lead level > 30 pg/dl and an EP pg/dl. The term "lead toxicity" Is not used In a toxicological sense. 

Table XIII. Distribution of Lead Toxicity and High Blood Levels by Race at the Reference Area...

Traffic Density Percent with Lead Toxicity Percent with Blood Lead Levels >30 g/dl ... 

Table XVII shows that 5.6 percent of black children living within 0.5 mile of RSR were found to have lead toxicity, and no child living beyond 0.5 mile of RSR was found to have lead toxicity.

Table XVII. Distribution of Lead Toxicity by Race and Distance from RSR Site...

Approximate Distance (miles) Traffic Density Sample Size Percent with Lead Toxicity ... 

Less than 0.5 percent of the black children at the Dixie site were found to have lead toxicity (Table XX). As previously noted, the three non-black children (6.6 percent of non-black children) found to have lead toxicity were siblings In a household where the father had an occupational exposure to lead. 

Tables XXI and XXII show that for the RSR site the differences In mean blood-lead levels and proportion of children with lead toxicity remain evident even when other sources of potential exposure (as determined from the questionnaire) were taken Into consideration Tables XXIII and XXIV show this Is not the case for the Dixie site ...

Table XXI Percent Lead Toxicity by Distance, Traffic,...

Table XXIV. Percent Lead Toxicity by Distance and Other Potential Sources of Exposure for Dixie Site...

Approximate Distance Sample Size Potential Exposure Percent with Lead Toxicity Potential Exposure ... 

At neither site is there evidence of absorption of lead to the degree usually associated with clinical symptoms of lead poisoning, and the reported blood-lead levels are not high enough to make this likely. However, a public health concern exists, particularly in the RSR area, since 5 percent of these black children were found to have lead toxicity. 

When the Dixie site is compared to the reference area, proximity to the smelter (within 0.5 mile) contributed 1.85 pg/dl to the mean blood-lead level. The potential contribution of traffic density could not be determined because of the configuration of the roadway and the distance of the roadway from the smelter site. Although an elevated mean blood-lead level was found for children living close to the Dixie site, the increase was not as great as observed in the RSR site and the few children found to have lead toxicity, as defined previously, appear to have lead exposure due to occupation of parents. 

Deputy Surgeon General L. H. Gehrig spoke frankly Some maintain that a large segment of the population is already perilously close to the threshold of lead toxicity as a result of environmental exposure others take an almost diametrically opposed position. He also conceded that across the entire range of environmental health problems, we are making a rather belated start. Until the conference, the USPHS had focused on hydrocarbons and sulfur dioxide and rarely referred to tetraethyl lead as a pollution problem. 

Herbert L. Needleman. Clair Patterson and Robert Kehoe Two Views of Lead Toxicity. Environmental Research. 78 (Aug. 1998) 79-85. A good summary of Patterson versus Kehoe. 

Full Fanconi syndrome has been reported to be present in some children with lead encephalopathy (Chisolm 1968 Chisolm et al. 1955). According to the National Academy of Sciences (NAS 1972), the Fanconi syndrome is estimated to occur in approximately one out of three children with encephalopathy and PbB levels of approximately 150 pg/dL. Aminoaciduria occurs at PbB levels >80 pg/dL in children with acute symptomatic lead poisoning (Chisolm 1962). The aminoaciduria and symptoms of lead toxicity disappeared after treatment with chelating agents (Chisolm 1962). 

Several studies conducted in children known to have lead toxicity, indicate that nephropathy occurs in children only at PbB >80 pg/dL, and usually exceeding 120 pg/dL (NAS 1972). 

Susceptibility to lead toxicity is influenced by dietary levels of calcium, iron, phosphorus, vitamins A and D, dietary protein, and alcohol (Calabrese 1978). Low dietary ingestion of calcium or iron increased the predisposition to lead toxicity in animals (Barton et al. 1978a Carpenter 1982 Hashmi et al. 1989a Six and Goyer 1972 Waxman and Rabinowitz 1966). Iron deficiency combined with lead exposure acts synergistically to impair heme synthesis and cell metabolism (Waxman and Rabinowitz 1966). 

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