Behavioral Measures of Neurotoxicity (1990) / Chapter Skim
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The Health Effects of Environmental Lead Exosure: Closing Pandora's Box
The Health Effects of Environmental Lead Exosure: Closing Pandora's Box
Pages 243-267
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From page 243... ...
As such it can be used as a model for discussion in light of the theme of Part III of this volume chemical time bombs. All individuals in industrialized societies carry a significant body burden of lead, a situation that will take at least a generation to change even if lead were removed from the environment instantaneously tomorrow.
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From page 244... ...
The Romans used lead for plumbing as well as a sweetening agent in wine and other foods. The industrial revolution and the addition of lead to gasoline in the 1920s have resulted in dramatic increases in environmental lead levels (Elias et al., 1975~.
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From page 245... ...
In the 1940s, it was recognized by astute physicians that children who had been treated for lead poisoning suffered permanent sequelae in the form of neurological damage (Byers and Lord, 1943~. Highlevel lead exposure in children at that time was via lead-based paint.
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From page 246... ...
Prospective Studies Reproductive Effects It has long been recognized that industrial exposure to high lead levels produced an increased incidence of miscarriages and stillbirths, and that infants that did survive failed to thrive and exhibited neurological abnormalities. Although the situation is less clear for lower exposure to lead, recent studies provide evidence that low-level lead exposure causes reproductive problems.
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From page 247... ...
Increased maternal blood lead level is also associated with abnormal reflexes, poor muscle tone, and neurological soft signs such as jitteriness, hypersensitivity, and abnormal cry in the infant (Ernhart et al., 1985, 1986~. It must be stressed that the maternal and infant blood lead levels in these studies were in the range considered normal or average for people in industrialized societies (2-15,ug/dL in most cases)
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From page 248... ...
Performance was found to be more related to postnatal than prenatal blood lead levels; however, no assessment was performed before 2 years of age. It is possible that early testing would have revealed significant prenatal exposure effects.
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From page 249... ...
(This issue is discussed in a later section.) Treater Behavioral Concomitants of Increased Lead Burden The consequences of early poor performance as a result of lead exposure in terms of grade retention or need for special education have been little investigated.
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From page 250... ...
reported a dose-related increase in Satisfactory school performance as a function of increased free erythrocyte protoporphyrin (PEP) levels (a measure of lead exposure)
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From page 251... ...
~ ct ~ - 0 - to.
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From page 252... ...
. Other Health Effects of Environmental Lead Exposure In addition to effects on the nervous system, low-level exposure to lead affects a number of important metabolic processes.
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From page 253... ...
FIGURE 5 Relationship of 2-kHz pure tone hearing thresholds and blood lead levels in 4,519 NHANES II subjects aged 14-19 years. - SOURCE: Schwartz and Otto (1987)
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From page 254... ...
The positive results being obtained in prospective studies deserve attention in a different vein. The implication of these findings is that the blood lead body burden of women, reflected by maternal and cord blood lead levels, is important to at least the early well-being of children.
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From page 255... ...
Another example is the factoring out of mother's IQ and measures of socioeconomic status and maternal care scores, which may be influenced by the mother's lead burden, and may in turn influence the child's lead burden at birth as well as during childhood. A potential partial solution may be the choice of highly homogeneous populations for study, or even populations in which lead and the typical confounders vary inversely.
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From page 256... ...
RICE , 1 , 1 , , , 50 60 70 80 90 100 1 10 120 130 140 VERBAL l.Q. FIGURE 6 Cumulative frequency distribution of verbal IQ scores In high- and lowlevel lead subjects: A shift In me median of 6 points is associated with a fourfold increase In the risk of IQ below 80.
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From page 257... ...
The resulting distributions revealed that the number of children with IQs below 80 increased by a factor of four in the high-lead group, whereas the number of children with IQs over 120 decreased by an equal amount (Figure 6~. If it is in fact the case that increasing blood lead levels from 5 to 15 ~g/dL (or from 0 to 10 ,ug/dL)
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From page 258... ...
Developmental lead exposure also results in a decrease in the amount of dendritic branching from nerve cells, representing a decrease in the ability of the nerve to communicate with its neighbors. It is also established that aging can produce these same effects.
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From page 259... ...
2-vitamin D is a particularly robust one, with blood levels of 30-50 ,ug/dL resulting in decreases in the hormone that overlap comparable degrees of decrease seen in severe kidney injury or certain genetic diseases." Thus lead is implicated in the compromise of the body's ability to repair tissue, fight disease, regulate growth of abnormal cells, and maintain bone, among other effects. Such functions are often compromised in old age; lead may be contributing to these effects, particularly as a result of 1i-fetime exposure.
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From page 260... ...
The consequences to society of decreasing the IQ of thousands of individuals from 130 to 125 points, or of a few from 160 to 155, are of great significance but cannot be measured either in monetary terms or in terms of human suffering. What can be measured monetarily is the cost of inclividuals who require special services as a result of undue lead exposure.
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From page 261... ...
\ CNS Plasma Ligand ~ Teeth Bound Diffusive Hair Bone (Nondiffusible) 1 Reds ~ ~ Enosphalopathy Peripheral Anemia Neutopathy Screening Body Burden Treatment Kidney Mb~ Etre Tubular Dysfunction Endocrine Urinary Excretion Reprodwbve Cytogenetic FIGURE 8 Ecodiagram showing movement of lead in the environment and areas of U.S.
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From page 262... ...
As discussed above, the reasons for the controversy are due at least in part to the following factors: Methodological limitations including inadequate markers of lead exposure, environment-influenced instruments of neuropsychological function, and choice of populations in which these environmental factors and lead exposure are highly correlated · Evaluating the data by simply counting studies as positive or negative, without looking at direction of effect across studies or power of individual studies to find an effect, and failure to perform metaanalyses Failure to utilize the animal literature in interpreting data from human studies · Failure to recognize that a "small" effect (i.e., 2 to 3 percent of variance) does not translate to "insignificant" In addition, there may be a reluctance on the part of regulatory agencies to regulate on the basis of psychological test data.
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From page 263... ...
The ongoing insult of lead to the brain may also result in an accelerated decrease in mental functioning. These deleterious effects would presumably manifest themselves for a considerable period of time in our populations even if lead exposure ceased tomorrow.
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From page 264... ...
1987b. Low level lead exposure and child development: Assessment at age 5 of a cohort followed from birth.
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From page 265... ...
1980. Low Level Lead Exposure: The Clinical Implications of Current Research.
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From page 266... ...
Pp. 259-266 in Low Level Lead Exposure: The Clinical Implications of Current Research, H
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From page 267... ...
Pp. 279-284 in Low Level Lead Exposure: The Clinical Implications of Current Research, H
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