Blood lead (Pb) levels: further evidence for an environmental mechanism explaining the association between socioeconomic status and psychophysiological dysregulation in children

OBJECTIVE

The authors recently reported that blood lead (Pb) was a significant mediator for the positive association between socioeconomic status (SES) and peripheral vascular responses to acute stress in children (B. B. Gump et al., 2007). The present study considers the possibility that Pb may also mediate an association between SES and cortisol responses to acute stress.

DESIGN

Early childhood Pb exposure was tested as a mediator for cross-sectional associations between SES and cortisol responses.

MAIN OUTCOME MEASURES

The primary outcome was cortisol responses to acute stress in 9.5-year-old children (N = 108).

RESULTS

Lower family income was associated with significantly greater cortisol levels following an acute stress task. A mediational analysis confirmed that Pb was a significant mediator for this association.

CONCLUSION

These results reaffirm the importance of considering the chemical environment as well as social and psychological environment when evaluating psychophysiological effects of low SES.

Low-level prenatal and postnatal blood lead exposure and adrenocortical responses to acute stress in children

BACKGROUND

A few recent studies have demonstrated heightened hypothalamic-pituitary-adrenal (HPA) axis reactivity to acute stress in animals exposed to heavy metal contaminants, particularly lead. However, Pb-induced dysregulation of the HPA axis has not yet been studied in humans.

OBJECTIVE

In this study, we examined children's cortisol response to acute stress (the glucocorticoid product of HPA activation) in relation to low-level prenatal and postnatal Pb exposure.

METHODS

Children's prenatal blood Pb levels were determined from cord blood specimens, and postnatal lead levels were abstracted from pediatrician and state records. Children's adrenocortical responses to an acute stressor were measured using assays of salivary cortisol before and after administration of a standard cold pressor task.

RESULTS

Pb exposure was not associated with initial salivary cortisol levels. After an acute stressor, however, increasing prenatal and postnatal blood Pb levels were independently associated with significantly heightened salivary cortisol responses.

CONCLUSIONS

Our results suggest that relatively low prenatal and postnatal blood lead levels--notably those below the 10 microg/dL blood lead level identified by the Centers for Disease Control and Prevention for public health purposes--can alter children's adrenocortical responses to acute stress. The behavioral and health consequences of this Pb-induced HPA dysregulation in children have yet to be determined.

Blood lead (Pb) levels: a potential environmental mechanism explaining the relation between socioeconomic status and cardiovascular reactivity in children

OBJECTIVE

A number of studies have shown an association between socioeconomic status (SES) and cardiovascular reactivity to acute stress. In addition, the authors recently reported that higher early childhood blood lead (Pb) levels are associated with significantly greater total peripheral (vascular) resistance (TPR) responses to acute stress. It is not known whether the SES-TPR association is mediated by underlying differences in blood lead levels.

DESIGN

Participants were 9.5-year-old children (N=122) with established early childhood blood lead levels.

MAIN OUTCOME MEASURES

Family SES was measured using the Hollingshead Index, blood lead levels were abstracted from pediatrician and state records, and children's cardiovascular responses to acute stressors were measured in the laboratory with impedance cardiography and an automated blood pressure monitor.

RESULTS

Lower family SES was shown to be associated with significantly higher blood lead levels as well as significantly heightened systolic blood pressure, diastolic blood pressure, and TPR responses to acute stress tasks. A mediational analysis confirmed that Pb was a significant mediator of the SES-TPR reactivity association; some evidence also suggested moderation.

CONCLUSION

These results suggest the importance of considering the chemical environment as well as social and psychological environment when evaluating cardiovascular effects of low SES.

Terrorism and cardiovascular responses to acute stress in children

A number of studies have considered whether background stress affects cardiovascular responses to acute stress tasks. The present study considers the effect of a potent background stressor with a clear onset, namely the terrorist attacks on September 11, 2001. Specifically, the authors investigated differences among 9.5-year-old children tested before (N = 30) and then following (N = 20) the 9/11 attacks. In addition, a majority of these children (N = 37) were retested approximately 1 year later (i.e., before and after 9/11/2002). Children tested directly following 9/11/2001 exhibited significantly greater stroke volume and cardiac output responses to acute stress tasks compared with their responses 1 year later, and this change in reactivity differed significantly from the change in reactivity exhibited by children tested before 9/11/2001 and again 1 year later. These results suggest that a potent background stressor can temporarily heighten some children's cardiovascular responses to subsequent acute stressors.

Prenatal and early childhood blood lead levels and cardiovascular functioning in 9(1/2) year old children

A number of studies have found that increasing lead exposure is associated with increases in blood pressure in humans. Studies with animals suggest that lead-induced increases in vascular resistance account for these increases in blood pressure. The present study assessed cardiovascular functioning at rest and in response to acute stress for 9(1/2) year old children (N=122) having relatively low prenatal (cord) blood lead levels (M=1.98 microg/dL, SD=1.75) and low postnatal (early childhood) blood lead levels (M=4.62 microg/dL, SD=2.51). Higher cord blood levels were associated with higher baseline systolic blood pressure (SBP), and higher early childhood lead levels were associated with greater total peripheral (vascular) resistance (TPR) responses to acute stress. In addition, a negative association between blood lead levels and stroke volume (SV) suggests that lead-induced increases in vascular resistance were sufficient to produce cardiac afterload, a situation arising when blood pressure in the aorta makes it difficult for the left ventricle to eject blood. These effects were not mediated by differences in task performance or emotional responses to the acute stress tasks. Finally, these effects were significant for lead levels considered low, notably, below the 10 microg/dL threshold currently adopted by the CDC for deleterious effects.

Prenatal exposure to PCBs and infant performance on the fagan test of infant intelligence

A sample of infants was examined at conceptual age 67 weeks (6-month testing, N=230), and again at conceptual age 92 weeks (12-month testing, N=216) using the Fagan Test of Infant Intelligence (FTII). Analysis of the results revealed a dose-dependent relationship between total umbilical cord-blood PCB levels and poorer FTII performance at both ages. A similar relationship was observed using a subset of the persistent and heavily chlorinated PCB congeners associated with Lake Ontario fish consumption (septa-, octa-, and nonachlorinated biphenyls) in children tested at 12-months but not at 6-months. These data replicate previous research (Jacobson et al., 1985) which demonstrated a dose-dependent relationship between prenatal PCB exposure and FTII performance in infants of Lake Michigan fisheaters. Analyses of FTII scores with cord-blood DDE and maternal hair methylmercury (MeHg) revealed no significant associations between FTII performance and either of these toxicants. The latter results replicate those of Myers et al., (1995) who found no effect of MeHg on FTII performance in Seychellois infants.

Prenatal PCB exposure and neonatal behavioral assessment scale (NBAS) performance

We examined the relationship between prenatal (cord blood) polychlorinated biphenyls (PCBs) and Neonatal Behavioral Assessment Scale (NBAS) performance in babies born to women who consumed contaminated Lake Ontario fish. Cord blood PCBs, DDE, HCB, Mirex, lead, and hair mercury levels were determined for 152 women who reported never consuming Lake Ontario fish and 141 women who reported consuming at least 40 PCB-equivalent lbs. of Lake Ontario fish over their lifetime. Earlier work demonstrated that the newborns of fish eaters are exposed to a more heavily chlorinated distribution of PCB congeners, and that highly chlorinated PCBs (hepta-, octa-, and nonachlorinated biphenyls) are most strongly correlated with breast milk levels, perhaps providing the best index of PCB exposure in the Oswego cohort. Given the above, one would predict that these PCBs would be related to impaired performance on those NBAS clusters associated with fish consumption: namely Habituation, Autonomic, and Reflex clusters of the NBAS. Excepting the Relex cluster, these predictions were confirmed. Results revealed significant linear relationships between the most heavily chlorinated PCBs and performance impairments on the Habituation and Autonomic clusters of the NBAS at 25-48 h after birth. Additionally, higher prenatal PCB exposure was associated with a nonspecific performance impairment on the NBAS as evidenced by a significantly greater proportion of NBAS scales in which poor performance was exhibited (more than 1 standard deviation below the mean) in the most highly exposed neonates. Moreover, PCBs of lighter chlorination were unrelated to NBAS performance, as were DDE, Mirex, HCB, lead, and mercury. These results corroborate our earlier findings linking Lake Ontario fish consumption to the most heavily chlorinated PCB congeners, and suggest that the chlorination and persistence of PCBs may be an important factor both for exposure assessment and for determining relationships with neurobehavioral functions.

Effects of Great Lakes fish consumption on brain PCB pattern, concentration, and progressive-ratio performance

This study investigated the effects of consumption of Great Lakes fish on progressive ratio performance, and on the pattern and concentrations of brain polychlorinated biphenyls (PCBs), dichlorodiphenyldichloroethene (DDE), and mirex in the rat. Adult, male Sprague-Dawley rats were fed a 30% diet of either Lake Ontario salmon (LAKE), Pacific Ocean salmon, or lab chow control for 20 or 65 days. Following the treatment regimen, half the rats from each group were sacrificed immediately for gas chromatographic analysis of organochlorine contaminants, and the other half were tested on a multiple fixed-ratio-progressive-ratio reinforcement schedule and then sacrificed for analysis. Consumption of Lake Ontario fish resulted in significantly higher levels of brain PCBs, DDE, and mirex relative to controls, but still well within human exposure ranges (<1 microg/g fat). Consumption of Lake Ontario fish for 20 or 65 days produced an average brain PCB concentration of 457 and 934 ng/g fat, respectively. Consumption of laboratory rat chow or Pacific Ocean salmon for 20 or 65 days produced an average brain PCB concentration of 240, 464, and 441 ng/g fat, respectively. Moreover, both LAKE-fed groups showed a much more heavily chlorinated pattern of brain PCBs than all control groups, as evidenced by both significant increases in the most heavily chlorinated PCB congeners and significant increases in the average chlorine biphenyl. All LAKE brains contained significant concentrations of DDE and mirex, whereas no control brains contained any detectable quantities. Analysis of progressive-ratio performance indicated that LAKE rats responded normally during fixed-ratio schedules but quit significantly sooner than control rats on a progressive-ratio 5 (PR5) schedule, indicating reduced persistence on progressively leaner reinforcement schedules. Analysis of brain PCBs indicated that total PCBs were most strongly related to PR5 performance. These data indicate that consumption by rats of contaminated Lake Ontario fish produces (1) increased concentrations of PCBs, DDE, and mirex in the brain, (2) a more heavily chlorinated distribution of PCBs in the brain, and (3) reduced persistence of progressive-ratio reinforcement schedules. While these behavioral changes are related to brain PCB level, more work is necessary before the effects can be directly attributed to PCBs.

Assessment of prenatal exposure to PCBs from maternal consumption of Great Lakes fish: an analysis of PCB pattern and concentration

The current study was designed to assess the pattern and concentration of prenatal PCB exposure in the newborns of women who consumed Great Lakes fish. We compared the pattern and concentration of umbilical cord blood PCBs of 145 women who reported never having consumed Great Lakes fish to 134 women who reported consuming at least 40 PCB-equivalent fish lbs of Great Lakes fish in their lifetime (Lonky et al., 1996). Although the average levels of total PCBs in cord blood were exceedingly low (approximately 1.0 ppb), the data clearly indicated that both the proportion (mol%) and the absolute concentration (ppb) of the most heavily chlorinated and persistent PCB homologues (homologues C17-C19) were markedly elevated in the cord blood of fish eaters. This effect grew markedly as a function of the total PCBs detected in the sample. Moreover, the concentration of the most heavily chlorinated PCB homologues was significantly dependent on how recently the fish were consumed relative to pregnancy. The order of highly chlorinated PCB concentration was consumed fish throughout pregnancy > consumed fish up until pregnancy > stopped consuming fish in 1984 > never consumed Lake Ontario fish. In contrast, PCB homologues of light (Cl1-Cl3) or moderate (Cl4-Cl6) chlorination were unrelated to fish consumption. Analysis of the relationship between the PCB homologues in cord blood and their homologues in breast milk provided further converging evidence of these findings. While PCB homologues of light (Cl1-Cl3) or moderate (Cl4-Cl6) chlorination did not correlate with their breast milk homologues, the most persistent and heavily chlorinated PCB homologues (Cl7-Cl9) were significantly and positively correlated with breast milk levels. These data indicate that the most heavily chlorinated PCBs provide valid and reliable exposure information in a lean medium such as cord blood. We conclude that maternal consumption of Great Lakes fish increases the risk of prenatal exposure to the most heavily chlorinated PCB homologues.

Behavioral effects of prenatal and adult exposure to toxic chemicals found in Lake Ontario fish: two methodological approaches

Two research approaches are described that were used to determine behavioral changes following a diet of Lake Ontario fish. Approach 1 involved the correlational method, in which human subjects voluntarily ate contaminated Lake Ontario fish. Demographic information, data on the amount of Lake Ontario fish consumed, and control variables were obtained during an interview. Respondents' behavior, as well as the behavior of their children, then was measured. Because subjects were not assigned randomly to eat or not eat Lake Ontario fish, other variables that might have influenced both consumption of fish and behavior had to be considered. Therefore, confounding variables were measured and their influence controlled for using statistical techniques. Approach 2 involved the experimental method using laboratory rats, where subjects were assigned randomly to receive a diet of environmentally contaminated Lake Ontario salmon, relatively uncontaminated Pacific Ocean salmon, or no salmon. Since the rats fed Lake Ontario salmon behaved differently than the other two groups on nine tasks, it was concluded that the contaminants in Lake Ontario salmon caused behavioral changes. Random assignment of subjects to groups eliminated competing explanations. If similar behavioral (e.g., emotional or cognitive) results were obtained using the two approaches, then the results utilizing rats probably could be generalized to humans, and the correlational results found in humans probably were due to a cause and effect relationship.