Characterization of toxicokinetics and toxicodynamics with linear systems theory: application to lead-associated cognitive decline

Trace Elements in Alzheimer's Disease and Dementia: The Current State of Knowledge

Changes in trace element concentrations are being wildly considered when it comes to neurodegenerative disorders, such as Alzheimer's disease and Parkinson's disease. This study aims to present the role that trace elements play in the central nervous system. Moreover, we reviewed the mechanisms involved in their neurotoxicity. Low zinc concentrations, as well as high levels of copper, manganese, and iron, activate the signalling pathways of the inflammatory, oxidative and nitrosative stress response. Neurodegeneration occurs due to the association between metals and proteins, which is then followed by aggregate formation, mitochondrial disorder, and, ultimately, cell death. In Alzheimer's disease, low Zn levels suppress the neurotoxicity induced by β-amyloid through the selective precipitation of aggregation intermediates. High concentrations of copper, iron and manganese cause the aggregation of intracellular α-synuclein, which results in synaptic dysfunction and axonal transport disruption. Parkinson's disease is caused by the accumulation of Fe in the midbrain dopaminergic nucleus, and the pathogenesis of multiple sclerosis derives from Zn deficiency, leading to an imbalance between T cell functions. Aluminium disturbs the homeostasis of other metals through a rise in the production of oxygen reactive forms, which then leads to cellular death. Selenium, in association with iron, plays a distinct role in the process of ferroptosis. Outlining the influence that metals have on oxidoreduction processes is crucial to recognising the pathophysiology of neurodegenerative diseases and may provide possible new methods for both their avoidance and therapy.

Effect of environmental toxicants on neuronal functions

In the last few years, neurodegenerative diseases like Alzheimer's disease (AD) and Parkinson's disease (PD) have attracted attention due to their high prevalence worldwide. Environmental factors may be one of the biggest reasons for these diseases related to neuronal dysfunctions. Most of neuronal disorders are strongly associated with pre- and postnatal exposure to environmental toxins released from industries. Some of the neurotoxic metals such as lead, aluminum, mercury, manganese, cadmium, and arsenic as well as some pesticides and metal-based nanoparticles have been involved in AD and PD due to their ability to produce senile/amyloid plaques and NFTs which are the main feature of these neuronal dysfunctions. Exposure to solvents is also majorly responsible for neurodegenerative disorders. The present review highlights the impact of omnipresent heavy metals with some other neurotoxins on human health and how they give rise to neuronal dysfunctions which in turn causes socio-economic consequences due to increasing pollution worldwide. Graphical abstract.

Long-term consequences of early postnatal lead exposure on hippocampal synaptic activity in adult mice

INTRODUCTION

Lead (Pb) exposure yielding blood lead levels (BLL) as low as 2 µg/dl in children is an international problem. More common in US low-income neighborhoods, childhood Pb exposure can cause behavioral and cognitive deficits, including working memory impairments, which can persist into adulthood. So far, studies characterized short-term effects of high Pb exposure on neuronal structure and function. However, long-term consequences of early chronic Pb exposure on neuronal activity are poorly documented.

METHODS

Here, we exposed male and female mice (PND [postnatal day] 0 to PND 28) to one of three Pb treatments: 0 ppm (sodium-treated water, control), 30 ppm (low dose), and 330 ppm (high dose) lead acetate. Once the male and female mice were 9-12 months old, extracellular field recordings on hippocampal slices were performed.

RESULTS

We show that at CA3 to CA1 synapses, synaptic transmission was decreased and neuronal fiber activity was increased in males exposed to lowest level Pb. In contrast, both synaptic transmission and neuronal fiber activity were increased in females exposed to high Pb. The ventral hippocampus-medial prefrontal cortex (vHPC-mPFC) synapses are crucial for working memory in rodents. The lowest level Pb decreased vHPC-mPFC synaptic transmission, whereas high Pb decreased short-term synaptic depression.

CONCLUSIONS

Overall, we show for the first time that early exposure to either high or lowest level Pb has long-term consequences on different synaptic properties of at least two hippocampal synapses. Such consequences of early Pb exposure might worsen the cognitive decline observed in aging men and women. Our results suggest that additional efforts should focus on the consequences of early Pb exposure especially in at-risk communities.

Advancing the symptom science model with environmental health

OBJECTIVE

Globally, indoor and outdoor pollutants are leading risk factors for death and reduced quality of life. Few theories explicitly address environmental health within the nursing discipline with a focus on harmful environmental exposures. The objective here is to expand the National Institutes of Health Symptom Science Model to include the environmental health concepts of environmental endotype (causative pathway) and environmental exposure.

DESIGN

Meleis' research to theory strategy for theory refinement was used. Research workshop proceedings, environmental health nursing research expert consensus, panelist research trajectories, and review of the literature were utilized as data sources.

RESULTS

Ongoing emphasis on the physical environment as a key determinant of health and theoretical perspectives for including environmental exposures and endotypes in symptom science are presented. Definitions of these concepts, further developed, are provided. Recommendations to strengthen environmental health nursing research and practice through capacity building/infrastructure, methods/outcomes, translational/clinical research, and basic/mechanistic research are included.

CONCLUSION

The revised model deepens theoretical support for clinical actions that include environmental modification, environmental health education, and exposure reduction. This modification will enable a middle-range theory and shared mental model to inspire the prioritization of environmental health in nursing leadership, research, practice, and education.

Respiratory manganese particle size, time-course and neurobehavioral outcomes in workers at a manganese alloy production plant

The progression of manganism with chronic exposure to airborne manganese (Mn) is not well understood. Here, we further investigate the findings on exposure and neurobehavioral outcomes of workers from a silico- and ferromanganese production plant and non-exposed workers from the same community in 1990 and 2004, using a variety of exposure metrics that distinguish particle size and origin within the range of respirable airborne exposures. Mn exposure matrices for large respirable particulate (Mn-LRP, dust) and small respirable particulate (Mn-SRP, fume), based on process origins, were used together with detailed work histories since 1973 (plant opening), to construct exposure metrics including burdens and cumulative burdens with various clearance half-lives. For three out of eight 1990 neurobehavioral tests analyzed with linear regression models, duration of Mn exposure was the best predictor: Luria-Nebraska Neuropsychological Battery - Motor Scale, Trail-Making B and Finger Tapping. The Luria-Nebraska Motor Scale had the strongest association (t ∼ 5.0, p < 10(-6)). For outcomes on three other tests, the duration and Mn-SRP metrics were comparable: Trail Making Test A, Cancellation H and Stroop Color-Word Test (color/word subtest). Delayed Word Recall was best predicted by Mn-SRP (based on square root or truncated air-concentrations). The Word score on the Stroop Color-Word Test was the only outcome for which Mn-LRP was the leading predictor (t = -2.92, p = 0.003), while performance on the WAIS-R Digit Span Test was not significantly predicted by any metric. For outcomes evaluated in both 1990 and 2004, a mixed-effect linear regression model was used to examine estimates of within-individual trends. Duration and Mn-SRP were associated with performance on the Luria-Nebraska Motor Scale, as well as with other outcomes that appeared to have both reversible and progressive features, including Trail Making A and B, Cancellation H and Delayed Word Recall. With the mixed-effect model, Digit Span exhibited a significant irreversible association with exposure duration (t = -2.34, p = 0.021) and Mn-SRP (square root; t = -2.38, p = 0.019) metrics. The strong prediction using duration of exposure is consistent with effective homeostatic regulation of tissue-level Mn in the observed exposure range of respirable Mn (< 0.2mg/m(3)).

Pb neurotoxicity: neuropsychological effects of lead toxicity

Neurotoxicity is a term used to describe neurophysiological changes caused by exposure to toxic agents. Such exposure can result in neurocognitive symptoms and/or psychiatric disturbances. Common toxic agents include heavy metals, drugs, organophosphates, bacterial, and animal neurotoxins. Among heavy metal exposures, lead exposure is one of the most common exposures that can lead to significant neuropsychological and functional decline in humans. In this review, neurotoxic lead exposure's pathophysiology, etiology, and epidemiology are explored. In addition, commonly associated neuropsychological difficulties in intelligence, memory, executive functioning, attention, processing speed, language, visuospatial skills, motor skills, and affect/mood are explored.

Involvement of decreased glutamate receptor subunit GluR2 expression in lead-induced neuronal cell death

Lead is known to induce neurotoxicity, particularly in young children, and GluR2, an AMPA-type glutamate receptor subunit, plays an important role in neuronal cell survival. Therefore, we hypothesized that altered GluR2 expression plays a role in lead-induced neuronal cell death. To test this idea, we investigated the effect of exposure to 5 and 20 µM lead for 1-9 days on the viability and GluR2 expression of primary-cultured rat cortical neurons. The number of trypan-blue stained cells was increased by exposure to 5 µM lead for 9 days or 20 µM lead for 7-9 days, and LDH release was increased after exposure to 20 µM lead for 9 days. GluR2 expression was reduced by exposure to 5-100 µM lead, but not 0.1-1 µM lead, for 9 days. Immunocytochemistry also confirmed that GluR2 expression was decreased in the presence of lead. Application of 50 ng/ml brain-derived neurotrophic factor (BDNF) led to a recovery of lead-induced neuronal cell death, accompanied with increased GluR2 expression. Our results suggest that long-term exposure to lead induces neuronal cell death, in association with a decrease of GluR2 expression.

Silicosis exposure-response in a cohort of tin miners comparing alternate exposure metrics

BACKGROUND.: The detailed lung radiographic response to silica exposure has not been described. In estimating the exposure-response relationship in silicosis with statistical models, the absence of baseline (unattributable) risk can disable relative-rate estimation or produce widely varying estimates. This obstructs identification of optimum exposure metrics and invalidates comparisons and meta-analyses, which assume a common background rate. METHODS.: A cohort of 3,000 Chinese tin miners with more than 1,000 cases of silicosis was analyzed for the period 1961-1994. Regular surveillance documented three stages of silicosis. To examine the exposure-response relationship, the intercept in relative-rate models was fixed to correspond to 1% of the observed silicosis rate. Exposure metrics for contributions in different time-windows were simultaneously evaluated, as were burden and cumulative burden metrics. RESULTS.: Silica exposures that most contributed to silicosis onset occurred in the period 5-10 years prior (excess annual rate per 10 mg-year/m(3) , ER = 0.158, 95% CI = 0.125-0.192, or 16% per year). During 10-20 year prior, the excess rate contribution was much smaller (ER = 0.048, 95% CI = 0.037-0.060) but larger again during 20-30 year prior to onset (ER = 0.112, 95% CI = 0.098-0.126). For advanced silicosis, all time periods contributed about equally to the rate of onset. CONCLUSIONS.: Reliable estimates of parameters were observed, demonstrating exposure contributions over time. Burden metrics with different half-lives suggested some reversibility for silicosis onset with a half-life of 20 years. Advanced silicosis was best predicted with a cumulative burden metric which was consistent with prior observations that previously deposited silica continues to cause pulmonary damage.

Lead neurotoxicity: effects on brain nitric oxide synthase

Lead (Pb), a ubiquitous and potent neurotoxicant, induces several neurophysiological and behavioural changes, while Pb alters the function of multiple organs and systems, it primarily affects the central nervous system. In human adults, encephalopathy resulting from Pb intoxication is often characterized by sleeplessness, poor attention span, vomiting, convulsions and coma; in children, Pb-induced encephalopathy is associated with mental dullness, vomiting, irritability and anorexia; diminished cognitive function resulting in a mental deficit has been also observed during Prolonged exposure to Pb. Pb can produce oxidative stress, disrupt the blood-brain barrier and alter several Ca(2+)-dependent processes, including physiological processes that involve nitric oxide synthesis on central nervous system in development and adult animals. This review summarizes recent evidence showing that Pb can interfere with the production of nitric oxide and can disrupt the function of nitric oxide synthase. Lead interferes with nitric oxide-related physiological mechanisms, and Pb neurotoxicity may affect processes involved in learning and memory.

Evaluation of cumulative lead dose and longitudinal changes in structural magnetic resonance imaging in former organolead workers

OBJECTIVE

: We evaluated whether tibia lead was associated with longitudinal change in brain volumes and white matter lesions in male former lead workers and population-based controls in whom we have previously reported on the cognitive and structural consequences of cumulative lead dose.

METHODS

: We used linear regression to identify predictors of change in brain volumes and white matter lesion grade scores, using two magnetic resonance imaging scans an average of 5 years apart.

RESULTS

: On average, total brain volume declined almost 30 cm, predominantly in gray matter. Increasing age at the first magnetic resonance imaging was strongly associated with larger declines in volumes and greater increases in white matter lesion scores. Tibia lead was not associated with change in brain volumes or white matter lesion scores.

CONCLUSIONS

: In former lead workers in whom cumulative lead dose was associated with progressive declines in cognitive function decades after occupational exposure had ended, cumulative lead dose was associated with earlier persistent effects on brain structure but not with additional worsening during 5 years.

Exposure-response relationship and risk assessment for cognitive deficits in early welding-induced manganism

OBJECTIVE

The exposure-response relationship for manganese (Mn)-induced adverse nervous system effects is not well described. Symptoms and neuropsychological deficits associated with early manganism were previously reported for welders constructing bridge piers during 2003 to 2004. A reanalysis using improved exposure, work history information, and diverse exposure metrics is presented here.

METHODS

Ten neuropsychological performance measures were examined, including working memory index (WMI), verbal intelligence quotient, design fluency, Stroop color word test, Rey-Osterrieth Complex Figure, and Auditory Consonant Trigram tests. Mn blood levels and air sampling data in the form of both personal and area samples were available. The exposure metrics used were cumulative exposure to Mn, body burden assuming simple first-order kinetics for Mn elimination, and cumulative burden (effective dose). Benchmark doses were calculated.

RESULTS

Burden with a half-life of about 150 days was the best predictor of blood Mn. WMI performance declined by 3.6 (normal = 100, SD = 15) for each 1.0 mg/m3 x mo exposure (P = 0.02, one tailed). At the group mean exposure metric (burden; half-life = 275 days), WMI performance was at the lowest 17th percentile of normal, and at the maximum observed metric, performance was at the lowest 2.5 percentiles. Four other outcomes also exhibited statistically significant associations (verbal intelligence quotient, verbal comprehension index, design fluency, Stroop color word test); no dose-rate effect was observed for three of the five outcomes.

CONCLUSIONS

A risk assessment performed for the five stronger effects, choosing various percentiles of normal performance to represent impairment, identified benchmark doses for a 2-year exposure leading to 5% excess impairment prevalence in the range of 0.03 to 0.15 mg/m3, or 30 to 150 microg/m3, total Mn in air, levels that are far below those permitted by current occupational standards. More than one-third of workers would be impaired after working 2 years at 0.2 mg/m3 Mn (the current threshold limit value).

Surveillance results of depleted uranium-exposed Gulf War I veterans: sixteen years of follow-up

As part of a longitudinal surveillance program, 35 members of a larger cohort of 77 Gulf War I veterans who were victims of depleted uranium (DU) "friendly fire" during combat underwent a 3-day clinical assessment at the Baltimore Veterans Administration Medical Center (VAMC). The assessment included a detailed medical history, exposure history, physical examination, and laboratory studies. Spot and 24-h urine collections were obtained for renal function parameters and for urine uranium (U) measures. Blood U measures were also performed. Urine U excretion was significantly associated with DU retained shrapnel burden (8.821 mug U/g creatinine [creat.] vs. 0.005 mug U/g creat., p = .04). Blood as a U sampling matrix revealed satisfactory results for measures of total U with a high correlation with urine U results (r = .84) when urine U concentrations were >/=0.1 mug/g creatinine. However, isotopic results in blood detected DU in only half of the subcohort who had isotopic signatures for DU detectable in urine. After stratifying the cohort based on urine U concentration, the high-U group showed a trend toward higher concentrations of urine beta(2) microglobulin compared to the low-U group (81.7 v. 69.0 mug/g creat.; p = .11 respectively) and retinol binding protein (48.1 vs. 31.0 mug/g creat.; p = .07 respectively). Bone metabolism parameters showed only subtle differences between groups. Sixteen years after first exposure, this cohort continues to excrete elevated concentrations of urine U as a function of DU shrapnel burden. Although subtle trends emerge in renal proximal tubular function and bone formation, the cohort exhibits few clinically significant U-related health effects.

Gender and race/ethnicity differences in lead dose biomarkers

OBJECTIVES

We sought to identify predictors of lead concentrations in the blood, tibias, and patellae of older adults and to describe differences by gender, race/ethnicity, and other factors that can influence lead toxicokinetics and, thus modify health effects.

METHODS

Participants aged 50 to 70 years (N=1140) were randomly identified from selected neighborhoods in Baltimore, Maryland. We measured lead concentrations by anodic stripping voltammetry (in blood) and (109)Cd-induced K-shell x-ray fluorescence (in bone). We used multiple linear regression to identify predictors of lead concentrations.

RESULTS

Mean (SD) lead concentrations in blood, tibias, and patellae were 3.5 (2.4) mug/dL, 18.9 (12.5) mug/g, and 6.8 (18.1) mug/g, respectively. Tibia concentrations were 29% higher in African Americans than in Whites (P < .01). We observed effect modification by race/ethnicity on the association of gender and physical activity to blood lead concentrations and by gender on the association of age to tibia lead concentrations. Patella lead concentrations differed by gender; apolipoprotein E genotype modified this relation.

CONCLUSIONS

African Americans evidenced a prominent disparity in lifetime lead dose. Women may be at higher risk of release of lead from bone and consequent health effects because of increased bone demineralization with aging.

Are brain volumes based on magnetic resonance imaging mediators of the associations of cumulative lead dose with cognitive function?

The authors used cross-sectional data (2001-2003) to consider the pathway through which past occupational lead exposure impacts cognitive function. They were motivated by studies linking cumulative lead dose with brain volumes, volumes with cognitive function, and lead dose with cognitive function. It was hypothesized that the brain regions associated with lead mediate a portion of the relation between lead dose and cognitive function. Data were derived from an ongoing US study of 513 former organolead manufacturing workers. Magnetic resonance imaging was used to perform a novel analysis to investigate mediation. Volumes associated with cognitive function and lead dose were derived by using registered images and were used in a subsequent mediation analysis. Cumulative lead dose was associated with adverse function in the visuo-construction, executive function, and eye-hand coordination domains. Regarding these domains, there was strong evidence of volumetric mediation of lead's effect on cognition in the visuo-construction domain and a moderate amount for executive function and eye-hand coordination. A second path-analysis-based approach was also used. To address the possibility that chance associations explained these findings, a permuted analysis was conducted, the results of which supported the mediation inferences. The approach to evaluating volumetric mediation may have general applicability in epidemiologic neuroimaging settings.

Biomonitoring of lead exposure-alternatives to blood

Lead ( Pb) is one of the most important models for biomonitoring of exposure, with the blood Pb concentration as a predominant choice in practice and in epidemiology. In this article the alternatives for biomarkers to blood are reviewed. This overview focuses on a number of different qualities that are of importance in the evaluation of a biomarker's usefulness and performance. The qualities scrutinized included: (1) analytical accuracy and precision; (2) cost; (3) practical issues; (4) what is reflected by the biomarker; (5) relationship to exposure; and (6) relationship to effects. Data indicate that the best biomarker in some circumstances may be blood, but bone or teeth (for past exposures), feces (for current gastrointestinal exposure), or urine (for organic Pb) are sometimes more useful. A striking feature is that no generally accepted biomarker of bioavailable Pb exists, though plasma, bone, teeth, urine, and hair have all been discussed. For one of the most used applications of blood Pb, monitoring of lead workers' exposure, blood has important shortcomings in that it shows a poor response to changes in exposure at high levels. The alternative of plasma has not been sufficiently evaluated to be considered an alternative in occupational health services, although previous analytical problems are basically overcome. Possibly, urine deserves also more attention. Almost all biomarkers lack systematic data on variation within and between individuals.

Lead and cognitive function in adults: a questions and answers approach to a review of the evidence for cause, treatment, and prevention

Lead has been extensively used worldwide in gasoline, consumer products, commercial applications, and industrial settings. Its use in gasoline and paint has been particularly hazardous to public health leading to widespread population exposure and substantial lifetime cumulative doses in most Americans over age 40 years. Cumulative lead dose can be estimated by measuring the current concentration of lead in tibia bone by X-ray fluorescence. A growing literature has documented that tibia lead levels are associated with decrements in cognitive function and declines in cognitive function over time. Furthermore, there are several interesting lines of biochemical and epidemiological investigation that have demonstrated potential links of lead to neurodegenerative diseases. These studies support the inference that a proportion of what has been termed 'normal' age-related cognitive decline may, in fact, be due to exposure to neurotoxicants such as lead. Well-designed studies of cumulative lead dose and Alzheimer's disease risk should be conducted to follow-up on these leads. The strong and compelling body of literature on lead and cognitive dysfunction and decline also supports a need for intervention studies to prevent lead-related cognitive decline.

Effects of lead on the adult brain: a 15-year exploration

BACKGROUND

Historically, there has been minimal concern about the effect of adult lead exposure on the brain. Evidence from recent longitudinal studies raise concerns about the long-term effects of past exposure.

METHODS

We initiated three independent longitudinal studies to determine whether cumulative lead exposure was associated with persistent or progressive brain effects. The studies include 1,109 former U.S. organolead manufacturing workers, 803 current and former inorganic lead workers in Korea, and 1,140 50- to 70-year-old Baltimore residents with environmental lead exposure. The organolead workers had past exposure to inorganic and tetraethyl lead (TEL); in the other two studies, exposure was to inorganic lead. In each of these studies, we measured blood lead and tibia and patella lead by 109Cd K-shell-induced X-ray fluorescence.

RESULTS

Higher tibia lead was consistently associated with poorer measures of cognitive function. Longitudinal analysis of the Korean and organolead cohort indicate that the effect of lead is persistent. Moreover, MRI data on organolead workers indicates a possible progressive effect from past exposure; higher tibia lead was associated with lower brain volume. The latter study indicates that a difference in tibia lead equivalent to about one-sixth of the overall range was associated with a mean difference in these cognitive tests that was equivalent, on average, to what was observed for a five-year age difference.

CONCLUSIONS

Our data suggest that a significant proportion of what is considered to be "normal" age-related cognitive decline may, in fact, be due to past exposure to neurotoxicants such as lead.

Exposure and dose modelling in occupational epidemiology

Complex and dynamic physiologic processes underlie the exposure-response relations that occupational and environmental epidemiologists study. Simple summary measures of exposure such as the average, cumulative exposure, or duration of exposure, can be applied suitably in exposure-response analyses in many instances. However, there are situations where these metrics may not be directly proportional to risk, in which case their use will result in misclassification and biased estimates of exposure-response associations. We outline methods for developing exposure or dose metrics which may reduce misclassification, as illustrated with some recent examples. Selecting better exposure or dose metrics can be thought of as a problem of choosing appropriate weights on the exposure history of each cohort member. Dosimetric modeling involves choosing exposure weights based on formal hypotheses about underlying physiologic or pathogenetic processes. Dosimetric modeling is still not widely used in epidemiology, and so the forms of mathematical models and the criteria for choosing one model over another are not yet standardized. We hope to stimulate further applications through this presentation.

Relations of brain volumes with cognitive function in males 45 years and older with past lead exposure

We examined relations between brain volumes assessed by MRI and cognitive function in subjects in whom we have previously reported associations of cumulative lead dose with: (1) longitudinal declines in cognitive function; (2) smaller volumes of several regions of interest (ROIs) in the brain; and (3) increased prevalence and severity of white matter lesions. We used two complementary methods (ROI- [evaluating 20 ROIs] and voxel-wise) to examine associations between brain volumes and cognitive function using multiple linear regression. MRIs and cognitive testing were obtained from 532 former organolead workers with a mean (SD) age of 56.1 (7.7) years and a mean of 18.0 (11.0) years since the last occupational exposure to lead at the time of MRI acquisition. Cognitive testing was grouped into six domains of function (visuo-construction, verbal memory and learning, visual memory, executive functioning, eye-hand coordination, processing speed). Results indicated that larger ROI volumes were associated with better cognitive function in five of six cognitive domains, with significant associations observed for visuo-construction (15 of 20, p<or=0.05), processing speed (12, p<or=0.05), visual memory (11, p<or=0.05), executive functioning (11, p<or=0.05), and eye-hand coordination (11, p<or=0.05). Significant structure-function relations were also identified in the voxel-wise analysis with low false discovery rates (all less than 2.2%). Thus, larger volumes were associated with better cognitive function using both ROI- and voxel-based methods. In this cohort, an interesting group in which to examine structure-function relations, this finding provides a necessary condition to support the hypothesis that lead may influence cognitive function by its effect on brain volumes.

Total and leachable heavy metals in muddy and sandy sediments of Egyptian coast along Mediterranean Sea

The assessment of marine pollution due to metals was made for surficial sediments sampled from 20 sites along Mediterranean coast of Egypt. The samples were dried, acid digested and analyzed for leachable and total heavy metal contents (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn) by flame atomic absorption spectrophotometer (air-acetylene) with deuterium background correction. Evaluation of the heavy metals pollution status was carried out using enrichment factors (EFs), the effect range-low (ERL) and the effect range-median (ERM). The study showed high concentrations of Cd, Co, Pb, Ni and moderate concentrations of Cr, Cu and Mn were contaminated in the sediments of studied sites. The results of Spearman correlation, factor and cluster analysis of the heavy metals analyzed in the collected sediment were discussed. The main source of contamination is the offshore oil field and industrial wastes, which arise due to the ineffective and inefficient operation equipments, illegal discharge and lack of supervision and prosecution of offenders.

Cumulative lead dose and cognitive function in adults: a review of studies that measured both blood lead and bone lead

OBJECTIVE

We review empirical evidence for the relations of recent and cumulative lead dose with cognitive function in adults.

DATA SOURCES

A systematic search of electronic databases resulted in 21 environmental and occupational studies from 1996 to 2006 that examined and compared associations of recent (in blood) and cumulative (in bone) lead doses with neurobehavioral outcomes.

DATA EXTRACTION

Data were abstracted after consideration of exclusion criteria and quality assessment, and then compiled into summary tables.

CONCLUSIONS

At exposure levels encountered after environmental exposure, associations with bio-markers of cumulative dose (mainly lead in tibia) were stronger and more consistent than associations with blood lead levels. Similarly, in studies of former workers with past occupational lead exposure, associations were also stronger and more consistent with cumulative dose than with recent dose (in blood). In contrast, studies of currently exposed workers generally found associations that were more apparent with blood lead levels; we speculate that the acute effects of high, recent dose may mask the chronic effects of cumulative dose. There is moderate evidence for an association between psychiatric symptoms and lead dose but only at high levels of current occupational lead exposure or with cumulative dose in environmentally exposed adults.

Mercy Mercy Me: Social Injustice and the Prevention of Environmental Pollutant Exposures Among Ethnic Minority and Poor Children

Children's lead and pesticide exposures are used as examples to examine social disparities in exposure reduction efforts as well as environmental policies impacting children in poverty and minority children. The review also presents an estimate of the effect of social disparities in lead exposure on standardized test performance. Because including measures of pollutants with potential behavioral effects can alter the observed effects of race/ethnicity, income, and other variables, suggestions are made for including measures of pollutants in longitudinal studies and studies of multiple and cumulative risk. Continued basic research on developmental correlates and effects of pollution exposure, participatory action-research with at-risk and underrepresented populations, and contributions to public awareness and education are important leadership areas for developmental researchers.

Biological markers for metal toxicity

Exposure assessment is often considered the weakest link in risk assessment. It is important for investigators to continue to utilize the full potential of biomarkers for chemicals whose exposure is of global concern. This review is concerned with the biomarkers of metal toxicity, as the overall exposure to metals encountered occupationally or in the environment would continue causing indirect, delayed effects therefore ecoepidemiology, using designed molecular probes and noninvasive diagnostics will be the leading component for future management of environmental health. An attempt is made here at appraising the need for the development of more biomarkers for use in environmental epidemiology and health risk assessment.

Lead

Children differ from adults in the relative importance of lead sources and pathways, lead metabolism, and the toxicities expressed. The central nervous system effects of lead on children seem not to be reversible. Periods of enhanced vulnerability within childhood have not consistently been identified. The period of greatest vulnerability might be endpoint specific, perhaps accounting for the failure to identify a coherent “behavioral signature” for lead toxicity. The bases for the substantial individual variability in vulnerability to lead are uncertain, although they might include genetic polymorphisms and contextual factors. The current Centers for Disease Control and Prevention screening guideline of 10 μg/dL is a risk management tool and should not be interpreted as a threshold for toxicity. No threshold has been identified, and some data are consistent with effects well below 10. Historically, most studies have concentrated on neurocognitive effects of lead, but higher exposures have recently been associated with morbidities such as antisocial behavior and delinquency. Studies of lead toxicity in experimental animal models are critical to the interpretation of nonexperimental human studies, particularly in addressing the likelihood that associations observed in the latter studies can be attributed to residual confounding. Animal models are also helpful in investigating the behavioral and neurobiological mechanisms of the functional deficits observed in lead-exposed humans. Studies of adults who have been exposed to lead are of limited use in understanding childhood lead toxicity because developmental and acquired lead exposure differ in terms of the maturity of the organs affected, the presumed mechanisms of toxicity, and the forms in which toxicities are expressed.

The longitudinal association of lead with blood pressure

BACKGROUND

Several investigators have reported an association of blood lead or bone lead with increased blood pressure and hypertension, but questions remain concerning whether these effects are acute or chronic in nature.

METHODS

In this longitudinal study, we evaluated the relation of lead, measured in blood and tibia, to changes in blood pressure between 1994 and 1998. We studied 496 current and former employees of a chemical-manufacturing facility in the eastern United States who had previous occupational exposure to inorganic and organic lead. Cohort members who provided three or four blood pressure measurements during the study were included.

RESULTS

Mean age at baseline was 55.8 years with a mean of 18 years since last occupational exposure to lead. Blood lead at baseline averaged 4.6 microg/dL (standard deviation [SD] = 2.6) or 0.22 micromole/Liter (SD = 0.13). Tibia lead at year three averaged 14.7-microg/gm (SD = 9.4) bone mineral. Change in systolic blood pressure during the study was associated with lead dose, with an average annual increase of 0.64 mmHg (standard error [SE] = 0.25), 0.73 mmHg (SE = 0.26), and 0.61 mmHg (SE = 0.27) for every standard deviation increase in blood lead at baseline, tibia lead at year three, or peak past tibia lead, respectively.

CONCLUSIONS

The results support an etiologic role for lead in the elevation of systolic blood pressure among adult males and are consistent with both acute and chronic modes of action.

ApoE genotype, past adult lead exposure, and neurobehavioral function

Our objective in this study was to determine if the known relation between tibia bone lead levels and neurobehavioral test scores are influenced by the apolipoprotein E (ApoE) genotype. We collected data on 20 neurobehavioral tests in 529 former organolead workers who had an average of 16 years since last occupational exposure to lead. We used linear regression to model the relations between each of 20 neurobehavioral test scores and tibia lead, a binary variable for ApoE genotype (i.e., at least one Epsilon4 allele vs. none), and an interaction term between tibia lead and the binary term for ApoE genotype. At the time of testing, former lead workers were an average of 57.6 years of age; 82% were younger than 65 years. In regression analysis, we observed one statistically significant and one borderline significant coefficient for ApoE genotype alone. Coefficients for the ApoE and tibia lead interaction term were negative in 19 of the 20 regression models. This indicates that the slope for the relation between tibia lead and each neurobehavioral test was more negative for individuals with at least one Epsilon4 allele than for those who did not have an Epsilon4 allele. Four of 19 negative coefficients for the interaction term were statistically significant (digit symbol, Purdue pegboard assembly, Purdue pegboard-dominant hand, complex reaction time); another three of the remaining 16 coefficients (symbol digit, trail-making A, Stroop) were borderline significant (i.e., p < 0.10). This study suggests that individuals may vary in susceptibility to the long-term effects of lead on the central nervous system (CNS). In particular, the persistent CNS effect of lead may be more toxic in individuals who have at least one ApoE-Epsilon4 allele.