PbB Levels Research Articles

Changes in Serum PBB and PCB Levels over Time among Women of Varying Ages at Exposure

The identification of host factors that are predictors of changes in serum polyhalogenated biphenyl contaminants over time has been a difficult challenge in epidemiologic studies of exposed individuals. Of particular concern are age at exposure, reproductive and lactational histories, and changes in body mass index. Using both cross-sectional and longitudinal approaches, this study examined factors related to high initial serum PBB and PCB levels and changes in these levels over time among women of varying ages at exposure (n=1772; age range<1 to 45 years). In 1973, PBB exposure occurred through consumption of farm products contaminated with PBB added to cattle feed. Exposures to PCBs began in 1941 through PCB-contaminated silo sealant deteriorating into animal feed. The Michigan Department of Public Health began enrolling participants in 1977 and has continued to follow them through annual updates. At enrollment, questionnaires were administered to obtain demographic, lifestyle, and anthropometric measurements, medical/reproductive and occupational histories, and contaminated food consumption patterns. Blood samples were collected for PBB and PCB analysis at enrollment for all participants; additional serum tests were done on a subset of the population during follow-up. Median serum levels at enrollment were 2.0 ppb PBB and 5.0 ppb PCB. A decline in serum PBB level over an interval that ranged from 1 to 146 months (median=31) was observed for 44.6% of the women (median=1.0 ppb), while 12.2% showed an increase (median=1.0 ppb). PCB levels declined in 50.3% of the women (median=3.0 ppb) while 12.2% increased (median=2.0 ppb). Relative to women whose contaminant levels were stable, higher initial serum level was a predictor of decline for both PBB and PCB (OR=1.66, 95% CI 1.52–1.82; OR=3.26, 95% CI 2.58–4.12, respectively); a yearly increase in interval between tests was related to declining PCBs (OR=1.65, 95% CI 1.46–1.87). In addition, age≤10 years at exposure (OR=1.72, 95% CI 1.03–2.86) and residence on a quarantined farm (OR=1.40, 95− CI 1.03–1.90) were predictors of a decrease in PBBs. Factors related to an increase in PBB levels were age≤10 years at exposure (OR=0.30, 95% CI 0.10–0.96) and initial PBB level (OR=1.24, 95% CI 1.15–1.33); and for PCBs, high initial level (OR=1.34, 95% CI 1.17–1.53) and body mass index (OR=1.07, 95% CI 1.01–1.13). One or more live births during the interval between tests were not related to changing levels of either contaminant; breastfeeding data were not available for examination. Early age at exposure appears to be an important predictor of changes in serum PBB levels OVER TIME.

Gender Differences in Blood Lead and Hemoglobin Levels in Andean Adults with Chronic Lead Exposure

A field study of the prevalence of lead (Pb) intoxication was conducted in 158 adults (67 men and 91 women) living at 2,500-2,800 meters in Ecuadorian Andean villages with high Pb contamination from local small-scale Pb-glazing cottage industries. Venous blood samples showed mean blood lead (PbB) levels of 34.5 microg/dL (SD 22.2) for men and 27.0 microg/dL (SD 18.4) for women; this difference was significant (t-test, p = 0.022; Mann-Whitney U, p = 0.044). An ANOVA showed no significant main effect for gender (F = 0.118, p = 0.782) or age (F = 2.479, p = 0.117), and no significant gender-by-age interaction (F = 0.273, p = 0.602). In the Pb-glazing study group, 39% of the men had PbB levels > or = 40 microg/dL, while 41% of the women had PbB levels > or = 30 microg/dL (the WHO health-based biological limits). A reference group of 39 adults (24 men and 15 women) had a mean PbB level of 5.9 microg/dL (SD 2.8; range: 1.8-16.8), significantly different from that of the 158 subjects in the study group (t-test, p < 0.0001). The difference in mean PbB levels of men (6.8 microg/dL) and women (4.7 microg/dL) in the reference group was significant (t-test, p = 0.026; Mann-Whitney U, p = 0.019). The mean altitude-corrected hemoglobin levels in the study group were lower than normal, 11.3 g/dL for men and 10.9 g/dL for women.

Thyroid hormone changes in males exposed to lead in the buenos aires area (argentina)

The relationship between lead levels in blood (PbB) and hormones T3, T4, T4F and TSH were studied in 75 subjects exposed to lead at work. PbB levels in blood were determined by atomic absorption spectrophotometry and hormones by enzymoimmunoassay. Positive and significant correlations among thyroid hormones and TSH vs blood lead level in the ranges 8–50 and 26–50 μ g dl−1were found (‘r’ between 0.304 and 0.621 and 0.431 and 0.619, respectively). At PbB levels between 8 and 26 μ g dl−1significant correlation was only found for TSH (r= 0.731). In the range PbB 50–98 μ g dl−1, ‘r’ was significant only for T3 ( −0.746) and T4 ( −0.514). Significant differences were observed in T4 and T4F levels between exposed and non-exposed groups. The results obtained indicate the need for monitoring thyroid hormones and TSH levels in workers exposed to lead.

Negative relationships between erythrocyte Ca-pump activity and lead levels in mothers and newborns

Lead poisoning induces hematological, gastrointestinal and neurological dysfunctions. One of the potential mechanisms is the inhibition of calcium-pump (Ca-pump), a transport protein. We investigated the effects of an environmental low lead exposure on Ca-pump activity in 247 mothers and their newborns. Maternal and cord blood, and newborn and mother hair, were sampled at delivery. Geometric means for mother and cord blood lead (Pb-B), and for mother and newborn hair lead (Pb-H), were 6.3 and 4.8 μg/dl, and 1.7 and 1.1 μg/g. Means for mother and cord basal Ca-pump activities were 2442 and 2675 nM/mg/hr. Mother enzymatic activity was negatively related to her Pb-B and Pb-H and to the cord Pb-B and newborn Pb-H levels. Newborn enzymatic activity was negatively related to his Pb-H level only. Adjustment for gestational age, child's sex, mother's age at delivery, alcohol, coffee and tea consumption, and smoking habits during pregnancy did not modify these relationships. Our findings support the hypothesis that lead toxicity could be in part mediated by a reduction of Ca-pump activity. This effect could be observed at low environmental exposure, in mothers and newborns.

Relationship between delta‐aminolevulinic acid dehydratase genotypes and heme precursors in lead workers

Background The objective of this study was to investigate the relationships between genotypes of delta-aminolevulinic acid (ALA) dehydratase (ALAD) and disturbances in the heme biosynthetic pathway by lead exposure. Methods The subjects were 192 male lead workers and 125 control subjects. Blood lead concentrations (Pb-B), plasma ALA concentrations (ALA-P), and ALAD genotypes were determined for all subjects. In lead workers, ALAD activity, ALA in urine (ALA-U), and erythrocyte zinc protoporphyrin (ZP) were also determined. Results The frequency of ALAD2 (minor type of ALAD allele) was calculated to be 0.087 in all subjects. No significant relationship was found between ALAD2 frequency and Pb-B levels in lead workers. ALAD1 homozygotes showed significantly higher levels of ZP and ALA-P in comparison with those of ALAD2 carriers at Pb-B levels more than 20 μg/dL and 40 μg/dL, respectively. Conclusions ALAD1 homozygotes might be more susceptible than ALAD2 carriers to disturbances in heme metabolism caused by lead exposure. Am. J. Ind. Med. 38:355–360, 2000. © 2000 Wiley-Liss, Inc.

Urban population exposure to lead and cadmium in east and south-east Asia

Information is still scarce for many Asian countries on general population exposure to two potentially toxic heavy metals of lead (Pb) and cadmium (Cd). The present review on publications from this study group is intended to provide an overview of the non-occupational exposure to Pb and Cd among general populations in east and south-east Asia. During the period of 1991–1998, surveys were conducted in four cities in south-east Asia, five cities in mainland China, and two cities each in Japan and Korea. Peripheral blood, morning spot urine and 24-h food duplicate samples were collected from 20–50 non-smoking adult women in each survey site. The samples were digested by heating in the presence of mineral acids, and then analyzed by inductively-coupled plasma mass spectrometry for the metals in blood (Pb-B and Cd-B), in urine (Pb-U and Cd-U), and in food duplicate (Pb-F and Cd-F). Measures were subjected to statistical analysis with an assumption of log-normal distribution. Pb-B, Pb-U and Pb-F levels varied substantially among the 11 urban sites; GM distributed in ranges of 32–65 μg/l for Pb-B, 2.1–7.5 μg/g cr (creatinine) for Pb-U, and 7–32 μg/day for Pb-F. The same was also the case for Cd exposure parameters, the distribution ranges being 0.5–1.8 μg/l for Cd-B, 1.2–3.1 μg/g cr for Cd-U, and 5–32 μg/day for Cd-F. It appeared that the exposure to Pb and Cd was highest in Kuala Lumpur, and Tokyo+Kyoto, respectively, and lowest in Tokyo+Kyoto and in Manila. Additional surveys in Japan showed that Pb exposure was even lower in rural areas than in Tokyo+Kyoto. When compared with the values reported in the literature, Pb exposure levels among Asian populations appear to be similar to the levels in Europe and in the United States, whereas Cd exposure seems to be higher in Asia than in Europe. The contribution of the dietary route in Pb absorption was variable and was inversely related to the extent of air pollution, whereas Cd uptake was almost exclusively via the dietary route with little contribution of the respiratory route.

Lead Exposure among Small-Scale Battery Recyclers, Automobile Radiator Mechanics, and Their Children in Manila, the Philippines

Blood lead (PbB) and hemoglobin levels (Hb) were determined in 40 battery repair/recycling shop workers, 16 radiator repair shop workers, and 20 children living in the immediate vicinity of these shops. Unexposed residents with similar socioeconomic status were also investigated. Mean PbB level was significantly higher for battery workers (54.23 μg/dL) when compared to radiator workers (20.04 μg/dL) and unexposed adults (12.56 μg/dL) (P<0.001). Among battery workers, 94% had PbB levels above the WHO permissible exposure limit of 40 μg/dL for males and 30 μg/dL for females. There was no demarcation between workplace and living quarters; therefore, workers' families were similarly exposed to hazards. Children living in the immediate vicinity of battery shops also had significantly higher mean PbB levels (49.88 μg/dL) compared to radiator shop children (11.84 μg/dL) and unexposed children (9.92 μg/dL). For workers with PbB > 40 μg/dL, 90% were anemic (Hb < 13 g/dL for males and <11.5 g/dL for females). Linear regression showed a correlation (r=−0.214; P=0.03) between Hb level and log10PbB. There was no significant relationship between anemia and blood lead in children (r=−0.146). We conclude that radiator repair activities appeared to increase the body burden of lead, although not up to a level significantly different from unexposed counterparts. Battery recycling/repair activities, however, significantly increased blood lead levels in workers and their children.

Correlation between concentration in urine and in blood of cadmium and lead among women in Asia

The objectives of the present study are to examine if there exists a quantitative relationship between lead in urine (Pb-U) and that in blood (Pb-B), and also between cadmium in urine (Cd-U) and that in blood (Cd-B) among the general populations who are environmentally (and not occupationally) exposed to these elements at various levels. For this purpose, peripheral blood and morning spot urine samples were collected in 1991–1998 from approximately 50 non-smoking adult women each in four cities in south-east Asia and five cities in mainland China, and two cities each in Japan and Korea. The samples were wet-ashed and then analyzed by inductively-coupled plasma mass spectrometry for Pb-B, Cd-B, Pb-U and Cd-U. Measured values were subjected to analysis to detect possible correlation between the pairs of parameters. A significant correlation between Pb-B and Pb-U was observed when the intensity of Pb exposure (as expressed by Pb-B) was relatively high so that the correlation was significant in all cases studied when Pb-B level was, e.g. 50 μg/l or above. It was also observed that the correlation between Cd-B and Cd-U was significant when Cd-B was, e.g. >1 μg/l. Thus, it is possible to deduce that, in environmental health, Pb-B and Cd-U levels can be estimated on a group basis from Pb-U and Cd-B, respectively, when Pb and Cd exposure levels are relatively high, e.g. with Pb-B and Cd-B of >50 μg/l and >1 μg/l.

Relationship between blood lead level and urinary ALA level in workers exposed to very low levels of lead.

The relationship between blood lead (PbB) level and urinary delta-aminolevulinic acid (ALAU) level was examined in a total of 3,636 lead-exposed workers in a periodic medical examination in 1992, in accordance with the Ordinance on Prevention of Lead Poisoning. The results were consistent with previously reported results in that ALAU level was found to increase with an increase in PbB level above 22.4 micrograms/dl (1.35 as a logarithmic value) and to rise markedly above 35.5 micrograms/dl (1.55). On the contrary, the geometric means of ALAU levels appeared to decrease with an increase in PbB levels within a range between a logarithmic value of 0.15 (1.4 micrograms/dl) and 1.25 (17.8 micrograms/dl). Because the earliest sign of the adverse health effects of lead is reported to occur at a PbB level of of 20 micrograms/dl, the relationship between PbB level and ALAU level was examined at PbB levels below 20 micrograms/dl. A regression formula was obtained, Y (log ALAU (mg/l)) = -0.0570X (log PbB (microgram/dl) + 0.4099. This result indicates that ALAU level decreases with a concomitant increase in PbB level lower than 20 micrograms/dl.

Relationship between delta-aminolevulinic acid dehydratase genotypes and heme precursors in lead workers.

The objective of this study was to investigate the relationships between genotypes of delta-aminolevulinic acid (ALA) dehydratase (ALAD) and disturbances in the heme biosynthetic pathway by lead exposure. The subjects were 192 male lead workers and 125 control subjects. Blood lead concentrations (Pb-B), plasma ALA concentrations (ALA-P), and ALAD genotypes were determined for all subjects. In lead workers, ALAD activity, ALA in urine (ALA-U), and erythrocyte zinc protoporphyrin (ZP) were also determined. The frequency of ALAD2 (minor type of ALAD allele) was calculated to be 0.087 in all subjects. No significant relationship was found between ALAD2 frequency and Pb-B levels in lead workers. ALAD1 homozygotes showed significantly higher levels of ZP and ALA-P in comparison with those of ALAD2 carriers at Pb-B levels more than 20 microg/dL and 40 microg/dL, respectively. ALAD1 homozygotes might be more susceptible than ALAD2 carriers to disturbances in heme metabolism caused by lead exposure.

Impact of lead exposure on pituitary-thyroid axis in humans.

Thyroid function tests (serum levels of thyroxine-T4, triiodothyronine-T3 and thyroid stimulating hormone-TSH) were performed in fifty-eight men (mean age: 31.7 +/- 10.6 years; mean duration of lead exposure: 156.9 +/- 122.7 months). These subjects were exposed to lead either as petrol pump workers or automobile mechanics. The mean whole blood lead (Pb-B) levels were 2.49 +/- 0.45 micromole/l (51.90 +/- 9.40 microg/dl) in the lead exposed workers and were approximately 5 times higher than in the control (n = 35) subjects. No significant alteration was seen in their mean T3 and T4 levels as compared with the controls. Interestingly, T3 was significantly lower with the longer (210 months) exposure time in comparison with the group having shorter (29 months) exposure duration. The mean TSH levels were significantly (p < 0.01) higher in workers exposed in comparison with the control group. This rise in TSH was independent of exposure time, but it was definitely associated with the Pb-B levels. The increase being more pronounced with mean Pb-B levels of 2.66 +/- 0.2 micromole/l (55.4 +/- 4.25 microg/dl) when compared with the group having mean levels of 1.51 +/- 0.30 micromole/l (31.5 +/- 6.20 microg/dl). The rise is TSH associated with Pb-B levels was only statistical valid, however, the levels fall within the normal laboratory range. We thus conclude that the Pb-B levels of > or = 2.4 micromole/l (50 microg/dl) could enhance the pituitary release of TSH without having any significant alterations in the circulating levels of T3 and T4.

The effect of lead on male fertility: a time to pregnancy (TTP) study.

Growing attention has been paid in recent decades to the effects on male reproduction of occupational exposures to toxic agents. There is strong evidence that high level exposure to lead, i. e. blood lead level (PbB) > 70 microg/dl, is associated with male infertility and some reports suggest an effect even at lower PbB (i. e. < 50 microg/dl). The aim of this study is to shed more light on the postulated association between occupational exposure to relatively low levels of inorganic lead and reduced fertility in men estimated by the length of time taken to conceive: time to pregnancy (TTP). A survival analysis of TTP of the last pregnancy was performed adopting the Kaplan Meier methodology. The target population included 782 lead-exposed workers and 165 controls. 251 lead workers and 119 controls were finally eligible and interviewed. Lead-exposed subjects were distributed into four exposure levels according to their blood lead concentration (i.e. < 20; 20-29; 30-39, and >/= 40 microg/dl). The Cox model was adopted to estimate the Relative Risk of unsuccessful waiting time to pregnancy associated to the exposure to lead. A statistically significant difference in fecundability (shorter TTP) in favor of exposed subjects was detected. Nevertheless, longer TTP was associated within the exposed group to higher levels of PbB, even though the gradient is not statistically significant. The exposed workers revealed an average number of children larger than those not exposed, and a clear gradient of the same variable was evident from the lowest to the highest PbB level. Focusing on subjects with one child only, the Cox model confirmed no significant difference in fecundability between exposed and not exposed, whereas a statistically significant longer TTP was associated to the exposure level >/= 40 microg/dl. It is not easy to assert or to deny the effect of inorganic lead on male fecundity, quantitatively estimated by TTP, with the data available for this study. In fact, while the general data seem to exclude effects of Pb on male fecundability a more detailed analysis suggests an unfavorable effect at relatively high levels of exposure but some confounding attributable to personal and social conditions of the workers cannot be ruled out. Further investigations with a better control of confounding are needed.

Blood lead level to induce significant increase in urinary delta-aminolevulinic acid level among lead-exposed workers: a statistical approach.

The present study was initiated to examine the quantitative relationship between blood lead (Pb-B) and urinary delta-aminolevulinic acid (ALA-U) among Pb-exposed workers, and to find a threshold Pb-B level to induce an increase in ALA-U. For this purpose, pairs of venous blood and spot urine samples were collected from 8,274 men and 5,856 women (14,130 workers in total) who were occupationally exposed to inorganic lead. The blood and urine samples were analyzed for Pb-B and ALA-U by atomic absorption spectrometry and colorimetry, respectively, and the correlation between pairs of measures were subjected to statistical analysis. The assumption of the 3rd degree regression for correlation gave a substantially greater correlation coefficient (0.645 for men and 0.619 for women) than 1st or 2nd degree regression, whereas only very small improvement in the coefficient was achieved with 4th to 6th degree ones. Logarithmic conversion of the parameters was not effective in improving the correlation. The assumption of the 3rd degree regression followed by calculation of the local minimum gave 22, 29 and 23 micrograms/100 ml Pb-B for men, women, and men + women, respectively, as the threshold Pb-B to induce ALA-U increase. Pb-B to elevate ALA-U to the 95% upper normal limit (8 mg/l, common to men and women) was 62, 50 and 58 micrograms/100 ml for men, women and men + women, respectively. The validity of the 3rd degree regression assumption as a tool to calculate a threshold from experimental or epidemiological data is discussed.

Zinc protoporphyrin IX concentrations between normal adults and the lead-exposed workers measured by HPLC, spectrofluorometer, and hematofluorometer.

To establish the relationship between Zinc protoporphyrin (ZPP) concentrations and blood lead (PbB) levels and to identify reliable analytical methods of ZPP and Protoporhyrin (PP), blood samples were obtained from 263 office workers without the history of occupational lead exposure and 49 lead-acid battery workers. The mean concentrations of PbB for the normal adults and the battery workers were 9.26 microg/dl and 42.60 microg/dl, respectively. The geometric mean concentrations of ZPP and PP by HPLC were 18.73 microg/dl and 2.27 microg/dl for normal adults and were 46.99 microg/dl and 5.53 microg/dl for the exposed workers, respectively. The geometric mean concentrations of ZPP and PP by a spectrofluorometer (SF) were 30.27 microg/dl and 5.16 microg/dl for normal adults and were 50.91 microg/dl and 6.69 +/- 1.39 microg/dl for the exposed workers. The geometric mean ZPP concentration measured by a hematofluorometer (HF) was 30.88 microg/dl for normal adults. The results showed that ZPP concentrations measured by HF were consistently higher than those by HPLC and SF for normal adults, and lower for the exposed workers. ZPP concentrations were not correlated with PbB levels for normal adults but a statistically significant correlation was found among the exposed workers.

Comparison of blood lead levels in three groups of Sardinian children.

This paper reports blood lead levels in children from three Sardinian municipalities: Portoscuso, Iglesias, and Sestu. Portoscuso, chosen as the control area, is located about 2 km from one of the most important industrial complexes of the island. Iglesias was once an important zinc-lead mining centre. Sestu is a semi-urban centre located about 10 km from Cagliari (the islands's capital), and may be considered unexposed to lead pollution. Blood lead concentration was evaluated in heparinized venous blood samples by graphite furnace atomic absorption spectrophotometry. Children living in Portoscuso show a higher mean of blood lead levels (8.43 micrograms/dl) as compared to that of children of the same age living in Iglesias (6.92 micrograms/dl) and Sestu (5.71 micrograms/dl). By the Bonferroni t-tests procedure these mean differences appear to be statistically significant. The mean of PbB levels obtained in this investigation for children from Portoscuso showed a decrease of 33.62% with respect to that reported in a previous investigation carried out in 1987 (12.7 micrograms/dl).

Blood Lead Concentrations in Marine Mammals Validate Estimates of 102- to 103-fold Increase in Human Blood Lead Concentrations

Measurements of ultra-low ambient blood lead (PbB) concentrations (mean±SD=0.13±0.06 μg/dL) in Northern elephant seals (Mirounga angustirostris) validate previous estimates of ultra-low PbB levels in preindustrial humans. These estimates had been unsubstantiated, since PbB levels in this range had never been measured in any organisms prior to this study. Similarities in PbB levels among these contemporary and preindustrial mammals are consistent with similarities in their measured and estimated lead exposures, respectively. The marginally higher PbB levels and rates of lead exposure in contemporary marine mammals are, also, consistent with lead isotopic composition analyses that indicate their PbB levels have been elevated from exposure to industrial lead. Consequently, these analyses substantiate concerns that current baseline PbB levels in humans, which are estimated to be two to three orders of magnitude above natural levels, may still constitute public health risks.

Normal auditory brainstem and cochlear function in extreme pediatric plumbism

Lead (Pb) intoxication in children has been associated with encephalopathy, sensory and cognitive impairments. We investigated the prevalence and neuro-sensory effects of Pb exposure in children living in Andean villages of Ecuador with high Pb contamination from discarded automobile batteries used in the local ceramics glazing industry. Venous blood samples were collected from 107 children in the Pb glazing area and from 39 children living in a geographically distant area with no known Pb contamination and measured for blood lead (PbB) levels. Auditory brainstem responses (ABR) and audiological/otological tests were conducted on children in the Pb-Glazing Group. The median PbB level for children in the Pb-Glazing Group was 40.0 μg per dl (range: 6.2–128.2 μg per dl) and for the non Pb-Glazing Group 6.0 μg per dl (1.9–18.0 μg per dl). The differences in PbB levels for children in the study and control areas were statistically significant (t-test, P<0.0001). ABR tests on the Pb-Glazing Group indicated normal wave latencies and neural transmission times, and no statistical correlation between PbB level and interpeak latencies. Audiological tests showed normal cochlear function and no statistical relation between auditory thresholds and PbB level. Contrary to prevailing assumptions, elevated PbB levels in children do not invariably impair auditory brainstem neural transmission or sensory-neural cochlear function, both of which have been implicated as significant contributors to the neurodevelopmental disabilities associated with childhood plumbism.

Nicotinamide adenine dinucleotide synthetase activity in erythrocytes as a tool for the biological monitoring of lead exposure.

The objective of this study was to evaluate the usefulness of nicotinamide adenine dinucleotide synthetase (NADS) activity for the biological monitoring of lead exposure. The subjects were 76 male lead workers and 13 normal volunteers (7 males and 6 females). NADS activity and blood lead concentration (Pb-B) was determined in each subject. Delta-aminolevulinic acid dehydratase (ALAD) activity was determined in 58 lead workers out of 76 subjects. NADS activity in the lead workers ranged from 0.08 to 1.1 mumol/h per g of hemoglobin (gHb) and decreased linearly (r = -0.867) as Pb-B increased up to 81.6 micrograms/dl. The pattern of depressed activity of NADS was different from that of ALAD activity, which decreased rapidly and reached a plateau at the Pb-B level between 40 and 60 micrograms/dl. The Pb-B levels inducing 50% inhibition of the enzyme activities were calculated to be 43 micrograms/dl and 20 micrograms/dl for NADS and ALAD, respectively. At the Pb-B level of 40 micrograms/dl, NADS activity showed high validity (1.77) with predictivity of 0.92 at the cut-off level of 0.4 mumol/h per gHb, which were higher than those of ALAD activity. These results show an apparent dose-effect relationship of NADS activity versus Pb-B. NADS activity can be used for the biological monitoring of lead exposure.

EFFECTS ON THE MENTAL AND MOTOR ABILITIES OF CHILDREN EXPOSED TO LOW LEVELS OF LEAD IN BRATISLAVA

A cross-sectional clinical evaluation was performed on 395 children aged 9-10 yr residing in Bratislava, Republic of Slovakia, to examine the potential adverse effects of low lead levels in blood (PbB) on neuromotor and cognitive performance. Eight clinical evaluations comprised of neuromotor (simple reaction time, Vienna, tapping test) and cognitive tests (Benton, Bender, Raven, and WISC1 and 2) were conducted. Whole blood lead levels served as the surrogate for lead body-burden levels. The mean PbB of the study population was 36.5 ug/L (SD-16.2). A statistically significant negative association between PbB and global intelligence (Raven, p &lt;.001) visual short-term memory (Benton, p &lt;.05), and activity evaluations by teachers and parents ( p &lt;.05) was observed in the study population. Eight covariates were included in a multivariate analysis to examine the confounding effects of socioeconomic factors on the PbB-test performance relationship. A highly significant negative association was observed between psychometric intelligence tests (WISC1 and 2, p &lt;.0001) for children residing in the proximity of Slovnaft, a large petrochemical plant in Bratislava. A significant positive association was observed between global intelligence test scores (WISC1 and 2; .01 p &lt;.05) for children receiving parental assistance at home. On the results of psychometric intelligence test (WISC1) scores, a nonsignificant positive association was observed for children whose mother's educational-level was a high school diploma and above, whereas a nonsignificant negative association was observed for children whose mother's education was only up to a primary school level. Although the nature of influence of covariates on PbB-performance relationship was not clear, our investigations revealed that low levels of PbB produce subtle dysfunction in neuromotor and cognitive performance in older children.

Curvilinear relationship between blood lead level and reaction time. Differential association with blood lead fractions derived from exogenous and endogenous sources.

Prior studies demonstrate an inconsistent relationship between occupational inorganic lead exposure and simple reaction time (SRT) performance. In this study, we administered a computerized SRT test to 78 currently employed lead smelter workers and then investigated the relationship between different measures of blood lead and components of SRT performance. The measures of blood lead included current blood lead (PbB) and mathematically derived blood lead fractions from the environment (PbB-env) and from bone (PbB-bn). Measures of SRT performance, obtained from 44 trials with interstimulus intervals (ISIs) ranging from 1 to 10 seconds, included median SRT (SRT-md), mean SRT for ISIs between 1 and 5 seconds (SRT-1-5), and mean SRT for ISIs between 6 and 10 seconds (SRT-6-10). Multiple regression analysis after adjustment for age and education revealed a curvilinear relationship between PbB and SRT-md. As PbB increased from 0 to 30 micrograms dl-1, SRT-md decreased, and only with PbB levels above 30 micrograms dl-1 did SRT-md increase. PbB terms accounted for 13.7% of the variance in this SRT measure (P < 0.01). The longer ISI variable, SRT-6-10, was found to be more strongly related to PbB, to have lesser variability across ISIs, and to be unrelated to age. Additional multiple regression analysis to examine the relationship between components of SRT and the PbB fractions, PbB-env and PbB-bn, showed only PbB-env to account for significant variance in SRT-md, (14.4%, P < 0.01), SRT-1-5 (9.7%, P < 0.03), and SRT-1-6 (15%, P < 0.01). We conclude that the relationship between PbB and SRT is U-shaped, that the SRT measure SRT-6-10 has properties that make it the preferred measure of SRT performance in future studies, and finally that only PbB-env, and not PbB-bn, is related to components of SRT.