Slowed learning in lambs prenatally exposed to lead

Methods to identify and characterize developmental neurotoxicity for human health risk assessment. I: behavioral effects

Alterations in nervous system function after exposure to a developmental neurotoxicant may be identified and characterized using neurobehavioral methods. A number of methods can evaluate alterations in sensory, motor, and cognitive functions in laboratory animals exposed to toxicants during nervous system development. Fundamental issues underlying proper use and interpretation of these methods include a) consideration of the scientific goal in experimental design, b) selection of an appropriate animal model, c) expertise of the investigator, d) adequate statistical analysis, and e) proper data interpretation. Strengths and weaknesses of the assessment methods include sensitivity, selectivity, practicality, and variability. Research could improve current behavioral methods by providing a better understanding of the relationship between alterations in motor function and changes in the underlying structure of these systems. Research is also needed to develop simple and sensitive assays for use in screening assessments of sensory and cognitive function. Assessment methods are being developed to examine other nervous system functions, including social behavior, autonomic processes, and biologic rhythms. Social behaviors are modified by many classes of developmental neurotoxicants and hormonally active compounds that may act either through neuroendocrine mechanisms or by directly influencing brain morphology or neurochemistry. Autonomic and thermoregulatory functions have been the province of physiologists and neurobiologists rather than toxicologists, but this may change as developmental neurotoxicology progresses and toxicologists apply techniques developed by other disciplines to examine changes in function after toxicant exposure.

Enduring effects of early lead exposure: evidence for a specific deficit in associative ability

Long-Evans dams were exposed to Pb acetate in the drinking water during both gestation and lactation, or lactation only. This report presents the results of an automated, olfactory, serial reversal task administered to the adult offspring. Although overall learning rate was not significantly affected by Pb exposure, analyses of specific phases of the learning process revealed that all three exposed groups required significantly more trials than controls to reach criterion from the point at which perseverative responding to the previously correct cue ended. These in-depth analyses revealed that the reversal learning impairment of the Pb-exposed animals was not due to a deficit in inhibiting responses to the previously correct cue, the mechanism commonly assumed to underlie impaired reversal learning. Instead, the analyses revealed that two other independent Pb effects were responsible for the prolonged postperseverative learning period: a response bias and an impaired ability to associate cues and/or actions with affective consequences. The contribution of these two factors varied as a function of the timing and intensity of the Pb exposure. It is hypothesized that the Pb-induced associative deficit may reflect lasting damage to the amygdala and/or nucleus accumbens, which comprise a system thought to modulate the process by which environmental cues acquire affective significance.

In utero lead exposure in squirrel monkeys: motor effects seen with schedule-controlled behavior

Timed-pregnant squirrel monkeys were exposed orally to lead during the last 1/2 to 2/3 of gestation such that maternal lead levels ranged from 21 to 70 micrograms/dl in blood. Offspring of these lead-exposed monkeys were compared to gender-matched, untreated controls (blood-lead levels from 4 to 9 micrograms/dl), born at about the same time. When the monkeys were 3 to 7 years old they were trained to pull a T-shaped bar against 1 kg spring through a displacement of 1 cm. This performance was examined during acquisition of different fixed-ratio (1, 5, and 20) and fixed-interval (120", 300", and 600") schedules of reinforcement and during steady state under the fixed-ratio 5 and fixed-interval 600". Monkeys exposed prenatally to lead showed an increased number of responses failing to meet the requirement of pulling against 1 kg spring through a 1 cm displacement when behavior was maintained by a fixed-ratio schedule, which engenders a vigorous, high-rate pattern of responding. This increased number of incomplete responses first appeared in the acquisition of a fixed-ratio 5 and fixed-ratio 20 schedules of reinforcement, remained after the fixed-ratio 5 schedule was allowed to reach steady state, and did not appear under the fixed-interval schedule. Neither body weight not response rate were affected by lead, but it was necessary to control for these variables using multiple regression to isolate lead's effect. The appearance of incomplete responses while the monkeys pulled vigorously against a 1 kg spring suggests that lead exposure during gestation produced subtle motor impairments years after exposure has ended. Deficits in the acquisition of behavior (learning) under Concurrent Random Interval schedules of reinforcement have also been reported with these monkeys. Together, these reports reveal prolonged deficits in learning and motor function resulting from in utero exposure to lead at maternal blood lead levels (21-70 micrograms/dl) that could result from exposure to ambient air in heavily polluted urban environments or in occupational settings meeting current World Health Organization standards.

Physiological and toxicological changes in the skin resulting from the action and interaction of metal ions

The human environment contains more than 50 metal or metalloid elements. At least 15 are recognized as trace elements, with zinc, calcium, copper, magnesium, and iron having specific roles in skin morphogenesis and function. The present review focuses on the presumed role of metal ions in the skin, their competition for carrier proteins, and membrane receptors. Evidence presented shows that the balance of trace metal ions is critical for normal skin and repair mechanisms following injury. Xenobiotic ions can impair this balance, leading to pathological change. The skin acts as an organ of elimination of excess trace metals and xenobiotic ions from the body, but mechanisms of voidance vary for different metals. Metal ions are an important cause of allergies, and evidence is presented to show that the majority of metals or metal compounds can induce allergic changes. Except for chromium and nickel, which are among the most common human allergens, animal models have provided little information. At least cadmium, thorium, lead, chromium, nickel, beryllium, and arsenic and proven or putative carcinogens in animals or humans on the basis of cytological or epidemiological evidence. However, only arsenic exhibits a clear predilection for the skin. Other metals such as gold can induce subcutaneous sarcoma following injection, but the relevance of this observation in terms of human occupational risk is discounted.

A new operant discrimination test procedure for resident rats

An automated method for testing visual discrimination with water reinforcement using a modified residential Y-maze is described. The visual stimulus is presented above one of two water holes. Rats have been tested with different lengths of water periods and different intervals between the periods. During the 10 days of testing, overall activity decreased. Activity on the initial days was low during daytime, with few drinking attempts. Discrimination learning acquisition was measured as the increase in the percentage of water periods with drinking attempts in which the first attempt occurred on the correct side, and/or as the increase in the number of correct drinking attempts as a percentage of all drinking attempts. Acquisition was observed both when light indicated water and when it indicated no water. This test model may offer a useful method for standardized measurement of left/right, light on/off discriminations.

The comparative developmental neurotoxicity of lead in humans and animals

The effects of lead on neurobehavioral development have been extensively investigated in humans as well as animals. This valuable lode of research findings offers a basis for comparing the developmental neurobehavioral toxicity of lead across species and for assessing the validity of animal models of developmental neurotoxicity. Comparisons of human and animal findings suggest that the greatest qualitative similarities involve relatively complex behavioral processes such as cognition and learning. Quantitative comparisons based on dose-response relationships for these endpoints are difficult to make because the relationships are sometimes nonmonotonic (U-shaped) and because blood lead levels may not be directly comparable between species. However, the lowest levels of exposure at which developmental neurobehavioral effects have been observed are similar: 10-15 micrograms/dl in children, less than 15 micrograms/dl in primates, and less than 20 micrograms/dl in rodents. Although the convergence between animal and human findings for other neurobehavioral endpoints is not as striking, sensory-evoked potentials and communicative processes offer two promising areas for continued investigation and cross-species comparison.

Lead concentrations in maternal and cord blood in women users of surma eye cosmetics

A prospective study was undertaken to analyse the lead concentrations in maternal and cord blood of 71 pregnant Arab women at term who used eye cosmetics, particularly "surma". A total of 64 mothers (90%) used eye cosmetics throughout pregnancy, and, of these, 45% used surma. The lead content of the cosmetics available in the market was found to vary between zero and 88%. The mean lead concentrations in all blood samples were higher than the accepted natural levels of 0.001 mumol/l, but lower than the subtoxic level of 1.9 mumol/l. The mean lead concentration of all samples was lower than the subtoxic level of 1.9 mumol/l but higher than that quoted in the literature and suggested to be a natural level (0.001 mumol/l). This indicates that other lead pollutants may be involved. Lead concentrations in maternal and cord blood correlated well, but did not show any significant difference between surma and non-surma users. None of the newborns showed apparent congenital anomalies and their birthweights were comparable to average Saudi birthweights.

Potential human developmental toxicants and the role of animal testing in their identification and characterization

Some 50 chemicals have been identified from environmental, occupational, or therapeutic exposure data as being potential developmental toxicants in humans. The toxicity pattern of these chemicals in humans has been characterized and correlated with developmental toxicity end points in laboratory animal models in order to determine the relevance and predictiveness of the results of testing in animals in extrapolation to human data. In general, animal developmental toxicity data closely paralleled human outcomes, and while humans in most cases were more sensitive than animals, the data support the concept that, imperfections aside, studies in animals serve a vital role in the hazard identification process.

Lead retention in blood and brain after preweaning low-level lead exposure in the rat

Newborn rats of the albino Wistar strain were exposed to lead from birth to 20 days of age through mothers milk, from dams which were fed diets containing 0, 0.25, 0.5 or 1.0% powdered lead. Subsequent determination of tissue lead revealed a direct relationship between the lead levels in both blood and brain of the pups and the lead dosage to which they were indirectly exposed via the dams' milk. Lead retention in both tissues was still evident at 100 days of age, with the relative elevation of lead levels being an order of magnitude higher in brain than in blood. There were no obvious signs of lead intoxication in the pups, apart from mild growth retardation in the group with the highest lead burden. However there was a significant retardation in behavioral development observed on two of four measures which were employed. It was concluded that brief exposure to low lead levels in infancy can have long lasting consequences in the brain and in behavior.

Chronic low-lead exposure from birth produces deficits in discrimination reversal in monkeys

Cynomolgus monkeys (Macaca fascicularis) were dosed from birth with 100, 50, or 0 micrograms/kg/day of lead. This protocol resulted in blood lead concentrations of 25, 15, or 3 micrograms/dl, respectively, before withdrawal of infant formula at 200 days of age. Blood lead concentration declined thereafter over the next 100 to 150 days to steady-state levels of 13, 11, or 3 micrograms/dl. At approximately 3 years of age, monkeys were tested on a series of three discrimination reversal tasks: nonspatial form discrimination, nonspatial color discrimination with irrelevant form cues, and nonspatial form discrimination with irrelevant color cues. The higher dose group was impaired relative to controls over the entire experiment (all three tasks combined), the two form discrimination tasks combined, and the form discrimination with no irrelevant cues. Deficits were most marked over the first several reversals. The lower dose group was impaired on the color discrimination task and on the last several reversals of all tasks combined. In addition, the higher dose group was impaired relative to the lower dose group over the entire experiment.

Low level lead effects on activity under varying stress conditions in the developing rat

The study was designed to determine whether lead ingestion by nursing rats would affect the way offspring reacted to the stress inducing properties of the test environment both as juveniles and mature rats. Dams were exposed to diets with 0.0, 0.2, 0.4 or 1.0 percent by weight metallic lead. Mean blood-lead levels of pups at weaning were 4, 25, 36 and 55 micrograms/100 ml of blood respectively. The stress factor was varied by (1) changing the test apparatus, i.e., forcing rats to occupy an open field or allowing the animal to be a free agent in the start box of a T-maze; (2) testing rats under a longitudinal and a cross-sectional experimental design to vary familiarity with the apparatus; and (3) comparing behavior in the presence or absence of noise. Reactivity was assessed by examining the inter-and intra-session pattern of ambulations and defecations. Analysis of data revealed that lead treated rats demonstrated the greater response to stress. This response was generally dose related although recovery was dependent upon the test applied and measures taken. The findings provide a conceptual framework to account for varied results across previous studies.

Effects of low lead exposure on neuro-behavioral function in the rat

Small doses (45-180 micrograms/g) of lead acetate were administered to male rats by gavage every day during the first 3 wk of life. A blood concentration of approximately 59 micrograms/100 ml blood produced signs of disturbances in reflex development and some changes in emotional behavior. Larger doses resulted in subtle changes in the neuromotor coordination function. The effect of low levels of lead exposure on the cognitive function in operant conditioning could not clearly be observed. Brain lead concentration tended to be higher than in other tissues examined. At approximately 10 months following cessation of lead acetate administration, the brain lead concentration had decreased to almost the same level found in control rats, and no distinguishable differences were observed between the lead-treated rats and controls in emotional behavior and neuromotor coordination.

Neuropsychological studies in children with elevated tooth-lead concentrations. I. Pilot study

In contrast to blood-lead (PbB), tooth-lead concentrations (PbT) provide retrospective information about longterm, cumulative childhood lead-intake. From a basic sample of 458 school age children from the city of Duisburg (FRG), whose lead-concentrations in shed incisor teeth had been measured (means = 4.6 ppm; range: 1.4-12.7 ppm), two extreme-groups of 26 children each (mean age: 8.5 years) with low (means = 2.4 ppm) and elevated (means = 9.2 ppm) PbT were selected. After pair-matching both groups for age, sex, and father's occupational status, these children were tested under double-blind precautions for intellectual performance (German WISC), for perceptual-motor integration (Göttinger Formreproduktionstest = GFT, Diagnostikum für Cerebralschädigung = DCS, Benton-Test), and for gross motor-coordination (Körper-Koordinationstest für Kinder = KTK). Significant (P less than 0.05) inferiority of the lead-children was found in two tests of perceptual-motor integration (increased GFT-errors; lower success rate for DCS). In addition a near significant (P less than 0.1) reduction of 5-7 IQ-points was determined in these children. Although this pilot study has provided some evidence for an association between childhood lead-exposure and neuropsychological impairment, this association cannot yet be considered proven, because the observed effects were discrete and statistically confirmed only in part, and because there was a slight prevalence of perinatal risk factors in the lead group. Further research to clarify the issue is necessary.

Task dependent neurobehavioral effects of lead in rats

In order to test neurobehavioral effects of low-level lead exposure during early development, Wistar-rats were given pre- and postnatal dietary lead as lead acetate in four concentrations: 0, 80, 250, and 750 ppm. These diets, known to give rise to blood lead-levels (PbB) of less than 5, 11, 18, and 31 micrograms/dl, resulted in erythrocyte ALAD-inhibition of 40, 73, and 83%, respectively. The animals were tested first at 70 to 100 days postnatal (PN 70-100) in a 2-way active avoidance-task, and then at PN 190-250 in a visual discrimination-task. Lead-exposure was associated with performance-disruption in the discrimination-task, significant (p less than 0.001) already for the 250 ppm-exposure, but with significant (p less than 0.05) performance-facilitation in the avoidance-task. If learning and retention in animals is taken as a measure of cognitive performance neurobehavioral lead-toxicity cannot easily be explained in terms of cognitive deficit. An interpretation in terms of emotional reactivity or behavioral disinhibition would seem more convincing, which covers the results from activity-studies as well. 70% ALAD-inhibition corresponds to PbBs of about 20 micrograms/dl in rats, and to about 40 micrograms/dl in children. Some implications of animal studies for neuropsychological results from Pb-exposed children are discussed.

Changes in operant behavior of rats exposed to lead at the accepted no-effect level

After weaning, male and female Wistar rats were fed a daily diet containing 1 g lead acetate/kg food until a level of about 20 micrograms/100 mL blood was obtained. The male rats were subjected to the different behavioral tests, whereas the females were mated to untreated males and further exposed until weaning of the offspring. Behavioral testing of the male offspring was performed between 3 and 4 months of age. General behavior of both groups was tested in the open-field task including locomotion, local movements, and emotionality. The conditioned instrumental behavior was tested in the Skinner box from simple to more complex programs. The blood-lead level was measured by flameless atomic absorption spectrometry. No behavioral changes became apparent in the open-field task and in the preliminary operant training. In the more complex programs (DRH = Differential Reinforcement of High Rates), the rats exposed to lead after weaning showed slight changes of DRH performance. By contrast, in pre- and neonatally exposed animals, DRH performance was significantly increased, although blood-lead levels had returned to normal at the time of testing. A comparison of lead effects in animals to possible effects in man is discussed in this paper, and it is concluded that lead exposure to man at doses which presently are suggested to be innocuous may result in subclinical functional changes of the central nervous system.

Is low-level lead pollution dangerous?

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Environmental pollution and pregnancy: risks and uncertainties for the fetus and infant

Numerous environmental contaminants can affect the developing embryo, fetus, or infant. This essay explores such questions as these: What is the importance in mutagenesis and teratogenesis of macroenvironmental pollutants such as the heavy metals, dioxin derivatives, polychlorinated diphenyl compounds, and pesticides? What is the significance of microenvironmental pollutants (or social environmental factors) such as tobacco smoke, alcohol, and pharmacologic agents over which exposed individuals have considerable control? What are some of the ethical and legal implications of these toxins of which clinicians should be aware?

Effects of lead, cadmium and mercury on brain adenylate cyclase

The effects of lead, cadmium and mercury ions on adenylate cyclase activity of rat cerebrum, cerebellum and brain stem were studied in vitro and in vivo. Adenylate cyclase activity in homogenates of cerebellum as well as cerebrum and brain stem was found to be inhibited by micromolar concentrations of these heavy metal ions in vitro. Administration of lead acetate trihydrate (25 mg/kg body wt i.v.) produced an initial increase of adenylate cyclase activity in the cerebellum and brain stem 1 h after injection, followed by a significant decrease of enzyme activity in cerebrum and cerebellum 4 h after the injection. Chronic lead treatment achieved by feeding lead containing diets, which generated blood lead levels of 31.3 +/- 3.8, 68.8 +/- 1.5 and 121.5 +/- 8.6 microgram Pb/100 g blood resp., produced a significant increase of brain lead levels and a 10-30% reduction of adenylate cyclase activity in cerebrum, cerebellum and brain stem. Phosphodiesterase activity was reduced under these conditions in the range of 10-20% in cerebellum and brain stem, but not in cerebrum.

Effects of low levels of lead exposure on cognitive function--a review

The relationship between low levels of lead and cognitive functioning in animals is reviewed. The data suggest that within animals lead can produce a massive disruption of learning ability while not affecting either morbidity or mortality. Concentration of lead appears to insidiously cause damage to learning function where extremely low doses disrupt the hard-to-measure higher levels of cognitive function. It is concluded that the current standards of lead concentration should be reappraised in terms of measures of damage to cognitive learning.

Influence of prenatal and postnatal lead exposure on discrimination learning in rats

The animals in this study were the offspring of dams, who, from 21-99 days of age, were exposed to 1000 mg/kg of lead acetate via a daily restricted watering schedule with exposure continuing throughout gestation and nursing. Control dams received distilled water under the same watering schedule. Offspring were weaned at 21 days of age and did not received lead treatment from that point. Testing began at 30 days of age with animals receiving 10 trials/day for 10 days on a brightness discrimination task conducted in a water-escape T-maze. This task was followed by a shape discrimination problem in the same apparatus. Analysis of results revealed that the lead-exposed pups made significantly more errors than the controls but had significantly shorter swimming times on both the brightness and shape discrimination tasks. The failure to attend to relevant discriminative cues may account for the observed deficits in lead-exposed animals.

The influence of oral penicillamine and diet on lead poisoning in rats

In spite of continued lead intake, the oral chelate d-penicillamine was effective in reducing blood lead levels of lead-poisoned weanling rats on three different low-residue diets: a standard rat diet, a low calcium diet, and the trace metal salt modified EPA diet. A significant lessening of weight gain was evident in those on the low calcium diet.

Neurobehavioral and systemic effects of longterm blood lead-elevation in rats. I. Discrimination learning and open field-behavior

In order to assess neurobehavioral deficit subsequent to early low-level lead-exposure, Wistar-rats were prenatally Pb-exposed via their mothers, neonatally via their dams' milk, and later on via their diet containing lead acetate (745 mg Pb/kg diet). Blood-lead levels (PbB) of dams increased from 24.2-31.2 microgram-% during pregnancy and suckling-periods, those of offsprings were 26.6 microgram-% at about 16 days of age and 28.5 microgram-% at about 190 days of age. Between 100 and 200 days of age 40 male offsprings were subjected to behavioral testing, namely an open field-test and a visual discrimination-learning task. Two learning-tasks of different complexity, i.e. orientation- and size-discrimination, were used. Data of 20 lead-treated animals were compared with those of 20 age-matched controls. In the open-field test lead-fed animals were significantly more restless than controls; an increase of ambulation, rearing and grooming was observed. In the difficult learning-task, i.e. size discrimination, only the controls did learn the problem, whereas only one of the lead-group did; there was, however, no difference between lead- and control-animals for the easy task, i.e. orientation-discrimination. The observed effects, namely overreaction in the open field and a deficit of visual discrimination learning, may be interpreted in terms of lead-induced CNS-dysfunction. They clearly suggest that the "no-response level" for neurobehavioral damage in the rat, subsequent to early lead-exposure, must be assumed to be lower than 35 microgram/100 ml.

Heavy metal pollution among autoworkers. I. Lead

Lead pollution was evaluated in 216 individuals working in 10 garages on the Island of Funen, Denmark and related to data from biochemical and medical examinations. Clinical symptoms were recorded by means of a questionnaire. Increased blood test lead levels were foun in 59% with 9% having above 80 microgram lead/100 ml (3-86mumol/1) whole blood. Mechanics in eight out of ten garages had significantly increased blood lead levels. A decrease in delta-aminolevulinic acid dehydratase (ALAD) activity was associated with increased blood lead levels but the latter were not related to haematological changes, tobacco consumption or to length of service in the trade. Particulate lead air pollution was not the sole cause of increased blood lead levels. Raised lead values were maximal among diesel engine workers who are exposed to high pressure-resistant lubricants containing lead naphthenate. As these workers complained of skin damage, lead absorption may have occurred through the skin. Assay of lead content showed 9290 ppm in gear oil and 1500-3500 ppm in used motor oils. The data are discussed in relation to the occupational risks in auto repair shops.

Behavioral effects of low level neonatal lead exposure

Rats exposed to lead via maternal milk were tested at various stages of development on a number of behavioral tasks. Beginning at paturition, the dams were given either tap water, 0.02%, or 0.10% lead acetate in the drinking water. Pups from all three groups were weaned to normal chow and tap water at 21 days of age. The mean lead concentration of the dam's blood and of neonatal (20 days of age) brain and blood were all below 50 microgram/100 ml. No significant differences were found between the high lead-exposed group and controls in general as measured by wheel running over a 21 day period beginning at 30 days of age. However, there was a significant difference in wheel running behavior during the first three hr of testing. Both lead-exposed groups were found to display significantly less aggressive behavior as measured by the shock-elicited aggression test. Low level lead exposure had no discernable effect on the acquisition and subsequent reversal of a successive brightness discrimination task. Lead exposure under these conditions appears to affect some aspects of emotional behavior, while having little effect on general activity or cognitive function.

Scotopic vision deficits in young monkeys exposed to lead

Rhesus monkeys were reared on diets designed to produce blood lead concentrations of 14 (untreated), 55, or 85 micrograms per 100 milliliters for the first year of life. Eighteen months later, blood lead levels were normal in all animals. At this time, however, visual discrimination performance in the 85-microgram group was impaired under dim light relative both to their own performance under bright light and to the performance of the other groups under all light levels used. We interpret these results to reflect a deleterious, enduring impairment of scotopic visual function (night blindness) as a result of early lead intoxication.

Impact of air pollution by lead on the heme biosynthetic pathway in school-age children

Blood-lead level (Pb-B), erythrocyte delta-aminolevulinic acid dehydratase (ALAD) activity, free erythrocyte porphyrin (FEP) concentration, delta-aminolevulinic acid concentration in urine (ALAU), hematocrit value, and hemoglobin concentration were compared for groups of children 10-13 years old from areas differently polluted by lead (rural area and lead smelter area). The biological responses of the children were also compared with those observed in adults similarly exposed to lead (Pb-B: 10-40 mug/100 ml). Compared with the rural children, children living less than 1 km from the smelter exhibited a significant increase of Pb-B and FEP, a significant inhibition of ALAD, and a slight positive correlation of ALAU with Pb-B; however, they showed no biological signs of anemia. In children living approximately 1.5 km from the smelter, there was still a significant increase of Pb-B and a concomitant inhibition of ALAD, but no change in FEP concentration. Comparison of the dose-response curves between Pb-B and FEP in adult males, adult females, and children indicates that the sensitivity to lead is in the order of children larger than or equal to women greater than men. Based on the FEP response, it is proposed that 25 mug Pb/100 ml blood be regarded as the maximum biologically allowable concentration of lead in blood of school-age children.

Behavioral effects of chronic lead ingestion on laboratory rats

Rats continuously exposed to lead acetate solutions were tested on a visual discrimination reversal problem, on the open field and in 2 shuttle avoidance situations. High lead intake produced slower acquisition of the visual discrimination problem but had no effect on reversal performance. High lead intake reduced activity on the open field and improved performance on both shuttle avoidance problems. Results are interpreted to indicate that the effects produced by exposure to lead may involve an increase in responsiveness to aversive situations.

Heavy metal levels and delta-amino-levulinic acid dehydrase levels in peripheral polyneuropathy

On the basis of assay of heavy metals in whole blood (lead, cadimum, chromium, copper, nickel and manganese) and delta-amino-levulinic-acid dehydrase (ALA-D) and ALA in urine in a normal Danish population, the levels of these clinco-chemical factors were assayed in 23 patients with peripheral neuropathy of unknown etiology. All patients studied showed electro-physiological sign of denervation and/or reduced motor or sensoric nerve conduction velocity. Cadmium and manganese were never found to be increased. In all but four patients, an increase of one or more heavy metals was found. Ten patients showed raised levels of two or more metals, the dominant metal being lead (10 cases), nine patients showed increased in chromium. A significant corrleation was found between increasing lead levels and decreasing ALA-D activity. Although normal concentrations of manganese were found, correlation analysis revealed a significant correlation between increased manganese and decreased ALA-D. The raised values of heavy metals could not be traced to occupational or other exposure to heavy metals and the increased values were not related to tobacco consumption. The findings are discussed in relation to known data on neuropathy and the results seem to indicate a multifactorial patholgenesis of the disease. Among factors contributing to the precipitation of the syndrome may be raised levels of heavy metals.

Neuropsychological dysfunction in children with chronic low-level lead absorption

To investigate the relation between low-level absorption and neuropsychological function, blind evaluations were under-taken in forty-six symptom-free children aged 3-15 years with blood-lead concentrations of 40-68 mug. per 100 ml. (mean 48 mug. per 100 ml.) and in seventy-eight ethnically and socioeconomically similar controls with levels greater than mug. per 100 ml. (mean 27 mug. per (100 ml). All children lived within 6-6 km. of a large, lead-emitting smelter, and in many cases residence there had been lifelong. Mean age in the lead group was 8-3 years and in the controls 9-3. Testing with Wechsler intelligence scales for schoolchildren and preschool children (W.I.S.C. and W.P.P.S.I.) showed age-adjusted performance I.Q. to be significantly decreased in the group with higher lead levels (mean scores, W.I.S.C. plus W.P.P.S.I., 95 v. 103). Children in all ages in the lead group also had significant slowing in a finger-wrist tapping test. Full-scale I.Q., verbal I.Q., BEHAVIOUR, AND HYPERACTIVITY RATINGS DID NOT DIFFER.

Role of chronic low-level lead exposure in the aetiology of mental retardation

Water-lead levels were measured in the homes occupied during the first year of life by 77 mentally retarded children aged two to six years and 77 non-retarded matched controls, and in the homes occupied by their mothers during pregnancy. The water-lead content was significantly higher in the retarded group, and the probability of mental retardation was significantly increased when water lead exceeded 800 mug. per litre. Blood-lead levels were also significantly higher in the retarded group. It is concluded that lead contamination of water may be one factor in the multifactorial aetiology of mental retardation and that every effort should be made to reduce the lead content of drinking-water.