Review of adverse health effects of odours in field studies.

UNLABELLED: Exposure to environmental odours from industrial and agricultural premises, in addition to inducing annoyance responses in a dose-dependent manner, have been shown to be either directly associated with gastric symptoms as well as general health-related complaints under extreme exposure conditions, or indirectly mediated through odour annoyance under moderate odour exposure conditions. OBJECTIVE: In order to examine the influence of hedonic tone (pleasantness-unpleasantness) and perceived odour strength (intensity) on symptom reporting the results of two pertinent field studies were analysed. METHODS: In the vicinity of six industrial plants (sweets, rusk, textile, seed-oil, fat, cast iron) and eleven livestock operations (poultry, pig, cattle) assessment of odour exposure was done by means of systematic field inspections. Effect assessment was done by means of direct interviews (industrial: N=1456, agricultural: N=1053) using questionnaires covering odour annoyance, symptom reporting and relevant covariates. DATA ANALYSIS: Multiple logistic regression analysis was used to establish dose-response associations between odour frequency, intensity and hedonic tone as independent variables and symptom reporting as dependent variable. RESULTS: Exposure-symptom associations are strongly influenced by hedonic tone, whereas intensity has no additional predictive value. Adding odour annoyance to the regression model shows that symptom reporting is exclusively mediated by annoyance.

Acute behavioral effects of exposure to some organic solvents -psychophysiological aspects.

Acute low-level exposure to organic solvent vapours may result in prenarcotic states of CNS-depression, often characterized by behavioral dysfunction. Behavioral findings from experimental acute human exposures to toluene, trichloroethylene (TCE), and methylene chloride (MC) are covered in this review. Perceptual measures (e.g. critical flicker fusion = CFF), measures of sustained attention (vigilance), measures of psychomotor performance (as e.g. reaction time, motor speed, coordination) as well as EEG-measures (sensory evoked potentials) are used to illustrate the main effects from such studies. Progressive increase of reaction time was observed at toluene-exposures of only 300 ppm (30 minutes). No consistent behavioral deficit has been reported for trichloroethylene below 300 ppm; instead, visual and auditory evoked potentials were found to be affected at TCE vapour-concentrations between 50 and 100 ppm (3 1/2 - 7 1/2 hours of exposure). CFF-depression, vigilance-decrement and disruption of psychomotor performance has been observed during MC-exposure (200 - 800 ppm; 2-4 hours). Although such behavioral effects are usually considered reversible and of no demonstrated pathological impact, they may nevertheless contribute to accident-prone behavior in occupational settings.

Effects of lead on neurophysiological and performance measures: animal and human data.

This paper reports lead-induced changes in neuropsychological measures and behavioral performance measures in monkeys and children. Monkeys were pre- and postnatally exposed to lead via the diet. Blood lead levels at the time of testing were 9.3, 40.3, and 55.7 micrograms/dL in controls, and animals exposed to 350 ppm or 600 ppm lead acetate, respectively. Flash-evoked and brainstem auditory-evoked potentials were recorded in adult animals. Results indicate latency increases in both measures as well as amplitude decreases in the flash-evoked response. Delayed reaction time and serial choice reaction were determined as measures of behavioral performance in lead-exposed school-age children from two lead smelter areas. In addition, pattern-reversal-evoked potentials and nerve conduction velocity were investigated. Neither nerve conduction velocity nor latency of the pattern-reversal-evoked potential were consistently influenced by lead. Of the behavioral measures, serial choice reaction performance revealed a consistent lead-related deficit, which became more pronounced with increasing task difficulty.

Characterization of potential endocrine-related health effects at low-dose levels of exposure to PCBs.

This article addresses issues related to the characterization of endocrine-related health effects resulting from low-level exposures to polychlorinated biphenyls (PCBs). It is not intended to be a comprehensive review of the literature but reflects workshop discussions. "The Characterizing the Effects of Endocrine Disruptors on Human Health at Environmental Exposure Levels," workshop provided a forum to discuss the methods and data needed to improve risk assessments of endocrine disruptors. This article contains an overview of endocrine-related (estrogen and thyroid system) interactions and other low-dose effects of PCBs. The data set on endocrine effects includes results obtained from mechanistic methods/ and models (receptor based, metabolism based, and transport protein based), as well as from (italic)in vivo(/italic) models, including studies with experimental animals and wildlife species. Other low-dose effects induced by PCBs, such as neurodevelopmental and reproductive effects and endocrine-sensitive tumors, have been evaluated with respect to a possible causative linkage with PCB-induced alterations in endocrine systems. In addition, studies of low-dose exposure and effects in human populations are presented and critically evaluated. A list of conclusions and recommendations is included.

Structure and determinants of psychophysiological response to odorant/irritant air pollution.

From a psychophysiological point of view, acute effects of indoor air pollution with odorant/irritant properties can be evaluated in terms of sensory/perceptual factors, in terms of objective eye/mucous membrane irritation or systemic responses of the orienting reflex, as well as in terms of either specific or systemic psychological responses. Formaldehyde and hydrogen sulfide are used to illustrate sensory evaluation in terms of detection (absolute thresholds), suprathreshold intensity, and hedonic tone. Dose-response contingencies are exemplified for ETS-induced eye irritation in terms of eyeblinks and lacrymal flow. Orienting responses to odorant stimuli are illustrated using peripheral vasoconstriction and pupil dilation as outcome measures. Specific (descriptive statements and symptoms) as well as systemic psychological responses (annoyance) exhibited clear-cut dose-response association in chamber studies using ETS and hydrogen sulfide exposures. It is, furthermore, shown that environmental annoyance to different environmental stressors exhibits both trait and state characteristics, and that age, perceived health, and (to a smaller degree) gender moderate the response. Based on this information proposals for research needs are given.

Reduced levels of 1,25-dihydroxyvitamin D(3) in rat dams and offspring after exposure to a reconstituted PCB mixture.

Previous studies revealed effects of polychlorinated biphenyls (PCBs) and other polyhalogenated hydrocarbons on steroid hormone levels and hormone-dependent functions including behavior. In the present study serum concentrations of the vitamin D(3) metabolites 25-hydroxycholecalciferol (25-D) and 1,25-dihydroxycholecalciferol (1,25-D) were determined in rat dams and offspring after exposure to a PCB mixture that was reconstituted according to the congener pattern found in human breast milk. Unmated females were exposed to diets adulterated with 0; 5; 20; or 40 mg PCBs/kg diet. Exposure started 50 days prior to mating and was terminated at birth. Gestational exposure reduced serum concentrations of 1,25-D in dams in a dose-dependent manner. Concentration of 25-D was also decreased at the time of delivery, but not at weaning. Determination of 1,25-D in offspring at weaning revealed reductions in both high-exposure groups. Levels of 25-D were diminished only at the highest exposure level. Internal PCB concentrations in adipose tissue and brains exhibited a linear relation to dosages in diet. Concentrations of PCBs in brains were similar in dams and offspring at birth, but decreased at the end of lactation in dams. In offspring, values increased during this period because of continued exposure via the milk. In the adipose tissue, PCB levels were much lower in offspring than in dams. To our knowledge, this is the first report of PCB-induced effects on vitamin D(3) metabolites. In dams, reductions were seen even at the lowest exposure level used. Further studies are needed to evaluate the biological significance of these reductions in pregnant dams and possible consequences for the developing offspring.

Chronic prenatal and postnatal Pb2+ exposure increases [3H]MK801 binding sites in adult rat forebrain.

We have measured the binding of [3H]MK801 to the N-methyl-D-aspartate (NMDA) receptor-ion channel in membrane preparations from adult rat forebrain exposed to lead (Pb2+) during gestation, lactation, and postweaning. Our results indicate a 30.9% increase in the number of [3H]MK801 binding sites in Pb2+ exposed animals relative to controls. No significant changes in the affinity constant were observed. The level of blood Pb2+ for which such changes were measured was 13.9 +/- 2.8 micrograms/dl. These results indicate that alterations in the NMDA receptor-ion channel complex are present at blood Pb2+ levels which are environmentally relevant and suggest that chronic Pb2+ exposure during development can influence the NMDA receptor complex in the adult rat brain.

The effects of lead in laboratory animals and environmentally-exposed children.

Consistent association has been found in 4 independent studies between disruption of visual-motor integration and reaction performance and markers of lead exposure (blood, teeth) in children, but not for intelligence deficit; blood-lead levels were typically below 30 micrograms/dl in these children. In order to demonstrate the persistent nature of Pb-induced neurobehavioral deficit experimentally rats were studied after cessation of dietary Pb-exposure in a variety of behavioral tasks. Persistent retention-deficit was found for visual discrimination-learning and for radical arm-maze performance.

Cross species extrapolation in neurotoxicology: neurophysiological and neurobehavioral aspects.

The theory of phylogenetic continuity of animal species is the basis of any comparative or extrapolative endeavour (Calabrese, 1983). Cross species extrapolation is also a prerequisite for hazard identification in general and developmental neurotoxicology. Two steps must be distinguished: The first step is endpoint-based or qualitative, whereas the second is dose-based or quantitative. Comparison of different species, typically rodents, nonhuman primates and humans, in terms of endpoints is preferentially done within a framework of broad functional categories, such as sensory, motivational, cognitive, motor, and social variables. Within each category specific neurobehavioral as well as electrophysiological measures need to be considered; typically the degree of comparability is higher for electrophysiological than for most behavioral measures. For some frequently used behavioral endpoints in human neurotoxicology, such as psychometric IQ, there is no direct animal counterpart. Once the neural substrate of a particular neurotoxic effect has been identified, as is true for several chemicals such as the pyrethroid insecticides, the organophosphates, most nerve gases or MPTP, or if interspecies comparability in terms of endpoints has proven satisfactory, an effort towards quantitative, dose-based extrapolation is needed. Here species-specific differences in toxicokinetics and metabolism must be taken into consideration in order to arrive at valid translations of dose-response contingencies. If at all possible internal rather than external doses should serve as the frame of reference here. Neurotoxic chemicals of environmental concern for which an adequate data base is available for comparative purposes include alcohol, carbon monoxide, lead, methylmercury and polychlorinated biphenyls (PCB). Principles of cross species extrapolation in neurotoxicology will be illustrated by means of representative neurobehavioral and electrophysiological findings.

Inorganic lead as a developmental neurotoxicant: some basic issues and the Düsseldorf experience.

The developmental neurotoxicity of inorganic lead is well established at different levels of biointegration, as well as in a variety of test models and species. Despite such knowledge some important issues are still being discussed. Work from the Düsseldorf laboratory and from the broader literature is compared for some of those issues, namely the spectrum of lead-induced neurobehavioral deficit in children, as well as issues mainly related to experimental models, namely functional recovery of deficit, developmental periods of particular vulnerability, and dose-response contingencies including the no-threshold hypothesis. Neurobehavioral studies in environmentally lead-exposed children suggest that non-IQ measures relating to visual-motor integration and to reaction performance may be more consistently associated with lead-exposure than psychometric intelligence. Experimental information is important for those issues which cannot convincingly be dealt with in human epidemiology. In animals (rats, monkeys) observations based on a broad spectrum of learning- and retention models with positive and negative reinforcement contingencies, as well as neurophysiological tests of visual and auditory processing, support the idea, that early lead-induced neurobehavioral deficit extends long into adulthood after cessation of exposure, primarily after gestational/preweaning and less clearly so following postweaning lead-exposure, that the no-threshold hypothesis based on epidemiological studies in children is only partly supported by experimental findings, and that both glutamatergic and dopaminergic transmitter systems are involved in lead-induced developmental neurotoxicity.

Developmental delay of astrocytes in hippocampus of rhesus monkeys reflects the effect of pre- and postnatal chronic low level lead exposure.

Rhesus monkeys were pre- and postnatally exposed to lead-acetate at 0, 350, or 600 ppm in diet for nine years, followed by a period of lead-free diet for 32 months. During this time blood lead levels declined to normal, but still showed dose-related differences. In behavioral and neurophysiological studies the rhesus monkeys exhibited dose-related cognitive and functional deficits. After sacrifice hippocampal sections were processed for immunohistological staining. GFAP, introduced as a marker of neurotoxicity and Vimentin, which is expressed by immature or reactive astrocytes were investigated. A dose-dependent increase of GFAP due to prenatal and chronic low level lead exposure was not observed. We found a dose-related increase of GFAP-positive radial glia and star-shaped Vimentin-positive astrocytes in the high lead group. We consider these findings as indication of immature astrocytes, which are not able to react with gliosis in respond to pre- and postnatal low level lead exposure. The lack of pronounced glial response due to low level lead exposure may result in a delay of astrocytic differentiation, shown by persistence of radial glia.

Immunohistochemical localization of neuronal and glial calcium-binding proteins in hippocampus of chronically low level lead exposed rhesus monkeys.

The purpose of this study was to investigate the distribution of the neuronal calcium-binding proteins parvalbumin, calbindin D28k, calretinin and the glial protein S100 in the hippocampus of lead exposed rhesus monkeys. It has been suggested that lead may exert its toxic effects by perturbing the intracellular calcium homeostasis. Lead is able to increase the intracellular Ca2+ concentration and can serve as a calcium substitute. It has been shown that some calcium-binding proteins are capable of binding lead. We tried to find a putative dose-depending relation between long-term low level lead exposure and the expression of the proteins investigated. Rhesus monkeys were pre- and postnatally exposed to 600 mg-350 mg-0 mg lead-acetate in diet for nine years, as described by Lilienthal et al. (1986). After a lead-free period of 32 months animals were sacrificed. Hippocampal paraffin sections were stained for parvalbumin (PV), calbindin D28k (CB), calretinin (CR), and S100 with immunohistochemical methods. The distribution of the neuronal calcium-binding proteins was almost identical for the different exposure groups. The most striking observation was a marked decrease of S100 immunoreactivity in astrocytes in the high lead group. Considering a protective role against high Ca2+ concentration and Pb2+ accumulation respectively the unchanged expression of PV, CB, and CR remains to be clarified. The apparent difference in S100 expression supports the hypothesis that glial cells are the main target of lead toxicity. The reduced expression may indicate a developmental retardation of astroglia.

Persistent decrease of the dopamine-synthesizing enzyme tyrosine hydroxylase in the rhesus monkey retina after chronic lead exposure.

One of the toxic effects of lead in the CNS is an altered functional state of the catecholamine system, especially a reduction in the activity of tyrosine hydroxylase (TH), the rate-limiting enzyme of catecholamine synthesis. Here we report on a lead-induced decrease in TH-content in neurones of the rhesus monkey retina. Rhesus monkeys were pre- and postnatally exposed to 0, 350, or 600 ppm of lead acetate (Pb) in the diet over 9 years. Lead exposure was followed by a 35-month period of lead-free diet. During this period, blood lead levels of the treated animals declined to nearly those of the untreated controls. Subsequently the animals were sacrificed and the retinas processed for TH immunocytochemistry. The fluorescent dye FITC was used to visualise the antibody reaction. Photometric measurements of the fluorescence intensity of stained neurones were made with a laser scanning microscope. In the rhesus monkey retina two types of TH-immunoreactive neurones are present. In the bright fluorescent type, lead exposure resulted in decreased fluorescence intensity and altered the intensity profile of the TH-immunoreactive cells in a dose-dependent manner. In these cells, fluorescence intensity was 0.53 and 0.22 for 350 ppm Pb and 600 ppm Pb respectively when the fluorescence intensity of the untreated controls (0 ppm Pb) is taken as 1. Both lead doses also reduced the number of ascending fibres in the inner nuclear layer and the dense staining of fibres in sublayer 1 of the inner plexiform layer. The weakly fluorescent cell type disappeared to a large extent under 350 ppm Pb treatment and was not detectable in the 600 ppm Pb group. The results demonstrate that lead exposure affects the dopaminergic retinal amacrine cells by reducing the TH-content in these neurones and that this neurotoxic effect persists beyond the end of exposure.

Myopathy: a possible effect of chronic low level lead exposure.

Morphological changes in the central nervous system and other organs have been reported in numerous studies investigating low level lead exposure. To date, however, there are no investigations on the effect of low level lead exposure on striated muscles, although varying neuromuscular changes in different species have been known for years. Rhesus monkeys were exposed pre- and postnatally to lead acetate in the diet (350 ppm or 600 ppm) over 9 years, followed by a lead free period of 32 months, while a control-group received regular diet. No signs of muscular dysfunction were evident. To elucidate neuromuscular pathomorphology frozen sections of the vastus medialis muscle were processed for routine and enzymohistological staining (Hematoxilin and Eosin, Sudan Black, Gomori, NADH, ATPase). Resin histology was processed for electron microscopy. Morphometric analysis was made with commercial software. Light microscopy revealed dose-related signs of myopathy in the lead-exposed groups. The scatter of fibre diameters was increased, and split fibers and internal nuclei were more frequent. Fibres became separated from each other by copious endomysial connective tissue. Ultrastructural examination showed hydropic mitochondria and a massively dilated sarcotubular system in the 600 ppm group. Dose-related extracellular collagen deposition increased. A heavy fibrosis was seen in the 600 ppm group. These findings are interpreted as myopathical reaction due to chronic low level lead exposure, as there were no signs of neurogenical lesion. It remains unknown how the fibrosis developed. A primary fibrosis could be based upon a developmental delay of satellite cells (expressing metalloproteases for collagen-catabolism). Lead is known to inhibit regular development in many ways if exposure has started prenatally. As the skeletal muscle is a common target of toxicity, the myotoxic effects of chronic low level lead exposure comes into question.

Neurobehavioral and neurophysiological observations in six year old children with low lead levels in East and West Germany.

Within a larger comparative environmental health screening program in East and West Germany neurobehavioral and neurophysiological measures were taken in 367 six year old children in Leipzig (N = 179), Gardelegen (N = 68), and Duisburg (N = 120). Lead concentrations from venous blood samples (PbB) and from deciduous teeth (PbT) were measured as markers of environmental lead exposure by electrothermal AAS. Dependent variables included four subtests from NES1 (tapping, reaction time, pattern comparison, and Benton visual retention), as well as VEP-latencies (N2, P100, N3) evoked by checkerboard patterns of different size and contrast. The overall median blood lead-concentration was 5 micrograms/dl (range: 1.3-19.0 micrograms/dl), and the corresponding tooth lead-concentration was 2 micrograms/g (0.2-14 micrograms/g). The 95-percentile of the overall frequency distribution for PbB was below 10 micrograms/dl. Associations between markers of lead-exposure and neurobehavioral or neurophysiological outcome were assessed by means of multiple linear or logistic regression analyses. After adjusting for relevant confounders/covariates significant (p < 0.05) Pb-related deficit was found for tapping and pattern recognition with respect to PbB but not PbT. No such associations could be established for VEP-latencies. These results are compatible with the hypothesis that subtle neurobehavioral dysfunction in children may be associated with very low PbB.

The IPCS Collaborative Study on Neurobehavioral Screening. I. Background and genesis.

Numerous events over several years culminated in recognition of the need to explicitly evaluate the nervous system as a potential target for environmental chemicals. Based on recommendations from several international expert panels, the International Programme on Chemical Safety (IPCS) sponsored the Collaborative Study on Neurobehavioral Screening Methods. A Steering Committee was created to oversee the project, develop the testing protocol, recruit participating laboratories and review and analyze the data. The protocol specified the tests, the chemicals (supplied from a common source) and the exposure conditions (acute and repeated dosing). Test methods were based upon existing practices in toxicological screening as well as recent advances in neurotoxicity screening. Chemicals were selected to produce different profiles of neurobehavioral effects. Considerable latitude was afforded the participating laboratories in the choice of several key variables (e.g., strain of rat, testing device for motor activity assessment) that could potentially affect the results of the experiments. The approach therefore provided a standardized yet flexible protocol for evaluating the reproducibility of neurobehavioral screening data in diverse laboratory settings.

The IPCS Collaborative Study on Neurobehavioral Screening Methods: II. Protocol design and testing procedures.

This paper describes the development of the protocol for the International Programme on Chemical Safety (IPCS)-sponsored Collaborative Study on Neurobehavioral Screening Methods, including background on the methods and chemicals selected, as well as details concerning the conduct of the collaborative study, including proficiency testing, range-finding and main study. Participating laboratories in the collaborative study received training in the conduct and scoring of the behavioral tests and each laboratory received a video training film to train additional personnel as needed. Each of the eight laboratories that chose to participate in the study completed proficiency testing and assessed seven representative chemicals using a functional observational battery and automated motor activity assessment. The seven chemicals studied were acrylamide, bis-acrylamide, p,p'-DDT, lead acetate, parathion, toluene, and triethyl tin. Participants received coded samples of the chemicals from a common source. Each laboratory derived doses for single and repeated administration based on the determination of a within-laboratory acute "top dose." Animal strains were not standardized and laboratory conditions were standardized to a limited degree in order to judge the general utility and robustness of these procedures in a diversity of testing situations.

The IPCS Collaborative Study on Neurobehavioral Screening Methods: VII. Summary and conclusions.

In the International Programme on Chemical Safety (IPCS) Collaborative Study on Neurobehavioral Screening Methods, eight participating laboratories used a standard battery of behavioral tests to determine, in rats, the effects of seven representative chemicals following acute and repeated dosing. The results of the collaborative study indicate good agreement across laboratories with regard to the data collected in vehicle controls. It was clear, however, that some behavioral measures had significantly more variability than other tests. The laboratories also demonstrated the ability to detect known neurotoxic chemicals and identify profiles of effects that differed from non-neurotoxic agents. The results of the study suggest that appropriate training of personnel is crucial to ensure the reliability of the test battery. The results also underscore the importance of dose selection in behavioral screening studies, since it is sometimes difficult to determine the specificity of behavioral changes in animals receiving high doses of some chemicals. The collaborative study also emphasizes the need to utilize a battery of tests in screening a wide range of potential neurotoxic agents. Analysis of data from such studies poses unique challenges due to the large number of tests and test times, and the consequent possibility of false positives. Some statistical concerns may be alleviated by grouping the results from tests that measure similar functions into neurobiological domains. Although this approach improves confidence in the biological relevance of chemical-induced changes in behavior, it may also lead to false negatives. The exploration of other statistical approaches to analyze data from experiments using a test battery is encouraged. Nevertheless, results of the collaborative study strongly support the use of behavioral tests in hazard identification.

The IPCS Collaborative Study on Neurobehavioral Screening Methods: III. Results of proficiency studies. Steering Group.

The goal of the IPCS Collaborative Study on Neurobehavioral Screening Methods was to determine the intra- and inter-laboratory reliability of a functional observational battery (FOB) and an automated assessment of motor activity in eight laboratories world-wide. The first phase of the Collaborative Study involved training the participants: evidence of training was then evaluated using positive-control compounds. The positive-control studies required the laboratories to identify, using the FOB, specific neurotoxic syndromes produced by acute exposure to p,p'-DDT, parathion, and by short-term repeated dosing with acrylamide. For the sake of expediency, only one dose of each chemical was used instead of collecting dose-response data. Motor activity test chambers were not of uniform design. The laboratories were therefore required to demonstrate adequate sensitivity by the ability to detect statistically-significant activity increases and decreases produced by triadimefon and chlorpromazine, respectively, following acute administration of a range of doses. The resulting FOB and motor activity data showed variability in the magnitude of effects obtained: some of these differences were attributed to miscommunications, difficulties with the techniques or protocol, or the limitations of having only one dose. All laboratories, however, successfully met the criteria set forth by the Study Steering Committee.

The IPCS Collaborative Study on Neurobehavioral Screening Methods: IV. Control data. Steering Group.

The goal of the International Programme on Chemical Safety (IPCS) Collaborative Study on Neurobehavioral Screening Methods was to determine the intra- and inter-laboratory reliability of a functional observational battery (FOB) and an automated assessment of motor activity in eight laboratories worldwide. The control data were crucial to the outcome of the studies in terms of sensitivity and reliability of the test measures, which in turn impact on the between-laboratory comparisons of chemical effects. In addition, analyses of control data can aid in determining endpoints that may require modification to improve their sensitivity and reliability. The control data from the eight laboratories were examined in terms of the following parameters: 1) control variability within studies for each laboratory; 2) within-laboratory replicability of control values across studies; 3) within-laboratory stability of control values over the course of testing for a given study; and 4) between-laboratory comparisons of parameters (1), (2), and (3). The analyses indicated considerable differences across endpoints, wherein some measures showed high variability and little replicability, while others were extremely reproducible. Generally, there were similar ranges of variability and replicability of control data across laboratories, although in some cases one or two laboratories were markedly different from the others. The physiological (weight, body temperature) and neuromuscular (grip strength, landing foot splay) endpoints exhibited the least variability, whereas the subjective assessments of reactivity varied the most. These data indicate a reasonable degree of comparability in the data generated in the participating laboratories.