Exposure-effect and exposure-response relationships between occupational exposure to styrene and neuropsychological functions

Health Risk Assessment of Residents' Exposure to Air Pollutants around the Sinpyeong-Jangrim Industrial Complex in Busan

In this study, we aimed to evaluate the health effects of heavy metals and volatile organic compounds (VOCs) in fine particulate matter (PM2.5) in the air around the Sinpyeong-Jangrim Industrial Complex, Busan, and the necessity of reduction measures. We measured the concentrations of heavy metals and VOCs in PM2.5 in five areas with dense population around the Sinpyeong-Jangrim Industrial Complex. A health risk assessment was conducted, and the spatial risk distribution for the entire Saha-gu area was predicted using inverse distance weighting (IDW). Our results indicated that the carcinogens benzene, As, and Cr6+, and the non-carcinogen m,p-xylene, have the potential to adversely affect health. In particular, As was found to have the potential to express health effects at all measurement points. Additionally, based on the IDW results, the minimum values of benzene, arsenic, and m,p-xylene exceeded the threshold level, potentially affecting the health of residents across the entire Saha-gu area. In contrast, Cr6+ could potentially impact health only in some parts of Saha-gu as only its maximum value exceeded the threshold level. We demonstrated the importance of reducing air pollutant emissions from general industrial complexes. Our results will be useful in establishing more systematic mitigation measures to protect the health of residents near the Sinpyeong-Jangrim Industrial Complex and developing air pollutant management systems.

Harmonization of acronyms for volatile organic compound metabolites using a standardized naming system

Increased interest in volatile organic compound (VOC) exposure has led to an increased need for consistent, systematic, and informative naming of VOC metabolites. As analytical methods have expanded to include many metabolites in a single assay, the number of acronyms in use for a single metabolite has expanded in an unplanned and inconsistent manner due to a lack of guidance or group consensus. Even though the measurement of VOC metabolites is a well-established means to investigate exposure to VOCs, a formal attempt to harmonize acronyms amongst investigators has not been published. The aim of this work is to establish a system of acronym naming that provides consistency in current acronym usage and a foundation for creating acronyms for future VOC metabolites.

Associations of Occupational Styrene Exposure With Risk of Encephalopathy and Unspecified Dementia: A Long-Term Follow-up Study of Workers in the Reinforced Plastics Industry

Exposure to industrial solvents has been associated with encephalopathy. Styrene is a neurotoxic industrial solvent, and we investigated the long-term risk of encephalopathy and unspecified dementia following styrene exposure. We followed 72,465 workers in the reinforced plastics industry in Denmark (1977–2011) and identified incident cases of encephalopathy (n = 228) and unspecified dementia (n = 565) in national registers. Individual styrene exposure levels were modeled from information on occupation, measurements of work place styrene levels, product, process, and years of employment. Adjusted analyses were performed using a discrete survival function. A positive trend for encephalopathy (P < 0.01) and a negative trend for unspecified dementia (P = 0.03) were seen with cumulative styrene exposure accrued during the recent period of up to 15 years. For unspecified dementia and the combination of unspecified dementia and encephalopathy, a positive trend was indicated when applying a 30-year exposure lag (P = 0.13 and P = 0.07). The risk patterns seen following recent exposure probably reflect diagnostic criteria for encephalopathy requiring recent industrial solvent exposure and referral bias rather than association with styrene exposure, while the increasing risk observed for unspecified dementia and the combination of encephalopathy and unspecified dementia following distant exposure indicates an increased risk of dementia following styrene exposure with a long latency period.

Characteristics of exposure and health risk air pollutants in public buses in Korea

The objective of this study was to estimate the concentrations of indoor air pollutants in unregulated public transport means in Korea and to determine the factors affecting the air quality as well as to assess the harmful effects of indoor air pollutants on the health of passengers. The correlation between particulate matter (PM₁₀) and number of passengers on intra-city buses, express buses, town shuttle buses, or rural buses was insignificant whether it was during rush hours or non-rush hours. In regard to PM₁₀ on express buses, there was no case where the standard limit was exceeded during the winter and summer seasons. In winter, however, the average concentration of PM10 increased by the travel distance. In regard to CO₂, there was a statistically significant correlation (p < 0.05) between CO₂ concentrations and the number of passengers, owing to human respiration. Unlike the case of PM₁₀, there was a difference between rush hours and non-rush hours. Regarding volatile organic compounds (VOCs) and aldehydes, the values were high among recently manufactured vehicles regardless of bus types. The standard limit was exceeded during the summer season, which seemed to be related to the temperature and humidity in both indoor and outdoor. The results of this study indicate that the excess mortality resulting from PM₁₀ was as high as the safety margin during both non-rush hours and rush hours among all unregulated public transportation means. The excess cancer risk and non-cancer risk of VOCs and aldehydes were as high as the safety margin during both non-rush hours and rush hours.

Emission fluxes of styrene monomers and other chemicals for products containing expanded polystyrene beads

Styrene in indoor air can adversely affect human health. In this study, styrene monomer and other chemical emission fluxes for products containing expanded polystyrene beads (pillows, cushions, and soft toys) were measured at various temperatures to simulate typical product use. The contributions of the products to styrene and other chemical concentrations in indoor air and human exposure to these chemicals were estimated, and health risk assessments were performed. The styrene monomer emission fluxes for the samples at 25°C were between 25.3 and 8.73×103 μg/(m2 h). The styrene emission fluxes for the product surfaces increased strongly as the temperature increased, from between 124 and 2.44×104 μg/(m2 h) at 36°C (simulating human body temperature) to between 474 and 4.59×104 μg/(m2 h) at 50°C (simulating inside an automobile in summer). The hexane, heptane, toluene, octane, ethylbenzene, m- and p-xylene, o-xylene, and dodecane emission fluxes at 25°C for the sample that emitted the analytes most readily were high. The maximum estimated styrene and xylene concentrations in indoor air caused by emissions from expanded polystyrene beads at 36°C in a bedroom and automobile were higher than the relevant guidelines. The maximum contribution of a product containing expanded polystyrene beads in a living room, bedroom, or automobile could cause the total volatile organic compound concentration in air to exceed the advisable value (400 μg/m3). The estimated maximum hazard quotients for styrene, toluene, and xylene emitted by a product containing expanded polystyrene beads at 36°C in a bedroom were 0.59, 0.30, and 0.37, respectively. These non-carcinogenic risk values for single products could contribute to the non-carcinogenic risk thresholds being exceeded when multiple products and other sources of chemicals are taken into consideration. The estimated styrene concentrations suggest that products containing expanded polystyrene beads are important sources of styrene to indoor air.

Concentrations of particulate matter, carbon dioxide, VOCs and risk assessment inside Korean taxis and ships

The objective of this study was to investigate the concentration distribution of indoor air pollutants in taxis and ships (passengers) which are frequently used for public transportation and recreational activities in South Korea. In addition, it aimed to assess air quality factors to establish and evaluate the health risks of exposure to polluted indoor air. Particulate matter (PM₁₀) concentrations were not affected by the number of passengers, time of day, and driving characteristics because there were only a few passengers (2 to 4 people) and the space was confined. In the ships, indoor air pollutants responded more sensitively to the operation characteristics depending on the time of sailing (i.e., anchoring and departure, movement of vehicles on the ship, movement of passengers, combustion in the shop, and ventilation) than to the number of people boarding and alighting. The carbon dioxide concentrations in different ship rooms did not vary according to season and degree of congestion; however, there were differences between different ships. These differences may result from the size, type, and operating characteristics of the ships. Volatile organic compounds (VOCs) and aldehydes in new taxis exceeded the standard levels during summer. VOC concentrations in ships were particularly high during summer when the outdoor temperature was high. Similar observations were made for other means of transportation. The risk assessment depended on the means of transportation and demonstrated that mortality risks due to PM₁₀ and excess carcinogenic and non-carcinogenic risks from VOCs and aldehydes were within safety levels.

Mass casualties and health care following the release of toxic chemicals or radioactive material--contribution of modern biotechnology

Catastrophic chemical or radiological events can cause thousands of casualties. Such disasters require triage procedures to identify the development of health consequences requiring medical intervention. Our objective is to analyze recent advancements in biotechnology for triage in mass emergency situations. In addition to identifying persons "at risk" of developing health problems, these technologies can aid in securing the unaffected or "worried well". We also highlight the need for public/private partnerships to engage in some of the underpinning sciences, such as patho-physiological mechanisms of chemical and radiological hazards, and for the necessary investment in the development of rapid assessment tools through identification of biochemical, molecular, and genetic biomarkers to predict health effects. For chemical agents, biomarkers of neurotoxicity, lung damage, and clinical and epidemiological databases are needed to assess acute and chronic effects of exposures. For radiological exposures, development of rapid, sensitive biomarkers using advanced biotechnologies are needed to sort exposed persons at risk of life-threatening effects from persons with long-term risk or no risk. The final implementation of rapid and portable diagnostics tools suitable for emergency care providers to guide triage and medical countermeasures use will need public support, since commercial incentives are lacking.

Trends in occupational exposure to styrene in the European glass fibre-reinforced plastics industry

Aim: This study presents temporal trends of styrene exposure for workers in the European glass fibre-reinforced plastics (GRP) industry during the period 1966–2002.

Methods: Data of personal styrene exposure measurements were retrieved from reports, databases and peer-reviewed papers. Only sources with descriptive statistics of personal measurements were accepted. The styrene exposure data cover personal air samples and biological monitoring data, that is, urinary styrene metabolites (mandelic acid and/or phenylglyoxylic acid) and styrene in blood. Means of series of measurements were categorized by year, country, production process, job and sampling strategy. Linear mixed models were used to identify temporal trends and factors affecting exposure levels.

Results: Personal exposure measurements were available from 60 reports providing data on 24145 1–8-h time-weighted average shift personal air samples. Available data of biological exposure indicators included measurements of mandelic acid in post-shift urine (6361 urine samples being analysed). Trend analyses of the available styrene exposure data showed that the average styrene concentration in the breathing zone of open-mould workers in the European GRP industry has decreased on average by 5.3% per year during the period 1966–1990 and by only 0.4% annually in the period after 1990. The highest exposures were measured in Southern Europe and the lowest exposures in Northern Europe with Central Europe in between. Biological indicators of styrene (mandelic acid in post-shift urine) showed a somewhat steeper decline (8.9%), most likely because urine samples were collected in companies that showed a stronger decrease of styrene exposure in air than GRP companies where no biological measurements were carried out.

The application of non-default uncertainty factors in the U.S. EPA's Integrated Risk Information System (IRIS). Part I: UF(L), UF(S), and "other uncertainty factors"

The United States Environmental Protection Agency's Integrated Risk Information System (IRIS) includes hazard identification and dose-response assessment values developed by Agency scientists. Uncertainty factors (UFs) are used in the development of IRIS values to address the lack of information in five main areas. The standard UFs account for interspecies uncertainty (UF(A)) and intraspecies variability (UF(H)). The UF(A) addresses uncertainty related to the extrapolation of data from animals to humans, whereas the UF(H) addresses variability amongst individuals (i.e., intrahuman). Additional UFs have been employed to account for database incompleteness, extrapolations from a lowest-observed-adverse-effect level in the absence of a no-observed-adverse-effect level (UF(L)), and subchronic-to-chronic extrapolation (UF(S)). A sixth UF designated as "other uncertainty factors" (UF(O)) has also been applied in place of the UF(L) to account for uncertainty with the adversity of points of departure obtained using benchmark dose modeling. This review will discuss how UF(L), UF(S), and UF(O) have been applied in IRIS assessments, along with the rationale used to describe the choice of UF values that deviate from the standard default of 10.

Analysis of oxidative stress in SK-N-MC neurons exposed to styrene-7,8-oxide

Styrene-7,8-oxide (SO) is the main metabolite of styrene, a neurotoxic volatile organic compound used industrially. Here we report the novel observation that several markers of oxidative stress were affected in SK-N-MC cells exposed for 16 h to concentrations of SO that induce apoptotic cell death. The production of Thiobarbituric Acid Reactive Substances (TBARS), rose from 69.1 +/- 15.7 nmol/g protein (control) to 119.3 +/- 39.2 and 102.0 +/- 17.3 nmol/g protein after exposure to 0.3 and 1 mM SO, respectively. Carbonyl group levels were significantly enhanced by SO at both concentrations. The lower dose also decreased sulphydryl groups. SO caused a marked oxidative DNA damage, as shown by a fivefold increase in 8-hydroxy-2(')-deoxyguanosine (8-OHdG). In addition, SO exposure resulted in alterations of scavenging abilities, given the reduction of both glutathione (GSH) and glutathione-S-transferase (GST) activity. Induction of expression of the oxidative stress response gene heme-oxygenase-1 (HO-1) and an increased HO-1 activity were also observed. These data provide compelling evidence that oxidative stress significantly contributes to SO toxicity in neuronal cells.

Human neurobehavioral effects of long-term exposure to styrene: a meta-analysis

Many reports in the literature suggest that long-term exposure to styrene may exert a variety of effects on the nervous system, including increased choice reaction time and decreased performance of color discrimination and color arrangement tasks. Sufficient information exists to perform a meta-analysis of these observations quantifying the relationships between exposure (estimated from biomarkers) and effects on two measures of central nervous system function: reaction time and color vision. To perform the meta-analysis, we pooled data into a single database for each end point. End-point data were transformed to a common metric of effect magnitude (percentage of baseline). We estimated styrene concentration from biomarkers of exposure and fitted linear least-squares equations to the pooled data to produce dose-effect relationships. Statistically significant relationships were demonstrated between cumulative styrene exposure and increased choice reaction time as well as increased color confusion index. Eight work-years of exposure to 20 ppm styrene was estimated to produce a 6.5% increase in choice reaction time, which has been shown to significantly increase the probability of automobile accidents. The same exposure history was predicted to increase the color confusion index as much as 1.7 additional years of age in men.

Styrene 7,8-oxide induces mitochondrial damage and oxidative stress in neurons

Styrene 7,8-oxide (SO) is the main metabolite of styrene, a neurotoxic compound used industrially. Neurons exposed to SO undergo apoptosis with characteristic features including chromatin rearrangements and caspase activation. We report that the execution phase of apoptosis induced by SO (0.3 mM) in SK-N-MC neurons is triggered by translocation of apoptogenic factors (e.g., cytochrome c) into the cytosol. In addition, mitochondria exhibit lower Ca2+ capacity and loss of mitochondrial membrane potential (DeltaPsi). Lipid peroxidation, measured as thiobarbituric acid reactive substances (TBARS), is increased after 12 h. Pre-treatment with the antioxidant MnTBAP (100 microM) prevents the decrease of Ca2+ capacity, cytochrome c release, activation of caspases, exposure of phosphatidylserine and cell death. Hence, the neurotoxic effects of SO are related to mitochondrial damage and oxidative stress.

Neurobehavioral effects of experimental exposures to low levels of styrene

Two experimental studies were conducted with the intention to simulate exposure characteristics of work places with styrene exposure and to investigate the risk for neurobehavioral impairments. In experiment I 16 volunteers (8 in the morning, 8 in the afternoon) were exposed to 0.5 and 20 ppm styrene on a constant level for 3h. In experiment II 24 volunteers (12 in the morning, 12 in the afternoon) were exposed for 4h to 0.5 and 20 ppm styrene on a constant level as well as to a changing exposure between 0.5 and 40 ppm with a TWA of 14 ppm. Simple reaction, choice reaction, attention, acute symptoms, and ratings for well-being were measured. Exposure related performance effects could not be detected. However, 6h time change resulted in delayed choice reactions in the morning hours. Analysing acute symptoms and the state of well-being the impact of styrene did not reach adverse extents of impaired well-being.

Temporal association between serum prolactin concentration and exposure to styrene

BACKGROUND

Previous studies have suggested that occupational exposure to styrene is associated with increased serum levels of the anterior pituitary hormone prolactin (PRL).

AIMS

To test the hypotheses that: (1) the effect of styrene exposure on PRL secretion is an acute effect, not a subchronic or chronic effect; (2) blood styrene, as a measure of absorbed dose, is a stronger predictor of serum PRL level than personal breathing zone air styrene concentration.

METHODS

Subjects were recruited from 17 workplaces in the reinforced plastics industry. Personal breathing zone air styrene, whole blood styrene, and serum PRL were measured during one to three sessions, approximately one year apart. Linear multiple regression was used to model the relations between acute (air styrene or blood styrene obtained at same time as PRL), subchronic (average air or blood styrene over two or three sessions), and chronic (years of work in industry or facility times average air styrene over all sessions) indices of styrene exposure and serum PRL.

RESULTS

Acute blood styrene concentration was the strongest predictor of serum PRL concentration, with the model predicting a 2.06-fold increase in PRL (95% CI 1.11 to 3.84) for every 10-fold increase in blood styrene. Serum PRL tended to increase with increasing styrene exposure in both men and women; however, women tended to have higher PRL levels. For women, the change in blood styrene between sessions 1 and 2 was a significant predictor of the change in serum PRL between sessions.

CONCLUSIONS

Results confirm that styrene exposure enhances serum PRL concentrations and support an acute effect of styrene on PRL secretion.

Styrene 7,8-oxide induces caspase activation and regular DNA fragmentation in neuronal cells

Neurobehavioral changes have been described in workers occupationally exposed to styrene vapors. Alterations of neurotransmitters and loss of neurons have been observed in brains of styrene-exposed rats. However, the mechanisms of neuronal damage are not yet clearly understood. We have characterized the cellular alterations induced by the main reactive intermediate of styrene metabolism, styrene 7,8-oxide (SO) in the human neuroblastoma SK-N-MC cell line and primary culture of rat cerebellar granule cells (CGC). SK-N-MC cells exposed to SO (0.3-1 mM) displayed apoptotic morphology, together with chromatin condensation and DNA cleavage into high molecular weight fragments of regular size. These features were accompanied by the activation of class II caspases, as detected with the DEVD assay, by following the cleavage of the caspase-substrate poly (ADP-ribose) polymerase (PARP) and by detection of the active fragment of caspase-3. Pre-incubation of the cells with the caspase inhibitor z-VAD-fmk reduced the cellular damage induced by SO, suggesting that caspases play an important role in SO toxicity. Increased proteolysis by class II caspases was detected also in primary culture of CGC exposed to SO. In addition, the presence of the 150-kDa cleavage product of alpha-fodrin suggests a possible activation of calpains in SK-N-MC cells. Moreover, SO did not affect the level of expression of the p53 protein, even though it is known to cause DNA damage. The identified intracellular pathways affected by SO exposure provides end-points that can be used in future studies for the evaluation of the neurotoxic effect of styrene in vivo.

Metabolism of styrene in the human liver in vitro: interindividual variation and enantioselectivity

1. The interindividual variation and enantioselectivity of the in vitro styrene oxidation by cytochrome P450 have been investigated in 20 human microsomal liver samples. Liver samples were genotyped for the CYP2E1*6 and CYP2E1*5B alleles. 2. Kinetic analysis indicated the presence of at least two forms of styrene-metabolizing cytochrome P450. The enzyme constants for the high-affinity component were subject to appreciable interindividual variation, i.e. Vmax1 ranged from 0.39 to 3.20 nmol mg protein(-1) min(-1) (0.96+/-0.63) and Km1 ranged from 0.005 to 0.03 mM (0.011+/-0.006). Inhibition studies with chemical inhibitors of CYP2E1, CYP1A2, CYP2C8/9 and CYP3A4 demonstrated that CYP2E1 was the primary enzyme involved in the high-affinity component of styrene oxidation. No relationship between the interindividual variation in Vmax1 and Km1 and the genetic polymorphisms of the CYP2E1 gene was found. 3. Cytochrome P450-mediated oxidation of styrene demonstrated a moderate enantioselectivity, with an enantiomeric excess (ee) of (S)-styrene oxide of 15% (range 4-27%) at low styrene concentration and an ee of (R)-styrene oxide of 7% (range -11 to +22%) at high styrene concentration. This points towards the involvement of at least two cytochrome P450, with different enantioselectivities. 4. The data indicate that cytochrome P450-mediated styrene oxidation is subject to considerable interindividual variation, but only to a moderate product enantioselectivity.

Neurobehavioural changes and persistence of complaints in workers exposed to styrene in a polyester boat building plant: influence of exposure characteristics and microsomal epoxide hydrolase phenotype

OBJECTIVES

To investigate neurobehavioural effects and the persistence of complaints in workers exposed to styrene relative to exposure characteristics and the enzyme microsomal epoxide hydrolase (mEH) activity.

METHODS

A cross sectional study was performed in a retrospective cohort of workers of a polyester boat building plant 3 years after the main activity shut down in 1989. Workers still currently exposed to a much lower concentration of styrene in air than before (n=27) and formerly exposed workers (n=90) were compared with matched control workers (n=64). Currently and formerly exposed workers laminated 4700 and 3610 hours on average at mean exposure to styrene concentrations of 148 and 157 mg/m(3) respectively. A structured neurological anamnesis into former and present complaints, the NSC-60 questionnaire, and computer assisted neurobehavioural tests (NES) were administered. The mEH phenotype activity was measured in lymphocytes with a novel gas chromatography-mass spectroscopy (GC-MS) method.

RESULTS

For the period before 1989, currently and formerly exposed workers reported more complaints than control workers which related well with the mean exposure to airborn styrene concentration (p=0.03). Most complaints disappeared after the end of exposure, although the chest, equilibrium, and somatic category scores of NSC-60 and the number of workers reporting diminished sense of smell remained increased in formerly exposed workers (p<or=0.05). Symbol-digit substitution and digit span forwards test results were worse in currently and formerly exposed workers (p<or=0.01). In the combined group of currently and formerly exposed workers, the symbol-digit substitution and colour-word vigilance results related well to duration of exposure (p<0.01 and p=0.03) and mEH phenotype activity (p=0.01 and p=0.05), whereas the digit span forwards results only showed associations of borderline significance (duration of exposure (p=0.08) and mEH phenotype activity (p=0.08)).

CONCLUSION

Most subjective symptoms were reversible but some persisted after the end of exposure to styrene, whereas dysfunction of visuomotor performance and perceptual speed seemed to persist. Duration of exposure at lamination tasks and the interaction, duration of exposurexconcentration of exposure, were found to be the best predictors of worsening visuomotor and perceptual speed performances. Activity of the mEH phenotype may play a modulating part in styrene neurotoxicity. The results suggested that less than 10 years of exposure to atmospheric styrene at an average concentration of 155 mg/m(3) may result in persistent neurotoxic effects.

Styrene inhibits monoamine oxidase A, but not monoamine oxidase B in monkey brain mitochondria

The effects of styrene on mitochondrial monoamine oxidase (MAO) activity in rat and monkey brains were compared in vitro. After preincubation at 25 degrees C for 20 min with 1 mM styrene monomer MAO-A activity in monkey brain was inhibited potently using 5-HT (for MAO-A substrate), but MAO-B activity in monkey brain and platelets were slightly inhibited using beta-PEA (for MAO-B substrate). Styrene monomer also competitively inhibited MAO-A activity in a dose-dependent manner. MAO-A in monkey brain was inhibited by styrene in ascending order of potency: styrene trimer>styrene dimer>styrene monomer. In contrast styrene monomer slightly inhibited both MAO-A and MAO-B activities in rat brain mitochondria. In the present study styrene monomer potently inhibits MAO-A activity, but not MAO-B activity, in monkey brain mitochondria in vitro. These results indicate the inhibiting action of styrene differs depending on animal species and MAO isoforms.

Occupational exposures to solvents and aluminium and estimated risk of Alzheimer's disease

OBJECTIVES

To study the role of occupational exposures to solvents and aluminium in the aetiology of Alzheimer's disease (AD). An industrial hygienist rated exposure.

METHODS

89 subjects diagnosed with probable AD were matched by age, sex, and type of informant to 89 controls. Subjects were identified from a large health maintenance organisation in Seattle, WA. A complete occupational history was obtained from spouses of cases and controls as well as from controls themselves. After the interview an industrial hygienist, blinded to case-control status, rated exposures.

RESULTS

Non-significant associations were found between AD and ever having been occupationally exposed to solvents (odds ratio (OR) 1.77, 95% confidence interval (95% CI) 0.81 to 3.90) and aluminium (OR 1.46, 95% CI 0.62 to 3.42). Although an increasing risk was found with increasing number of years of exposure to solvents, there was an inverse association between exposure intensity and AD, and measures of cumulative exposure taking into account both intensity and duration of exposure were not significant. Analysis of the age at which half the cumulative exposure to solvents was achieved showed that an older age incurred a greater risk of AD than a younger age. However, the total amount of exposure carried no risk.

CONCLUSIONS

The results suggest that lifetime occupational exposure to solvents and aluminium are not likely to be important risk factors for Alzheimer's disease.

Health effects classification and its role in the derivation of minimal risk levels: neurological effects

The agency for Toxic Substances and Disease Registry (ATSDR) uses substance-specific minimal risk levels (MRLs) to assist in evaluating public health risks associated with exposure to hazardous substances. By definition, "MRLs are estimates of daily human exposure to a chemical that are likely to be without an appreciable risk of adverse noncancer health effects over a specified duration of exposure." MRLs serve as screening levels for health assessors to identify contaminants and potential health effects that may be of concern for population living near hazardous waste sites and chemical releases. MRLs for each substance are derived for acute (1-14 days), intermediate (15-364 days), and chronic (365 days and longer) exposure durations, and for the oral and inhalation routes of exposure. The MRLs are derived from data compiled from a current comprehensive literature search and are presented in ATSDR's toxicological profile for that substance. In this paper we outline ATSDR's guidance for evaluating the neurological end point as discussed in the agency's toxicological profiles. Ranking neurological effects into less serious and serious categories and applying this procedure to the derivation of health guidance values or MRLs are also described. Specific examples of ATSDR MRLs based on neurological effects are presented.

Modeling the acute neurotoxicity of styrene

Styrene is a widely used industrial solvent associated with acute neurotoxicity. To investigate the relationships between exposure, blood concentrations, and the appearance of neurotoxic effects, four healthy males were exposed to styrene concentrations of 5-200 ppm in four different exposure-time profiles. A digit recognition test and P300 event-related evoked potential were used to measure neurologic function. A physiologically based kinetic (PBK) model generated close predictions of measured styrene blood concentrations, in the range of 0.01-12 mg/L, from this and 21 previous studies. Simulated peak brain concentration, durationXaverage exposure, and peak exposure level were predictive of toxicity. Central nervous system effects were expected at a blood concentration near 2.4 mg/L. A standard of 20 ppm was expected to protect styrene-exposed workers from acute central nervous system toxicity under light work conditions.

Neurobehavioral effects of occupational exposure to low-level styrene

Eighty-six workers in six fiberglass-reinforced plastics manufacturing plants in Taiwan were given a detailed evaluation including medical and occupational questionnaires, symptom questionnaires, blood sampling, and neurobehavioral tests, including cognitive performance, vibratory perception threshold, and thermal perception threshold. A Chinese version of cognitive tests modified from the Neurobehavioral Evaluation System 2 was applied. Forty-one workers directly exposed to styrene at the mean concentration of 22 ppm are compared with 45 workers not subject to styrene exposure. Multiple linear regression analysis controlling for age, sex, education, and alcohol intake revealed significant associations between styrene exposure and responses in some neuropsychologic measurements. No acute or chronic symptom had significant correlation with styrene exposure. Among the neurobehavioral tests, only the continuous performance test and vibration threshold were significantly and adversely affected in workers exposed to styrene. Significant changes in the central and peripheral nervous system were thus detected at a mean styrene exposure of 22 ppm.

Otoneurological study in workers exposed to styrene in the fiberglass industry

Twenty workers exposed to styrene and acetone in small fiberglass factories were monitored for 8 h using passive dosimeters. Urine samples were collected at the end of the workshift and before the start of work on the next morning. The 8-h time-weighted average exposure values for styrene and acetone ranged from 14 to 416 mg/m3 and from 70 to 277 mg/m3, respectively. The sum of styrene metabolites, mandelic acid and phenylglyoxylic acid (MA + PGA), in the next-morning urine samples ranged from 81 to 943 mg/g creatinine. Different test sensitivity was identified in the otoneurological battery: it was low for audiometric tests and ABR, and relatively high for vestibular tests. The vestibular system seems partially sensitive to the toxic effects of styrene in the absence of clinical signs and symptoms. The actual exposure levels for styrene cannot be considered devoid of functional subclinical consequences.

Multiple choice vocabulary test MWT as a valid and short test to estimate premorbid intelligence

The discrepancy between current and premorbid ability is a relevant indicator of acquired mental impairment, which itself is closely related to general cerebral dysfunction. The use of tests sensitive to cerebral dysfunction, raises relatively few problems compared with tests being resistant that are used to estimate premorbid mental ability. For premorbid ability, verbal tests assessing knowledge, especially vocabulary, have been shown to be valid. A test, possibly more insensitive to brain dysfunction than the ones usually administered, is the multiple choice vocabulary test (MWT = Mehrfachwahl-Wortschatz-Test). At present only German versions are available. They are presented in some detail because of their advantages. Construction of the MWT is simple, and it can be easily administered in about five minutes. The results correlate fairly well with global IQ in healthy adults (median of r = 0.72 in 22 samples) and are more insensitive to current disturbances than such tests as the WAIS vocabulary test. The limitations of premorbid tests with respect to diagnostic validity are discussed. It is concluded, that studies which do not control premorbid intelligence have to be considered as a "malpractice" and should not be accepted by scientists.

Assessment of the neurotoxicity of styrene, styrene oxide, and styrene glycol in primary cultures of motor and sensory neurons

The neurotoxicity of styrene and its major metabolites, styrene oxide and styrene glycol, was investigated in dissociated primary cultures of murine spinal cord-dorsal root ganglia (DRG)-skeletal muscle using morphological and electrophysiological endpoints. Styrene and styrene oxide (but not styrene glycol) were acutely cytotoxic to both neuronal and non-neuronal cells in the cultures; concentrations in excess of 2 and 0.2 mM, respectively, induced blebbing, vacuolation, detachment from the substratum and cell death in neuronal and non-neuronal cells within 4 days. No effects on neuronal morphology were observed in cultures treated with sublethal concentrations of styrene or styrene oxide for up to 3 weeks. The results suggest that oxidation of multiple cellular macromolecules that underlies the toxicity of styrene in other organ systems may also be responsible for damage to cells in the nervous system. No changes in action potential production indicative of a 'solvent effect' on membrane electrical properties was apparent in cultures treated with up to 8 mM styrene or 10 mM styrene glycol.

Impairment of color vision among workers exposed to low concentrations of styrene

A field study was conducted among 21 male workers exposed to styrene of concentration below 30 ppm in a fiber-reinforced plastic boat manufacturing plant. Twenty-one male workers with similar age groupings, years of education, and social and occupational state served as referents. The mean end-of-shift urinary mandelic acid (MA) and phenylglycoxylic acid (PGA) for the exposed workers were 84 mg/g creatinine and 66 mg/g creatinine, respectively. The Lanthony D-15 Hue Desaturated Panel was used to evaluate color discrimination of the exposed and referent groups. The results of the test were expressed as total color difference score (TCDS). The exposed workers' mean TCDS (a higher score denotes poorer color discrimination ability) was significantly (p < 0.0006) higher than the referents'. Neurobehavioral tests were also conducted, using the World Health Organization's Neurobehavioral Core Test Battery (NCTB). All the results of the NCTB were poorer for the exposed than for the referents. However, significant differences were observed only for Digit Span, Digit Symbol, and Benton Visual Retention tests. These results suggest that low exposure to styrene could affect some psychometric performance and may impair color vision.

Kinetics of styrene urinary metabolites: a study in a low-level occupational exposure setting in Singapore

Biological monitoring of styrene exposure commonly involves measurement of styrene metabolites, mainly mandelic acid (MA) and phenylglyoxylic acid (PGA), in the urine of exposed subjects. Previous studies on the kinetics of styrene metabolites in urine were mostly conducted in a controlled environment on subjects exposed to high concentrations of styrene. In this study, we examined subjects exposed to low levels of styrene in a fiber-reinforced plastics (FRP) plant to see whether the excretion kinetics of styrene metabolites are similar under field conditions. Eight healthy Chinese male volunteers were exposed to styrene for 4 h with a mean environmental concentration of 11 ppm. Urine samples were collected continuously for 20 h after termination of the exposure and concentrations of urinary MA and PCA were determined. The results showed that MA was rapidly excreted in urine after the exposure, with a half-life of 2.1 h or 1.9 h when corrected with urine creatinine. The excretion of PGA followed that of MA and the half-life was 8.1 h or 5.1 h after correction with creatinine. The half-lives are considerably shorter compared to those in previous reports, suggesting that environmental factors, exposure conditions, or ethnic differences may affect the excretion kinetics of styrene metabolites. The fast excretion of styrene metabolites is also consistent with the observation that urine MA and PGA levels correlated better with the half-day time-weighted average (TWA) concentration of environmental styrene than with the whole-day TWA concentration. Our findings thus underscore the need for information on excretion kinetics in order to develop an appropriate biological monitoring scheme for specific exposure settings and subjects.

The neuroepidemiology of styrene: a critical review of representative literature

Because exposure to styrene occurs commonly in some industries and styrene is highly lipid soluble, it is reasonable to be concerned about the possibility that styrene is neurotoxic. Styrene, like many other solvents, volatile anesthetics, and drugs, does, at certain concentrations, produce acute changes in consciousness with consequent alterations of feelings, cognition, and psychomotor functioning. Such acute actions do not imply that styrene also would produce reversible or irreversible damage to the nervous system; the evaluation of long-term exposures to styrene also is necessary to draw conclusions about the full range of neural effects that styrene might produce. To that end, several studies of workers exposed to styrene for up to 30 years have been undertaken in factories in many parts of the world. Epidemiologists have suggested that neuropsychological deficits such as slowing of reaction time, loss of color vision, and vestibulooculomotor dysfunction are reliably induced by styrene at levels near or below current exposure standards, which range from 20 to 50 ppm in most of the world. However, the workers so studied always were described as healthy, and the effects noted were considered to be subclinical. A detailed evaluation of much of the neuroepidemiological literature on styrene (38 papers and related literature), however, indicated that the findings were, almost universally, false positive outcomes due to (1) type I statistical error, (2) the action of some factor other than styrene, and (3) misinterpretation of data. Despite the study of workers exposed for many years, no indications of persisting damage to the nervous system were evident from this review. The conclusions of this review of the neuroepidemiology of styrene are consistent with those based on critical reviews of the solvent literature in general, with specific reference to the probable absence of such an entity as the "painter's syndrome" or "chronic toxic encephalopathy". Because the results on styrene neurotoxicity that provide an inclination to lower the current threshold limit values (TLVs) are false positive findings, there is no scientific basis for a reduction in the current TLV.

Biological monitoring of styrene in the reinforced plastics industry in Emilia Romagna, Italy

Biological monitoring of styrene exposure among workers in the reinforced plastics industry is widely implemented in the region of Emilia Romagna, Italy. More than 18,000 urine samples measurements of the main metabolites of styrene, mandelic (MA) and phenylglyoxylic acid, were retrieved for the period 1978-1990, and 4689 values of MA in postshift urine samples were analyzed for various variables thought to influence styrene exposure. The job performed was found to be the most important predictor of styrene exposure. Hand laminators had the highest exposure (mean MA 682 mg/g creatinine); spray laminators showed lower values (404 mg/g), while levels in semiautomatic process operators (243 mg/g) were only slightly higher than in nonprocess workers (186 mg/g). The use of ventilation resulted in lower exposure, but differences in average values were not particularly wide. Exposure decreased weakly during the study period in all work categories, but the percentage of measurements exceeding the current biological limit value (900 mg/g creatinine, 1300 mg/l corrected for density) is still very high (20% of measurements among hand laminators in 1990). These results indicate that the control measures implemented are only partially effective for the prevention of styrene exposure.

Study of the neurobehavioural toxicity of styrene at low levels of exposure

Thirty workers in a dockyard exposed to concentrations of styrene lower than the TLV-TWA of 50 ppm and 30 control workers not subject to exposure but employed by the same company were subjected to three psychometric tests on one Monday morning and evening. The results were usually better in the evening than in the morning in both groups, which proves the lack of acute intoxication at the end of the day at this level of exposure. On the other hand, all of the tests conducted on the exposed subjects are significantly less good than those on the controls. The results suggest the existence of minor but significant organic mental disorders in the subjects exposed to a mean dose of 30 ppm in this study. These results are inconsistent with those of several recent studies. The advisability of lowering the TLV of 50 ppm in discussed.

Subclinical impairment of colour vision among workers exposed to styrene

The effects of exposure to styrene were studied among 60 men aged 20 to 56 (mean 29.5) employed in shipbuilding. Exposure was due to the handling of glass reinforced polyester materials. The study was cross sectional and the workers were compared with a control group matched for age, social and occupational state, and ethnic origin. During the study, the mean atmospheric exposure to styrene was 24.3 ppm. Mean urinary elimination was 230 mg/g creatinine for mandelic acid and 57.4 mg/g creatinine for phenylglyoxylic acid. The Farnsworth 100 hue test showed no significant differences between the exposed and control groups for error scores. A significant difference was found, however, for the number of subjects with errors axis in the red-green, or blue-yellow ranges, or both, which was larger among the exposed workers (32/60 v 20/60 for the controls (p < 0.05)). Psychometric tests were also conducted, using the World Health Organisation (WHO) neurobehavioural core test battery. Of the seven tests it included, anomalies were only found for the aiming test. These results suggest that exposure to moderate styrene concentrations of the order of 25 ppm can lead to impairment of colour vision.

The clinical significance of sleep apnoea in workers exposed to organic solvents: implications for the diagnosis of organic solvent encephalopathy

Among 51 patients referred for investigation of possible organic solvent encephalopathy 20 (39%) had pathological sleep apnoea [apnoea index (AI) greater than 5], compared with 5 of 16 house painters exposed to solvents (31%) who were screened for the disorder, and 1 of 18 (6%) age-matched controls. Twelve of the patients with AI greater than 5 were retested after 2 or more weeks without exposure to solvents, and showed a significant drop in AI. Likewise, significantly lower AI was seen in patients who were no longer exposed to solvents, compared with recently exposed patients. The implications of these findings for diagnostic evaluation of solvent encephalopathy and sleep apnoea are discussed.

Neurobehavioral effects of acute styrene exposure in fiberglass boatbuilders

A field investigation of the effects of acute exposure to styrene among fiberglass boatbuilders was performed. Personal samples of styrene in breathing zone air and postshift urinary mandelic acid were collected for 105 workers exposed and not exposed to styrene in 6 fiberglass boatbuilding companies in New England. Three tests from the computerized Neurobehavioral Evaluation System (NES) were performed by the subjects in the morning before exposure to styrene, near midday, and at the end of the work day. Duration of exposure averaged 2.9 years (SD = 4.6), 8-hour TWA styrene exposure averaged 29.9 ppm (SD = 36.2), and urinary mandelic acid averaged 347 mg/g creatinine (SD = 465). Regression analyses indicated a statistically significant relationship between postshift performance on the Symbol-Digit test and both acute styrene exposure and mandelic acid. Other analyses comparing workers exposed to less than 50 ppm and greater than 50 ppm styrene also showed a significant effect on Symbol-Digit performance. All three NES tests showed test-retest correlation coefficients above .80, and ease of use for collection of neurobehavioral data under field conditions was demonstrated.

Health effects of long-term solvent exposure among women in blue-collar occupations

The relationship of solvent exposure to self-reported neurologic and somatic symptoms as well as neuropsychological performance was examined in a sample of 567 female blue collar workers who were members of the International Brotherhood of Electrical Workers (IBEW). Structured interviews were conducted at IBEW offices. Five solvent exposure categories were derived--never exposed, exposed prior to but not during the past year, exposed during the past year but not currently, currently exposed less than 50% of the time, and currently exposed more than 50% of the time. No differences among the groups on neuropsychological performance were found. On the other hand, heightened exposure was significantly related to depression, severe headaches, light-headedness, room spinning, appetite difficulties, funny taste in mouth, weakness/fatigue, rashes, and abdominal pain after controlling for the effects of seven risk factors (age, smoking, moderate-heavy alcohol consumption, severe obesity, history of physician-diagnosed chronic illness, working in a clean room, and exposure to other chemicals). These findings are consistent with Scandinavian studies of solvent-exposed male workers and point to the need for careful prospective research.

Neurotoxic effects of styrene: further evidence

The relation of exposure to styrene to measures of nervous system function was investigated in 70 men working in four factories in the Montreal area of Quebec. Mild sensory nerve conduction deficits were found, the proportion with such deficits rising from 23% in those exposed to less than 50 ppm to 71% in those exposed to more than 100 ppm. Reaction time was slower for those with a larger body burden, as indicated by area under the excretion curve, and for those who failed to clear the metabolite during the weekend. No slowing in conduction time was found among a small group of five men exposed to more than 100 ppm for less than four weeks. There was some evidence that both central and peripheral slowing recovered when workers were removed from exposure. Uptake, storage, or elimination of styrene was influenced by the physical demands of the work, skinfold thickness, cumulative exposure, and alcohol consumption. Nevertheless, only the wearing of a mask and current consumption of alcohol were associated with a lower risk of sensory conduction deficit. While there was no clear indication that neurotoxic effects were related to individual differences in the capacity to metabolise high concentrations of styrene, measurement of urinary metabolites may be helpful in identifying those at highest risk.

Influence of occupational styrene exposure on memory and attention

Short-term memory, perceptual speed, attention and psychomotor function were studied in 55 workers professionally exposed to styrene. The subjects were grouped according to their urinary styrene metabolites. Those with higher styrene exposure showed a significant impairment of short-term memory only.

Clinical and neurobehavioural study of the acute and chronic neurotoxicity of styrene

A cross sectional field study of workers exposed to styrene was performed to evaluate possible acute and chronic neurotoxic effects. A total of 36 workers of four companies handling polyester resin materials for one to 16 years (median: 7 years) and two control groups were each examined on a Monday. The control group 1 (formed to compare acute effects) consisted of 20 men from two companies with no exposure to neurotoxic chemicals. To compare chronic effects, a second control group was formed by "one to one matching" with respect to age, socioeconomic status, and pre-exposure intelligence level. Ambient air monitoring using active sampling (short time) and passive samplers (long time) showed styrene in air concentrations as follows: range 3-251 ppm (median: 18 ppm) and concentrations 140-600 ppm during lamination of the inside of boats. For biological monitoring the results were as follows (postshift samples: range/median): styrene in blood: 5-482 micrograms/dl (39 micrograms/dl), mandelic acid urine: 0.01-3.64 g/l (0.21 g/l), and phenylglyoxylic acid urine: 0.01-0.87 g/l (0.19 g/l). The clinical examination found no signs or symptoms of peripheral neuropathy or encephalopathy. The principal work related health complaints were acute, reversible irritation of the eyes that occurred after exposure to styrene concentrations of 200 ppm or more. The neurobehavioural tests showed no significant differences in acute effects (p greater than 0.05) between the two groups or between preshift and postshift testing. Nor were there any significant differences in the relevant neurobehavioural variables between the styrene workers and the controls. It is concluded that occupational exposure to styrene concentrations in air up to 100 ppm causes no adverse acute or chronic effects on the central nervous system.

Neuropsychiatric effects of low exposure to styrene

Workers exposed to styrene concentrations of about 50 mg/m3 at a plant manufacturing reinforced polyester boats were examined for neuropsychiatric symptoms both in close connection with exposure and also seven months after exposure had ceased. Physical workload is important for the uptake of styrene and was about 50 W at this plant. On the first occasion, after one week with no exposure, the workers reported a high frequency of neuropsychiatric symptoms such as fatigue, irritation, and forgetfulness whereas seven months later the frequency of these symptoms was low. These observations indicate that exposure to styrene at about 50 mg/m3 may induce reversible neuraesthenic symptoms. Even the relatively low Swedish standard (110 mg/m3 = 25 ppm) may, therefore, need revising.

Exposure-outcome relationships between organic solvent exposure and neuropsychiatric disorders: results from a Dutch case-control study

In this article the material collected for a case-control study is analyzed in order to evaluate the existence of relationships between organic solvent exposure and the entitlement to disability benefits due to neuropsychiatric disorders. Questionnaires were used to collect information on 252 cases receiving compensation due to neuropsychiatric disorders and 822 controls about their occupational history and work practices related to organic solvent exposure. In order to estimate the exposure to organic solvents, three exposure indices were used: duration of exposure, painters' index, and general exposure index. Analysis showed some tendencies indicating positive exposure-outcome relationships. Furthermore, some work activities and working conditions associated with high exposure to organic solvents (e.g., poor ventilation, using paint removers) resulted in a marked increase of the likelihood for receiving disability benefits due to neuropsychiatric disorders.

The neurobehavioral effects of chronic styrene exposure in the rat

Groups of rats were exposed by inhalation to either clear air (controls) or styrene monomer (STY) at 350, 700 or 1400 ppm for 16 hr/day, 5 days/week for 18 weeks. At preselected intervals, animals were evaluated for changes in: 1) spontaneous activity, 2) grip-strength, 3) coordinated hindlimb movement, 4) performance on a discrete-trial two-choice visual discrimination task, and 5) peripheral nerve conduction velocity. Compared to controls, STY-treated rats showed a mild but somewhat inconsistent reduction in activity and gripstrength during the course of exposure. Coordinated movement and peripheral nerve conduction time were unaffected. With respect to discrimination performance, exposure on Day 1 produced marked deficits in response speed and accuracy. By Day 2, deficits in discrimination performance were reduced by greater than 50% and the performance of STY-treated rats continued to improve as exposure continued. Finally, during the last weeks of exposure, the performance of STY-treated rats was equivalent to that of controls and no styrene-related deficits could be measured in the postexposure period.

Effects on human performance from acute and chronic exposure to organic solvents: a short review

The present short review deals with investigations of CNS-effects from acute and chronic exposure to some organic solvents and solvent mixtures, as measured by human performance. Some of the methodological problems in experimental and epidemiological investigations of effects from solvent exposure are discussed. Problem areas where further research is needed are indicated, and some methodological suggestions for future studies are presented.

Brain dopamine as a target for solvent toxicity: effects of some monocyclic aromatic hydrocarbons

Adult male rabbits were exposed to toluene, xylene, styrene, ethylbenzene, vinyltoluene or were dosed with hippuric, methylhippuric, mandelic, phenylglyoxylic, and 7-methyl-mandelic acids. Styrene, vinyltoluene and ethylbenzene caused a marked depletion of striatal and tubero-infundibular dopamine. Such an effect was also caused by treatment with mandelic and phenylglyoxylic acids. These results indicate that dopamine is a target for some solvents of their metabolites, the presence of a lateral vinyl- or ethyl-chain which may be biotransformed into alpha-keto acids being crucial for the effect. Experiments in vitro suggest that dopamine condenses non-enzymatically with reactive carbonylic groups of such and other alpha-keto acids, thus becoming ineffective as neurotransmitter. This mechanism might account for the neurobehavioral and neuroendocrine changes which have been reported in workers occupationally exposed to styrene and to some solvent mixtures.

Neurotoxic effects of organic solvents in exposed workers: two controlled follow-up studies after 5.5 and 10.6 years

The findings of acute and/or chronic central and peripheral neurotoxic effects of organic solvents in workers from a previous controlled cross-sectional study (65 exposed and 33 unexposed) were re-assessed to ascertain whether the neurotoxic symptoms and signs had become chronic. These follow-ups were performed 5.5 years later by occupational medical and clinical neurological examination (59 exposed and 30 unexposed) and again 10.6 years later by a mailed questionnaire (53 exposed and 30 unexposed). Both follow-ups revealed more acute neurotoxic symptoms in the exposed workers than in the unexposed workers, but fewer than previously, and indeed, the current exposure to solvents had been reduced. However, at both follow-ups, the exposed workers showed significantly more symptoms of chronic encephalopathy, in particular, memory and concentration impairment. These latter symptoms had also significantly worsened in the workers who were still being exposed, while they were presently unchanged in the previously exposed workers who had been free of exposure for 6.6 years at the latter follow-up. On the other hand, symptoms of chronic encephalopathy had not appeared in the unexposed group. Among workers, both still and previously exposed, there were also social consequences in the form of occupational disqualification. According to the findings, long-term occupational exposure to organic solvents in concentrations that are not unusual at workplaces may lead to development of chronic neurotoxic symptoms.