Time-weighted Average Threshold Limit Value Research Articles

Carcinogenic and non-carcinogenic risk of exposure to metal fume in different types of welding processes.

The international agency for cancer research (IARC) has classified welding fumes as definitive carcinogens. The aim of the present study was to assess health risk due to exposure to welding fumes in different welding types. In this study, exposure to fumes of iron (Fe), chromium (Cr), and nickel (Ni) in the breathing zone air of 31 welder engaged in arc, argon and CO2 welding was assessed. Carcinogenic and non-carcinogenic risk assessments due to exposure to fumes were performed using the method proposed by the Environmental Protection Agency (EPA) by Monte Carlo simulation. The results showed that in the CO2 welding, concentration of Ni, Cr, and Fe was lower than the 8-h Time-Weighted Average Threshold Limit Value (TWA-TLV), recommended by the American Conference of Governmental Industrial Hygienists (ACGIH). In argon welding, Cr and Fe concentrations were higher than the TWA-TLV. In arc welding, concentrations of Ni and Fe were more than the TWA-TLV. In addition, the risk of non-carcinogenicity due to exposure to Ni and Fe in all three types of welding was more than standard level (HQ>1). The results indicated that the welders are at health risk due to exposure to metal fumes. Preventive exposure control measures such as local ventilation need to be implemented in welding workplaces.

The exposure to formaldehyde in industries and health care centers: A systematic review and probabilistic health risk assessment

Formaldehyde is classified as a definitive human carcinogen by the International Agency for Research on Cancer (IARC). The workers in several industries such as foundry, melamine, resin, and health care centers (pathology and anatomy laboratories and operating rooms) are exposed to airborne formaldehyde. In this systematic review, studies conducted from 2000 to 2020 on occupational exposure to airborne formaldehyde in Iran were collected and analyzed. The carcinogenic and non-carcinogenic risk assessments of exposure to airborne formaldehyde were estimated using the recommended United State Environmental Protection Agency (USEPA) method by Monte-Carlo simulation. Results demonstrated that in both health care centers and industrial settings, mean concentrations of airborne formaldehyde were higher than that 8- hour time-weighted average threshold limit value (TWA-TLV) recommended by the American Conference of Governmental Industrial Hygienists (ACGIH). Also, results showed that cancer and non-cancer risks due to exposure to airborne formaldehyde (Neurological, dermal, respiratory effects and so on) were considerable in both industrial settings and health care settings. The results of this study could be used by health policy makers to eliminate or reduce exposure to airborne formaldehyde in workplaces.

Risk analysis of a supercritical fluid extraction plant affected by a gas release using a commercial software

This work presents a risk analysis of a plant that uses supercritical fluid extraction technology with carbon dioxide as a solvent to obtain bioproducts from microalgae.Given the high pressure at which it operates, the extraction plant called Luwar could be affected by dangerous events, such as the gas release in concentrations that are harmful to human health. In order to limit the damage, the risk analysis is of primary importance.The gas release could occur following the breakage of a pipe, which was the scenario being considered. It was analyzed using the commercial software Phast & Safeti, an alternative tool to the methods traditionally used in the literature in hazard events of this type, such as the Threshold Limit Value-Time Weighted Average (TLV-TWA) and the Threshold Limit Value-Short Term Exposure Limit (TLV-STEL), that are defined on the basis of the characteristics of the substance dispersed in the air.Since the pressure of the extraction vessel is the highest in the system, the risk analysis was carried out on the breakage of a pipe coming out of the extractor. The results obtained made it possible to identify the risk parameters on the basis of which to make the best choices in terms of safety to cope with the type of hazard analyzed.

Welder Exposure to NO and NO2 during Argon-Shielded Arc Welding on Aluminum Alloys

This work was performed to assess welder exposure to NO and NO2 and to assess the importance of these gases in the hierarchy of contaminants produced during welding (GMAW [MIG welding], GTAW [TIG welding], plasma cutting) on aluminum alloys. Personal air samples in the breathing zone were collected on welders using a small, person-portable, direct-reading, datalogging instrument containing an electrochemical sensor rated for NO2 and colorimetric detector tubes rated for NO to assess exposure during welding. Exceedance of the Threshold Limit Value -Time-Weighted Average (TLV-TWA) of 0.2 ppm (parts per million) averaged over 8 hours for NO2 and the Ceiling Limit of 1 ppm used by some jurisdictions was likely during GTAW (TIG welding) in poorly ventilated conditions. Exceedance of these limits was unlikely during plasma arc cutting and GMAW (MIG welding). Exceedance of the TLV-TWA of 25 ppm for NO was unlikely to occur. Exceedance of the TLV-TWA of 0.2 ppm and the Ceiling Limit of 1 ppm mandated in some jurisdictions for exposure to NO2 during argon-shielded GTAW on aluminium alloys is likely to occur in the shipyard environment examined during this study. Exceedance of Exposure Limits for NO2 during GMAW or plasma arc cutting is unlikely to occur. The critical substance at the top of the exposure hierarchy involving a complex mixture could be a gas. As well, this substance could be process-specific (GTAW versus GMAW). This situation illustrates the importance of monitoring worker exposure in consideration about the likelihood of exceedance of Exposure Limits and identification of critical substance(s) in the hierarchy of contaminants produced during a process.

Ozone: a critical contaminant produced during gas metal arc welding (GMAW) on aluminum alloys—resolving the short- versus long-duration sampling discrepancy

Ozone is one of the gases produced during argon-shielded arc welding on aluminum alloys. Arc welding superimposes multiple episodes of intense emission of short duration onto the background level during the work shift. Short-duration exposures during welding were measured using colorimetric detector tubes and long-duration exposures, by colorimetric badges utilizing similar chemistry. Both devices were positioned on the lapel in the breathing zone. Many of the short-duration samples exceeded the 8-h TLV–TWA (threshold limit value–time-weighted average) of 0.08 ppm for moderate work during argon-shielded gas metal arc welding (GMAW) also known as metal inert gas (MIG) welding. Some short-duration samples exceeded the transient limit of 0.24 ppm (3× the TLV–TWA), and several exceeded the maximum of 0.40 ppm (5× the TLV–TWA). Exceedance of the maximum in jurisdictions using TLVs as exposure limits necessitates control measures including effective local exhaust ventilation and respiratory protection. Ozone was undetectable (< 0.04 ppm) during gas tungsten arc welding (GTAW) also known as tungsten inert gas (TIG) welding. During long-duration sampling, almost all levels during GMAW were ≤ 0.08 ppm h (≤ 0.01 ppm averaged over 8 h), the limit of detection of the sampling device. As a result, ozone is a critical gaseous contaminant (requiring control measures) during GMAW (MIG welding). Protection of the eyes against irritation in sensitive individuals dominates other considerations.

Quantitative assessment of occupational exposure to total indium dust in Japanese indium plants.

This study quantitatively assessed personal exposure of 86 workers to indium compounds as total dust at 11 Japanese indium plants. The personal exposures to indium concentrations in the breathing zone during an 8 h work-shift were determined by ICP-MS. The arithmetic mean indium concentration of all the workers was 0.098 mg Indium (In)/m3, with individual values ranging from 0.0001 to 1.421 mg In/m3. There were 11 workers whose exposure to indium concentrations exceeded the American Conference of Governmental Industrial Hygienists’ Threshold Limit Value-Time Weighted Average (TLV-TWA) of 0.1 mg In/m3. Based on the condition TLV-TWA<X95 (upper 95th percentile of log-normal distribution), five indium plants were judged as “control measures required”, while 3 other plants were evaluated as “control measures not required”. Five workers belonging to the worst group were exposed to far higher indium concentrations than the TLV-TWA. Another group of 5 workers belonging to the best group was exposed to far lower indium concentrations than the TLV-TWA, and this was attributed to the stringent engineering control measures used at their workplaces. The quantitative assessment of occupational exposure to indium dust was influenced by different occupational exposure limit values without carcinogenicity and particle size-selectivity of indium particulates or “total” dust.

Use of Methanol as a Coolant During Machining of Aluminum in a Shipbuilding Environment: A Failure to Assess and Manage Risk

Minimization of harm during the conduct of work is one of the most important tenets of industrial hygiene. Organizations make changes to solve perceived problems. What appears to be expedient for solving a problem can create serious risks totally unrecognized by the proponent. This investigation reports on such a situation involving the use of methanol as a lubricant during machining of aluminium panels using a router. Spot samples for methanol were measured using colorimetric detector tubes and samples of long duration by colorimetric diffusion tubes utilizing similar chemistry. Both were positioned in the breathing zone. Most of the spot samples exceeded the 8-hour TLV-TWA (Threshold Limit Value-Time-Weighted Average) of 200 ppm and the TLV-STEL (Short-Term Exposure Limit) of 250 ppm. The two long duration samples also exceeded the TLV-TWA. A change in the operation prevented collection of additional long duration samples. By these measures, workers were overexposed to methanol during this activity. An additional serious consequence from use of methanol in this manner was risk of fire. This situation illustrates the complexity of decisions affecting workplace operations. What appears to be expedient for solving a problem may be totally inappropriate.

Evaluation of Cut-Off Saw Exposure Control Methods for Respirable Dust and Crystalline Silica in Roadway Construction

Dust reduction equipment adapted for single-person operation was evaluated for gas-powered, commercially available cut-off saws during concrete curb cutting. Cutting was performed without dust control and with two individual exposure control methods: wet suppression and local exhaust ventilation (LEV). The wet suppression system comprised a two-nozzle spray system and a 13.3-L hand-pressurized water supply system with an optimum mean flow rate of 0.83 L/min for 16 min of cutting. The LEV system consisted of a spring-loaded guard, an 18.9-L collection bag, and a centrifugal fan with an estimated exhaust rate of 91 ft3/min. Task-based, personal filter samples were obtained for four saw operators during cutting durations of 4 to 16 min on five job sites. Seventeen filter samples were collected without dust control, 14 with wet suppression, and 12 with LEV, yielding a geometric mean respirable dust concentration of 16.4 mg/m3, 3.60 mg/m3, and 4.40 mg/m3, respectively. A dust reduction of 78.0% for wet suppression and 73.2% for LEV was observed vs. no dust control. A statistically significant difference (p < 0.001) was also revealed for wet suppression and LEV when compared with no dust control; however, a significant difference (p = 0.09) was not observed between wet suppression and LEV. Despite these significant dust reductions, workers are still projected to exceed the ACGIH 8-hr time-weighted average threshold limit value for quartz (0.025 mg/m3) in less than 1 hr of cutting for both dust control methods. Further research is still needed to improve dust reduction and portability of both control methods, but the current LEV system offers important advantages, including a drier, less slippery work area and year-round functionality in cold weather.

Exposure to Styrene in Fiberglass-Reinforced Plastic Manufacture

The aim of the work is to define occupational exposure to styrene in fiberglass manufacture; the phase of stretching styrene resins needs some manual handling and leads workers to be exposed to styrene. We surveyed 20 workers in two companies manufacturing fiberglass, checking environmental levels and urinary concentrations of mandelic acid (MA), and phenylglioxylic acid (PGA). Workers completed a questionnaire collecting their medical history. Environmental monitoring showed some styrene concentrations higher than the threshold limit value-time-weighted average. Biological monitoring confirmed these findings and four workers had levels of urinary PGA and MA concentrations higher than the Biological Exposure Indices of the American Conference of Governmental Industrial Hygienists. This picture confirms that, even though the risk is known and the manufacturing cycle is well-defined, workers nevertheless risk exposure. More research is needed to optimize the work processes and the protection systems to lower this risk.

Trends in Pulmonary Function and Prevalence of Asthma in Hexamethylene Diisocyanate Workers During a 19-Year Period

To identify if 1,6-hexamethylene diisocyanate (HDI) workers demonstrated an increased prevalence of occupational asthma or accelerated decline in pulmonary function. Employees from two plants manufacturing or producing 1,6-HDI monomer and/or HDI polyisocyanates were matched to a control population by age, gender, race, and smoking status. A random coefficient regression analysis compared the decline in pulmonary function test values over time. Retrospective medical review was used to identify potential cases of occupationally induced asthma. No significantly accelerated annual decline in force expiratory volume after 1 second in the HDI exposure group compared to the matched control group was observed. No cases of adult onset asthma, beyond those present at time of hire, and no cases of occupational asthma were identified. This study provides support for the current American Conference of Governmental Industrial Hygienists threshold limit value time-weighted average of 5 ppb.

Occupational Exposure to Cobalt: A Population Toxicokinetic Modeling Approach Validated by Field Results Challenges the Biological Exposure Index for Urinary Cobalt

This study modeled the urinary toxicokinetics of cobalt exposure based on 507 urine samples from 16 workers, followed up for 1 week, and 108 related atmospheric cobalt measurements to determine an optimal urinary cobalt sampling strategy at work and a corresponding urinary exposure threshold (UET). These data have been used to calibrate a population toxicokinetic model, taking into account both the measurement uncertainty and intra- and interindividual variability. Using the calibrated model, urinary sampling sensitivity and specificity performance in detecting exposure above the 20 μg/m3 threshold limit value – time-weighted average (TLV-TWA) has been applied to identify an optimal urine sampling time. The UET value is obtained by minimizing misclassification rates in workplace exposures below or above the TLV. Total atmospheric cobalt concentrations are in the 5–144 μg/m3 range, and total urinary cobalt concentrations are 0.5–88 μg/g creatinine. A two-compartment toxicokinetic model best described urinary elimination. Terminal elimination half-time from the central compartment is 10.0 hr (95% confidence interval [8.3–12.3]). The optimal urinary sampling time has been identified as 3 hr before the end of shift at the end of workweek. If we assume that misclassification errors are of equal cost, the UET associated with the TLV of 20 μg/m3 is 5 μg/L, which is lower than the ACGIH-recommended biological exposure index of 15 μg/L. [Supplemental materials are available for this article. Go to the publisher's online edition of the Journal of Occupational and Environmental Hygiene for the following free supplemental resource: an appendix with discussion of the toxicokinetic model, priors, model checking, cross validation, and comparison of ROC curves for various urinary sampling strategy.]

Exposure to Hydrogen Peroxide and Eye and Nose Symptoms Among Workers in a Beverage Processing Plant

Two cross-sectional studies were undertaken on workers in a beverage processing plant to investigate the association between low H(2)O(2) exposure and symptoms of irritation (2005 study) and to investigate the effect of wearing respiratory protection (2006 study). The study comprised 69 workers exposed to H(2)O(2) in sterile chambers and 65 unexposed controls. The exposure was assessed from measurements and work task information from employment records. The severity of work-related symptoms was evaluated using questionnaires. Data were analyzed by the Student's t-test, multiple linear regression and analysis of variance for repeated measures of symptoms. Symptoms of eye, nose and throat irritation were significantly (P < 0.001) more severe among exposed workers compared to controls. Exposure values were occasionally above American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit value-time-weighted average (TLV-TWA) in the sterile chambers. The relationship between the severity of symptoms and the number of entrances in the chambers was significant (P < 0.0001) in 2005 but not in 2006, when respirators were used during work in the sterile chamber. No differences were found between exposed who entered a sterile chamber in 2005 but not in 2006 and exposed who entered a sterile chamber both in 2005 and 2006. This suggests that respirators provided an efficient protection and that the irritative effects of exposure to H(2)O(2) in 2005 did not disappear after 1 year. The source of risk was exposure in the sterile chamber, even though the time of exposure was generally only approximately 30 min. To ensure complete worker protection, there is a need for a short-term exposure limit for H(2)O(2) in addition to the existing ACGIH TLV-TWA value.

Simulation of repeated dose kinetics of methyl isobutyl ketone in humans from experimental single-dose inhalation exposure

Methyl isobutyl ketone (MIBK) is a solvent used in numerous products and processes and may be present in the air of the workplace as a vapor. The American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit value-time-weighted average (TLV-TWA) and TLV-short term exposure limit (TLV-STEL) for MIBK are 50 and 75 ppm, respectively. These workplace air concentration limits were set to protect workers from irritation, neurasthenic symptoms and possible adverse effects to their livers and kidneys. A recent revision of the ACGIH limit value has been proposed, to reduce the current TLV-TWA to 30 ppm. This article predicts the kinetics and accumulation of MIBK in humans exposed repeatedly in various exposure scenarios (8, 12, and 24 h/day for 7 days) to the current ACGIH TLV-TWA of 50 ppm. The kinetic parameters of the model were derived from published human time-course blood MIBK data from a single 2 h inhalation exposure to 48.9 ppm MIBK. The model correctly simulated single exposure experimental data with a rapid rise in blood concentration to 1.06 μg/ml within 1 h and approached ⩾99% steady-state blood level in 4 h of exposure. MIBK was predicted to be rapidly eliminated from blood after terminating the exposure, reaching 0.53 μg/ml and 0.13 μg/ml within 0.5 and 2 h post-exposure, respectively. Within 4 h after the termination of exposure, blood concentration would be expected to <1% of the steady-state concentration. On the basis of these results, it is concluded that accumulation of MIBK in workers due to repeated inhalation exposure is not likely to occur at the current TLV-TWA concentration of 50 ppm.

Generation, Sampling, and Analysis for Low-Level GB (Sarin) and GF (Cyclosarin) Vapor for Inhalation Toxicology Studies

This study tested and optimized various methodologies to generate, sample, and characterize GB and GF test atmospheres in an inhalation chamber, particularly at low vapor levels. A syringe drive/spray atomization system produced vapor concentrations at a range of 1–50 mg/m3. A saturator cell was used to generate vapor at sub-lethal concentrations ranging from 1 mg/m3 down to low levels approaching the threshold limit value time-weighted average (TLV-TWA) of 0.0001 mg/m3 for GB. Both generation techniques demonstrated the ability to produce stable vapor concentrations over extended exposure periods. This capability was important to determine sublethal nerve agent effects, such as miosis, for inhalation toxicology studies. In addition, the techniques employed for producing and maintaining low-level agent vapor would lay the foundation for testing less volatile chemical warfare agents such as VX.

Exposure to Low Molecular Weight Isocyanates and Formaldehyde in Foundries Using Hot Box Core Binders

Emissions from a chemical core binder system (Hot Box) based on a formaldehyde-carbamide resin have been investigated. The binder is used in some Swedish die-casting foundries. During core-making and casting, low molecular monoisocyanates, in particular methyl isocyanate (MIC) and isocyanic acid (ICA), were identified. Exposure to air concentrations of MIC, ICA and formaldehyde were subsequently determined in all Swedish foundries using the Hot Box binder, and involved three brass and one grey iron foundry. The survey was carried out in the winter period of 2001, and involved core-makers, casters and fettlers in the brass foundries, whereas only core-makers were included in the grey iron foundry. For each worker, four to five short-term samples of isocyanates (n = 298) and one 8 h sample of formaldehyde (n = 64) were collected during one shift for 15 die-casters, 39 core-makers and 10 other workers in the foundry. The air concentrations of the MIC short-term samples varied between <4 and 68 microg m(-3), with corresponding ICA levels between <4 and 280 microg m(-3). Calculated 8 h time weighted average air concentrations of MIC, based on short-term samples for each individual, varied between <4 and 31 microg m(-3); for ICA the corresponding levels varied from <4 to 190 microg m(-3). The formaldehyde time weighted average concentration levels ranged from 14 to 1600 microg m(-3), and the Swedish occupational exposure limit (600 microg m(-3)) was exceeded only in 3% of the samples. In general, the core-makers were exposed to higher average formaldehyde levels compared to the casters, the latter being more exposed to monoisocyanates. During core-making and die-casting, low molecular monoisocyanates, in particular MIC and ICA, were identified. Compared to the American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit value-time weighted average (TLV-TWA) for MIC, the exposures were low. The lack of toxicological and human data for ICA and the relatively high air concentrations call for medical examination and preventive measures in production, ventilation and the use of personal safety equipment in the investigated foundries.

Monitoring Human Exposures to Upper-Room Germicidal Ultraviolet Irradiation

After decades of neglect, the resurgence of tuberculosis in the United States between 1985 and 1992 renewed interest in the use of upper room ultraviolet germicidal irradiation to interrupt the transmission of airborne infections. More recently the bioterrorism threat and the appearance of new pathogens with the potential for airborne spread, such as severe acute respiratory syndrome (SARS), have stimulated installations of upper-room irradiation systems. The objective is to flood the entire volume of a room above 6.5 ft with high intensity ultraviolet germicidal irradiation, while minimizing unintentional irradiance below 6.5 ft to avoid eye and skin irritation. Air exchanges between the upper and lower room result in air disinfection of the occupied space. Designers of these systems have adopted the practice of limiting the maximum lower room irradiance at every point to less than the continuous 8-hour time-weighted average threshold limit value, severely limiting the irradiation intensity in the upper room and thereby reducing one of the two major factors determining germicidal effectiveness, the other being room air mixing. The hypothesis of this study is that eye and skin exposure will be well below the recommended safe dose even when maximum eye-level irradiance levels in the room exceed the 8-hour continuous exposure threshold limit. The method employed was to have subjects wear a small photometer that recorded total ultraviolet dose over the period of exposure while subjects went about their normal routine, and comparing this value with a hypothetical dose calculated from the highest measured eye-level irradiance. The results of the study, based on a limited number of observations, confirmed the hypothesis. Observed doses were one-third to a factor of a hundred or more lower than the doses calculated from maximum eye-level irradiances measurements in the occupants' spaces.

Fluoride compounds and their biological effects in aluminum potroom

Respiratory system disorders occur in aluminum potroom workers despite pre-employment medical examinations. The aims of this study were to measure fluoride and its compounds in the potroom workplace atmosphere as well as workers’ breathing zone air, examine the blood eozinophile cells count in the workers exposed to the fluoride compounds, and evaluate the respiratory symptoms and dysfunctions caused during the occupational exposure in potroom workers. To achieve these objectives, a study was carried out in 10 workplaces (potrooms) of Aluminum Producing Plants in Arak city located at Central Iran. Through this study, the data obtained from 160 workers (100 cases and 60 controls) were statically processed. The selected controls were matched for age, year of starting employment, smoking habit, and body mass index (BMI). The total fluoride compounds concentration of potroom, mean concentration of workers’ breathing zone air at different job positions were measured showed high concentration compared to the Threshold Limit Value-Time Weighted Average (TLV-TWA). The incidence of respiratory symptoms, the number of blood eozinophile, and WBC counts were higher than normal range in case group. During this study, the susceptible aluminum potroom workers to occupational asthma were also identified. Through this study, it was concluded that, workers employing in the potroom in aluminum industries are at risk for respiratory disorders and a continuous workplace monitoring is needed to evaluate workers exposures.

Current Man-Made Mineral Fibers (MMMF) Exposures Among Ontario Construction Workers

Current occupational exposures to man-made mineral fibers (MMMF), including refractory ceramic fibers (RCF), were measured as part of an exposure assessment program for an epidemiological study pertaining to cancer and mortality patterns of Ontario construction workers. The assessments were carried out at commercial and residential sites. A total of 130 MMMF samples (104 personal and 26 area) was collected and included 21 RCF (16 personal and 5 area). The samples were analyzed by the World Health Organization method in which both respirable and nonrespirable airborne fibers are counted. The results show that Ontario construction workers' full-shift exposure to MMMF (excluding RCF) is generally lower than the American Conference of Governmental Industrial Hygienists' (ACGIH®) recommended threshold limit value–time-weighted average (TLV®-TWA) of 1 fibers/cc and thus should not present any significant hazard. However, approximately 40% of the occupational exposures to RCF are higher than ACGIH's TLV-TWA of 0.2 fibers/cc and present a significant potential hazard. Workers generally wore adequate approved respiratory protection, especially while performing particularly dusty tasks such as blowing, spraying, and cutting, so the actual exposure received by workers was lower than the reported values. Adequate control measures such as ventilation and respiratory protection should always be used when work involves RCF.

Individual susceptibility to hexavalent chromium of workers of shoe, hide, and leather industries. Immunological pattern of HLA-B8,DR3-positive subjects

Background. This study was designed to examine the effects of hexavalent chromium [Cr(VI)] on the immunological pattern of shoe, hide, and leather industry workers, moving from the hypothesis that some haplotypes (HLA-B8,DR3) can be important hidden risk cofactors. Methods. Workplaces of 20 firms were monitored for total and respirable dusts and for total and hexavalent chromium. Cr(VI) on materials was also measured. Assay of chromium levels in blood and urine of 44 serological human leukocytes antigen (HLA)-typed workers (20 exposed, 15 HLA-B8,DR3-negative/5-positive and 24 non-exposed, 18 HLA-B8,DR3-negative/6-positive subjects) was performed by atomic absorption, and lymphocyte subsets (FACS-analysis), mitogen-mediate lympho-proliferation ([ 3H]thymidine incorporation), cytokine levels (ELISA), natural killer (NK) cytotoxic activity ( 51Cr-release assay) were determined. Results. The environmental parameter levels are lower than threshold limit value–time-weighted average (TLV-TWA); in the materials, the Cr(VI) values exceeded the levels allowed. The peripheral blood mononuclear cells (PBMC) proliferation and the T-helper1 (TH1) cytokine pattern of subjects chronically exposed were significantly raised; addition in vitro of Cr(VI) further stimulated these parameters and in general the entire TH1 system and NK activity. The TH2 system was unaltered. In the HLA-B8,DR3-positive workers, immunologically “low responders”, the addition of Cr(VI) in vitro caused a further reduction of the considered parameters in the exposed subjects with a dramatic deficit of the TH1 system. Conclusions. Results indicate the unsuitability of TLV-TWA as a line of demarcation between safe and dangerous Cr(VI) concentrations and the importance of individual genetic susceptibility for occupational and preventative medicine. In particular, the presence of the HLA-B8,DR3 alleles can represent an important cofactor of immunotoxic susceptibility consequent to chronic low-dose Cr(VI) exposure.

Coal tar pitch volatiles and polycyclic aromatic hydrocarbons exposures in expansion joint-making operations on a construction site: a case study.

This case study describes occupational exposures to coal tar pitch volatiles (CTPV) as benzene soluble fraction (BSF), polycyclic aromatic hydrocarbons (PAHs) and total particulates at a unique operation involving the use of coal tar in the making of expansion joints in construction of a multi-level airport parking garage. A task-based exposure assessment approach was used. A set of 32 samples was collected and analyzed for total particulate and CTPV-BSF. Twenty samples of this set were analyzed for PAHs. Current American Conference of Governmental Industrial Hygienists (ACGIH(R)) respective threshold limit value-time weighted average (TLV-TWA) for insoluble particulates not otherwise specified (PNOS) is 10 mg/m(3) as inhalable dust, which roughly corresponds to 4 mg/m(3) total particulate; for CTPV as BSF the TLV is 0.2 mg/m(3), and for specific PAHs such as benzo(a)-pyrene (B[a]P), ACGIH suggests keeping exposure as low as practicable. The recommended Swedish exposure limit for B(a)P is 2 microg/m(3). The highest exposure levels measured were 12.8 mg/m(3) for total particulate, 1.9 mg/m(3) for coal tar pitch volatiles as BSF, and 12.8 microg/m(3) for B(a)P. Several of the CTPV-BSF results were over the TLV of 0.2 mg/m(3). The data set is limited; therefore, caution should be used in its interpretation.