Current Threshold Limit Value Research Articles

The ACGIH TLV for lifting: Estimated TLVs for torso asymmetry beyond 30 degrees.

The American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Values (TLVs) for Lifting is a manual material handling (MMH) assessment method to identify weight limits that nearly all workers may be exposed to without developing work-related low back disorders (LBD). However, this assessment method only applies to lifting with the torso within 30° asymmetry of the sagittal plane. Estimate TLV weight limits while lifting with torso asymmetry greater than 30° beyond the sagittal plane. Lifting tasks were performed from various horizontal and vertical locations, at torso asymmetry angles of 0°, 15°, 30°, 45°, 60°, 75° and 90°, using ACGIH identified TLVs. Validated MMH assessment methods (NIOSH Lifting Equation, Ohio State University LBD Risk Model) were utilized to estimate TLVs at torso asymmetries greater than 30°. The current ACGIH TLVs resulted in low- to moderate-risk risk levels for torso asymmetries from 0° to 30°, and the risk incrementally increased as torso asymmetry increased to 90°. With the intention to keep the risk levels to that found at 30° torso asymmetry, lower TLV weight limits in the vertical and horizontal zones investigated were estimated for torso asymmetries from 45° to 90°. The resulting adjusted TLVs were consistent with weight limits identified for similar lifting conditions from other assessment methods that account for torso asymmetry. This research found current ACGIH-defined TLVs possess less than high-risk for LBD, and provided guidance to practitioners for reduced TLVs when torso asymmetry is greater than 30° from the sagittal plane.

Biochemical and hematological effects of lead exposure in Iranian battery workers

Objectives. The purpose of this study was to evaluate the hematotoxic, hepatotoxic and nephrotoxic responses following lead exposure among battery workers. Methods. Seventy-eight battery workers exposed to lead and 78 non-exposed subjects were studied. Fasting blood samples were collected to assess kidney and liver function and hematological parameters. To determine the breathing zone and blood lead levels (BLLs), the samples were analyzed in accordance with NIOSH methods 7082 and 8003, respectively. Results. The battery workers had significantly higher breathing zone lead and BLLs than the non-exposed group. In battery workers, most hematological parameters, including red blood cells, hemoglobin, mean corpuscular volume, mean corpuscular hemoglobin and mean corpuscular hemoglobin concentration, have significantly decreased. In contrast, the white blood cell count has shown a significant increase as compared to the controls. The mean levels of alanine aminotransferase and aspartate aminotransferase as biomarkers of liver damage and the creatinine serum levels as a result of renal failure were significantly higher in the exposed group than in the non-exposed group. Conclusions. These observations indicate that occupational exposure to lead exceeding its current threshold limit value and biological exposure index is associated with hematological symptoms and liver and kidney dysfunction.

Estimating Historical Exposure to Respirable Crystalline Silica in the Mining Industry in Ontario, Canada Using a Newly Developed Exposure Database.

To use the recently developed Ontario Mining Exposure Database (OMED) to describe historical silica exposure in the Ontario metal mining industry and identify predictors of historical silica exposure. Personal respirable crystalline silica (RCS) data for metal mines were extracted from OMED and included both individual and summary measures, where multiple exposure measurements (n > 1) were aggregated and entered as a single exposure value (n = 1). Data were stratified by sample location (underground/surface) for analysis. Monte Carlo simulation was used to simulate individual measures from the summary measures. A fixed effects multiple linear regression model was used to assess the effects of commodity (ore mined), sample year, source of exposure data, and occupational group on RCS concentration. Parameter estimates (β), standard errors, and 95% upper and lower confidence intervals were reported. The OMED contained 12 995 silica measurements. After limiting to RCS measurements in metal mines, and measures with sufficient information for analysis, 2883 RCS measurements collected from 1974 to 1991 remained, including 2816 individual and 67 summary measurements. In total, 321 individual RCS measurements were simulated from the 67 summary measures. The analysis database contained 2771 (12% simulated) underground measurements and 366 surface measurements (0% simulated). In the underground group, an overall geometric mean (GM) of 0.05 [geometric standard deviation (GSD) 3.09] mg m-3 was estimated with a 6% annual decrease over time. In this group, the commodity with the highest average RCS level was zinc mines (GM = 0.07 mg m-3) and the lowest was iron mines (GM = 0.01 mg m-3). In the surface group, an overall GM of 0.05 (GSD 3.70) mg m-3 was estimated with an 8% decreased over time. In this group, the commodity with the highest average RCS level was gold mines (GM = 0.07 mg m-3) and the lowest was zinc mines (GM = 0.03 mg m-3). In both groups, company collected data had lower estimated RCS compared with regulator collected data. Historical RCS levels decreased over time. Mean measurements exceeded the American Conference of Governmental Industrial Hygienists current health-based threshold limit value (0.025 mg m-3). The main predictors of exposure were commodity, source of exposure data, and sample year. However, low R2 and high GSD values suggest additional predictors of RCS exposures in Ontario's metal mines exist that were unavailable in OMED.

Exploring Localized Muscle Fatigue Responses at Current Upper-Extremity Ergonomics Threshold Limit Values.

The purpose of this study was to evaluate localized muscle fatigue responses at three upper-extremity ergonomics threshold limit value (TLV) duty cycles. Recently, a TLV equation was published to help mitigate excessive development of localized muscle fatigue in repetitive upper limb tasks. This equation predicts acceptable levels of maximal voluntary contraction (% MVC) for a given duty cycle (DC). Experimental validation of this TLV curve has not yet been reported, which can help guide utilization by practitioners. Eighteen participants performed intermittent isometric elbow flexion efforts, in three separate counter-balanced sessions, at workloads defined by the American Conference of Governmental Industrial Hygenists' (ACGIH) TLV equation: low DC (20% DC, 29.6% MVC), medium DC (40% DC, 19.7% MVC), and high DC (60% DC, 13.9% MVC). Targeted localized muscle fatigue (LMF) of the biceps brachii was tracked across numerous response variables, including decline in strength (MVC), electromyography (EMG) amplitude and mean power frequency (MnPF), and several psychophysical ratings. At task completion, biceps MnPF and MVC (strength) were significantly different between each TLV workload, with the high DC condition eliciting the largest declines in MnPF and MVC. Findings demonstrate that working at different DCs along the ACGIH TLV curve may not be equivalent in preventing excessive LMF. Higher DC workloads elicited a greater LMF response across several response variables. High DC work of the upper extremity should be avoided to mitigate excess LMF development. Current TLVs for repetitive upper-extremity work may overestimate acceptable relative contraction thresholds, particularly at higher duty cycles.

Assessment of exposure of gas station attendants in Sri Lanka to benzene, toluene and xylenes

Exposure to benzene, toluene and p-, m-, o-xylene (BTX) was studied in 29 gas station attendants and 16 office workers in Sri Lanka. The aim of this study was to assess the exposure level and identify potential exposure mitigating measures. Pre- and post-shift samples of end-exhaled air were collected and analysed for BTX on a thermal desorption gas chromatography mass spectrometry system (TD-GC-MS). Urine was collected at the same timepoints and analysed for a metabolite of benzene, S-phenyl mercapturic acid (SPMA), using liquid chromatography-mass spectrometry (LC-MS). Environmental exposure was measured by personal air sampling and analysed by gas chromatography flame ionization detection (GC-FID). Median (range) breathing zone air concentrations were 609 (65.1-1960) μg/m3 for benzene and 746 (<5.0-2770) μg/m3 for toluene. Taking into account long working hours, 28% of the measured exposures exceeded the ACGIH threshold limit value (TLV) for an 8-h time-weighted average of 1.6 mg/m3 for benzene. Xylene isomers were not detected. End-exhaled air concentrations were significantly increased for gas station attendants compared to office workers (p < 0.005). The difference was 1-3-fold in pre-shift and 2-5-fold in post-shift samples. The increase from pre-to post-shift amounted to 5-15-fold (p < 0.005). Pre-shift BTX concentrations in end-exhaled air were higher in smokers compared to non-smokers (p < 0.01). Exposure due to self-reported fuel spills was related to enhanced exhaled BTX (p < 0.05). The same was found for sleeping at the location of the gas station between two work-shifts. Benzene in end-exhaled air was moderately associated with benzene in the breathing zone (r = 0.422; p < 0.001). Median creatinine-corrected S-phenyl mercapturic acid (SPMA) was similar in pre- and post-shift (2.40 and 3.02 μg/g) in gas station attendants but increased in office workers (from 0.55 to 1.07 μg/g). In conclusion, working as a gas station attendant leads to inhalation exposure and occasional skin exposure to BTX. Smoking was identified as the most important co-exposure. Besides taking preventive measure to reduce exposure, the reduction of working hours to 40 h per week is expected to decrease benzene levels below the current TLV.

Heat stress assessment during intermittent work under different environmental conditions and clothing combinations of effective wet bulb globe temperature (WBGT)

This study examined whether different combinations of ambient temperature and relative humidity for the effective wet bulb globe temperature, in conjunction with two different levels of clothing adjustment factors, elicit a similar level of heat strain consistent with the current threshold limit value guidelines. Twelve healthy, physically active men performed four 15-min sessions of cycling at a fixed rate of metabolic heat production of 350 watts. Each trial was separated by a 15-min recovery period under four conditions: (1) Cotton coveralls + dry condition (WD: 45.5 °C dry-bulb, 15% relative humidity); (2) Cotton coveralls + humid condition (WH: 31 °C dry-bulb, 84% relative humidity); (3) Protective clothing + dry condition (PD: 30 °C dry-bulb, 15% relative humidity); and (4) Protective clothing + humid condition (PH: 20 °C dry-bulb, 80% relative humidity). Gloves (mining or chemical) and headgear (helmet or powered air-purifying respirator) were removed during recovery with hydration ad libitum. Rectal temperature (Tre), skin temperature (Tsk), physiological heat strain (PSI), perceptual heat strain (PeSI), and body heat content were calculated. At the end of the 2-hr trials, Tre remained below 38 °C and the magnitude of Tre elevation was not greater than 1 °C in all conditions (WD: 0.9, WH: 0.8, WH: 0.7, and PD: 0.6 °C). However, Tsk was significantly increased by approximately 2.1 ± 0.8 °C across all conditions (all p ≤ 0.001). The increase in Tsk was the highest in WD followed by PD, WH, and PH conditions (all p ≤ 0.001). Although PSI and PeSI did not indicate severe heat strain during the 2-hr intermittent work period, PSI and PeSI were significantly increased over time (p ≤ 0.001). This study showed that core temperature and heat strain indices (PSI and PeSI) increased similarly across the four conditions. However, given that core temperature increased continuously during the work session, it is likely that the American Conference of Governmental Industrial Hygienist’s TLV® upper limit core temperature of 38.0 °C may be surpassed during extended work periods under all conditions.

Feasibility the Biological Monitoring of Workers Exposed to Benzene and Toluene via Measuring the Parent Compounds in the Exhaled Breath

Background: Solvents such as benzene and toluene are commonly used in tire manufacturing, and significant occupational exposure to these chemicals adversely affects the health of workers. In biological monitoring, a complementary method for personal monitoring, the internal absorbed dose is measured and individual, environmental, and exposure differences are taken into consideration. Objectives: The present study evaluated external doses by personal monitoring and investigated a more practical approach to biological monitoring by measuring the internal doses of benzene and toluene in workers involved in tire manufacturing. Materials and Methods: Personal monitoring of 100 workers in tire factories A and B (n = 50 samples from each factory, n = 100 total personal samples) was performed using the national institute for occupational safety and health 1501 method. Biological monitoring of the workers was performed by collecting exhaled air in Tedlar ® bags (n = 100). Personal and biological samples were analyzed by a gas chromatograph equipped with a flame ionization detector. Data were analyzed by independent t-test and correlation coefficients. Results: There were no significant differences between factories with respect to worker age or work history. Personal exposure to benzene exceeded the current threshold limit value in 68% of workers. Occupational exposure to benzene and toluene as external (i.e. in the breathing area) and internal doses (i.e. in the exhaled air) were significantly higher in factory B than factory A. In addition, the external and internal doses of both compounds were significantly correlated. Conclusions: The workplace conditions of tire factories must be improved. The biological exposure index can be calculated by determining the unchanged benzene and toluene concentrations in exhaled air; this can be used as a more reliable method for personal monitoring.

Early Liver and Kidney Dysfunction Associated with Occupational Exposure to Sub-Threshold Limit Value Levels of Benzene, Toluene, and Xylenes in Unleaded Petrol

BackgroundUnleaded petrol contains significant amounts of monocyclic aromatic hydrocarbons such as benzene, toluene, and xylenes (BTX). Toxic responses following occupational exposure to unleaded petrol have been evaluated only in limited studies. The main purpose of this study was to ascertain whether (or not) exposure to unleaded petrol, under normal working conditions, is associated with any hepatotoxic or nephrotoxic response.MethodsThis was a cross-sectional study in which 200 employees of Shiraz petrol stations with current exposure to unleaded petrol, as well as 200 unexposed employees, were investigated. Atmospheric concentrations of BTX were measured using standard methods. Additionally, urine and fasting blood samples were taken from individuals for urinalysis and routine biochemical tests of kidney and liver function.ResultsThe geometric means of airborne concentrations of BTX were found to be 0.8 mg m−3, 1.4 mg m−3, and 2.8 mg m−3, respectively. Additionally, means of direct bilirubin, alanine aminotransferase, aspartate aminotransferase, blood urea and plasma creatinine were significantly higher in exposed individuals than in unexposed employees. Conversely, serum albumin, total protein, and serum concentrations of calcium and sodium were significantly lower in petrol station workers than in their unexposed counterparts.ConclusionThe average exposure of petrol station workers to BTX did not exceed the current threshold limit values (TLVs) for these chemicals. However, evidence of subtle, subclinical and prepathologic early liver and kidney dysfunction was evident in exposed individuals.

Hematological study of petrol station workers exposed to unleaded petrol

This study was undertaken to assess the level of exposure of petrol station workers to toxic components of unleaded petrol and to investigate whether this exposure, under normal working conditions, is associated with any significant changes in hematological parameters. In this cross-sectional study, 400 subjects (200 exposed and 200 reference subjects) were included. Atmospheric concentrations of benzene (B), toluene (T), and xylene (X) (BTX) were measured and all subjects underwent complete blood counts and white blood cell differential tests. The geometric means of airborne concentrations of BTX were lower than their recommended exposure limits. The results of blood tests showed that the means of red blood cell distribution width and hematocrit parameters, while within the normal range, were significantly different in the two groups. In conclusions, the average exposure level of petrol station workers to BTX did not exceed the current threshold limit values for these chemicals. Additionally, overt hematotoxicity is unlikely to be the outcome of exposure to unleaded petrol under the conditions described in our study. Possible long-term consequences of subtle, clinically insignificant changes in the hematological parameters of exposed employees observed in this study deserve further investigation.

The health risk of chrysotile asbestos.

The word asbestos is a poorly attributed term, as it refers to two very different minerals with very different characteristics. One is the serpentine mineral of which the white asbestos, chrysotile, is the most common. The other is the amphibole asbestos, which includes the blue asbestos crocidolite and the brown asbestos amosite. Although today chrysotile is the only type used commercially, the legacy of past use of amphibole asbestos remains. This review clarifies the differences between the two mineral families referred to as asbestos and summarizes the scientific basis for understanding the important differences in the toxicology and epidemiology of these two minerals. Biopersistence and sub-chronic inhalation toxicology studies have shown that exposure to chrysotile at up to 5000 times the current threshold limit value (0.1 fibers/cm) produces no pathological response. These studies demonstrate as well that following short-term exposure the longer chrysotile fibers rapidly clear from the lung and are not observed in the pleural cavity. In contrast, short-term exposure to amphibole asbestos results quickly in the initiation of a pathological response in the lung and the pleural cavity. Significant progress has been made in understanding the factors that influence inhalation toxicology studies of fibers and epidemiological studies of workers. Evaluation of the toxicology and epidemiology studies of chrysotile indicates that it can be used safely under controlled use. In contrast, even short-term exposure to amphibole asbestos can result in disease.

Asphalt Fume Exposure Levels in North American Asphalt Production and Roofing Manufacturing Operations

This study extends by 8 years (1998–2005) a previous survey of asphalt fume exposures within North American asphalt processing and roofing product manufacturing workers. It focuses on characterizing personal, full-shift samples and seeks to address several limitations of the previous survey. Five major roofing manufacturers with established occupational health programs submitted workplace asphalt fume sampling results to a central repository for review and analysis. A certified industrial hygienist-led quality assurance team oversaw the data collection, consolidation, and analysis efforts. The analysis dataset consisted of 1261 personal exposure samples analyzed for total particulate (TP) and benzene soluble fraction (BSF) using existing NIOSH methods. For BSF, the survey's arithmetic (0.25 mg/m3, SD = 0.62) and geometric (0.12 mg/m3, GSD = 2.88) means indicate that the industry has sustained the control levels achieved in the late 1980s, early 1990s. Similar results were found for TP. The survey-wide summary statistics are consistent with other post-1990 multi-company exposure studies. Although these findings indicate that currently available controls are capable of achieving substantial (95%) compliance with the current threshold limit value in asphalt processing and inorganic shingle and roll plants, they also show that the majority of plants are not achieving this level of exposure control, and that exposures are significantly higher in plants making other product lines, particularly organic felt products. The current retrospective survey of existing company exposure data, like its predecessor, has several important limitations. These include lack of data on smaller manufacturers and on several commercially important product lines; insufficient information on the prevalence and effectiveness of engineering controls; no standard criteria by which to define and assess exposures in non-routine operations; and a paucity of exposure data collected as part of a random sampling strategy. To improve efforts to characterize exposures and potential health risks in roofing plants, a prospective program is currently being developed and piloted with the aim of building a more complete, higher-quality database based on a common industrial hygiene protocol.

Short-Term Rat Inhalation Study With Aerosols of Acrylic Ester-Based Polymer Dispersions Containing a Fraction of Nanoparticles

Aqueous polymer dispersions are important raw materials used in a variety of industrial processes. They may contain particles with diameters ranging from 10 to 1500 nm. Polymer exposure alone may cause pulmonary lesions after inhalation exposure. Polymer dispersions with increased proportions of nano-sized particles are being developed for improved material characteristics, and this may pose even increased pulmonary hazards upon potential inhalation exposure. In a 5-day screening study, male rats were nose-only exposed to aerosols generated from 2 dispersions of acrylic ester polymers with identical chemical composition but different nano-sized particle proportions at particle concentrations of 3 and 10 mg/m³. Immediately and 19 days after the end of inhalation, necropsies were conducted with major emphasis on respiratory tract histopathology. Three and 23 days after the end of inhalation, bronchoalveolar lavage was performed to screen for early pulmonary injury and inflammation. In contrast to the adverse effects known for other materials in short-term inhalation studies, none of the tested preparations of acrylic ester polymers elicited any adverse effect at the end of the inhalation or postinhalation periods. No shift in toxicity could be observed by the increased proportion of nano-sized polymer particles. Under the conditions of this study, the no observable adverse effect levels for both preparations were >10 mg/m³, that is 2- to 3-fold beyond current nuisance dust threshold limit values.

Historical exposure to wood dust in Ontario, Canada

ObjectivesSinonasal cancer due to wood dust exposure is well-recognised as an occupational cancer in Europe, but not in North America, possibly due to differences in tree species or exposure levels....

Adjuvant effects of gaseous formaldehyde on the hyper-responsiveness and inflammation in a mouse asthma model immunized by ovalbumin

Asthma is a complex pulmonary inflammatory disease, which is characterized by airway hyper-responsiveness, airflow obstruction, and airway inflammation. Exposure to a number of chemicals including formaldehyde (FA) can lead to asthma. This study aimed to explore the underlying role of FA exposure in occupational asthma, especially when it is combined with allergen exposure. Balb/c mice were randomly divided into six groups (n = 6/group): (1) saline control; (2) ovalbumin (OVA)-immunized (OVAimm) only; (3) 0.5 mg FA/m3 exposure; (4) OVAimm + 0.5 mg FA/m3; (5) 3.0 mg FA/m3 FA exposure; and, (6) OVAimm + 3.0 mg FA/m3. These low and high exposure FA levels were adopted from current (0.5 mg/m3) and original (3.0 mg/m3) Chinese Occupational Threshold Limit Values. Experiments were conducted after 3 week of combined exposure and a 1-week challenge with aerosolized OVA. Airway hyper-responsiveness, pulmonary tissue damage, eosinophil infiltration, and increased interleukin (IL)-4 and IL-6 levels in lung tissues were found in the OVA + 3.0 mg FA/m3 hosts as compared to values seen in the OVA-immunized only mice. The results here suggest to us that FA exposure can induce and aggravate asthma in Balb/c mice when it is combined with OVA immunization.

Pulmonary Toxicity in Mice by 2‐ and 13‐week Inhalation Exposures to Indium‐tin Oxide and Indium Oxide Aerosols

Inhalation toxicities of indium-tin oxide (ITO) and indium oxide (IO) in mice were characterized in comparison with those previously reported in rats. B6C3F(1) mice of both sexes were exposed by inhalation to ITO or IO aerosol for 6 h/day, 5 day/wk for 2 wk at 0, 0.1, 1, 10 or 100 mg/m(3) or 13 wk at 0, 0.1or 1 mg/m(3). ITO and IO particles were deposited in the lung, mediastinal lymph node (MLN) and nasal-associated lymphoid tissue. Alveolar proteinosis, infiltrations of alveolar macrophages and inflammatory cells and increased lung weight were induced by 2- and 13-week exposures to ITO and IO, while alveolar epithelial hyperplasia occurred only in the 2-week exposures. Thickened pleural wall, hyperplastic MLN, extramedullary hematopoiesis in the spleen and increased levels of erythrocyte parameters were induced by 13-week exposure to ITO. The ITO- and IO-induced pulmonary lesions were milder in mice than those previously reported in rats, and the fibrotic lesions were different between these two species. Indium levels in the lung and pooled blood were analyzed in the mice exposed to ITO and IO for 13 wk. In the 13-week inhalation exposure of mice to ITO, alveolar proteinosis and significantly increased lung weight were induced at the same exposure concentration as the current threshold limit value for indium and its compounds.

Exposure-Response Relationship and Risk Assessment for Cognitive Deficits in Early Welding-Induced Manganism

The exposure-response relationship for manganese (Mn)-induced adverse nervous system effects is not well described. Symptoms and neuropsychological deficits associated with early manganism were previously reported for welders constructing bridge piers during 2003 to 2004. A reanalysis using improved exposure, work history information, and diverse exposure metrics is presented here. Ten neuropsychological performance measures were examined, including working memory index (WMI), verbal intelligence quotient, design fluency, Stroop color word test, Rey-Osterrieth Complex Figure, and Auditory Consonant Trigram tests. Mn blood levels and air sampling data in the form of both personal and area samples were available. The exposure metrics used were cumulative exposure to Mn, body burden assuming simple first-order kinetics for Mn elimination, and cumulative burden (effective dose). Benchmark doses were calculated. Burden with a half-life of about 150 days was the best predictor of blood Mn. WMI performance declined by 3.6 (normal = 100, SD = 15) for each 1.0 mg/m3 x mo exposure (P = 0.02, one tailed). At the group mean exposure metric (burden; half-life = 275 days), WMI performance was at the lowest 17th percentile of normal, and at the maximum observed metric, performance was at the lowest 2.5 percentiles. Four other outcomes also exhibited statistically significant associations (verbal intelligence quotient, verbal comprehension index, design fluency, Stroop color word test); no dose-rate effect was observed for three of the five outcomes. A risk assessment performed for the five stronger effects, choosing various percentiles of normal performance to represent impairment, identified benchmark doses for a 2-year exposure leading to 5% excess impairment prevalence in the range of 0.03 to 0.15 mg/m3, or 30 to 150 microg/m3, total Mn in air, levels that are far below those permitted by current occupational standards. More than one-third of workers would be impaired after working 2 years at 0.2 mg/m3 Mn (the current threshold limit value).

The Effect of Workload on Biological Monitoring of Occupational Exposure to Toluene and N-Hexane: Contribution of Physiologically Based Toxicokinetic Modeling

A physiologically based toxicokinetic model was used to examine the impact of work load on the relationship between the airborne concentrations and exposure indicator levels of two industrial solvents, toluene and n-Hexane. The authors simulated occupational exposure (8 hr/day, 5 days/week) at different concentrations, notably 20 ppm and 50 ppm, which are the current threshold limit values recommended by ACGIH® for toluene and n-hexane, respectively. Different levels of physical activity, namely, rest, 25 W, and 50 W (for 12 hr followed by 12 hr at rest) were simulated to assess the impact of work load on the recommended biological exposure indices: toluene in blood prior to the last shift of the workweek, urinary o-cresol (a metabolite of toluene) at the end of the shift, and free (nonhydrolyzed) 2,5-hexanedione (a metabolite of n-hexane) at the end of the shift at the end of the workweek. In addition, urinary excretion of unchanged toluene was simulated. The predicted biological concentrations were compared with the results of both experimental studies among human volunteers and field studies among workers. The highest predicted increase with physical exercise was noted for toluene in blood (39 μg/L at 50 W vs. 14 μg/L at rest for 20 ppm, i.e., a 2.8-fold increase). The end-of-shift urinary concentrations of o-cresol and toluene were two times higher at 50 W than at rest (for 20 ppm, 0.65 vs. 0.33 mg/L for o-cresol and 43 vs. 21 μg/L for toluene). Urinary 2,5-hexanedione predicted for 50 ppm was 1.07 mg/L at 50 W and 0.92 mg/L at rest (+16%). The simulations that best describe the concentrations among workers exposed to toluene are those corresponding to 25 W or less. In conclusion, toxicokinetic modeling confirms the significant impact of work load on toluene exposure indicators, whereas only a very slight effect is noted on n-hexane kinetics. These results highlight the necessity of taking work load into account in risk assessment relative to toluene exposure.

All-Optical Fuel Leak Detector for Monomethylhydrazine

Hydrazine-based fuels are commonly used in missiles, spacecraft and space launch vehicles. These chemicals are extremely toxic, highly energetic, and consequentially very hazardous. Currently, monomethylhydrazine (MMH) is considered to be the predominant fuel for spontaneous ignition. The current threshold limit value (TLV) is established at 10 ppb by the American Conference of Governmental Industrial Hygienists (ACGIH). Therefore, monitoring leakage of these chemicals in ambient air becomes highly important for compliance monitoring. InnoSense LLC's (ISL) all-optical leak detector can be calibrated to detect leaks in the parts-per-million to parts-per-billion range. ISL's innovative sensor device incorporates a self-referenced, fiber-optics-based sensor platform for detecting MMH from -46{degree sign}C to +71{degree sign}C. Additionally, an optical sensor system can decrease payload in space applications, and be networked to monitor multiple locations in situ and in real time. This paper discusses the use of an organically modified silicate (Ormosil) matrix to develop the optical leak detector for MMH.

Exposure assessment of household mercury spills

Elemental mercury spills in households still occur with unfortunate regularity. Devices that contain enough mercury to pose exposure concerns are common to many homes. Response to household spills differs substantially from industrial settings and improper response can increase the risk of harmful health effects. Suggested inhalation exposure levels for residential settings are much different than occupational guidelines. The characteristics of the exposed population in homes differ greatly from industrial workplace spills. Exposure assessment in the home requires the use and understanding of non-occupational guidance. The current occupational OSHA permissible exposure limit and ACGIH threshold limit value are 100 μg/m3 and 25 μg/m3, respectively. By contrast, the Agency for Toxic Substances and Disease Registry (ATSDR) Minimum Risk Level (MRL) for elemental mercury vapors is 0.2 μg/m3, well below occupational levels. The derivation of the MRL considers sensitive populations and 24 hour-a-day, seven days-a-week lifetime exposure. Occupancy criteria of 1.0 μg/m3 and 3.0 μg/m3 for residential and commercial settings have been proposed. These low levels dictate sophisticated analytical equipment or laboratory methods of analysis. Two cases illustrate how difficult it may be to assess hazards based solely on spill amount. In both cases a direct reading cold vapor atomic absorption unit was used to measure airborne mercury concentrations. Case A involved a broken thermometer spill (about 0.5 g) in a master bedroom that was cleaned using a household vacuum. Airborne concentrations throughout the home exceeded recommended exposure levels for residential settings (range of 2.5–14 μg/m3). Case B involved a broken thermostat spill (about 3.0 g) cleaned with a shop vacuum. Exposure levels were less than 1 μg/m3 throughout the home (range 0.4–0.7 μg/m3). When vacuums are used to remove mercury, quantities of mercury as small as that associated with a fever thermometer can represent an exposure hazard. The difference in exposure levels between the two cases is thought to be related to the operational differences between vacuum cleaners and the impact they had on vapor production. Unfamiliarity with the hazards posed by seemingly small amounts of mercury in the home and workplace can lead to undesirable and often costly consequences.

Analytical Performance Criteria

Column Editor Kevin Ashley