Methanol Depletion in Solvents

Industrial workers make up the segment of the population that is most vulnerable to chemical injury. To protect them from occupation-related harm, the American Conference of Governmental and Industrial Hygienists publishes annually revised threshold limit values (TLVs) (1), guidelines for permissible chemical exposure at the work place. TLV refers to concentrations of substances in parts per million or milligrams per cubic meter in the air to which most workers can be exposed on a daily basis without harm. These values apply to the work place only. They are not intended as guidelines for ambient air quality standards for the population at large. Obviously, genetic variations and diverse lifestyles (such as smoking, alcohol use, medication, and drug use) must be considered. Hypersensitive individuals may be adversely affected by exposure to certain chemicals even within the limits of the TLV. Thus, TLVs should be treated as guidelines only and not as fixed standards. The recommended goal is to minimize chemical exposure in the work place as much as possible. TLVs are expressed in three ways: 1. Time-weighted average (TLV–TWA) designates the average concentration of a chemical to which workers may safely be exposed for 8 h per day and 5 days per week. 2. Short-term exposure limit (TLV–STEL) designates permissible exposure for no more than 15 min, and no more than four times per day, with at least 60-min intervals between exposures. 3. Ceiling concentrations (TLV–C) are concentrations that should not be exceeded at any time. How protective the TLVs are is being questioned. The 1990 report that analyzed the scientific underpinnings of the TLVs revealed that at the exposure at or below the TLV, only few cases showed no adverse effect (2). In some cases even 100% of those exposed were affected. On the other hand, there was a good correlation between the TLVs and the measured exposure occurring in the work place. Thus, it appears that the TLVs represent levels of contaminants that may be encountered in the work place, rather than protective thresholds. Biological exposure indices (BEIs) provide another way of looking at exposure to chemicals.

Threshold Limit Values (TLVs) represent conditions under which the TLV Committee of the American Conference of Governmental Industrial Hygienists (ACGIH) believes that nearly all workers may be repeatedly exposed without adverse effect. A detailed research was made of the references in the 1976 Documentation to data on "industrial experience" and "experimental human studies." The references, sorted for those including both the incidence of adverse effects and the corresponding exposure, yielded 158 paired sets of data. Upon analysis it was found that, where the exposure was at or below the TLV, only a minority of studies showed no adverse effects (11 instances) and the remainder indicated that up to 100% of those exposed had been affected (8 instances of 100%). Although, the TLVs were poorly correlated with the incidence of adverse effects, a surprisingly strong correlation was found between the TLVs and the exposures reported in the corresponding studies cited in the Documentation. Upon repeating the search of references to human experience, at or below the TLVs, listed in the more recent, 1986 edition of the Documentation, a very similar picture has emerged from the 72 sets of clear data which were found. Again, only a minority of studies showed no adverse effects and TLVs were poorly correlated with the incidence of adverse effect and well correlated with the measured exposure. Finally, a careful analysis revealed that authors' conclusions in the references (cited in the 1976 Documentation) regarding exposure-response relationships at or below the TLVs were generally found to be at odds with the conclusions of the TLV Committee. These findings suggest that those TLVs which are justified on the basis of "industrial experience" are not based purely upon health considerations. Rather, those TLVs appear to reflect the levels of exposure which were perceived at the time to be achievable in industry. Thus, ACGIH TLVs may represent guides of levels which have been achieved, but they are certainly not thresholds.

The ACGIH Worldwide Threshold Limit Value (TLV) for hand activity "considers average hand activity level or "HAL" and peak hand force." We report cross-sectional data that assess the validity of the TLV with respect to symptoms and selected upper extremity musculoskeletal disorders among workers. The prevalence of symptoms and specific disorders were examined among 908 workers from 7 different job sites in relation to the TLV. Worker exposures were categorized as above the TLV, above the TLV Action Limit but below the TLV, or below the TLV Action Limit. Symptoms in the distal upper extremities did not vary by TLV category. Tendonitis in the wrist/hands/fingers did not vary by TLV category, but elbow/forearm tendonitis was significantly associated with TLV category. All measures of carpal tunnel syndrome were associated with TLV category. In all instances, prevalence of symptoms and specific disorders were substantial in jobs that were below the TLV action limit, suggesting that even at "acceptable" levels of hand activity, many workers will still experience symptoms and/or upper extremity musculoskeletal disorders, which may be important in the rehabilitation and return to work of injured workers. Future analyses need to examine the incidence of symptoms and upper extremity musculoskeletal disorders prospectively among workers in relation to the TLV for hand activity.

ObjectivesEvidence on occupational determinants of Carpal Tunnel Syndrome (CTS) mainly derived from cross-sectional or retrospective studies. We conducted a cohort study to investigate the association between biomechanical occupational exposures and...

The terms maximum allowable concentration (M.A.C.) and threshold limit value (T.L.V.) differ in their respective meanings. The M.A.C. is a ceiling concentration whereas the T.L.V. is a time-weighted average of the concentration of the hazardous agent in the atmosphere. The value attributed to M.A.C. or T.L.V. will vary with the criteria decided upon for the response selected. This response may be a clinical or biochemical change in human subjects resulting from the hazardous agent. An investigation of lead workers is reported, and from the data obtained from them and from their working environment recommendations have been made. The survey was carried out in printing works and storage battery factories; the order of development of abnormal biochemical findings was reconfirmed. The T.L.V. was determined for each stage of lead absorption by a graphic method. T.L.V.s for an eight to 10-hour working day were determined as 0·10 mg./m.³ to produce a urinary lead of 0·15 mg./l., 0·12 mg./m.³ for a coproporphyrinuria of about 50 μg./l., 0·14 mg./m.³ for basophilic stippling at the 0·3 per thousand level, and most likely 0·14 to 0·15 mg./m.³ for lead anaemia. The biochemical function chosen was an increased excretion of coproporphyrin, and to keep this below 50 μg./l. we would suggest that the T.L.V. should be about 0·12 mg./m.³ or a little more in the case of a 40-hour week.

Heat Stress: A Hazardous Occupational Risk for Vulnerable Workers

Investigations into the historical development of specific Threshold Limit Values (TLVs) for many substances have revealed serious shortcomings in the process followed by the American Conference of Governmental Industrial Hygienists. Unpublished corporate communications were important in developing TLVs for 104 substances; for 15 of these, the TLV documentation was based solely on such information. Efforts to obtain written copies of this unpublished material were mostly unsuccessful. Case studies on the TLV Committee's handling of lead and seven carcinogens illustrate various aspects of corporate influence and interaction with the committee. Corporate representatives listed officially as "consultants" since 1970 were given primary responsibility for developing TLVs on proprietary chemicals of the companies that employed them (Dow, DuPont). It is concluded that an ongoing international effort is needed to develop scientifically based guidelines to replace the TLVs in a climate of openness and without manipulation by vested interests.

Threshold limit values (TLVs) designed to restrict the severity of the vascular component of the hand-arm vibration syndrome (HAVS) have been proposed by the American Conference of Governmental Industrial Hygienists. A proposed revision to the TLVs would employ the same frequency-weighted accelerations measured according to ISO 5349 (1986), and daily exposure durations, but would associate the mild signs of stage 1 in the Stockholm workshop classification (SWS) with these exposure conditions, rather than, as previously, the severe signs of stage 3 [Anon. Appl. Occup. Environ. Hygiene 5, 464–470 (1990)]. Recent epidemiological data from populations of power tool operators experiencing exposure conditions close to those described in the TLVs reveal that prevalences of stage 2 + stage 3 white fingers of up to 20% have commonly occurred. It thus appears the claim of the revised TLVs, namely, to “represent conditions under which it is believed that nearly all workers may be exposed repeatedly without progressing beyond stage 1,” cannot be supported by epidemiological data.

Chapter sixteen - Step Four: Establish Permissible Levels of Exposure

Methanol will be present as a new air pollutant when methanol-powered vehicles are introduced in the United States. Little is known about the effect of low-dose methanol exposure. It is controversial whether or not formate, the main metabolite responsible for methanol's acute toxicity, is a sensitive biological marker of toxicity or exposure. We studied the effect of a 4-hr exposure at rest to 200 ppm of methanol vapors on endogenous serum formate and on urinary formic acid excretion. A randomized, double-blind study of human exposure to a constant concentration of methanol was performed in a whole-body exposure chamber. Twenty-six healthy volunteers, each serving as his or her own control, participated in sham and methanol exposures. Urine (at 0, 4, 8 hr) and serum specimens (15 time points over 8 hr) collected before, during, and after the exposure were measured for formate. We found no significant differences in serum formate concentration between exposure and control conditions either at any time point or for area under the curve. Mean concentrations at the end of the exposure were: exposed 14.28 +/- 8.90 mg/l and control 12.68 +/- 6.43 mg/l. A slight, but nonsignificant (p = 0.08), increase in urine formate excretion rate was found at 4 hr (exposed 2.17 +/- 1.69 mg/4 hr and control 1.67 +/- 1.02 mg/4 hr). Age, sex, folic acid level, and smoking were not significant covariates. At 200 ppm, methanol exposure does not contribute substantially to endogenous formate quantities. Serum and urine formate determinations are not sensitive biological markers of methanol exposure at the threshold limit value.

The determination of respirable particles in talcum powder

Furfuryl alcohol and formaldehyde concentrations in the air of coremaking areas of 10 iron and steel foundries were measured. The mean concentration of furfuryl alcohol and formaldehyde was 4.3 cm3/m3 and 2.7 cm3/m3, respectively. Furfuryl alcohol exceeded its threshold limit value (TLV) of 5 cm3/m3 in 22% of the determinations; and formaldehyde (TLV=2 cm3/m3) in 38%. In addition phenol concentration was determined in one foundry; and phosphoric acid concentration, in two foundries. The concentrations of phenol and phosphoric acid were far lower than their TLVs. The question is raised as to whether exposure to furfuryl alcohol and formaldehyde in foundries in combination with exposure to dust and smoking can increase the risk of chronic bronchitis.

BackgroundAirborne fumigants and other hazardous chemicals inside unopened shipping containers may pose a risk to workers handling containers.MethodsGrab air samples from 490 sealed containers arriving in New Zealand were analysed for fumigants and other hazardous chemicals. We also collected grab air samples of 46 containers immediately upon opening and measured the total concentration of volatile organic compounds in real-time during ventilation. Additive Mixture Values (AMV) were calculated using the New Zealand Workplace Exposure standard (WES) and ACGIH Threshold Limit Values (TLV) of the 8-h, time-weighted average (TWA) exposure limit. Regression analyses assessed associations with container characteristics.ResultsFumigants were detectable in 11.4% of sealed containers, with ethylene oxide detected most frequently (4.7%), followed by methyl bromide (3.5%). Other chemicals, mainly formaldehyde, were detected more frequently (84.7%). Fumigants and other chemicals exceeded the WES/TLV in 6.7%/7.8%, and 7.8%/20.0% of all containers, respectively. Correspondingly, they more frequently exceeded ‘1’ for the AMV-TLV compared to the AMV-WES (25.7% versus 7.8%). In samples taken upon opening of doors, fumigants were detected in both fumigated and non-fumigated containers, but detection frequencies and exceedances of the WES, TLV, and AMVs were generally higher in fumigated containers. Detection frequencies for other chemicals were similar in fumigated and non-fumigated containers, and only formaldehyde exceeded both the WES and TLV in both container groups. Volatile compounds in container air reduced rapidly during ventilation. Some cargo types (tyres; personal hygiene, beauty and medical products; stone and ceramics; metal and glass; and pet food) and countries of origin (China) were associated with elevated airborne chemical and fumigant concentrations.ConclusionAirborne chemicals in sealed containers frequently exceed exposure limits, both in fumigated and non-fumigated containers, and may contribute to short-term peak exposures of workers unloading or inspecting containers.

Here, we report a threshold limit value (TLV) of on-chip cytotoxicity of Nepali Chiya, the Nepali traditional black tea. To demonstrate our proof-of-concept validation, we used the active sealing chip with serial dilution that can directly perform on-chip cytotoxicity testing onto the cells cultured in a petri dish. In our experiments, the TLV for mortality on HeLa cells was observed as 400 μg/ml for Nepali Chiya extract. We believe this approach would be a rapid and simple method for on-chip TLV screening of potability of tea extract at the laboratory level, and furthermore as a new potential drug supplement in pharmaceutical industries.

The occupational exposure limit of 2.0 microg/m3 for beryllium has been used in the workplace since the late 1940s. In particular, the adequacy of the American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Value (TLV) for beryllium has recently come into question. The symposium "Beryllium: Effect on Worker Health" was convened in September 1999, to bring together leading scientists to present and discuss current research activities on beryllium exposure and chronic beryllium disease (CBD). One of the key questions to be resolved at the symposium was, "Is there a sufficient understanding of exposure and the cause of CBD that would allow us to develop a TLV that we believe would prevent disease?" Seven scientists presented information regarding the current understanding of the disease, possible causes, and ongoing research. The topics were (1) biomonitoring approaches and their relationship with clinical effects, (2) historical and current exposure assessments, (3) sampling methods and aerosol characterization, and (4) epidemiology. Six basic hypotheses regarding the relationship between exposure to beryllium and CBD were generated from the information presented at the symposium. The six hypotheses that are related to issues such as beryllium form, particle size, industrial hygiene practices, extrapulmonary routes of exposure, and genetic susceptibility also appear to be the focus of ongoing and likely future research initiatives. This article summarizes both the presentations made at the meeting and the hypotheses generated. It is expected that an understanding of these issues should explain the inconsistent dose-response relationship observed between exposure and CBD. The ongoing and planned research is anticipated to provide sufficient data within two to three years to develop one or more scientifically sound TLVs for the different chemical forms of beryllium.