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PubMed1991

Chromated steel and contact allergy. Recommendation concerning a "threshold limit value" for the release of hexavalent chromium.

Steel surfaces can be treated with zinc and chromates to prevent the steel from rusting. Cases of allergic contact dermatitis due to the release of hexavalent chromium (Cr64) from chromated surfaces have been reported. The main purpose of the present study was to develop a simple procedure for the determination of leachable Cr64 that could be used in industrial applications to check the quality of chromated products and to establish a "threshold limit value" for such products. Occlusive tests were performed in chromate-sensitive patients using chromated discs, and discs representing a release of 0.6 microgram/cm2 or more elicited positive results in all patients tested. It was proposed that the mean release of Cr64 from chromated parts should not exceed 0.3 microgram/cm2. Approximately 1 out of 4 yellow chromated parts, collected from a chromating plant and a car assembly plant, gave values above this limit. Today, several tests are performed to evaluate the technical quality of the chromate layers. It is suggested that the present method should be added to the test program in order to reduce the risk of causing chromate allergy.

Chromates↗
PubMed1989

Threshold limit values: historical perspectives and current practice.

A 1989 Occupational Safety and Health Administration standard mandates that workplace air concentrations be held below new permissible exposure limits for 376 substances. As more than 350 of these limits came from the 1987 list of "Threshold Limit Values" (TLVs), the medical basis of the TLVs is of direct importance to the health of millions of workers. However, the TLV development process has been gravely flawed by lack of scientific rigor, inadequate medical input, and lack of attention to financial conflicts of interest. The adoption by the Occupational Safety and Health Administration of many poorly supported values as permissible exposure limits reflects also the underutilization of industrial medicine in identifying health effects of exposures below the TLVs. It is thus the responsibility of the medical profession to act on the presumption that the TLV permissible exposure limits are unsafe limits until a sound underlying body of medical and scientific literature exists for the substances on the list. It is industry's responsibility to commit itself seriously to medical and exposure monitoring and to begin to remedy the knowledge deficit that exists about the less immediate health effects of most industrial materials.

Air Pollutants, Occupational↗
PubMed1994

Olfactory mucosal lesions in F344 rats following inhalation exposure to pyridine at threshold limit value concentrations.

Pyridine is a volatile solvent used as an intermediate in the production of insecticides, herbicides, pharmaceuticals, and dyes. Pyridine is also found in tobacco smoke. Because inhalation is a primary route of exposure to pyridine, we examined the effect of inhaled pyridine on morphology at the portal of entry, the nose. Nasal tissues from F344/N rats exposed using a nose-only mode 6 hr/day for 4 days to either filtered air (controls) or one of two concentrations of pyridine vapor were examined histologically. The rats had been killed 18 hr after the last exposure. The two pyridine concentrations were the current threshold limit value (TLV, 5 ppm) and a high concentration (444 ppm). Olfactory epithelial lesions in rats exposed to both concentrations of pyridine included vacuolar degeneration of sustentacular cells; focal, marked attenuation of the epithelium; loss of vacuolar degeneration of sustentacular cells; focal, marked attenuation of the epithelium; loss of neurons; and the presence of intraepithelial luminal structures. The lesions were only slightly more severe in the rats exposed to 444 ppm compared to those rats exposed to 5 ppm pyridine. The results show that inhalation of pyridine at the current TLV concentration of 5 or 444 ppm causes lesions in the olfactory epithelium of rats.

Administration, Inhalation↗
PubMed1984

Psychological performance of workers with blood-lead concentration below the current threshold limit value.

The effects of lead exposure on psychological test performance and subjective feelings of well-being were investigated in 40 exposed workers whose PbB levels had never exceeded 60 micrograms/100 ml and in 20 controls matched for sex, age and educational level. The exposed workers were divided into two groups of 20, with recent PbB levels in the range 45-60 micrograms/100 ml or below 35 micrograms/100 ml. The group of workers with the higher PbB levels showed significantly poorer performance and reported more physical symptoms than the other two groups. These differences were unrelated to sociodemographic and personality characteristics. A principal component analysis suggested that the poorer performance was mainly due to an impairment of general functioning and only to some extent to a deterioration in specific functions, such as verbal reasoning and abstraction. Higher lead concentrations were correlated with poorer performance and a higher number of physical complaints. These results indicate that in exposed workers the threshold for impaired performance lies below the blood-lead concentration of 60 micrograms/100 ml, which is the current threshold limit value (TLV).

Adult↗
PubMed1985

Surveillance of workers exposed to mercury vapour:validation of a previously proposed biological threshold limit value for mercury concentration in urine.

A cross-sectional epidemiological study was carried out among subjects exposed to mercury (Hg) vapour, ie, a group of 131 male workers (mean age: 30.9 yr; average duration of exposure, 4.8 yr) and a group of 54 female workers (mean age, 29.9 yr; average duration of exposure 7 yr). The results were compared with those obtained in well-matched control groups comprising 114 and 48 male and female workers, respectively. The intensity of current Hg vapour exposure was rather moderate as reflected by the levels of mercury in urine (HgU) (mean and 95th percentile: males 52 and 147 micrograms/g creatinine; females 37 and 63 micrograms/g creatinine) and of mercury in blood (mean and 95th percentile: males 1.4 and 3.7 micrograms/dl; females 0.9 and 1.4 microgram/dl). Several symptoms mainly related to the central nervous system (memory disturbances, depressive feelings, fatigue, irritability) were more prevalent in the Hg-exposed subjects. They were, however, not related to exposure parameters. In both male and female Hg-exposed workers no significant disturbances were found in short-term memory (audioverbal), simple reaction time (visual), critical flicker fusion, and colour discrimination ability. Only slight renal tubular effects were detected in Hg-exposed males and females, ie, an increased urinary beta-galactosidase activity and an increased urinary excretion of retinol-binding protein. The prevalence of these preclinical renal effects was more related to the current exposure intensity (HgU) than to the duration of exposure and was detected mainly when HgU exceeds 50 micrograms/g creatinine. Changes in hand tremor spectrum recorded with an accelerometer were found in the Hg-exposed males only. The prevalence of abnormal values for some hand tremor parameters (total velocity and total displacement in the 2-50-Hz band) was mainly increased in male workers exposed for more than 10 yr. Unlike the renal tubular effects, the preclinical signs of tremor were more related to the integrated exposure than to the current exposure. Since the female workers, who have been exposed to Hg vapour levels usually insufficient to increase their HgU levels above 50 micrograms/g creatinine, did not exhibit any change in hand tremor pattern, the results of the present study tend to validate our previously proposed biological threshold limit value of a HgU of 50 micrograms/g creatinine for workers chronically exposed to mercury vapour.

Belgium↗
PubMed1994

Formate in serum and urine after controlled methanol exposure at the threshold limit value.

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.

Absorption↗
PubMed2001

Are we closer to developing threshold limit values for allergens in the workplace?

The use of immunoassays has facilitated the measurement of high molecular weight sensitizers, usually protein molecules, in the picogram and nanogram per cubic meter range. This facilitated the evaluation of exposure response relationships for bakery workers, exposed to wheat allergens and fungal alpha-amylase and other groups exposed to other allergens such as laboratory animal workers. The application for the standard setting is still limited and requires rigorous standardization, but can be expected in the near future.

Allergens↗
PubMedDate not supplied

Quantitative level of protection offered to workers by ACGIH threshold limit values occupational exposure limits.

The details of the example or modeling methodologies used herein are not critical to the general point of this article, which advises the estimation of residual risk at the OEL by using some quantitative modeling structure. Specifically, the authors believe that an explicit attempt to gauge the level of residual risk at the OEL based on conceptual stochastic models with transparent and testable assumptions could be seen as an important enhancement to the process. This is especially true in sharing the OEL deliberations and explaining OEL decisions to the stakeholders. Indeed, if this approach is used, it is critically important to understand and continually communicate that this "cloud of uncertainty" represents model estimates in which the true risk would most likely be less than worst case estimates and could possibly be zero. It is also possible but highly unlikely that it could be higher than the worst case upper-bound estimate. The above quantitative estimation scheme represents a possible improvement that could provide a reasoned attempt on the part of the risk assessors to use rational science (i.e., conceptual models with transparent and testable assumptions) to inform all of the OEL users and stakeholders of their meaning.

Air Pollutants, Occupational↗
PubMed1991

Perspectives on what we formerly called threshold limit values.

From the point of view of an epidemiologist with experience in community air quality standards, occupational health standards, radiation standards, and water quality standards, reasons are given for discarding the assumption that occupational health protection should be based on threshold concepts. The weakness of worker health protection based on prescription of maximal exposure levels is noted, regardless of whose judgement is used for such levels.

Air Pollutants, Occupational↗
PubMed1998

Can a threshold limit value for natural rubber latex airborne allergens be defined?

BACKGROUND: Recent studies have shown that systemic or respiratory occupational responses to latex can be induced by inhalation of latex aeroallergens. OBJECTIVE: Our objectives were to study the relationship between exposure to different latex aeroallergen levels and type I allergic reactions in subjects with occupational contact with latex and to assess a threshold value for latex airborne allergens required for sensitization and symptom elicitation. METHODS: We screened 145 subjects working in 32 hospitals or operating rooms with different latex aeroallergen levels. The quantified latex aeroallergen concentrations in the 32 rooms were compared with latex-related allergic symptoms. RESULTS: Different latex aeroallergen concentrations could be detected in rooms where powdered latex gloves were used and no effective ventilation systems were installed. In environments with latex aeroallergen levels of 0.6 ng/m3 or greater, the reported workplace-related symptoms were significantly increased (p < 0.02). All 22 subjects with latex-specific IgE antibodies worked in rooms contaminated with latex aeroallergens (p < 0.05). CONCLUSIONS: Our results demonstrate that symptoms and presence of latex-specific IgE antibodies in subjects are significantly associated with measurable levels of latex aeroallergens. A latex aeroallergen level of 0.6 ng/m3 is a critical threshold, especially for health care workers who are sensitized to natural rubber latex.

Air Pollutants, Occupational↗