RESUMEN

Crystalline silica is a Group I lung carcinogen primarily known as a causative agent for silicosis. A study was performed to quantify respirable dust, and respirable crystalline silica (RCS) in the rice mills of northeast India. Seventy-two respirable dust samples were collected from the worker's breathing zone from four rice mills at three locations: feeding, sieving, and polishing sections for two paddy varieties: Ranjit and Sali. The National Institute of Occupational Safety and Health (NIOSH), method #7602, was used to determine RCS. The results show that geometric mean TWA dust and RCS emissions in the rice mills varied from 3.97 to 455.00 mg/m3 and 0.02 to 5.38 mg/m3, respectively. RCS exposures were higher during milling of the Sali variety paddy (GM: 0.76 mg/m3) than the Ranjit variety paddy (GM: 0.25 mg/m3). Respirable dust and RCS emissions were considerably higher in the feeding and sieving sections than in the polishing section. Respirable dust and RCS exposure varied significantly (p < 0.001) with paddy variety. Respirable dust and RCS were highly correlated for different rice mills; however, the proportion of RCS in the dust was higher in the Sali variety paddy than in the Ranjit variety paddy. RCS exposure to the workers at the feeding and sieving sections was observed to be higher than the occupational exposure limits (OELs) published by Safe Work Australia, American Conference of Governmental Industrial Hygienists (ACGIH), National Institute for Occupational Safety and Health (NIOSH), Health and Safety Executive (HSE), and Factories Amendment Act, 1987, Government of India.

RESUMEN

N-Nitrosamines are potent carcinogens and considered non-threshold carcinogens in various regulatory domains. However, recent data indicate the existence of a threshold for genotoxicity, which can be adequately demonstrated. This aspect has a critical impact on selecting the methodology that is applied to derive occupational exposure limits (OELs). OELs are used to protect workers potentially exposed to various chemicals by supporting the selection of appropriate control measures and ultimately reducing the risk of occupational cancer. Occupational exposures to nitrosamines occur during manufacturing processes, mainly in the rubber and chemical industry. The present study derives OELs for inhaled N-nitrosamines, employing the benchmark dose (BMD) approach if data are adequate and read-across for nitrosamines without adequate data. Additionally, benchmark dose lower confidence limit (BMDL) is preferred and more suitable point-of-departure (PoD) to calculate human health guidance values, including OEL. The lowest OEL (0.2 µg/m3 ) was derived for nitrosodiethylamine (NDEA), and nitrosopiperidine (NPIP) (OEL = 0.2 µg/m3 ), followed by nitrosopyrrolidine (NPYR) (0.4 µg/m3 ), nitrosodimethylamine (NDMA), nitrosodimethylamine (NMEA), and nitrosodipropylamine (NDPA) (0.5 µg/m3 ), nitrosomorpholine (NMOR) (OEL = 1 µg/m3 ), and nitrosodibutylamine (NDBA) (OEL = 2.5 µg/m3 ). Limits based on "non-threshold" TD50 slope calculation were within a 10-fold range. These proposed OELs do not consider skin absorption of nitrosamines, which is also a possible route of entry into the body, nor oral or other environmental sources. Furthermore, we recommend setting a limit for total nitrosamines based on the occupational exposure scenario and potency of components.

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RESUMEN

Many substances in workplace do not have occupational exposure limits. The threshold of toxicological concern (TTC) principle is part of the hierarchy of approaches useful in occupational health risk assessment. The aim of this study was to derive occupational TTCs (OTTCs) reflecting the airborne concentrations below which no significant risk to workers would be anticipated. A reference dataset consisting of the 8-h threshold limit values-Time-Weighted Average for 280 organic substances was compiled. Each substance was classified into low (class I), intermediate (class II), or high (class III) hazard categories as per Cramer rules. For each chemical, n-octanol:water partition coefficient and vapor pressure along with the molecular weight were used to predict the blood:air partition coefficient. The blood:air partition coefficient along with data on water solubility and ventilation rate allowed the prediction of pulmonary retention factor and absorbed dose in workers. For each Cramer class, the distribution of the predicted doses was analyzed to identify the various percentile values corresponding to the OTTC. Accordingly, for Cramer classes I-III, the OTTCs derived in this study correspond to 0.15, 0.0085, and 0.006 mmol/d, respectively, at the 10th percentile level, while these values were 1.5, 0.09 and 0.03 mmol/d at the 25th percentile level. The proposed OTTCs are not meant to replace the traditional occupational exposure limits, but can be used in data-poor situations along with exposure estimates to support screening level risk assessment and prioritization.

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BACKGROUND: The toxicological properties of manufactured nanomaterials (MNMs) can be different from their bulk-material and uncertainty remains about the adverse health effects they may have on humans. Proposals for OELs have been put forward which can be useful for risk management and workers' protection. We performed a systematic review of proposals for OELs for MNMs to better understand the extent of such proposals, as well as their derivation methods. METHODS: We searched PubMed and Embase with an extensive search string and also assessed the references in the included studies. Two authors extracted the data independently. RESULTS: We identified 20 studies that proposed in total 56 OEL values. Of these, two proposed a generic level for all MNMs, 14 proposed a generic OEL for a category of MNMs and 40 proposed an OEL for a specific nanomaterial. For specific fibers, four studies proposed a similar value but for carbon nanotubes (CNTs) the values differed with a factor ranging from 30 to 50 and for metals with a factor from 100 to 300. The studies did not provide explanations for this variation. We found that exposure to MNMs measured at selected workplaces may exceed even the highest proposed OEL. This indicates that the application and use of OELs may be useful for exposure reduction. CONCLUSION: OELs can provide a valuable reference point for exposure reduction measures in workplaces. There is a need for more and better supported OELs based on a more systematic approach to OEL derivation.

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