Modeling mesothelioma risk factors from amphibole fiber dimensionality: mineralogical and epidemiological perspective.

Amphiboles are common rock-forming minerals but when they form asbestos, they are known carcinogens. Mesothelioma mortality among miners and millers per the unit of asbestiform amphibole exposure varies significantly across cohorts when asbestos exposure measurements are based on the membrane filter method. Because the cohorts were exposed to different occurrences of asbestiform amphibole, variance in mesothelioma potency (RM ) among cohorts is likely due to differences in exposure characteristics not reflected by the membrane filter method. In this paper using both linear and nonlinear models we correlate RM from four mining and milling cohorts with two-dimensional parameters of the exposure. The parameters are based on the proportion of elongated minerals that are >5 µm in length from each occurrence that also have either (a) width ≤ 0.15 µm, or (b) width ≤ 0.25 µm. Based on the models we derived, it was possible to quantify RM for the occurrences of asbestiform amphibole associated with mesothelioma excess but for which epidemiologically based RM has not been published. It was demonstrated that modeled RM for amphibole occurrences in nonasbestiform habits are lower (fibrous glaucophane) or not significant (cleavage fragments). The results of the study can be used in a risk assessment of elongated mineral particles and have implications for public policy and regulations.

Inhalation exposure during spray application and subsequent sanding of a wood sealant containing zinc oxide nanoparticles.

Nano-enabled construction products have entered into commerce. There are concerns about the safety of manufactured nanomaterials, and exposure assessments are needed for a more complete understanding of risk. This study assessed potential inhalation exposure to ZnO nanoparticles during spray application and power sanding of a commercially available wood sealant and evaluated the effectiveness of local exhaust ventilation in reducing exposure. A tradesperson performed the spraying and sanding inside an environmentally-controlled chamber. Dust control methods during sanding were compared. Filter-based sampling, electron microscopy, and real-time particle counters provided measures of exposure. Airborne nanoparticles above background levels were detected by particle counters for all exposure scenarios. Nanoparticle number concentrations and particle size distributions were similar for sanding of treated versus untreated wood. Very few unbound nanoparticles were detected in aerosol samples via electron microscopy, rather nano-sized ZnO was contained within, or on the surface of larger airborne particles. Whether the presence of nanoscale ZnO in these aerosols affects toxicity merits further investigation. Mass-based exposure measurements were below the NIOSH Recommended Exposure Limit for Zn, although there are no established exposure limits for nanoscale ZnO. Local exhaust ventilation was effective, reducing airborne nanoparticle number concentrations by up to 92% and reducing personal exposure to total dust by at least 80% in terms of mass. Given the discrepancies between the particle count data and electron microscopy observations, the chemical identity of the airborne nanoparticles detected by the particle counters remains uncertain. Prior studies attributed the main source of nanoparticle emissions during sanding to copper nanoparticles generated from electric sander motors. Potentially contrary results are presented suggesting the sander motor may not have been the primary source of nanoparticle emissions in this study. Further research is needed to understand potential risks faced by construction workers exposed to mixed aerosols containing manufactured nanomaterials. Until these risks are better understood, this study demonstrates that engineering controls can reduce exposure to manufactured nanomaterials; doing so may be prudent for protecting worker health.

Wollastonite toxicity: an update.

This review updates earlier work addressing the epidemiology and toxicity of wollastonite. Earlier chronic animal bioassay and human mortality data were inadequate (IARC term) or negative and no new studies of these types have been published. Wollastonite has been determined to have low biopersistence in both in vivo and in vitro studies, which probably accounts for its relative lack of toxicity. Earlier morbidity studies of mining/mineral processing facilities in Finland and New York State indicated that exposure to wollastonite might result in pleural plaques (Finland) or decrements in certain measures of lung function (New York). More recent analysis of data from an ongoing health surveillance program at one facility (New York) indicates that there are no pleural plaques or interstitial lung disease or decrements in lung function among never smokers or former smokers occupationally exposed to wollastonite. This result probably reflects continued reduction in exposures as part of an ongoing product stewardship program at this facility and suggests that wollastonite has relatively low toxicity as currently managed.

Occupational exposure to carbon/coke fibers in plants that produce green or calcined petroleum coke and potential health effects: 1. Fiber characteristics.

Carbon/coke fibers are found in bulk samples of calcined petroleum coke. Carbon/coke and other fibers, including calcium silicate, cellulose, gypsum, and iron silicate, have been found in exposure monitoring of workers who make or handle green or calcined petroleum coke. Carbon/coke fibers are not classified or regulated as carcinogens by any agency, and the available literature (summarized in this article) has not reported significant adverse health effects associated with exposure to these fibers or dusts containing these fibers. However, available epidemiological and toxicological studies have limitations that prevent a definitive assessment of carbon/coke fiber toxicity. Therefore, it is prudent to monitor and control workplace concentrations. Analyses by transmission electron microscopy (TEM) indicate that the carbon/coke fibers are amorphous, irregularly shaped, and generally rather short (94% less than 20 microm long). Nearly all carbon/ coke fibers satisfying NIOSH 7400 B counting criteria are detectable by phase-contrast optical microscopy (PCOM), which permits the use of a highly efficient sequential sampling strategy for analysis. Data are presented on the distribution of carbon/coke structure and fiber lengths and diameters. Bootstrap resampling results are presented to determine confidence intervals for structure/fiber length and diameter. Data on time-weighted average concentrations are given in a companion article, but nearly all time-weighted average carbon/coke fiber concentrations were beneath 0.1 fibers per milliliter.

Occupational exposure to carbon/coke fibers in plants that produce green or calcined petroleum coke and potential health effects: 2. Fiber concentrations.

We monitored exposure to various fibers among workers in eight plants operated by ConocoPhillips that produce green or calcined petroleum coke. Carbon/coke and other fibers, including calcium silicate, cellulose, gypsum, and iron silicate, were found in occupational samples. Carbon/coke fibers were found in bulk samples of calcined petroleum coke, the probable source of these fibers in occupational samples. Time-weighted average (TWA) total fiber concentrations were approximately lognormally distributed; 90% were < or = 0.1 f/ml. Although consistently low, TWA total fiber concentrations varied with plant, job (tasks), and type of coke. This was expected given the substantial differences in plant configuration, technology, and workplace practices among refineries and carbon plants. Carbon/coke fibers (identified and measured using transmission electron microscopy [TEM]) were found at all plants producing all types of calcined coke and not detected at any plant producing only green coke. Approximately 98% of all carbon/coke TWAs were < or = 0.1 f/ml. Analysis of task length average (TLA) data by various statistical techniques indicates that the average carbon/coke TLA is certainly < or = 0.05 f/ml and probably < 0.03 f/ml.