Quantification of historical dust exposures in the diatomaceous earth industry

Abstract

Quantitative estimates of dust exposure in a diatomaceous earth (DE) mining and milling operation have been derived based on air sampling records for the period 1948-1988. A total of 6395 records was included in the analysis. Conversion of results obtained by particle counting, expressed as millions of particles per cubic feet (mppcf) of gravimetrically from a filter cassette and expressed as mg m-3 total, were converted to mg m-3 respirable dust using a conversion factor derived from data obtained during the same periods at the plant. Conversion factors were calculated as the average difference of means on the log scale in order to provide stable and consistent conversions and as a ratio of arithmetic means so that the results could be compared with similar studies. After converting the available data to mg m-3 respirable dust, geometric mean (geometric standard deviation) concentrations were 0.37 (2.43) during the 1950s and 0.17 (2.35) during later periods. Exposures were estimated using two linear models, one estimating the changes in concentration over time, and the other providing job-specific mean exposures during the more recent period. Extrapolation of the estimates to periods prior to the availability of any data was done using a subjectively-determined scaling factor. The average estimated respirable dust concentrations for 135 jobs were 3.55 (+/-1.25), 1.37 (+/-0.48), 0.47 (+/-0.16) and 0.29 (+/-0.10) mg m-3 prior to 1949, 1949-1953, 1954-1973 and 1974-1988, respectively. Despite the limitations of the available data, the estimation procedures used are expected to provide reasonable quantitative estimates of silica-containing dust exposure for subsequent exposure-response analyses.

A Statistical Evaluation of Asbestos Air Concentrations

“…For area samples the lower and upper CI are 0.004 and 0.006 fWcm -3 , respectively, and for personal samples the lower and upper CI are 0.019 and 0.029 f W cm -3 , respectively. These analyses suggest that personal samples have a higher airborne concentration than area samples as has been reported in other publications [35,45,47,[50][51][52]. A higher personal concentration as compared to area concentration also has been reported to be statistically different in non-asbestos exposure studies [47,51].…”

“…These analyses suggest that personal samples have a higher airborne concentration than area samples as has been reported in other publications [35,45,47,[50][51][52]. A higher personal concentration as compared to area concentration also has been reported to be statistically different in non-asbestos exposure studies [47,51]. The purpose of occupational sampling is to determine the exposure dose of airborne material to the worker with this information used for a hazard assessment [35,48,55,63,81,[90][91][92][93][94][95][96][97][98][99][100].…”

“…It has also been suggested [35] that there is no statistical difference for concentration values between area and personal measurements, although other studies have not supported such findings [38,46,50,51]. OSHA requires employers to collect personal samples for assessing potential exposure to workers of airborne asbestos [29].…”

“…However, area sample data are often used for determining exposure of workers in lieu of personal sample data [35]. Information regarding associations between area and personal airborne asbestos samples are important for evaluating exposure criteria and determination of the hazard assessment, as well as the underlying distribution [35,38,51,68]. Generally, area samples are employed for environmental and public health protection, evaluation of emission controls (engineering controls) and general concentrations of fibres or other contaminants in the work location, including inside and outside the regulated area (containment area) [2,[35][36][37][87][88][89].…”

“…Evaluation of this relationship is important to the abatement industry since area and personal samples are often viewed as interchangeable [35]. However, this concept is in contradiction with regulatory requirements [8,29] and previous publications that suggest there is no relationship or association between the two sampling methods [44,45,[50][51][52][53][54][55]. Thus, evaluation of this relationship is warranted especially since area samples are commonly used in the abatement industry to represent occupational exposure [3,21,35].…”