Monitoring of airborne particulates near industrial silica sand mining and processing facilities.

To quantify risk of ambient exposure to airborne particulates around industrial silica sand operations, this study used EPA-certified federal reference method monitors to measure the levels of PM10 and PM2.5 particulate matter. The monitoring sites were chosen based upon EPA siting criteria, dichotomous samplers were calibrated before and after sampling, and pre- and post-weight filter weights were recorded. PM2.5 levels were significantly higher (paired t-tests) at both sites - averages of 7.70 ± 6.15 and 22.7 ± 31.714;µg/m3 - than concurrent background levels of 5.11 and 6.57µg/m3 respectively; and 98th percentile values were 24.9 and 111 µg/m3, respectively. Average PM10 levels were 24.2 and 49.0 µg/m3, and second-highest annual levels were 45.5 and 69.1 µg/m3 (two years) and 62.9 ug/m3 (2015) and 61.5 ug/m3 (2016), respectively for the two sites. Neither precipitation nor wind speed or direction appeared to affect PM2.5 or PM10 concentrations.

PM 2.5 Airborne Particulates Near Frac Sand Operations.

The rapid growth of hydraulic fracturing for oil and gas extraction in the U.S. has led to 135 active "frac" sand mines, processing plants, and rail transfer stations in Wisconsin. Potential environmental health risks include increased truck traffic, noise, ecosystem loss, and groundwater, light, and air pollution. Emitted air contaminants include fine particulate matter (PM2.5) and respirable crystalline silica. Inhalation of fine dust particles causes increased mortality, cardiovascular disease, lung disease, and lung cancer. In the authors' pilot study, use of a filter-based ambient particulate monitor found PM2.5 levels of 5.82-50.8 µg/m3 in six 24-hour samples around frac sand mines and processing sites. Enforcement of the existing U.S. Environmental Protection Agency annual PM2.5 standard of 12 µg/m3 is likely to protect the public from silica exposure risks as well. PM2.5 monitoring around frac sand sites is needed to ensure regulatory compliance, inform nearby communities, and protect public health.

Exponential modeling, washout curve reconstruction, and estimation of half-life of toluene and its metabolites.

Health risks from ostensible occupational and environmental toxicant exposure are difficult to quantify. Maximal use of limited biological measurements of xenobiotic or metabolite concentration in the body is therefore essential. Elimination rates of exhaled [2H8]toluene and urinary metabolites were analyzed from 33 exposures of males to 50 ppm [2H8]toluene for 2 h at rest. It was hypothesized that the shapes from our decay curves would be applicable to any occupational or environmental toluene exposure. Except for a rapid decline in toluene blood and breath levels in the 0-0.1 h period, this "curve reconstruction" method successfully fit data from published studies. Urinary hippuric acid concentrations were not well fit due to substantial background levels, whereas o-cresol levels were accurately described. Our approach was able to reconstruct data from studies where exposure duration ranged from 10 min to 7 h, and where activity level ranged from rest to 150 W (strenuous exercise). Using this approach, limited biological data following toluene exposure could be back-extrapolated to immediate postexposure concentrations, which in turn could be compared to biological indicators of exposure to determine risk.

Toluene metabolites as biological indicators of exposure.

The measurement of exhaled and excreted xenobiotics and their metabolites can provide accurate, non-invasive, and time-flexible measurements of internal dose. We analyzed rates of exhaled (2)H(8)-toluene and excreted urinary metabolites from 33 exposures of men to 50 ppm of (2)H(8)-toluene for 2 h at rest. The total dose was distributed as follows: exhaled (2)H(8)-toluene, 13 +/- 6.2%; (2)H(5)-hippuric acid, 75 +/- 6.4%; (2)H(7)-o-cresol, 0.31 +/- 0.22%; (2)H(7)-m-cresol, 0.53 +/- 0.44%; and (2)H(7)-p-cresol, 11 +/- 3.8%. Interindividual variability was assessed using the coefficients of variation for peak exhalation or excretion rates, and fractions of dose excreted: (2)H(8)-toluene, c.v.=60, 47%; (2)H(5)-hippuric acid, 29, 8.6%; (2)H(7)-o-cresol, 80, 73%; (2)H(7)-m-cresol, 37, 83%; and (2)H(7)-p-cresol, 38, 34%. Excretion rates of the cresols were stable over the first 5 h post-exposure, and o-cresol was determined to be the best urinary indicator of exposure, given the lower background levels of this isomer. The hippuric acid/cresol rate ratios for the first 5 h post-exposure could be described by single exponential terms, and thus provided a means for estimating time since exposure for any finite toluene duration/exposure combination.