Analysis of polycyclic aromatic hydrocarbons (PAHs) in air using passive sampling calibrated with active measurements.

There are limited ambient air measurements of extended (beyond EPA Priority 16) lists of polycyclic aromatic hydrocarbons (PAHs). We measured air concentrations of 45 PAHs using passive and active air sampling at 15 sites in a central urban community and one rural site for two years. Passive sampling was conducted with cylindrical XAD-based samplers deployed to capture spatial variability. High volume active samplers with quartz fiber filters for particles and XAD-4 absorbent for gases were deployed at two urban sites and the rural site to calibrate the passive measurements directly. Estimated passive sampling rates (PSRs) were evaluated as functions of meteorological data, seasons, locations, study year, and compared with other studies. Possible particle collection by the passive samplers was evaluated using a variety of particle measurements (TSP, PM10, PM2.5 and ultrafines <100 nm). Total PAHs were statistically associated with ultrafine particle concentrations and to a lesser extent PM2.5 and PM10, but not TSP. PSRs were more variable when PAH mass loadings were lower and near method detection limits; this occurred more often at the rural site. The PSRs were not statistically associated with meteorological conditions in this study, but wind speed had the highest potential to impact PSR results. The resulting passive PAH measurements are reported with respect to proximity to major roadways and other known air emissions types. PSRs were quantifiable for some PAHs that were found predominantly in the particulate phase in active sampling. This information, together with particle fraction calculations from active sampling, were used to estimate the particulate PAH capture of the passive sampler. Summed PAH (∑PAH) passive concentrations were measured within the range of 10-265 ng/m3, with the highest concentrations from naphthalene and the lowest detected concentrations from anthracene. These results indicated a stronger seasonal signal within 200 m of a major roadway.

The bioaccessibility of low level radionuclides from two Savannah river site soils.

Risk assessments for inorganic contaminated soils are often based on total concentration of a contaminant. However, strong binding of metals in soil can reduce the oral bioavailability. Since oral bioavailability of inorganics is generally less than 100% and partially dissolution-limited, human gastrointestinal dissolution models that measure bioaccessibility instead of the total extractable mass should be used to develop radionuclide source terms. For the reported study, a published bioaccessibility method was modified to allow measurements of bioaccessible radionuclides. The technique can be used to model human exposure and radionuclide dose from soil ingestion pathways. A step that included the addition of organic acids to the gastrointestinal fluids did not considerably affect the bioaccessibility of 90Sr and 137Cs. The bioaccessibility of 137Cs in the soils was significantly correlated to soil physicochemical characteristics, with a negative correlation with clay content, while 90Sr was significantly correlated to calcium bioaccessibility. These relationships can be used to prioritize remediation according to soil type.

Oral bioavailability of lead and arsenic from a NIST standard reference soil material.

The oral bioavailability of soil contaminants is measured using in vitro or in vivo techniques. Current efforts in our laboratory are focused on the comparisons of in vitro methods for bioavailability estimation with the presently employed in vivo techniques, such as animal models. We present a comparison of two techniques for oral bioavailability estimation: in vitro dissolution and in vivo rat feeding using a standard reference soil. Lead (Pb) and arsenic (As) were chosen because of the range of concentration in this soil as well as the large historical database of bioavailability values for these metals. Metal solubility was measured using a sequential soil extraction in synthetic analogues of human saliva, gastric and intestinal fluids. The soluble metal was defined as the bioaccessible fraction. Oral bioavailability of Pb and As was measured in Sprague Dawley rats by determining metal levels in the major organs and urine, feces, and blood at 1-, 2-, and 3-day time points. Extractions to determine bioaccessibility yielded a gastric component of 76.1% and 69.4% for Pb and As, respectively, and intestinal components were 10.7% and 65.9%. The oral bioavailability of the standard reference soil was 0.7% and 37.8% for Pb and As, respectively. Bioaccessibility was greater than bioavailability for both metals in both gastrointestinal compartments. Although Pb had the highest soil concentration of the selected metals, it was the least bioavailable, while As was highly available in both the in vitro and in vivo method. These types of data allow for an in vitro-in vivo comparison of a soil whose metal concentrations have been certified and validated.

The estimation of the bioaccessibility of heavy metals in soils using artificial biofluids by two novel methods: mass-balance and soil recapture.

The possible human health effects resulting from the ingestion of soil bound heavy metals can be poorly estimated if concentration of total metals in soil, rather than bioavailable fraction of metals, are incorporated into dose calculations. Information regarding bioavailability often is obtained from animal studies, which are not easily conducted and still may not represent human conditions. A rapid simulation of the bioaccessible fraction of contaminant in a soil, in which that fraction is mass soluble in gastrointestinal tract fluids, has been employed in an in vitro sequential extraction technique. Using a mass-balance analytical approach to measure bioaccessibility in four soils, the results indicated that each metal had a bioaccessible fraction less than its total metal content. Lead (Pb) in Standard Reference Material, Montana SRM 2710, was found to be 62 +/- 1% bioaccessible; Pb in contaminated soil collected from Bunker Hill, ID, USA was 70 +/- 11%. Lead in Jersey City, NJ, USA slag material was only 39 +/- 14% bioaccessible while Pb in a residential soil was 69%. Arsenic (As) and chromium (Cr) data from select soils also have bioaccessibility less than the corresponding total metal in soil, with 41 +/- 2% As in a residential soil, 66 +/- 8% As in SRM 2710, and 34 +/- 14% Cr in Jersey City slag material. Recovering the soil at the end of the in vitro extraction allowed for the determination of the insoluble fraction of total metal in soil. This recaptured soil metal mass was a valuable measurement since it greatly reduced analysis and therefore labor and time, yet also provided a reasonable estimate of bioaccessibility. It also allowed for calculation of a bioaccessibility value in a soil containing very low metal mass, which would otherwise have resulted in a non-detectable concentration at the dilutions required in the synthetic human biofluid system.