Brorby G, Proctor D, Perry C, Fitzgerald L, Tachovsky A. 2012. Probabilistic risk assessment of human exposure to iron and steel slag. Presented at the Society of Toxicology’s 51st Annual Meeting, March 11-15, San Francisco, CA.
A probabilistic risk assessment (PRA) was conducted to evaluate the potential for adverse human health effects associated with environmental exposures to iron and steel slags. These materials have a wide range of applications, but are used primarily as construction aggregates. The concentration of 26 metals was characterized in 41 samples of three types of slag, for three size fractions each: 1) processed slag (PS, 0- 1 inch), which is the primary commercial product, 2) PS samples screened to <300 μm, and 3) PS samples screened to <75 μm. The bioaccessible fraction for ingestion exposure (Boral) was also measured for the <300 μm fraction. Chemicals of interest (COIs) were identified through a two-tier screening process, considering four exposure scenarios: 1) slag on a residential driveway, 2) residence near a slag-covered road, 3) construction worker building road base with slag, and 4) industrial/maintenance worker. Incidental ingestion and inhalation were quantitatively evaluated. Following the screening steps, COIs were limited to CrVI, Mn, and V for residential scenarios only. COIs were found to be concentrated in larger particles, and not readily soluble in gastric conditions. Distributions were developed for soil ingestion rate; inhalation rate; exposure time, frequency and duration; Boral; BW and PEF. The PRA-calculated risk-based concentrations (RBCs) for each COI and scenario were calculated from distributions of risk/hazard generated using unit concentrations, corresponding to a specific risk (10-5) or hazard index (1) estimated at a specified point in the distribution. Only the 95% UCL concentrations of Mn in the largest PS-sized samples exceeded the 90th percentile of the RBC distributions. However, the 95% UCL concentrations of the more biologically relevant size fraction (<300 μm), which is more representative of the fraction that could be incidentally ingested, and the smallest size fraction (<75 μm), which is most representative of the fraction that could be inhaled, were below the Mn RBCs.