An Assessment and Quantitative Uncertainty Analysis of the Health Risks to Workers Exposed to Chromium Contaminated Soils

Abstract

Millions of tons of chromite-ore processing residue have been used as fill in various locations in Northern New Jersey and elsewhere in the United States. The primary toxicants in the residue are trivalent chromium [Cr(III)] and hexavalent chromium [Cr(VI)]. The hazard posed by Cr(III) is negligible due to its low acute and chronic toxicity. In contrast, Cr(VI) is considered a inhalation human carcinogen at high concentrations. Approximately 40 commercial and industrial properties in Northern New Jersey have been identified as containing chromite ore processing residue in the soil. One site, a partially-paved trucking terminal, was evaluated in this assessment. The arithmetic mean and geometric mean concentrations of total chromium in soil were 977 and 359 mg/kg, respectively. The data were log-normal distributed. The arithmetic mean and geometric mean concentrations of Cr(VI) in surface soil were 37.6 and 3.1 mg/kg, respectively. The data could not be fit to a standard distribution, likely due to the large number of samples with concentrations below the method detection limit (65%). Dose was calculated for each exposure route using a Monte Carlo statistical simulation. Probability distributions of most exposure parameters were incorporated into the analyses to predict the range and probability of uptake for persons in the exposed population. The exposure parameter distributions included in this assessment are: the concentrations of Cr(VI) and total chromium in air and soil, fraction of the year when suspension of airborne soil particulates is likely to occur due to weather conditions, fraction of Cr(VI) in air which is respirable (less than 10 microns), soil loading rate on skin, occupational tenure, and body weight. The techniques used in this assessment are applicable for evaluating the human health risks posed by most industrial sites having contaminated soil. The estimated average daily dose (ADD) via ingestion and dermal absorption for the individual exposed at the 95th percentile was about 48,000- and 91-fold below the U.S. EPA reference dose (RfD) for Cr(III) and Cr(VI), respectively. Since inhalation of Cr(VI) contaminated dust (but not ingestion or dermal contact) poses a cancer hazard, the lifetime average daily doses (LADDs) associated with exposure at the 50th and 95th percentile were calculated to be 9.8 x 10(-8) and 1.3 x 10(-6), respectively. Based on this analysis, industrial sites having soil concentrations of Cr(VI) below 230 ppm do not pose a significant noncarcinogenic or carcinogenic health hazard following acute or chronic exposure. These risks would be even smaller if the sites were paved.