Particle-Size Distribution of Chromium: Total and Hexavalent Chromium in Inspirable, Thoracic, and Respirable Soil Particles from Contaminated Sites in New Jersey

Abstract

Chromate slag is found mixed with soil at several sites in New Jersey. Previous analyses of the contaminated soil were limited to particle sizes > 30 μm. This study focuses on the inspirable, thoracic, and respirable particles that would enter the human respiratory tract, should the contaminated soil become airborne. This article discusses the soil-sampling procedure used at a slag-contaminated site and a site with visible hexavalent chromium crystals. In addition, the drying and sieving procedures and the techniques needed to resuspend the contaminated dust in a sealed chamber are described for aerodynamic size fractionation (30, 10, and 2.5 μm). The resuspended dust was collected on filters and analyzed for 38 elements by x-ray fluorescence (XRF). Wet chemistry techniques were used to measure total extractable and hexavalent chromium. It was found that 1.6% of the slag had a particle aerodynamic diameter (at 50% cut-point) d ₅₀ = 30 μm, of that 1.1% was d ₅₀ = 10 μm and 0.26% was d ₅₀ = 2.5 μm. Total chromium and lead concentrations above 1000 ppm were found in all particle sizes. Comparison of the total chromium results derived for two analytical techniques showed that the total chromium, in the contaminated soil exists in soluble and nonsoluble forms, and that the nitric acid method extracts ∼ 30% of the total chromium present in the slag measured by XRF. Hexavalent chromium concentrations > 1000 ppm were found in the contaminated soil that contained visible chromium blooms, and were 1800, 1700, and 1200 ppm for the inhalable, thoracic, and respirable size ranges, respectively.