Hexavalent chromium causes two types of dermatological toxicities: allergic contact dermatitis (ACD) and skin ulcers. This report reviews the etiology, prevalence, pathology, dose-response, and prognosis of both of these reactions. Reports in the literature indicate that repeated exposure to hexavalent chromium in concentrations of 4-25 ppm can both induce sensitization and elicit chromium ACD. Exposure to 20 ppm hexavalent chromium can cause skin ulcers in nonsensitized people. The prevalence of chromium sensitivity in cement workers, exposed to 10-20 ppm hexavalent chromium for years, is approximately 4-5%. Chromium ACD can be a chronic debilitating disease, perhaps because chromium is ubiquitous in foods and in the environment and is difficult to avoid. Due to the high rates of sensitization in populations chronically exposed to chromium and the chronic nature of chromium ACD, some investigators recommend reducing the hexavalent chromiumconcentrations in consumer products, such as detergents, to less than 5 ppm.

Previous investigations into lead bioavailability have focused on the solubility of the mineralogic fraction. However, the potential for surface-bound (sorbed) lead to contribute to the bioavailable fraction has not yet been determined. This study investigated the Pb distribution between the mineralogic and surface-bound pools in aggregate generated by thermal vitrification of a Pb-bearing organic and metalliferous waste feedstock. Electron microprobe and laser ion mass spectroscopy demonstrated that amorphous slag comprised >95% of the vitreous material, with lead sulfosalts, oxides, and carbonates encapsulated in the refractory slag matrix representing the mineralogic Pb fraction. The maximum potentially bioavailable surfacebound fraction was 27% in the 467 mg/kg primary aggregateimpacted soil and 5% in the 6520 mg/kg slagged aggregate, averaging 14% of the Pb pool for the six samples evaluated. The low concentration of Pb on the surface of aggregate particles, the refractory nature of the Pb-bearing slag, the low percentage of liberated Pb-bearing (non-slag) particles (1:6300 to 1:38 000 of the total grain population), and the large size of the slag particles explain the low bioaccessibility of Pb in modern aggregate (1.5%) as compared to urban Cincinnati soils (51%) and street dusts (77%).

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