Lead speciation and occupational exposure.

A field of growing interest in environmental health is that of lead speciation, the study of the various chemical forms of lead. Different lead compounds have different solubilities, which in turn affect bioavailability. Descriptions of lead exposure such as concentrations in air or settled dust are telling quantities, but can only relate part of the story. A variety of biological and geochemical influences will determine how much lead ultimately reaches the blood and becomes available to exert toxic effects. Previous studies have identified the major lead-bearing constituents associated with lead smelting procedures (1,2) and examined the role of speciation and particle size in solubility (3). In the current research article, Spear et al. investigate the geochemical factors of lead speciation and particle size, and their potential role in the bioavailability of lead from bulk and airborne smelter dusts. The authors present results from a primary lead smelter. Dust samples were obtained from a variety of locations representing different stages of processing. Quantities of bulk dust were taken directly from surface areas within the smelter. Airborne dust was sampled with an apparatus that simulates intake by the human respiratory system. Samples were subjected to X-ray diffraction to identify the leaded compounds associated with the smelter dust. A chemical extraction method was applied to examine the relative solubilities of the dusts. The important characteristics of this study are therefore its abilities to comment on lead speciation and particle size over a range of locations in a lead smelter and to infer how these factors may influence human health. From X-ray diffraction results, the smelter dust mineralogy is reported to be heavily influenced by lead sulfide. Dusts sampled in the processing areas of the plant reveal proportions of sulfates and complex oxides. The abundance of lead sulfide throughout the smelter is reflected in chemical extraction results from the bulk dust samples, which generally display low solubilities. Bulk dusts from furnace locations tend to be more soluble than those that accumulate near ore storage areas. This locational trend is reinforced by airborne dust results, which are probably more indicative of direct worker exposure. The air sampler allowed dust to also be examined by partide size. Fine partides of leaded dust are more commonly observed in furnace areas than in storage or sinter locations. Regardless of mineralogy, finer particles are reported to be more soluble. Coupled with the intrinsic solubility of the lead sulfates and …