Air Quality Criteria for Lead Volume II of II - (NEPIS)(EPA) - US ...

Chemical Form of Species
The solid phase in a medium controls the activity of a metal in solution, whether the
solution is surface, ground, or pore water or GI fluids, and plays a profound role in metal
bioavailability. This is perhaps best illustrated by in vivo and in vitro results for many of the
common Pb-bearing minerals (Drexler, 1997) (Figure AX7-1.1.1). The metal species found in
media are often diverse, and data suggest that their bioavailability may be significantly
influenced by site-specific variations within these identified metal species (Davis et al., 1993;
Ruby et al., 1992; Drexler and Mushak, 1995).
Figure AX7-1.1.1. Relationship of bioaccessibility (low, medium, high) versus speciation
as shown with scanning electron micrographs of various Pb-bearing
materials.
Particle Size of Metal Species
Particle size of a metal form is an important factor in the mobilization of the metal,
primarily because as size decreases, the surface area of the particle increases, thereby increasing
solubility. Thus, although solubility is not the only control for bioavailability, an increase in
bioavailability has been directly attributed to a decrease in particle size: Barltrop and Meek
AX7-5