Oral Bioavailability - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 302

constraints on the bioaccessibility of arsenic in mining sites. They concluded that
the arsenic bioaccessibility compared to the total arsenic content in the soils was
constrained by:

• encapsulation in insoluble matrices, e.g. energite in quartz;

• formation of insoluble alteration or precipitation rinds, e.g. authigenic iron

hydroxide and silicate rinds precipitating on arsenic phosphate grains; and

• formation of iron oxide and arsenic oxide and arsenic phosphate cements that

reduce the arsenic-bearing surface area available for dissolution.

In a previous study on lead in Montana soils, Davis et al. ( 1993 ) found similar
results in which the solubility was constrained by alteration and encapsulation which
limited the available lead-bearing surface area. Ruby et al. ( 1996 ) diagrammatically
summarised how the chemical and mineralogical forms of arsenic and lead relate
to their bioaccessibility. Figure 7.7 shows the possible physico-chemical processes
governing the bioaccessibility of lead at a contaminated site.
Whilst these early studies provided a good insight into the factors governing
arsenic and lead bioaccessibility they were very much aimed at soils from mining
areas where the contaminants were introduced into the soils as products from ore
processing.

Fig. 7.7 Schematic diagram of how different lead species, particle size and morphologies affect
lead bioavailability (after Ruby et al. 1996 )