Dynamic Risk Assessment of Lead Pollution of Shooting Range Soil by Applying the Delayed Geochemical Hazard Model - A Case Study in Botswana

The delayed geochemical hazard (DGH) model was used to show that environmental pollution risk from Pb is a dynamic process as opposed to static. The DGH model describes the potential transformation and release of Pb partitioned in the different fractions of the soil that may be inert but becoming reactive when the conditions of the soil such as pH, moisture, and organic matter become favorable or when the Pb deposited into the soil exceeds the soil-holding capacity. As opposed to single extraction procedures that investigate the total amount of Pb deposited into shooting range soils, irrespective of whether that Pb is from inert or labile Pb species, the DGH model takes into consideration the mineralogical state of the Pb species and the ever-changing physicochemical characteristics of the soil. The total concentration of Pb does not give details on the bioaccessibility, bioavailability, mobility, and quantitative environmental pollution risk of deposited Pb to biota. This model was applied on a case study in shooting range soils highly polluted with Pb at concentrations of up to 38 406.87 mg/kg. The findings indicated that TAB shooting range located inside a military airbase in the southern part of Botswana may be classified as high-risk area of Pb DGH with over 65% of Pb capable of being transformed into the mobile and bioavailable chemical forms.