Long-term simulation of lead concentrations in agricultural soils in relation to human adverse health effects

Abstract

Lead (Pb) exposure of consumers and the environment has been reduced over the past decades. Despite all measures taken, immission of Pb onto agricultural soils still occurs, with fertilizer application, lead shot from hunting activities, and Pb from air deposition representing major sources. Little is known about the intermediate and long-term consequences of these emissions. To gain more insight, we established a mathematical model that considers input from fertilizer, ammunition, deposition from air, uptake of Pb by crops, and wash-out to simulate the resulting Pb concentrations in soil over extended periods. In a further step, human oral exposure by crop-based food was simulated and blood concentrations were derived to estimate the margin of exposure to Pb-induced toxic effects. Simulating current farming scenarios, a new equilibrium concentration of Pb in soil would be established after several centuries. Developmental neurotoxicity represents the most critical toxicological effect of Pb for humans. According to our model, a Pb concentration of ~ 5 mg/kg in agricultural soil leads to an intake of approximately 10 µg Pb per person per day by the consumption of agricultural products, the dose corresponding to the tolerable daily intake (TDI). Therefore, 5 mg Pb/kg represents a critical concentration in soil that should not be exceeded. Starting with a soil concentration of 0.1 mg/kg, the current control level for crop fields, our simulation predicts periods of ~ 50 and ~ 175 years for two Pb immission scenarios for mass of Pb per area and year [scenario 1: ~ 400 g Pb/(ha × a); scenario 2: ~ 175 g Pb/(ha × a)], until the critical concentration of ~ 5 mg/kg Pb in soil would be reached. The two scenarios, which differ in their Pb input via fertilizer, represent relatively high but not unrealistic Pb immissions. From these scenarios, we calculated that the annual deposition of Pb onto soil should remain below ~ 100 g/(ha × a) in order not to exceed the critical soil level of 5 mg/kg. We propose as efficient measures to reduce Pb input into agricultural soil to lower the Pb content of compost and to use alternatives to Pb ammunition for hunting.

Keywords: Consumer risk; Fertilizer; Food contamination; Gunshot; Hunting; Lead; Pb; Soil contamination.

Fig. 1

Model for human oral exposure via vegetable products and crops by dispersive deposition of Pb on agricultural soil

Fig. 2

Annual Pb input on fields by gun shot, air deposition and fertilizer, g/(ha × a) for four different farming scenarios (Knappe et al. 2008): Scenario A use of cattle manure and mineral fertilizer; Scenario B use of compost and mineral fertilizer; Scenario C use of sewage sludge and mineral fertilizer; Scenario D exclusive use of mineral fertilizer

Fig. 3

Simulation of Pb concentrations in soil for 100 years for Pb input scenarios A1, B1 and C1

Fig. 4

Long-term simulation of Pb concentrations under the same input scenarios shown in Fig. 3

Fig. 5

Time-dependent Pb concentration in soil for scenarios A2, B2 and C2 for constant Pb input

Fig. 6

Equilibrium soil concentration of Pb according to four farming scenarios

Fig. 7

Time periods in years until critical soil concentration of Pb would be exceeded with respect to developmental neurotoxicity. The simulations are based on farming scenario B1 (black bars) and C1 (grey bars). The initial Pb concentration in soil are given on the x-axis