Assessing the link between the Geochemistry of Soils and the Bioaccessibility of Arsenic, Chromium and Lead in the Urban Environment

One of the principal pathways for potentially harmful elements (PHE) in soil to enter the human body is through ingestion. The amount of PHE which enters the systemic circulation is governed by the amount of PHE released in the Gastrointestinal Tract, this is the bioaccessible fraction. A geochemical survey of the soils of Northampton, located on ironstone soils with naturally elevated arsenic concentrations, carried out by the BGS G-BASE project showed that 45% of the 275 soils sampled contained total arsenic concentrations exceeding the Environment Agency soil guideline value (SGV) of 32 mg kg-1. A newly validated in-vitro bioaccessibility test was used to measure the bioaccessibility of arsenic and other PHEs on a representative subset of 50 of the soils showed a maximum bioaccessibility value of 10 mg kg-1 arsenic. A systematic study of the relationship between the bioaccessible fraction of arsenic and other PHE with the geochemical make up of the soil, the solid phase distribution of PHE as measured by sequential extraction and the physical properties of the soil( as measured using NIR spectroscopy) showed that the bioaccessibility of different PHEs were governed by the source of the PHE (i.e. anthropogenic or geogenic) and their relative solid phase distribution between iron oxide phases and carbonates. Statistical modelling of the bioaccessible fraction using geochemistry and NIR data also helped to identify the factors controlling the mobility of PHE’s and provided a potential means for predicting bioaccessibility.