What a waste: controls on the solid-phase distribution and bioaccessibility of As at former industrial sites impacted by ash, clinker and galligu.the overall solubility of Pb in topsoils and metalifferous wastes

Statutory guidance in the UK requires local Councils to prioritise sites which pose a potential risk to human health on the basis of their past industrial land use and their proximity to receptors. The NW of England has a rich industrial heritage and our two study sites both contain areas identified as priority areas under the ‘Contaminated Land Inspection Strategy’. Both sites are residential housing estates, with gardens and communal areas, in St Helen’s, Merseyside. Site 1 was formerly occupied by a chemical works and associated alkali industry producing sodium carbonate from sodium chloride/sodium sulphate using the LeBlanc processes. A by-product is the solid waste referred to locally as ‘galligu’. Galligu is rich in As. Site 2 was formerly occupied by a glass and chemical works. Intrusive investigations were undertaken by St Helen’s Council which revealed made-ground rich in ash, clinker, slag and alkali waste, with As concentrations ranging from 9.47 – 24,900 mg/kg. The Generic Quantitative Risk Assessment identified the potential for a significant risk to residents from As. Our analyses revealed in vitro oral As bioaccessibilities (Unified BARGE method or UBM) of between 11.2 and 50.2%, pHs of 5.24 – 7.44, loss-on-ignition of 6.07 -18.9%, total organic carbon of 5.31 – 20.5% and cation exchange capacities of 4.14 – 45 cmol/kg in the sandy loam 0-30 cm horizon. Using the Chemometric Identification of Substrates and Element Distribution (CISED) protocol (a non-specific sequential extraction followed by chemometric data analysis) As was found to be primarily associated with Fe and Ca, and these phases are important in controlling the As solubility/bioaccessibility. Site 1 typically has lower bioaccessibilities than site 2 and this appears to be related to the presence of an Fe-As-Ca phase. Further work using scanning electron spectroscopy and laser Raman is currently underway to corroborate the mineral fractions identified via CISED