Rothamsted was the pioneer in studying the impacts of soil pollutants, especially toxic metals from sewage sludge, on soil microbes. Our objective is to develop methods for metal/metalloid speciation in soil, to assess their bioavailability and toxicity, and to quantify the factors controlling toxicity for use in empirical or mechanistic models. We will develop a more mechanistic biotic ligand model in which toxicity is related only to the fraction of the total biotic ligand sites occupied by M²⁺, and includes the partitioning of the metal and competing ions from soil solid phase to solution and their competition at the organism level. This model represents a further step forward as it is applicable to all soils, irrespective of their properties, which will be an essential tool for environmental risk assessment. Accumulation of arsenic in rice due to water and soil contamination represents a major threat to human health and trade in rice. We will investigate the dynamics of As speciation in soils under both field and controlled environment conditions, paying particular attention to soil factors that control bioavailability including the speciation of As in soils and rhizosphere and its uptake and efflux from plants in collaboration with Aberdeen University and Okayama University in Japan.