Dynamics of metal nanoparticles in soil environments

The use of metal-based nanoparticles (NPs) in consumer and industrial products has increased rapidly. Metal-based NPs are manufactured with a range of physicochemical properties including size, shape and chemical surface layer (coating). The most commonly used types of metal-based NPs are metal or metal oxide-based (e.g. TiO, silver, zinc oxide, cerium oxides) and metal sulphide/selenide-based materials, such as quantum dots (e.g. Cadmium). Wastewater treatment is a major pathway for nanoparticle release to soils, through the binding of NPs to activated sludge and subsequent incorporation into biosolids that are applied to land (>1 million tones dry weight per year in the UK). Transformations during the sewage treatment process are likely, so that the NP's in the sludge are often 'aged' and in the form of ZnS, AgS and Zn phosphates. It is the interactions of these 'aged' nanoparticles with the soil matrix and biota that will be examined within this PhD.
There is currently limited knowledge regarding the long term fate of 'aged' NPs in UK soils. This PhD seeks to address the key gaps in our understanding of their behaviour by quantifying changes in their speciation, mobility, bioaccumulation and toxicity across a range of soil types and time periods. The major issues include (i) the processes governing the rate at which these metallic NPs dissolve and eventually contribute to the ionic loading of the soil environment, (ii) the concentration of NP derived metal (NP metal + ionic) that can be remobilised and transported with time, (iii) the speciation of NP added metal in soil pore waters and implications for toxicity to plant and microbes.