Impact of sewage sludge application on soil microplastic accumulation and nutrient levels: Analysis of 22 years of data from central UK farmland

Water treatment plants effectively remove microplastics from influent water, but these contaminants concentrate in the resulting sludge, which is often applied to agricultural soils. While sewage sludge provides essential nutrients like nitrogen and phosphorus, and improves soil structure and water retention, it also introduces potentially harmful microplastics. Microplastics from sludge accumulate in soil with repeated applications, while nutrients are absorbed by crops. These microplastics can disrupt the geochemical cycling of elements such as carbon, nitrogen, and phosphorus. In the soil, microplastics increase porosity and water-holding capacity but decrease bulk density and moisture permeability. They can also alter soil pH, impacting microbial processes crucial for nutrient cycling. To investigate the relationship between sewage sludge application and nutrient levels in farmland, we analyzed a 22-year dataset from 5323 fields in central UK. The dataset includes sludge application history and nutrient levels, detailing concentrations of nitrogen, phosphate, sulphate, Mo, Cd, Cr, Co, Pb, Ni, Zn, F, Hg, As, Se, Mg, Ca, loss on ignition, dry solids, and pH. Preliminary results indicate significant changes in nutrient levels. Phosphate levels increased, sulphate levels decreased, and nitrogen levels remained unchanged. Among micronutrients, potassium, magnesium, selenium, and phosphorus levels increased, while calcium and fluoride levels decreased. No significant changes were observed for other micronutrients. Additionally, dry solids decreased, and pH increased, potentially influencing nutrient dynamics. Further site analyses will compare nutrient levels across fields with different sludge application histories to better understand these impacts. Also see: https://micro2024.sciencesconf.org/559734/document