A quantitative exposure assessment for metals and faecal coliforms in surface runoff following land spreading of biosolids to agricultural grasslands

Long-term application of biosolids to agricultural land has led to concerns regarding the potential accumulation of metals and faecal coliforms in soil, the subsequent runoff into surface waters, and the potential risk to... [ view full abstract ]

Long-term application of biosolids to agricultural land has led to concerns regarding the potential accumulation of metals and faecal coliforms in soil, the subsequent runoff into surface waters, and the potential risk to human health through drinking water. This study used surface runoff water quality data generated from a field-scale study in which three types of biosolids (anaerobically digested (AD), lime stabilised (LS), and thermally dried (TD)) were spread on micro-plots of land. The aim of this research was to conduct a human health risk assessment of metals and faecal coliforms, which may persist in drinking water after treatment in a WTP. A quantitative drinking water treatment model was developed that was capable of predicting likely human exposure and resulting risk from six metals (Cu, Cd, Cr, Pb, Ni and Zn) and faecal coliforms present in the final drinking water. Different dose-response relationships were characterised for the different pollutants with reference Lifetime Average Daily Dose (LADD) and Hazard quotient (HQ) used for metals, whereas a worst-case negative exponential dose-response model was used for faecal coliforms. Mean metal results showed that mean Cu exposure concentrations for children were highest in all three time frames corresponding to the LS biosolids, but all were below regulatory limits. With regard to coliforms, the risk of illness was negligible for healthy individuals; however, care is required with immunocompromised individuals where the annual risk was greater than the threshold risk of illness (10-4) as set by the USEPA.