Comparative assessment of the risks associated with use of manure and sewage sludge in Danish agriculture

Summary

Sewage sludge is widely used as an organic fertilizer, but also presents several risks to environmental and human health. This chapter presents a quantitative environmental risk assessment (ERA) and a qualitative human health risk assessment associated with farmland application of sewage sludge as compared to cattle and pig slurry. The analysis reflects conditions pertaining to Denmark, and neighboring European countries. The quantitative ERA was performed by estimating the cumulative risk of 138 (sludge) or 20 (slurry) identified contaminants 6 months after the 100th year of application.
Environmental risk was quantified as the ratio of the predicted environmental concentration (PEC) divided by the predicted no effect concentration (PNEC). PEC/PNEC was 2–3 for sewage sludge and cattle slurry, whereas it was 8 for pig slurry. Metal compounds (especially Zn and Cu) accounted for the majority (>50%) of the environmental risk associated with farmland application of animal slurries, whereas phthalates and triclocarban collectively accounted for more than 50% of the corresponding risk associated with sewage sludge. Human health risks via dietary exposure to potentially toxic elements (PTEs) and pharmaceuticals in food crops were concluded not to cause any reason for concern. Based on reviewed literature, we further conclude that Danish sewage sludge does not represent a higher risk than animal manure for environmental dissemination of antibiotic resistance. Overall, it is concluded that sewage sludge from contemporary Danish society does not constitute a higher risk to soil organisms or human health than pig slurry.