Decay of Escherichia Coli in Biosolids Applied to Agricultural Soil

Abstract

There is little scientific data available on the survival patterns of pathogenic microorganisms introduced into the soil through the broad acre application of biosolids. This study was conducted to investigate the decay rates of Escherichia coli in agricultural soil amended with biosolids during two different growing seasons in a dry temperature cropping region in Western Australia.Biosolids-amended and unamended soil were inoculated with E. coli (ACM 1803), inserted into sentinel chambers and placed into the topsoil (0-10 cm) of a wheat crop. Biosolids were applied to designated biosolids plots, according to normal district practice, and E. coli numbers within the sentinel chambers were monitored over time. E. coli numbers in biosolids-amended soil reached detection limits (>10 cfu/mL) within 6 to 7 months. The decay patterns of E. coli, by treatment difference (biosolids-amended or unamended), linear and quadratic relationships of sampling time, and their interactions were highly significant. The T90 or time taken for a 90% reduction in numbers in the biosolids-amended soil was estimated to be 74, 143, 183 days (2006) and 173, 211 days (2008) as compared with 188 days (2006) and 156, 242 days (2008) in the unamended soil. This research provides scientific data on the survival times of E. coli in agricultural soil, with and without biosolids and can thus be helpful to public health policy.