Fig. 3.

Concentrations of total and antibiotic-resistant presumptive E. coli and enterococci in biosolids-amended soil with water or treated wastewater effluent irrigation. Soil samples were collected as cores from pots over 77 days of carrot growth from seeds in a greenhouse. The lower limit of detection was 0.39 log₁₀ CFU/g-TS in soil. Error bars represent standard error of three replicates. Results show that irrigation with TWE or DI water did not have an impact on total or antibiotic-resistant E. coli or enterococci concentrations in biosolids-amended soil during the course of the study (Kruskal-Wallis, p > 0.05; Fig. 3). The slight increase in concentrations of E. coli or enterococci a few days after amendment, followed by a period of decay, has been reported in other studies (Montealegre et al., 2018; Sharma and Millner, 2016), and could be due to the initial ability of the bacteria to access and utilize the nutrients and moisture in the soil (Sharma and Reynnells, 2018).