Pattern of microbial degradation of estrone and triclosan mixture and its effect on soil bacterial community

Pharmaceutical and personal care products (PPCPs) associated with land farming of municipal wastewater effluent may potentially, persist in the soil and alter soil microbial community processes. Estrone (E1) and the anti-microbial agent, Triclosan, were examined for their potential to persist and disrupt soil microbial community function. Soil with 7 decades-long exposure to these chemicals (conditioned soil) and naive soil, which has not been previously exposed (unconditioned soil), was spiked with estrone, triclosan, or a 1:1 mixture of estrone: triclosan, and incubated for 90 days in the dark at 27°C. Control samples consisting of unspiked conditioned and unconditioned soil were included in the analysis. The community level physiological profile was examined using BIOLOG® EcoPlates™ for the ability of their microflora to utilize ecologically relevant carbon sources. There was a significant increase in substrate activity and substrate richness in all treatments. Principal component analysis (PCA) of the data showed the microbial community utilized different carbon substrates by day 90 whereas they had exhibited similar substrate utilization at day 0. Microbial degradation rates were compared over the 90 days incubation period using high performance liquid chromatography (HPLC). Estrone and Triclosan showed the same pattern of biological degradation in both conditioned and unconditioned soils. Half-lives were determined to range between 5.9-6.8 days for the estrone treatments and 24.1-26.9 days in the triclosan treatments. The rate of degradation of the estrone:triclosan mixture was the same as the individual compound. 16S metagenome analysis of the conditioned day 0 control soil and the conditioned day 90 control, E1, triclosan and the binary mixture of estrone and triclosan was done. The result showed that there was a decrease in species diversity between the control at day 0 and the other treatments at day 90, establishment of unique OTUs in each treatment group at day 90 and Bacillus sp. being the most dominant bacterium specie in all the day 90 treatments.