| dc.description.abstract | Over the past seven years, the Taiwan EPA and Council of Agriculture have been vigorously encouraging farmers of the husbandry to treat livestock excretion through conventional (i.e., non-thermophilic) anaerobic digestion processes and use the treated biogas slurry/residues as a new kind of fertilizer in arable soils, echoing the current ＂circular economy＂ policy. However, previous studies have shown that compared to the thermophilic biochemical treatment including composting, digestion of livestock feces under ambient temperature and mesophilic conditions fails to substantially diminish the abundance of the antibiotic resistance genes (ARGs) inherent in manure. Given that (i) environmental antibiotic resistance is being shown to have a cyclical relationship to clinical antimicrobial resistance and (ii) according to the WHO, the rising level of antimicrobial resistance is positioned to endanger “the very core of modern medicine”, the new fertilizer practice is of concern. To probe whether this policy execution would result in facilitating antibiotic resistome proliferation in farmland and thus ultimately imposing risks to public health, the first step undoubtedly is to compare the abundance of ARGs harbored in the new (i.e., biogas residue) versus old (i.e., compost) fertilizer. Consequently, in this study we collected 27 biogas residue samples of swine and cattle farms from Hsinchu to Yunlin. We then analyzed ARGs of four common antibiotics (namely tetracyclines, sulfonamides, β-lactams, and macrolides) as well as intI1, in addition to characterizing the basic physicochemical properties of the samples. Results indeed show that the relative abundance of the most target ARG in biogas residue samples was significantly higher than that in compost samples (p < .05). Moreover, the sum of ARG relative abundance was more elevated in swine biogas residue samples than in cattle samples (p < .05). To confirm the soil environmental fate of ARGs from biogas residues after fertilizing, the soil microcosm test was performed to quantify the ARGs reduction ratios of biogas residue-applied soil, and the results were also compared with the compost-soil microcosm test. The results show that the sums of ARG relative abundance in swine biogas residue-applied soils and compost-applied soils were not significantly different on the zeroth day and the thirtieth day, but the levels of the summed ARGs of both groups were significantly higher than cattle biogas residue-applied soils and environmental background (p < .05). The abundances of total ARGs in soil microcosms were not significantly reduced during 30 days after applying biogas residues/composts, which suggested the ARGs in biogas residue/compost-applied soils were quite persistent. If the frequencies of fertilizing were not controlled well, the ARGs perhaps accumulated in arable soil and promote agriculture workers′ ARGs exposure. However, the results of the soil microcosm only represented the situation of topsoil due to the limitation of the experimental design. Future research on the abundance and fate of in situ ARGs in arable soils is warranted, to obtain a complete picture of the potential risk and impact. | en_US |