| The emerging pollution of antibiotics and antibiotic resistance genes (ARGs) has gained great attention around the globe in recent years. At the same time, the pollution of heavy metals is also increased. Eight antibiotic resistance genes (ARGs), seven heavy metals, and six antibiotics were quantified in manures, soils and waters collected from multiple feedlots in Shanghai. And we analysied the correlations between metal content and ARGs and correlations between the antibiotics and ARGs. The main Conclusions are as follows:(1) We detected the concentrations of6kinds of antibiotics in all samples collected from feedlots in Shanghai. The results revealed the presence of sulfonamides, tetracyclines and chloramphenicol at concentration ranges of0.20-24.66,0.29～33.37and0.11～17.85mg·kg-1respectively. Overall, the concentrations of tetracycline residues were significantly higher than sulfonamides.(2) Inductively coupled plasma-atomic emission spectroscopy (ICP-AES) and an AMS-254solid/liquid mercury analyzer was used to quantify concentrations of seven typical heavy metals including Cu, Zn, Cd, Cr, Pb, As, Hg in all samples. Except Cd, the other heavy metals were all detected of different levels in all samples. Hg was found in a range of121.67～400.00μg.kg-1in manures, soils, and river sediment collected from feedlot in Shanghai. The other five heavy metals were also found at high in all samples. Zn was observed to be the highest accumulated, ranging from75.9～4333.8mg·kg-1. Cu was the second-most accumulated in the samples, ranging from32.3～730.1mg·kg-1. In addition to high Zn and Cu content, the manure, soil, and river sediment samples also contained high concentrations of As (2.6～617.2mg·kg-1), Cr (0.0～70.4mg·kg-1), and Pb (2.7～50.0mg·kg-1). However, the leves of heavy metals in all water samples were very lower (<0.2mg·kg-1) or not detected.(3) The results of real-time quantitative PCR (RT-qPCR) showed that the relative abundances of sulfonamide resistance genes (sul(Ⅰ),sul(Ⅱ), sul(Ⅲ), and sul(A)) were higher than tetracycline resistance genes (tet(M),tet(W), tet(O), tet(B/P)) in all samples. For sulfonamide ARGs, the following trend was observed with respect to the relative abundances:sul(A)>sul(Ⅰ)> sul(Ⅱ)> sul(Ⅲ). For tetracycline resistance genes, the trend was as follows:tet(M)> tet(W)> tet(O)> tet(B/P). Additionally, all ARGs were detected except tet(B/P), which was absent from all animal manures and swine wastewater.(4) The results of correlation analysis of antibiotics and resistance genes showed that except sul(Ⅱ), only a weak correlations existed between the abundance of other ARGs and the content of "their" corresponding antibiotics in samples. However, a common positive correlation between the abundance of ARGs and the content of different families of antibiotics was found, which might due to the co-selective effect of other antibiotics in the environment.(5) The results of correlations between heavy metals and relative abundance of ARGs showed that Cu, Zn and Hg existed a positively correlated with sulfonamide ARGs, except for sul(Ⅱ). The coefficients were also notably higher (r values ranging from0.028to0.888) when compared to those between ARGs and their corresponding antibiotics. However, an opposite trend was observed between heavy metals and tetracycline ARGs; almost no consistent positive correlations were found except for the significant positive correlation between As and tet(B/P)(r=0.824, p=0.023).(6) Correlations between metal content and ARGs were stronger than those between antibiotic residues and ARGs. In addition to antibiotics, toxic heavy metals, such as Hg, Cu, and Zn, exerted a strong selection pressure and acted as complementary factors for ARG abundance. |
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