Effects of struvite-loaded zeolite amendment on the fate of copper, tetracycline and antibiotic resistance genes in microplastic-contaminated soil

In this study, struvite-loaded zeolite (SZ) obtained by nutrient recovery from biogas slurry was prepared and used as a soil amendment to treat the combined pollution of Cu, tetracycline (TC) and antibiotic resistance genes (ARGs) in microplastic-contaminated soil. The adsorption of Cu and TC by SZ, environmental microplastics (EMs) and soil particles was investigated using batch experiments. Isothermal adsorption of Cu and TC onto SZ was well fitted by the Langmuir isotherm model, with maximum adsorption capacities of 103 mg g−1 and 158 mg g−1, respectively, which were much higher than the corresponding sorption capacities of EMs and soil particles. Three % SZ amendment reduced bioavailable Cu and TC by more than 73.0% and 71.3%, respectively, in 1% EMs contaminated soil. At the same time, the total relative abundance of ARGs was reduced by 76.2–80.3%. Redundancy analysis and network analysis showed that the relative abundance of most ARGs such as sul1, tetG, tetX and intl1 were significantly correlated to bio-available Cu and TC in soil. In presence of SZ, lower pollutant accumulation alleviated the selection pressure for ARGs on EMs. Structure equation models further indicated that SZ indirectly abated ARG proliferation in microplastic-contaminated soil by altering pollutant bioavailability, soil properties and soil microbe communities. These results demonstrate that SZ amendment could effectively alleviate the combined pollution of heavy metals, antibiotics and ARGs in microplastic-contaminated soil.