Impacts of straw return and high-temperature solarization on antibiotics and estrogens reduction in greenhouse soil

Intensive livestock farming has been driven by high demands for meat, eggs, and dairy in recent years. Among them, the antibiotics and estrogens can release into the environment via livestock and poultry manure during breeding. These contaminants can be accumulated in the edible parts of crops in the antibiotic and estrogen contaminated farmland soil, thereby increasing the risk of their transmission to humans through the food chain. It is an urgent need to simultaneously reduce both antibiotics and estrogens in soil. Such approaches can be expected to combine with existing agricultural practices. Optimal parameters are also essential for the concurrent removal of the contaminants. This study aims to explore the impact of straw incorporation coupled with solarization on the attenuation of antibiotics and estrogens in vegetable soil. The resource utilization of agricultural waste was also promoted using high-temperature solarization. Tomato straw and wheat straw were incorporated with/without the supplementary high-temperature decomposing microbial inoculants. A systematic investigation was implemented to examine the effects of the varying incorporation ratios of tomato straw to wheat straw on: (1) soil chemical properties; (2) concentrations of target antibiotics (tetracycline, oxytetracycline, and chlortetracycline) and estrogens (estrone, 17β-estradiol, and estriol); (3) composition and structure shifts in bacterial communities. The optimal straw incorporation ratio was then identified to maximize the attenuation of soil antibiotics and estrogens via the straw-solarization approach. Four treatments included: CK (control, solarization without straw incorporation), LO (solarization with tomato and wheat straw incorporation at a 3:1 ratio), LB (solarization with tomato and wheat straw incorporation at a 3:1 ratio plus microbial agent), and HB (solarization with tomato and wheat straw incorporation at a 3:2 ratio plus microbial agent). The results showed that the straw incorporation and solarization were combined to significantly elevate the soil pH for the less total nitrogen content. The most performance was observed at a tomato straw to wheat straw ratio of 3:1. Concurrently, the optimal ratio (3:1) also yielded the superior attenuation efficiencies for both antibiotics and estrogens, compared with the CK. The total reduction rates reached 75.78% and 17.03%, respectively. The residual levels were reduced below the detection limit in the cases. Microbial degradation was identified as the critical driving factor to reduce the antibiotics and estrogens. Microbial activity was primarily attributed to the soil environment by different straw incorporation ratios and the addition of microbial agents, thus subsequently influencing on the microbial community structure, activity, and the secretion of degradation enzymes. Soil bacterial diversity and community composition further revealed that the solarization with the 3:1 straw ratio was significantly enhanced the bacterial richness. The relative abundance of the phylum Firmicutes and the genus Bacillus was optimized to alter the overall community structure, and then amplify the degradation for antibiotics and estrogens. The findings can provide a theoretical foundation and empirical data to support: (1) optimization of solarization technology; (2) resource-oriented utilization of agricultural waste; and (3) mitigation strategies for the antibiotic and estrogen contamination in protected agricultural soils.