Struvite-supported biochar composite effectively lowers Cu bio-availability and the abundance of antibiotic-resistance genes in soil

https://doi.org/10.1016/j.scitotenv.2020.138294Get rights and content

Highlights

  • MAP/BC amendment immobilized Cu by forming Cu-phosphate precipitation and surface complex.

  • MAP/BC amendment could mitigate the pollution of Cu and ARGs simultaneously.

  • Bio-Cu was the key factor affecting both ARGs distribution and bacterial community.

  • The potential hosts of ARGs mainly belonged to Actinobacteria and Firmicutes.

Abstract

The accumulation of heavy metals and the accelerated dissemination of antibiotic-resistance genes (ARGs) in soil receiving long-term manure application are causing worldwide concern. In this study, struvite-supported biochar composite (MAP/BC) obtained by N and P recovery from pig slurry with Mg(OH)2-modified biochar (Mg(OH)2/BC) was used as a novel amendment for the remediation of Cu- and ARG-contaminated agricultural soil. The effects of MAP/BC on Cu immobilization, ARG distribution, and the bacterial community in the soil were investigated simultaneously. The results showed that the mechanisms involved in the immobilization of Cu by MAP/BC included the formation of copper-phosphate precipitation and a surface complex. With a 10% MAP/BC modification, the acid-soluble Cu content in soil decreased by 0.47-fold at day 56 while the residual Cu content increased 1.41-fold. Meanwhile, the abundances of most of the target ARGs (tetX, tetT, tetW, tetG, ermB, sulI, sulII, and intlI) were reduced by 11.35–99.95%, and the abundance of total ARGs was reduced by 30.69%. The redundancy analysis indicated that the bio-available Cu content played a crucial role in the variations of both ARGs and bacterial communities. The network analysis further suggested that potential hosts of soil ARGs were mainly Firmicutes and Actinobacteria. The above results suggested that the application of MAP/BC can mitigate Cu and ARG pollution in manured soil.

Introduction

China's pig industry has entered into a fast growth period (Wang et al., 2016b). By the end of 2017, the number of slaughtered fattened pigs in China reached 70,202.1 million heads per year (Statistics, 2018). Meanwhile, massive amounts of pig manure are produced consequently. For integrated nutrient management, pig manure and its derivatives, such as biogas slurry, are extensively used as organic fertilizers in agriculture for their ability to enhance soil fertility and promote crop growth (Guo et al., 2019). However, the long-term application of manure has caused serious environmental problems in agricultural soil, such as pollution with heavy metals and antibiotics (Shi et al., 2019; Tang et al., 2015), increased risk of nitrate and phosphorus leaching (Sørensen and Rubæk, 2012), and rapid emergence of antibiotic resistance in the soil microbiome in particular (Xie et al., 2018). The high prevalence of antibiotic resistant genes (ARGs) in manured agricultural soils has caused worldwide concern (Chee-Sanford et al., 2009; Heuer et al., 2011). In view of the risk of ARG transmission between native biological communities and human pathogens (Fang et al., 2018; Forsberg et al., 2012), strategies to mitigate the dissemination of ARGs in manured soil are of great importance to human health.

Heavy metals and antibiotics as stressors all affect the transferability of soil ARGs, but heavy metals may be more important due to their ability to exert longer-term selective pressure on soil organisms (Knapp et al., 2017; Xu et al., 2017). For example, as a common heavy metal, Cu has been reported to be closely associated with the prevalence of ARGs in manured soils (Ji et al., 2012; Zhu et al., 2013). This may be because the stress of excessive Cu, especially its bio-available species, could select bacterial strains with a higher likelihood of expressing multidrug resistance (Berg et al., 2010). Therefore, with Cu pollution, the acquisition and maintenance of ARGs could be enhanced through the increased cross-resistance and co-resistance among bacterial communities (Gao et al., 2015; Xu et al., 2017).

Some of the available evidence show that reducing the migration activity or bio-availability of heavy metals in the environment could mitigate ARG proliferation. For instance, Li et al. (2017) noted that the addition of biochar could immobilize bio-available Cu and bio-available Zn and decrease their co-selection pressure, thereby partially mitigating the propagation of ARGs during chicken manure composting. Zhang et al. (2018) also suggested that the reduced ARG copies during sludge composting are related to the immobilization of heavy metals by natural zeolite application.

In recent years, our team has developed various magnesium-modified materials and used them for simultaneously recovering N and P nutrients from wastewater and pig slurry (Jing et al., 2019; Wang et al., 2019; Xia et al., 2016). Further studies have confirmed that reusing the recovered struvite-contained products as soil amendments could efficiently immobilize heavy metals and consequently reduce the mobility and bio-availability of heavy metals (Li et al., 2018; Wang et al., 2018; Wang et al., 2016a). As the selective pressure of heavy metals exerted on organisms would decrease with immobilization, the application of the N and P recovery products as amendments could further help mitigate the ARG pollution in manured soil.

This study prepared a struvite-supported biochar composite (MAP/BC) by recovering N and P from pig slurry with Mg(OH)2-modified biochar (Mg(OH)2/BC). MAP/BC was subsequently used as an eco-friendly amendment for in situ remediation of Cu- and ARG-contaminated soil. The simultaneous effects of MAP/BC on Cu immobilization, ARG profiles and soil microbial were explored. The correlations among bio-available Cu (biosingle bondCu), ARG abundance, and bacterial composition during soil remediation were also studied. The results will provide insights for the evaluation of the potential for struvite-based nitrogen and phosphorus recovery products.

Section snippets

Preparation of MAP/BC

The preparation procedures of MAP/BC were as follows. First, a pig slurry was filtered with a 0.45 μm acetate fiber membrane filter. The characteristics of the filtered pig slurry are given in Table S1. Second, 0.4 g Mg(OH)2/BC (detailed preparation procedures and micromorphology information are given in Text. S1 and Fig. S1) was added to 1 L of pig slurry, and the mixture was shaken horizontally at 180 rpm on a shaking table for 24 h at 25 °C. Third, the filtered precipitate was washed by

Characterization of MAP/BC

The surface morphological properties and chemical composition of MAP/BC are given in Fig. S2. The SEM images indicated that after the nutrient recovery process, clustered-growing prismatic-shaped crystals mainly comprising Mg, O, N and P were formed (Fig. S3). The XRD patterns showed that the diffraction peaks corresponding to Mg(NH4)PO4·6H2O were identified in MAP/BC. The above results suggest that MAP/BC is a bamboo biochar-based phosphorus-rich material recovered from pig slurry, and the

Conclusion

This study investigated the effects of a nutrient-recovery product MAP/BC on Cu immobilization, ARG composition, and bacterial community in Cu-contaminated agricultural soil. MAP/BC amendment could immobilize Cu through the formation of copper-phosphate precipitation and surface complex. With MAP/BC treatment, the acid-soluble Cu content decreased by 0.47-fold while the residual Cu content increased by 1.41-fold. Moreover, the total abundance of nine target ARGs in Cu-contaminated soil were

CRediT authorship contribution statement

Yuan Li:Conceptualization, Methodology, Software, Visualization, Investigation, Writing - original draft.Xuejiang Wang:Resources, Supervision, Data curation, Project administration, Writing - review & editing.Yuan Wang:Formal analysis, Software.Fei Wang:Software, Writing - review & editing.Siqing Xia:Writing - review & editing.Jianfu Zhao:Resources, Project administration, Supervision, Writing - review & editing.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

The authors thanks for the support of the National Natural Science Foundation of China (51678421, 41571301, 21777120).

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