Metal ion–oxytetracycline interactions on maize straw biochar pyrolyzed at different temperatures Mingyun Jia a , Fang Wang a,⇑ , Xin Jin a , Yang Song a , Yongrong Bian a , Lisa A. Boughner b , Xinglun Yang a , Chenggang Gu a , Xin Jiang a,⇑ , Qiguo Zhao a a Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, PR China b Department of Plant, Soil and Microbial Sciences, Michigan State University, East Lansing, MI 48824, United States highlights  Pyrolytic temperature and the metals species governs the adsorption interaction.  Copper facilitated the sorption of oxytetracycline to BC300 yet negligible to BC600.  Oxytetracycline facilitated the sorption of Cu 2+ to BC600 yet negligible to BC300.  Sorption of Cd 2+ to BC600 was approximately linear.  Oxytetracycline and Cd 2+ displayed independent sorption to biochars. article info Article history: Received 2 March 2016 Received in revised form 11 May 2016 Accepted 13 May 2016 Available online 14 May 2016 Keywords: Trace metals Antibiotics Biochars Bridging effect Ternary complexes abstract The interaction between metal ions and antibiotics greatly influences their fate and transport in the envi- ronment, but knowledge on the interaction between metal ions and antibiotics to biochar is still limited. Sorption of oxytetracycline (OTC) and metal ions (Cu 2+ or Cd 2+ ) to biochars pyrolyzed at 300 °C (BC300) and 600 °C (BC600) in single or binary systems (OTC with metal ion) were investigated. The sorption and interaction mechanisms involved were also explored. The results showed that biochars can effectively adsorb OTC, Cu 2+ and Cd 2+ . The Langmuir parameter q max for OTC was 26.12 mmol kg 1 for BC600, and Freundlich parameter K f for Cu 2+ and Cd 2+ were 92.40 mmol 1n L n kg 1 and 83.42 mmol 1n L n kg 1 for BC300, respectively. The pyrolytic temperature of the biochars and metallic species co-determines the adsorption interaction of both OTC and metal ions in binary systems. In the presence of Cu 2+ , sorption of OTC to BC300 was dramatically enhanced, yet to BC600 it was insignificantly affected. Inversely, in the presence of OTC, the sorption of Cu 2+ to BC600 was improved, yet to BC300 it was not influenced. The interaction among OTC, Cu 2+ and biochars, namely the bridging effect, led to the formation of ternary complexes that enhanced the adsorption of biochars. However, the interaction between OTC and Cd 2+ was not found through the UV–vis spectrum scanning, and the sorption of OTC with Cd 2+ to the biochars was independent. Ó 2016 Published by Elsevier B.V. 1. Introduction Antibiotics have been widely used to treat or prevent infectious diseases in both humans and animals. Since the early 1990s, large quantities of antibiotics have been incorporated into animal feed at sub-therapeutic levels in attempt to improve growth and feeding efficiency [1–3]. However, such intensive use of antibiotics can cause serious problems, because their presence in the environment may lead to the development of antimicrobial resistance genes [4– 6]. Antibiotics and antibiotic resistance genes (ARGs) have been identified as newly emerging persistent organic pollutants [7,8]. The leading cause of environmental contamination with antibiotics is due to the ingested animal feed, supplemented with antibiotics that are poorly absorbed by the animals. Ultimately, these antibi- otics may be discharged into the environment as unmetabolized parent compounds directly within urine and feces [9]. Moreover, the repeated application of unprocessed manure to agriculture soil is another way that leads to antibiotic contamination [1–3,10]. Despite antibiotic contamination is one of key environmental http://dx.doi.org/10.1016/j.cej.2016.05.064 1385-8947/Ó 2016 Published by Elsevier B.V. ⇑ Corresponding authors at: 71 East Beijing Road, Nanjing 21008, China. E-mail addresses: wangfang@issas.ac.cn (F. Wang), jiangxin@issas.ac.cn (X. Jiang). Chemical Engineering Journal 304 (2016) 934–940 Contents lists available at ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej