Enrofloxacin and copper plant uptake by Phragmites australis from a liquid digestate: Single versus combined...

Application of anaerobically digested sludges and manure (digestates) to agricultural fields reduces the need for fertilizer application, but might also pose environmental risks due to the introduction of various pollutants -including metal trace elements and pharmaceuticals- to amended soils. The simultaneous presence of different contaminants can affect plant uptake, altering the performance of phytoremediation. This work aims to investigate and compare the single and combined effects of Enrofloxacin (Enro) and Cu on their plant uptake from digestate solutions. Plant uptake experiments were carried out by exposing, for 5 days, Phragmites australis to three different concentrations of a liquid digestate doped with Cu and/or Enro. Contaminant concentrations were afterward determined in both plant tissues and digestate solutions. Contaminant speciation in solution and Cu speciation in plant roots were also assessed. Cu plant uptake (mostly in plant roots, Cu concentration varied between 55 and 254 μg·g^-1) was observed, especially at low concentration of digestate. At high digestate concentration, Cu uptake decreased due to the formation of Cu-DOC complexes rendering Cu less bioavailable. The presence of the antibiotic slightly further reduced Cu plant uptake due to the formation of Cu-Enro complexes. Plant roots also accumulated Enro, an accumulation also higher for the lowest concentration of digestate (an increase of 40%), and that slightly increased in the presence of Cu (up to 226 μg·g^-1). However, proportion of free Enro in solution decreased (up to 70%) in the presence of Cu due to complexation. Cu speciation in plant roots confirmed the implication of the complexation in the uptake of Cu and Enro when they are simultaneously present in solution. Thus, the presence of amendments (such as digestates) increasing the DOC content, in addition to the interactions between contaminants, should be taken into account for field crop soils as well as for phytoremediation technologies.