Development and evaluation of diffusive gradients in thin films based on nano-sized zinc oxide particles for the in situ sampling of tetracyclines in pig breeding wastewater.

The pollution of antibiotics, including tetracyclines (TCs), in aquatic environments has become an issue of concern in recent years. Herein, an in situ sampling of TCs in pig breeding wastewater that utilizes the technique of diffusive gradients in thin films (DGT), based on commercial nanosized ZnO (nanoZnO) particles as the potential effective binding agent and a polyethersulfone (PES) membrane as the diffusion layer, was developed. The diffusion coefficients of tetracycline (TC), oxytetracycline (OTC) and chlortetracycline (CTC) in a PES membrane at 25 °C were (1.37 ± 0.06) × 10-6  cm2  s-1 , (1.29 ± 0.05) × 10-6  cm2  s-1 and (1.94 ± 0.07) × 10-6  cm2  s-1 , respectively. The results showed that the adsorption capacities of a gel disc containing 2.5 g L-1 of nanoZnO particles were as high as 3.93 ± 0.20 mg disc-1 for TC, 3.21 ± 0.20 mg disc-1 for OTC and 4.62 ± 0.22 mg disc-1 for CTC. Both a solution pH in the range of 5-9 and an ionic strength (as pNaCl) in the range of 1-3 had an insignificant influence on the TCs uptake by nanoZnO-DGT samplers. There was no significant influence of fulvic acid or tannic acid on the TC uptake by nanoZnO-DGT samplers at the tested mass ratios. For all spiked freshwater samples, there was no notable interference of matrices on the performance of the nanoZnO-DGT samplers, suggesting that the nanoZnO-DGT samplers yielded satisfactory results for the uptake of TCs at concentrations existing in the spiked freshwater samples. Field deployment of the nanoZnO-DGT samplers in pig breeding wastewater also exhibited excellent precision and accuracy, indicating that the nanoZnO-DGT samplers could be used as a promising method for the in situ sampling of TC antibiotics in aquatic environments.