Development and evaluation of diffusive gradients in thin films technique for measuring antibiotics in seawater

As coastal waters in many regions of the world have been polluted by organic micro-pollutants such as antibiotics that can promote the development of resistance genes, it is of importance to monitor the levels of antibiotics in coastal waters. For this purpose, a reliable and robust sampling approach based on diffusive gradients in thin films (DGT) was developed in this study. The DGT measurement can provide a time weighted average concentration of pollutants. A binding material (resin XDA-1) with a high adsorption capacity for antibiotics, which can resist the pH and ionic strength of seawaters, was selected. The DGT sampler exhibited linear accumulation for 20 antibiotics during a 12h deployment. The antibiotic measurement by the sampler was not affected by pH in the range of 7.3 to 8.9 and ionic strength in the range of 0.5 to 0.8M. After an 8-hour in situ DGT sampling, 10 antibiotics were detected in Dalian coastal seawaters with the concentrations ranging from 2.6 to 44.8ngL^-1, which was comparable to the results measured by an active sampling method. This study can be a first attempt to construct DGT sampler for determining antibiotics in seawaters.