Sensitivity improvement of o-DGT for organic micropollutants monitoring in waters: Application to neutral pesticides

Abstract

In this study, a larger configuration of the o-DGT, labelled “Large o-DGT” (Lo-DGT), was evaluated to increase its sensitivity. The Lo-DGT presents the same configuration as the conventional o-DGT except for a 4.8-fold increased sampling area (15.2 cm2) due to the use of a larger, commercially available, holder (Chemcatcher). The Lo-DGT was evaluated both in laboratory and on the field for the sampling of 24 model neutral pesticides and metabolites that have a large range of log Kow (from 0.43 to 3.95) and chemical groups. The elution procedure was adapted to the larger binding gels and gave similar elution factors than those of the o-DGT (elution factors between 0.74 and 0.96). The compounds accumulation behavior in the o-DGT and the Lo-DGT devices were compared at laboratory-scale through simultaneous deployments in a synthetic solution over different durations (4 h to 24 h). The accumulation in the Lo-DGT was consistent with the DGT theory, i.e., linear over time, and the accumulated masses were systematically 4.8-times higher than in the conventional o-DGT. Finally, both devices were compared under field conditions during a conventional 14-days deployment in two rivers with a context of low contamination by pesticides (total neutral pesticides < 0.1 µg L-1). In both rivers, the Lo-DGT allowed a higher quantification frequency than the conventional o-DGT, due to its lower LOQ (0.2 to 1.3 ng L-1 versus 0.8 to 8.1 ng L-1). For compounds quantified with both devices, the time-weighted average concentrations were similar. The Lo-DGT therefore appears as reliable as the o-DGT for the monitoring of the tested compounds in waters but with lower LOQ, consequently allowing a better assessment of the water quality.

Keywords

• Passive sampling
• DGT
• Pesticides
• Polar organic compounds
• Water monitoring