Calibration of silicone rubber rods as passive samplers for pesticides at two different flow velocities: Modeling of sampling rates under water boundary layer and polymer control.

There is a need to determine time-weighted average concentrations of polar contaminants such as pesticides by passive sampling in environmental waters. Calibration data for silicone rubber-based passive samplers are lacking for this class of compounds. The calibration data, sampling rate (R ), and partition coefficient between silicone rubber and water (K ) were precisely determined for 23 pesticides and 13 candidate performance reference compounds (PRCs) in a laboratory calibration system over 14 d for 2 water flow velocities, 5 and 20 cm s . The results showed that an in situ exposure duration of 7 d left a silicone rubber rod passive sampler configuration in the linear or curvilinear uptake period for 19 of the pesticides studied. A change in the transport mechanism from polymer control to water boundary layer control was observed for pesticides with a log K of approximately 3.3. The PRC candidates were not fully relevant to correct the impact of water flow velocity on R . We therefore propose an alternative method based on an overall resistance to mass transfer model to adjust R from laboratory experiments to in situ hydrodynamic conditions. We estimated diffusion coefficients (D ) and thickness of water boundary layer (δ ) as adjustable model parameters. Log D values ranged from -12.13 to -10.07 m  s . The estimated δ value showed a power function correlation with water flow velocity. Environ Toxicol Chem 2018;37:1208-1218. © 2017 SETAC.