Internal and external transport significance for predicting contaminant uptake rates in passive samplers.

A critical element in the application of passive sampling devices for estimating in situ the concentrations of contaminants in pore water of sediments is predicting the rate of uptake within the device. Herein, we demonstrate the relative importance of internal and external mass transport processes for sampling devices and show that external processes control the kinetics in many instances. As such uptake rates are closely related to the surface area to volume ratio of the sampling device and site-specific transport conditions. Models based on sorption-related molecular diffusion provide an upper bound on equilibrium times. The essential model parameters and corresponding kinetics at a site with more substantial mixing can be inferred using time series of sampler concentrations, concentrations in samplers with different geometry, or concentrations of performance reference compounds.