A case of anisotropic exchange of non-polar chemicals with absorption-based passive samplers in water

Passive sampling is a powerful technique for the sampling hydrophobic organic contaminants present at trace level in water. A robust application of performance reference compounds (PRCs) for the estimation of in situ sampling rates, requires that dissipation of PRC and uptake of target compounds follow the same processes, i.e. the existence of isotropic exchange between the sampler and water. We report circumstantial evidence that in the presence of heavy fouling of samplers by suspended particulate matter (SPM) when deployed in a freshwater environment, SPM deposited on the surface of the sampler enhances the release of PRCs and reduces the uptake of target compounds. In this case, anisotropy of exchange resulted in on average a factor of 3.9 difference in estimate freely dissolved concentration in water.