Investigation of pollution sources in rivers using passive sampling: a discussion based on in-situ experiments on PCBs
Tools able to investigate pollution sources at low cost are urgently needed to achieve the requirements of the Water Frame Directive and international treaties (such as the Stockholm Convention) which are to reduce, or even cease, pollution emissions to water and other parts of the environment. Based on in-situ experiments on PCBs, this study assesses the use of passive sampling as a tool to investigate point sources of hydrophobic pollutants in rivers. The proposed methodology deploys passive samplers downstream and upstream potential pollution sources (or even in their outlets) and considers that increases of aqueous concentration between sites may reveal the presence of pollution sources. The authors present data obtained from investigations carried out with low density polyethylene (LDPE) strips in the Venoge River (Switzerland) which is known to be polluted by PCBs (ou alors where fishes are known to be polluted by PCBs). Results are discussed taking into account, firstly, the variations of exposure conditions among sites (hydrodynamics, temperature and biofouling) which can cause different concentrations in samplers for equal contamination levels and, secondly, the fact that the uptake of pollutants having reached equilibrium is no more influenced by exposure conditions. It turns out that passive sampling offers a simple interpretation when equilibrium is reached and/or exposure conditions are similar since concentration in samplers can directly be compared among sites. When equilibrium is not reached and exposure conditions differ among sites, the release rate constants are necessary to calculate and compare aqueous concentrations. The efficiency of performance reference compounds (PRCs) to determine which compounds haven’t reached equilibrium and approximate their release rate constant is evaluated with in-situ experiments which are also presented here.