Taking samples of river water using the conventional method of filling bottles by hand can be costly and time-consuming. The results obtained from these ‘spot’ samples can, at best, only provide a snapshot of the concentration target compounds which may be present at the time of sampling.
Subsequent interpretation of the analytical results obtained is also difficult (was it the leading edge of a pollutant plume, the peak, or the trailing edge..?) and the time lag between these results and repeat samples or remedial action inevitably means the environmental investigation is reactive in nature.
Recently, a number of alternative and innovative monitoring strategies have been proposed to overcome these challenges. In particular, research is focusing on the use of passive samplers which can be deployed alone or, more often, in conjunction with spot sampling to provide addition data on water quality and pollutant loads in rivers.
Recently, a research collaboration between South West Water, the University of Portsmouth, Natural Resources Wales and the Westcountry Rivers Trust has been established to use the ChemcatcherTM passive sampler (developed at the University) to investigate water quality in this area. Chemcatcher™ is a small plastic device fitted with a specifically tailored receiving-phase disk that has a high affinity for the target compounds of interest.
In practice, the receiving phase disk is overlaid with a thin diffusion-limiting membrane. These devices can be used to obtain the equilibrium concentration of the pollutants or more typically the time-weighted average (TWA) concentration over the sampling period.
The first riverine trials using the ChemcatcherTM involved investigating pesticides along the River Exe; a river designated as a WFD Article 7 Drinking Water Protected Area (DrWPA) with additional Safeguard Zone (SGZ) status that requires a formal ‘action plan’ to be drawn up by the Environment Agency. In 2014, the first field deployments of passive samplers has been undertaken by Westcountry Rivers Trust in the Tamar and Fowey Catchments.