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Comparing Chemcatchers, Online Process Monitoring and Traditional Laboratory Measurements

Martin Perkins

14th August 2018

Chemcatcher, Drinking Water, Metaldehyde, Molluscicide, Natural Environment, NERC, Online Process Monitoring, Passive Sampling Devices, Pollutants, PSD's, Research Council, South West Water, University of Portsmout,


I am a final-year PhD student from the School of Earth and Environmental Sciences at the University of Portsmouth. I am currently working on a Natural Environment Research Council (NERC) funded project in partnership with South West Water titled ‘The development of a passive sampler for detecting sources and fluxes of metaldehyde in the surface waters in response to stochastic storm events‘.

Anatune has one of its Online Process Monitors in operation at a site where some of our Chemcatchers have been deployed.

This has enabled me to observe the two techniques running side-by-side, and I have seen that both sets of measurements correlate very well with each other, and also correlate well with the data generated in the lab.  This is all very promising.

To ensure both ecosystems and humans aren’t exposed to levels of toxins which could cause adverse effects, the measurement of pollutants in drinking water requires monitoring tools that are accurate and reliable.

Traditional methods for the monitoring of pollutants in water involves taking composite grab samples – the periodic removal of small volumes of water that are subsequently analysed in a laboratory.  Although this method is straightforward, there are some limitations to doing things this way.

  1. Pre-concentration methods are time consuming.
  2. Concentration data obtained can misrepresent the real picture – especially where there can be sporadic inputs of pollutants into the aquatic environment.
  3. Doesn’t enable time-weighted average (TWA) measurements to be made.

The use of passive sampling devices (PSD’s), provide an alternative to this monitoring strategy that can effectively overcome all of the limitations listed above.

PSDs can be deployed in the aquatic environment for extended periods (from days to months) where they remain submerged and continually sequester compounds. This can significantly lower analytical limits of detection and enable the identification of pollutants that are episodically present.  PSD’s can give a time weighted average concentration of a given pollutant within the environment rather than a snap-shot of concentration at one moment in time.

Chemcatcher is an example of a passive sampler which can be used for monitoring a suite of pollutants in the aquatic environment, and is described in this article from Environmental Technology: ‘The Many Faces of a New Versatile Passive Sampler’.

At the University of Portsmouth, with NERC funding, I’m developing the Chemcatcher passive sampler for the monitoring of the molluscicide metaldehyde in surface waters. The topic of metaldehyde in the environment has recently been reviewed in this paper.

Metaldehyde has become a problem for many UK water companies due to its high solubility, which leads to a presence in some water supplies used to provide drinking water.

The project has shown, through various field trials and calibrations, the Chemcatcher passive sampler to be an effective compliment to infrequent spot sampling.

However, comparing spot sampling with time weighted average concentrations has been difficult, especially in the case of sporadic contaminants like metaldehyde, as no information exists on the environmental status of the river between sampling events.  A possible solution to this problem is higher frequency monitoring or through the use of an automated time triggered sampling device – like the Anatune Online Process Monitor.

If online sampling with full automation is what is needed, then you know just who to call…

Currently, I am in the process of writing-up this study and I will check back-in with another blog to show you the results.

For more information, you can contact me by email.