HOW DOES CHEMCATCHER WORK?
The European Water Framework Directive has a ‘priority list’ of substances which pose a threat to or via the aquatic environment. The aim of this priority list is to reduce (or eliminate) pollution of surface water (rivers, lakes, estuaries and coastal waters) by the pollutants on the list.
However, there are also a number of emerging contaminants that are not included in routine monitoring programmes at EU level and whose fate, behaviour and (eco)toxicological effects are not well understood as yet. (http://www.norman-network.net/)
Typically Chemcatcher® measures the freely dissolved (sometimes called the biologically available fraction). Unlike spot samples, which only give a snapshot of the water quality at one moment in time, Chemcatcher® can provide time-weighted-average (TWA) and equilibrium concentrations over the deployment time, thus effectively concentrating the pollutants onto the receiving disk and lowering analytical detection limits.
South West Water wanted improvements in raw water quality, through identification of tributaries that were sources of acid herbicides in the water.
- Compounds such as mecoprop, MCPA, tricolpyr and clopyralid are widely used in South West England to control weeds in grassland.
- Due to their high water solubility, this can lead to frequent run-off.
- This in turn causes problems for South West Water as it is regularly detected in major drinking water catchments, above PCV level (0.1μg/l for a given pesticide). Indeed a single drop of MCPA in a water body like a stream of 1m wide, 0.30m deep, can be enough to exceed the legal limit for pesticides in drinking water of 0.1μg/l along 30km of its length. (1)
- Chemcatcher passive samplers were chosen for monitoring as they avoid the ‘hit and miss’ nature of spot sampling.
- Passive samplers can be deployed for extended periods (weeks) and can reveal time weighted average (TWA) concentrations of pollutants
- The TWA concentrations were calculated and this allowed better estimates of the overall inputs of these herbicides into the catchment.
- In addition, the samplers were able to detect sporadic inputs of these herbicides after rainfall events; these events were not picked up by spot water samples.
Mills G. A., Townsend, I., Jones, L., Broomb, M., Gravell, A. and Greenwood, R. (2016) Chemcatcher® for monitoring acidic herbicides in a river catchment in South West England [Oral Presentation] 8th International Passive sampling Workshop and Symposium. Prague. 7-10 September.
United Utilities used Chemcatchers at 13 sites across the Dee catchment, to measure metaldehyde and different acid herbicides at each site was to better understand the concentration of pesticides in the river water over continued periods of time (spot samples can often miss pesticide spikes) and also to assess the spatial characteristics of pesticide application across the catchment.
These herbicides included:
- Seasonal variation of pesticides occurs during the year, e.g. MCPA had a relatively high average concentration in the catchments during the spring and summer months, while autumn and winter measurements were low.
- With the Chemcatchers, United Utilities was able to identify particular problem areas with two areas identified as being particularly problematic, with high amounts of 2,4-D and MCPA in the late spring/early summer. Other pesticides, such as clopyralid and fluroxypyr, were present consistently at lower levels for many sub-catchments all year round.
- The data provided by the Chemcatchers helped United Utilities to prioritise the sub-catchments according to how much of a risk they present to drinking water quality.
United Utilities (2017) River Dee Catchment Using Data and Evidence to Target
Water Quality Measures Westcountry Rivers Trust. Available at: http://www.welshdeetrust.com/wp-content/uploads/2017/10/UU_Dee_Catchment_Report_11-09-17_WEB-MEDIUM-2.pdf [Accessed 11 April 2018]
Following a major earthquake, a 15-metre tsunami disabled the power supply and cooling of three Fukushima Daiichi reactors, causing a nuclear accident on 11 March 2011. The accident was rated 7 on the INES scale, due to high radioactive releases over days 4 to 6, eventually a total of some 940 PBq (I-131 eq) (2).
- The main radionuclide which was emitted due to the accident was caesium-137, which has a 30-year half-life, is easily carried in a plume, and when it lands it may contaminate land for some time. It is a strong gamma-emitter in its decay.
- Cs-134 is also produced and dispersed, it has a two-year half-life.
- Caesium is soluble and can be taken into the body, but does not concentrate in any particular organs, and has a biological half-life of about 70 days. (2).
- Collaborations with Chiba Institute of Technology, Japan and 3M Tokyo resulted in a modified Chemcatcher, suitable for monitoring radio-caesium in waters near the Fukushima reactor.
- A bespoke receiving phase with a high affinity for Caesium allows time integrative accumulation and lowers detection limits.
- Removes the need to collect of large volumes (c. 200 L) of potentially radioactive water.
Source: Research Excellence Framework (REF) 2014 Impact Case Studies. (2014) The Chemcatcher – an approved passive sampler for monitoring water quality. Available at: URL [http://impact.ref.ac.uk/CaseStudies/CaseStudy.aspx?Id=14991 [Accessed 11 April 2018].