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Water treatment works have previously shown high efficiency in removing microplastics > 25 µm from raw source water. However, what is less well known is the extent to which microplastics of this size class are generated or lost within the water distribution network, particularly whether there is a greater presence in the customer tap than in the water treatment works outlet. This study focused on the presence of 21 different types of synthetic polymer particles with sizes larger than 25 µm examined through multiple rounds of sampling at outlets of water treatment works (WTW), service reservoirs (SR), and customer taps (CT) managed by seven different water companies in Britain. Nineteen different types of polymers were detected; their signature and concentration varied based on the round of sampling, the location within the water supply network, and the water company responsible for managing the supply. Among the polymers examined, polyamide (PA), polyethene terephthalate (PET), polypropylene (PP), and polystyrene (PS) were the most commonly found. Apart from PET having its highest concentration of 0.0189 microplastic per litre (MP/L) in the SR, the concentrations of the other three most frequent polymers (PS = 0.017 MP/L, PA = 0.0752 MP/L, PP= 0.1513 MP/L) were highest in the CT. The overall prevalence of this size of microplastics in the network is low, but there was a high variability of polymer types and occurrences. These spatial and temporal variations suggested that the MP in the distribution network may exist as a series of pulses. Given the presence and polymer types, the potential for some of the microplastics to originate from materials used in the water network and domestic plumbing systems cannot be ruled out. As found before, the absolute number of microplastics in the water distribution network remained extremely low.

The objective of the project was to carry out a pilot study developing sampling and analytical protocols to determine the quantities, loads and types of microplastics (MP), in surface waters and sediments. Approaches to sampling surface waters and sediments would be reviewed and a selected approach tested on catchments agreed in consultation with the Environment Agency. From this, a provisional standard operating procedure (SOP) guideline is presented that may be used for sampling, processing and analysis of microplastics in river waters and sediments. In addition, it was investigated whether sediment samples collected in this manner could be analysed for the presence of vehicle tyre wear, through quantitative analysis of a common additive of tyre rubber, N-(1,3-Dimethylbutyl)-N’-phenyl-p-phenylenediamine (6PPD). This compound has been identified as a Priority 2 substance for freshwaters and groundwaters (high risk, low certainty) under the Environment Agency’s Prioritisation and Early Warning System (PEWS), flagging it for further consideration in sediments as it meets the toxicity criterion according to available ecotoxicity data and is not currently monitored (Environment Agency, 2023). The method is believed to be the first to be published to quantify this chemical marker in sediments using Gas Chromatography Mass Spectrometry.

Plastic litter is now pervasive in the aquatic environment. Several marine and terrestrial organisms can fragment plastic with their feeding appendages, facilitating its breakdown and generating microplastics. However, similar studies with freshwater organisms are extremely limited. We explored the interactions between the caddisfly larvae Agrypnia sp. and polylactic acid (PLA) film. The use of plastic by larvae to build their protective cases was investigated, along with their ability to fragment the plastic film as they do with leaf litter. Caddisfly consistently incorporated PLA into their cases alongside leaf material. They also used their feeding appendages to rapidly fragment PLA—forming hundreds of submillimeter-sized microplastics. Although larvae showed a preference for leaf material when constructing cases, plastic use and fragmentation still occurred when leaf material was replete, indicating that this behavior is likely to occur in natural environments that are polluted with plastics. This is thought to be the first documented evidence of active plastic modification by a freshwater invertebrate and therefore reveals a previously unidentified mechanism of plastic fragmentation and microplastic formation in freshwater. Further work is now needed to determine the extent of this behavior across freshwater taxa and the potential implications for the wider ecosystem.