The challenge of microplastics - measuring, monitoring and modelling

From wet wipes to water bottles - what is the scale of the microplastics challenge when looking at whole catchments?

Recent growing awareness of plastic pollution in the UK

Seeing images of the tragic impact that plastics has on birds and animals in the environment has challenged me to find plastic free alternatives to water bottles, wipes and packaging. Having spent some of the weekend vacuuming up glitter I resolve to ban it in our household – indeed a mild panic sets in as I think about the scale of the issue as plastics so frequently also offer convenience. 

As plastics break down into pieces smaller than 5mm, the term ‘microplastics’ is used, and they become an issue throughout the food chain having been shown to harm aquatic life. Microplastics include nurdles the lentil sized (2-3mm wide) plastic pellets used to make products. In this article I explore how this challenge to act on microplastics relates to the UK Water Industry where I work.

A shift in perspective

From a personal perspective, it took me a while to get serious on going plastic free: piecing together the urgency as seagulls pick up wet wipes from sewer overflows on the tidal Thames and weighing up the convenience of throwaway products versus the alternatives. I had a shift in thinking of wet wipes as single use plastics as my colleague Andy Drinkwater was interviewed on Radio 5 live about the Fine to Flush mark and wet wipes that are designed to break down in the sewers. 

It takes time for society too to recognise the need to clean up microplastics and for policy makers to act. When any new – or emerging - pollutants come to the awareness of the water industry there is a time lag in response as water companies are mandated to act in the interests of their customers within the environmental regulations. 

The response from water industry has to be considered in terms of what targets need to be met (the impact of a new pollutant on drinking water and the environment), what all of the regulators want, what actions are needed to deal with this, and what is the option that is best value for the customers who pay their water bills.

The problem with plastics is that they are everywhere – air, water, ground. I see litter in the streets and know it can go through the urban drainage systems and enter the river. The highways are covered with a layer of plastics and rubber from car tyres that include other chemicals that get washed off as it rains. One source of microplastics are the clothes that shed fibres as they are washed, then get to the local wastewater treatment plant and then the river. Globally what impact do supply chains and waste streams have on how this synthetic material moves around the planet? What effect do microplastics have on human health? What is the impact of microplastics when combined with other chemicals? Are some aquatic species affected more than others?

Regulatory recognition

Reflecting on recent activity, there has been plenty of work going on in the Water Industry around microplastics not least by UKWIR (research funded by water companies), DWI (the drinking water regulator) and the Environment Agency (the environmental regulator looking at rivers, groundwaters, beaches, wastewater treatment works and sewage sludge). I have recently joined webinars from the Oxford Water Network and the Institute of Water and although lockdown has delayed some legislation (the ban on single use plastic in England was pushed back by Defra to 1st October 2020) and I have been encouraged by the progress taking place.

There is recognition that, although the impact on the aquatic environment is not fully understood, microplastics and larger pieces of plastic cause harm and that action is needed. 

From the regulatory side, policy work is underway using the source–pathway–receptor model to inform the environmental management options. Regulators can then plan their interventions around these. For example, how does society tackle the plastic fibres that come from clothes washing machine laundry? Well, the source is the clothes being washed, going through the wastewater system of sewers as a pathway, then reaching the receptor of the local river or fields where sewage sludge is spread. For wider society, interventions could be the fashion industry looking at innovations in materials to reduce microfibres shedding and washing machines that capture the microplastics. The Environment Agency is reviewing its strategy for safe and sustainable sludge use to include microplastics and this needs to be addressed as wastewater sludge used on farmland as fertilisers is a key part of the circular economy. A mixture of these voluntary and legislation approaches will be needed to address microplastics.

The source-pathway-receptor model: avenues for control

• At source, single use plastics are being phased out in the UK and internationally. Consumers are shifting and some opt for plastic free products. Companies are responding by redesigning products (reusable period products, recyclable toothpaste tubes and refill laundry detergent containers). Circular economy thinking comes into play where whole life product design aims to minimise waste by having longer lasting products that designed to be recycled (I look out for ‘cradle to cradle’ toys that last and buy clothes with hand me downs in mind). For the water industry, there is the challenge of reviewing single use plastics versus long life plastics: do water pipes and treatment technology shed microplastics or put unnecessary plastic in the environment? Current water and wastewater treatment processes do remove microplastics – is that enough? Is there an issue with storm flows released to the environment?
• Looking at the pathways that microplastics move along, how do we design treatment options to meet permits that have yet to be set? By progressing along the water industry roadmaps and recognising if (or when) regulators bring in permitting, then measurements of microplastics are going to need to be certified with monitoring programmes set up to give confidence in the investment in new technology.
• Within the receptor (land, rivers, food chain), the broad challenges are clean up, mitigation, and assistance to the wildlife that are entangled. It is at this point in the next few years where data on types of litter from beach clean ups and the improved monitoring of microplastics will show where society has made progress. I would hope that less single use plastics finds their way to the beaches and that a national river monitoring programme is set up. This is not a quick fix – the legacy of dealing with persistent pollutants from past generations reminds us this will be a long haul. In the receptor, once the fate and behaviour of microplastics is better understood and measurements standardised, then environmental standards for what is acceptable in aquatic environments will be proposed.

The challenge of measurement and standardisation

A big challenge is the: ‘If you can’t measure it, you can’t manage it’ truism. The methods for measuring microplastics have yet to be standardised, as it is a challenge - there are many types of plastic and a range of sizes. The measurement technology is still being developed to find the best way of capturing the fractions down to the fine particle sizes that may have the greatest impact on aquatic life. The techniques involve time-consuming image recognition software to automatically count microplastics in a water sample. 

Once the measurement techniques have been standardised, then there will be a chance of setting up monitoring networks in rivers, seas, and in sewage at wastewater treatment plants.

By getting better methods of measuring microplastics, the management can be targeted, which is where river catchment management and modelling comes in. That’s where I hope to be involved in predicting microplastics travelling through sewer systems and rivers, if their transport can be represented along the lines of sediments in a model like WRc’s integrated catchment modelling tool SIMPOL ICM. These kind of modelling tools when used with reliable data and an understanding of the behaviour of microplastics can inform the regulators of the statistical values to use to set discharge permits.

The water industry has a key role in mapping the sources and pathways of microplastics with the aim of improving the receptor: the water environment and human health. It looks like the immediate challenges are in standardising measurement, setting up monitoring programmes, developing standards and modelling catchments alongside developing treatment technology to meet the new standards.