Water/Wastewater

Microplastic Pollution: Everyone’s problem - but what can be done about it?

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That was the question posed to over 70 delegates for the one-day workshop held at the Royal Society of Chemistry (RSC) in London on the 16th October 2017. 

The day was organised by the RSC Water Science Forum (WSF) and featured presentations from leading experts in microplastic pollution from marine and freshwater backgrounds (Figure 1). The event was endorsed by the Institute of Chemical Engineers (IChemE) Water Special Interest Group and the Society of Chemical Industry (SCI).

The aim of the workshop was to share the latest information and review the current understanding of the risks and knowledge gaps in this highly topical area.

Delegates were welcomed by Adrian Clark from the RSC WSF who introduced an opening video address by Dr Therese Coffey, the UK Parliamentary Under Secretary of State for the Environment and Rural Life Opportunities, who reinforced the UK government’s support for tackling the issues associated with microplastic pollution. 

The main scientific programme was introduced by Prof Richard Thompson from the Plymouth University who gave an excellent introduction and overview of microplastics. He began by clarifying the definition of microplastics based on their size and, although many define them as particles of < 1 mm, he quoted the USA Dept. of Commerce National Oceanic and Atmospheric Administration (NOAA) definition of particles < 5 mm as the now more generally accepted upper size limit. The lower bound size limit of microplastics is not defined, but the perceived risks associated with microplastics are mainly associated with particle ingestion and so particle sizes down to the micron level and lower were considered potentially important. It has been reported that ~75% of marine debris found on beaches originates from plastics and that ~10% of literature reports on plastics in the environment concerned microplastics. Prof Thompson mentioned similar quantities of plastic debris have also been found in the deep ocean (1).

Prof Thompson then discussed the primary and secondary routes by which microplastics are formed and enter a body of water (Figure 2). Primary microplastics consist of manufactured raw plastic material, such as virgin plastic pellets, scrubbers, and microbeads that enter the ocean via runoff from land. Secondary microplastic introduction occurs when larger plastic items enter a beach or ocean and undergo mechanical, photo and/or biological degradation. This degradation breaks the larger pieces into progressively smaller plastic fragments which eventually become undetectable to the naked eye. Microfibres from textiles were also highlighted as becoming increasingly prevalent in marine environments and was up to four orders of magnitude more abundant (per unit volume) in deep-sea sediments from the Atlantic Ocean, Mediterranean Sea and Indian Ocean than in contaminated sea-surface waters (1). He then went on to discuss the proposed sources of risk from microplastic ingestion by species. In addition to the physical risks from the polymer particles there are also chemical risks posed by the base polymer, its degradation products and chemical additives, such as antioxidants, which are added to improve polymer performance in use. Also, the oleophilic nature of many plastics mean they have the potential to absorb hydrophobic chemical contaminants present in the water and may provide a mechanism to transport concentrated contaminants to organisms. Prof Thompson then gave an overview of recent studies (2, 3, 4) into these areas of concern and also stated that there needs to be a harmonisation of monitoring procedures, that exposure studies should use concentrations which are environmentally relevant, and the impact evaluation should utilise recognised risk matrix analysis techniques. 

Turning to the future and where we should focus our efforts to reduce the routes to plastics pollution in the environment (Figure 3) he pointed out that ~40% of plastic is used for packaging which is a major component of plastic litter and that surveys of beach litter indicated that ~50% of it came from single use applications. He postulated that we need to re-educate ourselves in a more circular use of plastics and seek to recover the carbon we are currently wasting. Prof Thompson concluded that the problem of marine debris was a symptom of an inefficient outdated business model which is not directly coupled to societal benefits and was damaging our natural resources. He believed there were major synergistic benefits in resource efficiency and waste reduction which could be achieved by product redesign and he encouraged delegates to harness the interest in this highly visible and emotive problem to focus on better product design and waste management. 

Dr Danielle Green from Anglia Ruskin University followed on with a talk titled “Environmental Impacts of Plastic Debris in Marine Ecosystems” and described studies on the effects of microplastics on marine organisms in outdoor mesocosm systems. This included deposit-feeding marine worms spiked with microscopic unplasticised polyvinylchloride (UPVC) which had shown significantly depleted energy reserves (up to 50%) which was postulated to result from a combination of reduced feeding activity, longer gut residence times of ingested material and inflammation (5). Dr Green then described her work on the impacts of microplastics on the health and biological functioning of bivalve species such as mussels and oysters (6). Her results showed effects on the assemblages and the nitrogen cycle and reductions in the biodiversity and species noted when microplastics were present. This indicated that repeated exposure to high concentrations of microplastics could alter assemblages in an important marine habitat by reducing the abundance of benthic fauna. Dr Green also noted that some biodegradable plastics demonstrated the same effects as conventional plastics and that more research was needed in this area.

Dr Katie Whitlock, a Fisheries Research Scientist from the Environment Agency turned the focus to the freshwater environment where she believed research lagged the marine environment. She noted that the predicted global production of plastics in 2017 was 322 million tonnes, with Europe accounting for 58 million tonnes, and that since the 1950s 8.3 billion tonnes of plastics have been produced. Previous research from shoreline and beach surveys across all continents indicated that plastic waste commonly accounts for 50–90% of all marine litter and about 80% originates from land-based sources, suggesting fluvial systems are important transport routes of these contaminants to the sea. For freshwater systems the main sources of plastics were road runoff including tyre wear (66%), waste water (25%) and wind borne (7%) debris. Studies have shown that waste water treatment typically removes > 90% of microplastics but due to the huge volumes involved this means large quantities are still released into freshwater environments. In addition, microplastics removed by treatment can end up in organic sewage wastes which is applied to farmland and can then find its way into the freshwater environment due to run off. Dr Whitlock then turned to discussing the direct and indirect impacts of microplastics on organisms. Direct impact includes physical blockages, irritation immune responses and energy burden impacts and toxic chemical introduction whereas indirect impact includes absorbed chemical introduction and vector transport of pathogens. Dr Whitlock discussed an Environment Agency research project which used sticklebacks as a model organism in three experiments to assess the potential impacts of microplastics on fish (7) and which observed reduced productivity, reduced feeding, lower condition metrics and behavioural changes.

Dr Matt Hill, an Environmental Lead Advisor with Yorkshire Water gave a presentation entitled “Wastewater treatment and microplastics – Sink, Source or Solution” which introduced an industry view of the plastics problem they face in processing waste water from the sewage system. The key issues come from waste items wrongly flushed down toilets by their customers and he quoted that 9 of the 12 most common items flushed (but which should not be flushed!) contained plastic as a major component with disposable nappies posing a major problem. Microfibres resulting from the washing of synthetic textiles was also highlighted as major issue for the industry. In normal circumstances sewage enters the treatment plants and the macro plastics are trapped by screens and smaller particles are then separated by a combination of flotation, settlement and finally biological processing. Waste water processing produces sewage sludge which is often spread on farmland as an important route to replacing carbon back to the soil, but can also contain significant quantities of microplastics which end up in the environment. In addition, the water companies also use plastics in their treatment processes, including filters with fibre piles, which can also release microplastics into the process. Problems also occur when adverse weather means there is a flooding risk and sewers are operated in overflow mode and directed into rivers without treatment. The UK Water Industry Research (UKWIR) association runs a common research programme for UK water and sewage companies on ‘one voice’ issues and often collaborates with government departments and regulators in carrying out this research. UKWIR has issued a mission statement “to quantify the water industry contribution of microplastics to the environment in the context of ecotoxicology studies being carried out elsewhere, and so assist in the development of a strategic response” and is proposing an investigation into the prevalence, sources and variation of microplastics in effluent and sludge and the effect of current treatment processes.

Alison Horton, an Ecotoxicologist from the UK Centre for Ecology and Hydrology (CEH) discussed “Microplastics in freshwater systems: current and future research priorities”. She began by highlighting recent high-profile press articles including a recent article in the UK Guardian newspaper (8) with the strap line “Exclusive -Tests show billions of people globally are drinking water contaminated by plastic particles, with 83% of samples found to be polluted” and quoted that one study found that a fleece jacket can shed as many as 250,000 fibres per wash. Ms Horton then discussed the varied input routes for microplastic to our rivers and freshwater systems and highlighted that in studies of the River Thames road run off was found to be a major source of microplastics with the the degradation of polymer based painted road markings a major contributor. 

In 2007 the CEH and the Environment Agency began to build an archive of fish tissue from a selection of English rivers and this has provided a basis for many research projects. In a study on roach they found evidence of polypropylene, polyethylene and polyester in the gut proving that microplastics are ingested and that the amount found could be correlated with the size of the fish and the distance from the river source where the fish was caught. 

In the terrestrial environment studies on microplastic ingestion in earthworms using fluorescent nylon had shown no effect on their survival rate, but had shown a significant reduction in reproduction and on the organism energy budgets. However, it was stated that it was not certain how realistic these studies were compared to the actual exposure scenario in the terrestrial environment. Turning to human ingestion, there were no published studies yet on the health implications, but microplastics have been detected in the air, beer, seafood, honey, salt and tap water so there were clear routes for ingestion which could have implications for the accumulation of toxins, immune responses, respiratory problems and chemical leaching into the body. In terms of future research priorities 5 principal areas were suggested: - the effect of different polymer characteristics, areas where microplastics accumulate in the environment, what species and ecosystems are most vulnerable to microplastics, to what extent do microplastics act as a vector for bioaccumulation of organic chemicals and what are the human health consequences of microplastics.

In conclusion Ms Horton described an NERC Knowledge Exchange initiative to develop a Microplastic Network which will be starting in November 2017 and interested parties should contact her by email at alihort@ceh.ac.uk .

Dr Camilla Alexander-White, Programme Manager. Environment & Regulation at the RSC gave a brief overview of the organisation’s activities in addressing microplastics. She described how the Society had published extensively on the topic via its journals and had supplied written evidence to a UK Parliamentary Inquiry on Environmental Impact of Microplastics in 2016 (9). A special themed issue of Analytical Methods entitled ‘Microplastics in the environment’ containing 23 papers was published in 2017 (10). 

Dr Lucy Woodall from the University of Oxford discussed “The Ubiquity of microplastics in the marine environment, and the challenges of accurate reporting” and began by describing how early in her career she had been amazed to find microplastic fibres in mud sampled from the deep Indian Ocean and how the deep sea areas were a major sink for microplastic debris (1). However, in order to get a clear picture of the global extent of this issue, it was critical to work towards standardisation of sampling, measurement and reporting. In sampling it was important to standardise the sampling equipment, method and conditions and also to be aware of sources of cross contamination. Different sampling regimes are required depending on the substrate and its location and need to be carefully controlled. For the measurements it was important to have clear procedures to identify the plastic type and its physical properties. When quantifying and recording the amount of plastics she suggested particle images, size ranging and binning, area measurement and weight should all be recorded. It was also important to avoid post sampling contamination and include both positive and negative control samples to ensure consistency during measurement. In reporting, Dr Woodall suggested that it was important to include what had not been studied or found in addition to what had been.

Dr Thomas Maes the National & International Monitoring Programmes Co-ordinator for the Centre for Environment, Fisheries and Aquaculture Science in Lowestoft, UK gave a presentation titled “Micro & macro plastics, where do we go from here?” where he presented a more international view of the issues involved and the international initiatives to tackle the problem. He highlighted a wide range of topics where much more research is needed and described initiatives such as the International Pellet Watch (www.pelletwatch.org) and the Plastic Tide project (www.plastictide.com) which aims to harness cutting edge drone and algorithm technology to create an open source map of the plastic pollution problem, in the UK and beyond. He showed data from the IUCN on sources of microplastics washed into the sea and highlighted the major contributions from synthetic textiles (35%) and tyres (28%) which together with city dust (24%) contributed 87% of the total. In conclusion he re-echoed Prof Thompson in that we need to re-educate ourselves in a more circular use of plastics and seek to recover the carbon we are currently wasting through better products, systems and legislation. Dr Maes also emphasised the need to consider the differences between biodegradable plastics to minimise environmental impact as opposed to bio-based polymers aimed at reducing CO2. He highlighted as an example the Michelin revolutionary concept motor wheel and tyre where the biomimetic structured wheel was made from recycled material and was fully recyclable and had 3D printed tread which was biodegradable and could be reprinted with fresh tread as required (https://www.michelin.com/eng/media-room/press-and-news/michelin-news/Innovation/MICHELIN-Visionary-Concept).

The final presentation was given by Dr Sabine Pahl from the School of Psychology at Plymouth University and was titled “The human dimension: how social and behavioural research can help address plastics in the environment”. Dr Pahl and Prof Thompson collaborated in the large scale EU MARLISCO project to investigate shareholder perceptions on issues surrounding marine litter and her presentation focussed on how psychology and behavioural science can play a key role in helping to address the issues around plastics in the environment. This involved studies and surveys on the reactions of different sectors of society to issues around the use of plastic microbeads. If we accept the need to change how society tackles such global issues through behavioural changes then the perceptions of people from different sectors of society are important and understanding these perceptions and “mental models” is crucial for developing effective communications and solutions going forward. 

The final discussion session formed an important part of the workshop and covered knowledge gaps, research priorities and future policy needs. The output from this will be reviewed and shared by the RSC WSF

Overall this was a very interesting and highly informative meeting with consistent messages coming through that this was an area where much more research is needed in all areas to fully understand the possible implications for society of continuing with our current business models for plastic production, use and disposal. With this in mind the RSC and other interested partners are already planning further meetings on microplastics to cover analytical methodology and food.

 

References

(1) Woodall L.C. et al, 2014, R.Soc. Open SCI., 1:140317 http://dx.doi.org/10.1098/rsos.140317

(2) The physical impacts of microplastics on marine organisms: a review. 

Wright SL, Thompson RC, Galloway TS.

Environ Pollut. 2013, 178, 483-492. 

(3) Microplastic as a vector for chemicals in the aquatic environment: Critical review and model-supported reinterpretation of empirical studies

Albert A. Koelmans, Adil Bakir, G. Allen Burton, and Colin R. Janssen

Environ. Sci. Technol., 2016, 50 (7), 3315–3326

(4) Accumulation of plastic-derived chemicals in tissues of seabirds ingesting marine plastics

Kosuke Tanakaa, Hideshige Takadaa, Rei Yamashitaa, Kaoruko Mizukawaa, Masa-aki Fukuwakab, Yutaka Watanukic 

Mar Poll Bull, 2013, 69, 219-222

(5) Microplastic ingestion decreases energy reserves in marine worms

Stephanie L. Wright, Darren Rowe, Richard C. Thompson, Tamara S. Galloway

Curr Biol , 2013, 23, 1031–1033, 

(6) Effects of microplastics on European flat oysters, Ostrea edulis and their associated benthic communities, Dannielle S Green.

Environ Pollut, 2016, 216, 95-103

(7) Assessing the impact of exposure to microplastics in fish UK Environment Agency Report – SC120056

(8) The Guardian 6th Sept 2017 Plastic fibres found in tap water around the world, study reveals https://www.theguardian.com/environment/2017/sep/06/plastic-fibres-found-tap-water-around-world-study-reveals

(9) House of Commons, Environmental Audit Committee Environmental impact of Microplastics Fourth Report of Session 2016 -17 https://publications.parliament.uk/pa/cm201617/cmselect/cmenvaud/179/179.pdf

(10) Analytical Methods Themed collection Microplastics in the Environment http://pubs.rsc.org/en/journals/articlecollectionlanding?sercode=ay&themeid=401b7ae3-2d5e-423e-96c5-dc63f3629529


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