In an Expert Focus article for Waterbriefing, Rob Keirle, Senior Environmental Consultant, at WRc plc, looks at the presence of microplastics in the wider water environment and the implications for the industry.

Rob Keirle: All aspects of our lives today depend on plastic in one form or another, from the toothbrush we use in the morning, to the car we drive to work, the keyboard we use in the office, and the film wrapped around our lunchtime sandwiches. Because plastic is so deeply embedded within modern society, the flipside of this high dependency is a growing plastic litter legacy, approximately 70-80% of which ends up in our oceans.

When discussing plastics in the environment, it is important to make a distinction between macroplastics and microplastics. Macroplastics can be used as a general term for visible plastic pollution such as drinks bottles, carrier bags, packaging, sweet wrappers and polystyrene, all of which can be physically removed from the terrestrial environment manually or, if encountered on beaches, by mechanical means using sand scrapers or rakes.

Nurdles are the pre-production resin pellets used by industry to make the majority of our plastic products. As they are typically less than 5mm in diameter but visible to the naked eye they are often categorised as a macroplastic although, confusingly, they can also be referred to as a microplastic. However, their mechanical (i.e. by wave action) and photochemical (i.e. triggered by sunlight, especially UVB) degradation products do eventually end up as microplastics as plastic does not biodegrade – it just gets broken down into successively smaller pieces until it forms a plastic ‘flour’. Nurdles enter the environment via industrial spillages, mishandling or via the loss of shipping containers at sea.

Microplastics are either barely visible to the naked eye (they are often smaller than 1mm in diameter) or completely invisible (as some particles can be as small as 50 µm in diameter). Three out of four face scrubs and peels contain microplastics. Shampoos, soap, toothpaste eyeliners, lip gloss, deodorant and sunblock sticks may also contain plastic particles, and they can even be found in some domestic cleaning products. These micro particles are made of polyethylene (PE) (the main type of microplastic used in exfoliants), polypropylene (PP), polyethylene terephthalate (PET), polymethyl methacrylate (PMMA) and nylon. PE and PP are the most common.

The Institute for Environmental Studies carried out research on several products for the presence of microplastics on behalf of the North Sea Foundation. In one example 10.6% of the product weight consisted of PE. This means that for every bottle of 200ml used, 21g of microplastics would end up in the sewer system.

The average amount of microplastic used by consumers is about 2.4mg of microplastic/person/day. Some PCPs contain as much as 10% PE, the equivalent of one teaspoon or 500mg.

Natural alternatives do exist and are used in some products; these alternatives include oatmeal, sea salt, ground almond or crushed walnut shell.

Environmental fate and behaviour of microplastics

Although the full extent and consequences is hard to quantify, the accumulation of plastic, including microplastics, in the marine environment is today recognised as a serious, global environmental issue. As scientists and policymakers alike start to question the full extent of the problem in terms of impacts to marine biodiversity and associated implications for human health, the number of research programs studying microplastics is increasing consequentially.

Marine species are unable to distinguish between food and microplastics and therefore indiscriminately feed on microplastics. In an overview published for the Convention on Biological Diversity, it was shown that over 663 different species were negatively impacted by marine debris with approximately 11% of reported cases specifically related to the ingestion of microplastics. Some species of fish excrete plastic easily, but others do not and so accumulate plastic internally.

The surface of microplastics has been proven to attract and absorb persistent organic pollutants (POPs) such as PCBs and DDT from the marine environment. In theory, ingested POPs could remain on the surface of ingested microplastics and could be egested. However, fish and seafood regularly consumed by humans have been recorded with plastic fragments inside their guts and body tissues. Scientists hypothesise that over time, POPs will start accumulating in the food chain, transferring from species to species, with consequences ultimately for humans.

Legislative drivers

There are two European legislative drivers that are of particular relevance to the issue of microplastics in our oceans. These are:

• Marine Strategy Framework Directive – This Directive establishes a framework within which Member States shall take the necessary measures to achieve or maintain good environmental status in the marine environment by the year 2020 at the latest. Annex 1 contains 11 descriptors, of which descriptor 10 relates to marine litter.
• Environmental Liability Directive  – This Directive is aimed at the prevention and remediation of environmental damage; consequently, in theory, could be deployed against water companies where continuous treated effluent discharge or a combined sewer overflow spill has caused “land contamination that creates a significant risk of human health being adversely affected as a result of direct or indirect introduction in, on or under land of substances, preparations, organisms and micro-organisms” (one of the specific definitions of ‘environmental damage’).

Implications for the water industry

Wastewater treatment works (WwTWs) are not designed to filter out microplastics. A number of studies have found that WwTWs do not filter all microplastics from the wastewater. Moreover, not all wastewater gets purified. Following heavy rain, dilute untreated wastewater containing microplastics can overflow directly into surface waters via combined sewer overflows.

Once microplastics reach the marine environment, it is impossible to pinpoint the source of origin; similarly, it is impossible to practicably remove them. We therefore need to move our focus for action further up the pollution supply chain and, if we cannot remove the microplastics at source, there is a pressing need to understand and quantify the efficacy of current waste water treatment processes at removing microplastics from sewage.