Stark images of plastic floating in urban rivers and washing up on shorelines symbolize the magnitude of mismanaged plastic waste and its impact on the environment. Solid nano- and microplastic fragments and fibers have been detected in every place which has been sampled so far, in both urban and remote sites. This has sparked discussion amongst scientists, regulators and the public as how to minimize plastic debris of all sizes.
By definition, polymers (and subsequently, plastics) are a heterogeneous group of compounds, yet they are often considered collectively in the problemization of plastics and in the context of potential solutions. It is tempting to speak in broad terms about plastic pollution and to curb all usage, including microplastic, as plans for bans and restrictions in many countries show. But can we simply regulate our way out of microplastic misery? Unfortunately, the short answer is no.
Contaminants of emerging concern
Overarching chemical bans may be appropriate when there is clear and overwhelming evidence that targeted substances cause harm (e.g. DDT, CFC). But this isn’t (necessarily) the case with plastic or, more precisely, with microplastic.
Plastics can be lost to the environment across their entire value chain. This release of plastic from many diffuse sources is anticipated to negatively impact the water quality of lakes, rivers and oceans as well as impact soil ecosystems. Microplastics, small solid polymers smaller than 5mm in size, are currently considered as contaminants of emerging concern. This is a term used to describe pollutants that have been detected in the environment which may cause adverse ecological or human health impacts, and typically are not regulated under current environmental laws.
We should distinguish microplastics based on their source. The dominant fraction of nano- and microplastics in the environment originates from the breakdown of macroplastic litter or is released during product use (e.g. fibers from textiles or tire wear). For a relatively smaller fraction of materials, restrictions on the intentional use of primary microplastics, in applications ranging from agriculture to cosmetics, are under discussion globally.
Small(er) plastics, big(ger) problems?
Plastic pollution has negative impacts either directly from their accumulation in the environment or from the leaching of toxic additives and substances from the plastic. However, what is less clear is what specific role microplastics may play in this context and which transport and transformation processes these particles might have and what specific impacts different plastics or additives may have.
Beyond the attention-grabbing headlines and scientific studies demonstrating the presence of particulate plastic in a vast array of localities, there remain several basic research gaps which need to be filled. Many of these research questions stem from the lack of analytical tools to measure small plastic particles in trace concentrations in the environment or in organisms. Therefore, a systematic understanding of particulate plastic interactions with life processes still is missing.
For prioritizing needs for action, nano- and microplastic research should focus on better estimating exposure of these materials and identifying the magnitude of potential hazards. The current lack of information concerning the environmental fate and ecotoxicological impacts prevent a proper risk assessment of nano- and microplastics at the moment.
Towards reduction of microplastics
Ultimately, the final question is, how can we more effectively use plastics and make sure that less of it ends up in the environment?
A one size fits all regulation will not be able to encompass the universe of polymer species because of the diversity of materials. Also, technical bans alone are likely not the route to significantly reduce microplastics. A major part of the issue can and must be prevented by proper (macro)plastic waste collection and management. Circular economy, solid waste management and education can all be improved to reduce the burden of plastics in the environment.
Scientific impact assessment of primary microplastics compared to their alternatives for specific applications relies on a number of factors including, but not limited to, harm, existence of replacement materials, and the quality, cost and hazards of alternative materials. In some instances, replacement are technically simple and easily justified. But in others, substitutions may come with more uncertainty such as significant performance questions and monetary costs.
Biodegradable plastics, for example, have been touted as a key alternative, but not all intended uses of polymers allow for biodegradability and biodegradability vary significantly depending on which environment the plastic ends up in. Also, there are many examples of when (micro)plastics help to reach other sustainability goals, like agrocapsules for more targeted plant protection.
In my view, regulation should be considered as a catalyst for change and a nudge towards further development of improved practices. For this route, restrictions must have a precise focus and must be enforceable by these measurements. Policymakers must carefully evaluate under which contexts incentives to replace certain microplastics can stimulate innovation of new, more competitive and environmentally conscious materials.