Legacy plastics: interventions to remove existing plastic from aquatic environments

In accordance with the ‘waste hierarchy’, preventing plastic from entering the environment must be the policy priority. However, some amount of plastic removal from the environment will likely be necessary to reduce the risk of harm to ecosystems and potentially to humans.

Already, governments around the world are negotiating a legally binding agreement on plastic pollution – the United Nations (UN) Plastics Treaty. At the time of writing, the latest draft includes a potential obligation for member states to:

• Monitor plastic pollution within their jurisdiction
• Identify plastic pollution hotspots
• Adopt effective mitigation and remediation measures to reduce environmental plastic pollution, including clean-up activities within identified hotspots.

Against this backdrop, this report summarises some of the technologies and other interventions that are available to clean-up legacy plastics from the environment, as well as discussing their feasibility, effectiveness and environmental impacts. The report also presents approaches to identify accumulation hotspots – which may help to prioritise areas for clean-up. 

Key Findings

1. To tackle plastic pollution and its negative consequences prevention is, and should remain, the priority. Over-emphasis on clean-up interventions could divert attention away from more systemic solutions focused on minimising plastic use, including investing in more benign and sustainable alternatives, and efforts to move to a circular plastic economy through effective reuse and recycling.
2. Some amount of legacy plastic removal may be beneficial, particularly in environments that have high natural capital and/or social value, and where the risks associated with clean-up activities are shown to be lower than the risks associated with leaving plastic in the environment. 
3. Priority areas for clean-up (hotspots) in the environment can be identified according to:
   1. The natural and social capital value of the area
   2. The potential hazards that the plastic pollution poses in this area
   3. The feasibility and likely effectiveness of clean-up
   4. The risk of negative consequences from clean-up 

4. Based on the range of options currently available, those that involve hand-picking litter from shorelines and/or intervene close to the source of plastic pollution are likely to be the most effective.

5. The environmental impacts and cost effectiveness of clean-up technologies remain largely unknown. To address this gap, efficacy and environmental impact assessments are required in the locations where the technology is to be deployed.

Q&A

What are the negative impacts of plastic pollution in aquatic environments?

Negative impacts relating to plastic pollution include physical harm to wildlife such as injury, ingestion and entanglement. Plastic can also sorb and transport other pollutants such as chemicals, meaning that these pollutants can spread more widely in the environment and may be more likely to be ingested. In addition, as plastic degrades it releases additive chemicals which are used in its production. This includes endocrine disrupting phthalates which have been shown to cause harm in a range of species. 

Macroplastic litter can also provide a home for organisms which usually live in coastal environments, further out to sea, thereby altering the makeup of oceanic communities.

Is it possible to clean-up plastic from the aquatic environment?

In a word, yes, and this report summarises the technologies and interventions that currently exist to clean-up plastic from aquatic environments. However, most of these technologies are plastic-type or context specific and their efficiency, cost or environmental impact is not well understood. 

Microplastics will be very challenging if not impossible to remove due to their small size and once plastic debris becomes widely dispersed within the water column or buried in sediment – this also makes removal very challenging. Macroplastic litter either in rivers, floating on the surface of the ocean or washed up along coastlines are likely to be the most feasible targets.

So, is cleaning-up plastic the solution to the plastic pollution problem?

Cleaning up plastic from the environment will never be as efficient as taking preventative measures to tackle plastic pollution at source and it is important to recognise that clean-up is not, on its own, an effective solution to the plastic pollution problem. However, the combination of high uncertainty relating to human health impacts, and the strong evidence of negative consequences on wildlife, creates the rationale for a pro-active but considered approach to removing plastic from the environment. Especially given that environmental plastic concentrations are predicted to triple by 2060 under a business as usual scenario.

It is likely that all clean-up options will, themselves, have some negative environmental impact – these need to be further understood and compared to the harm of leaving plastic in the environment.

Which clean-up technologies or interventions seem the most promising?

There is no one ‘silver bullet’ solution which could be scaled up and used to remove plastic pollution from all aquatic environments. Instead, we suggest that a combination of different technologies and interventions will probably be required to target different circumstances.

Interventions which act closer to the source of plastic pollution, such as in rivers, are likely to more efficient in terms of capturing a larger amount of plastic while it is constrained and in a uni-directional flow – before it disperses widely in the ocean.

Beach cleans also seem to offer several advantages, being relatively cheap (when relying on volunteers), providing a sense of community and promoting psychological wellbeing. They also target coastal areas which are high in natural and social capital and where the majority of marine plastic debris accumulates.

Can science and technology help us to understand where plastic debris is accumulating in the environment?

Media attention has led to the assumption that plastic accumulates in large floating islands on the surface of the ocean, like the Great Pacific Garbage Patch. However, in reality, only 2% of all marine plastic is floating offshore on the surface of the ocean. Most plastic (88%) remains close to the shoreline and is also broadly dispersed within the water column, on the seabed and buried in sediment.

To optimise the efficiency and positive impacts of plastic pollution clean-up operations it will be necessary to understand where plastic originates, where it is accumulating and the pathways by which it got there. Science and technology can offer an important contribution to this.

For example, numerous hydrographic modelling studies have predicted the spatial distribution of plastic litter based on environmental monitoring data combined with broad scale ocean circulation patterns, or have scaled up observational data on the quantities of plastic recorded in rivers or from land. 

Remote sensing technologies such as satellites, drones, sensors on boats, underwater cameras and unmanned vehicles are also likely to prove useful for identifying the pathways, fluxes and places of accumulation for plastic debris. Some researchers are also starting to utilise machine learning and artificial intelligence to help to analyse this data and identify the presence and sometimes even type of litter in the environment.

It is likely that this detailed visual information will increasingly be able to be integrated with hydrological models and used to accurately map the distributions of plastic in aquatic environments.

Which areas should be prioritised for clean-up?

In terms of identifying priority areas for clean-up (or hotspots), we suggest that the following criteria are likely to be more important than the absolute concentration of plastic.

1. the natural and social capital value of the area
2. the potential hazards that plastic pollution poses in this area 
3. the feasibility and likely effectiveness of clean-up 
4. the risk of negative consequences from clean-up.

This will ensure that clean-up solutions are targeted to the most valuable environments, delivering the greatest amount of benefit and the minimum amount of harm.