Read the Press Release, Scientists provide first public guidance on array of challenges in cleaning up plastic litter from oceans successfully here.
Marine debris, and particularly plastic marine debris, poses a significant global threat to marine life. Growing public awareness of this threat, including the recognition that floating ocean plastics tend to congregate in remote areas of the open ocean (the so-called “garbage patches”), has inspired some individuals and groups to conceive of systems for cleaning up debris at sea. These systems have ranged from simple net-based methods to ambitious giant filtering systems that would stretch hundreds of kilometers across the sea surface, among other ideas.
These ideas are laudable for their goal of removing plastics from the sea. However, the proposed systems typically fail to account for real-world ocean conditions and/or the many ecological and engineering-related challenges that would face any cleanup effort on the open ocean. In fact, the array and scale of challenges involved in any realistic cleanup of remote ocean areas have been cited often by experts as evidence that marine debris management should focus on preventing new litter from entering the ocean, rather than attempting to remove the litter that is already there.1
Still, many seemingly intractable challenges faced by humans over time have been solved by bright ideas. And as long as people are aware of and moved by the problem of ocean plastic debris, there will be attempts to solve it. In this light, we do not want to dissuade potential innovators from examining the issue of marine debris cleanup. Rather, we want to inform and channel their innovation.
This document presents general guidance for the cleanup of floating plastic debris in the open ocean. This guidance was produced and edited in June-July 2013 by a team of experienced marine debris researchers (see “Background on this document”) and was shared in July with the global MarineDebris.Info community of marine debris managers, researchers, and conservationists for additional input. This list is intended to evolve and improve over time as further knowledge is gained. We also strongly recommend that all prospective inventors of cleanup systems consult experienced ocean engineers early in their development processes.
Systems for open ocean cleanup of marine plastics should account for, and overcome, the following challenges:
The size and depth of the ocean gyres within which floating marine plastics tend to gather.
The North Pacific Subtropical Gyre, the best-known location of a
“garbage patch” or trash vortex, has a surface area of approximately
20,000,000 km2 — more than twice the size of the U.S. Thus
any system that would tow nets through the gyre to capture debris, for
example, must either factor that surface area into its design or
determine a way to avoid having to transit the whole area. In addition,
in even the most densely polluted regions of the subtropical gyres,
microplastics (particles smaller than 5 mm in size) are frequently
present at concentrations of less than one piece per square meter,
requiring extensive areal coverage to recover just one kilogram of
plastic. Furthermore, average water depth of the open ocean is 4,000
meters (2.5 miles); therefore, any cleanup system relying upon moored
structures must account for this extreme depth.
Depth and concentration of microplastics. Floating
plastic debris, and particularly microplastics, can be mixed below the
surface in even light winds. The depth of the mixing depends on the
strength of the wind and the physical structure of the ocean in that
particular area. It may range from a few meters depth during typical low
wind conditions in summer months to 100-150 meters depth during
stormier winter months. Any cleanup system, particularly one that relies
on surface-floating mechanisms, must account for subsurface mixing of
Capturing plastics while not harming marine life that is co-located with the plastics.
The goal of ocean plastic removal is ultimately to help sea life. If
cleanup systems hurt or kill sea life in the process — such as fish or
even plankton — they are counterproductive. Most zooplankton, for
example, do not survive being caught in a standard net, never mind spun
in a centrifuge where they lose critical appendages like their antennae
and feeding apparatus. A system that relies on nets or centrifuges will
require engineered solutions to avoid or minimize these effects. In
addition, indirect environmental impacts of cleanup systems — such as
from fuel use by cleanup vessels scouring the ocean, or from
incineration of collected plastics at sea — should be considered and
Potential for entanglement of marine life in the systems.
Similar to the above guideline, any cleanup system that poses an
indirect entanglement threat to wildlife, such as seabirds or cetaceans,
must be reengineered. In the U.S., any activity that might harm
protected species is illegal without a permit.
Strength and stability in extreme sea conditions. Any
cleanup system is in danger of becoming marine debris itself if it
breaks up, such as from storm action, high waves, or ship collisions. A
successful system must be able to avoid extreme weather or be sturdy
enough to withstand such conditions, and must be detectable by
Maintenance and fouling. The reality of operating
equipment in extreme environments, of which the open ocean is an
example, is that equipment breaks down. There must be a cost-effective
means to maintain and repair the cleanup system over time, particularly
for systems that involve long-term deployment. Furthermore, there must
be a way to account for, and address, the rapid biofouling that occurs
when any equipment is placed in the ocean.
The physical properties of ocean-weathered plastic. Floating
marine debris is largely composed of polyethylene and polypropylene —
common plastic types with a density less than that of seawater.
(Polystyrene, which has a density roughly equal to that of seawater, may
also be present but is much less abundant in floating debris.)
Ultraviolet light degrades these plastic polymers, making them brittle
and difficult to recycle. Cleanup schemes that propose to recycle and/or
market the plastic they collect should be aware of the technical
issues, and of the actual market value of the plastic they collect,
which may be low. Recyclers with the technology to “upcycle” mixed ocean
plastic into consumer-quality polymers remain very few (Envision
Plastics, which partners with home products manufacturer Method on a
recycled ocean plastic bottle, is one). As a result, the market for
collected ocean plastic is underdeveloped at best.
- Legal issues. There are extensive laws and regulations governing the deployment of equipment at sea. For example, structures cannot be a hazard to navigation or a threat to protected species. In the U.S., multiple permits from state and/or federal agencies may be required for cleanup devices. The permitting process is lengthy, onerous, and expensive, and may require specialized legal consultation. On the high seas — marine areas beyond national jurisdiction — the applicability and relevance of the United Nations Convention on the Law of the Sea must be evaluated in each case.
This guidance was drafted by:
- John Davis, M.M.A., of MARE
- Miriam Goldstein, Ph.D., of California Sea Grant and Scripps Institution of Oceanography at UC San Diego
- Courtney Arthur, M.S., Research Specialist, NOAA Marine Debris Program
- Pete Davison, Ph.D., Postdoctoral Scholar, Scripps Institution of Oceanography
- Kara Lavender Law, Ph.D., Research Professor, Sea Education Association (SEA)
- Chelsea Rochman, Ph.D., Aquatic Health Program, School of Veterinary Medicine, University of California, Davis
We welcome additional editors and contributors; this guidance is intended to be a living document. To provide input, please contact John Davis, project supervisor of MarineDebris.Info, at firstname.lastname@example.org.
For interviews, please contact:
MarineDebris.Info is the global knowledge-sharing community for marine debris management and research, with members representing government agencies, research institutions, conservation organizations, industry, and more (www.marinedebris.info). It consists of a listserv, website, and live chat events allowing members of the MarineDebris.Info community to interact with leaders in the field.
MarineDebris.Info is a project of Marine Affairs Research and Education (MARE), a Seattle-based organization that provides a range of knowledge-sharing services to ocean managers and conservationists worldwide. These services include the OpenChannels forum on ocean planning (openchannels.org), the MPA News service on marine protected areas (mpanews.org), and the Marine Ecosystems and Management information service (meam.net). MARE collaborates on several of its projects, including MarineDebris.Info, with the University of Washington.