FAQ: Plastic debris in the ocean
What have scientists learned about plastic and other marine debris in the ocean? What questions have yet to be answered?
Marine debris can enter the ocean in a variety of ways. From land, trash may be carried to the ocean in rivers or storm and sewage drains, swept from the beach by waves and surf, or blown offshore by winds, especially during heavy storms. Trash may also come from ships or offshore platforms, although dumping of plastic at sea has been banned since 1988 (by MARPOL Annex V of the International Maritime Organization). We don’t know how much marine debris enters the ocean, or whether most of it comes from land or from vessels at sea. These are very difficult questions to answer because the sources are so widespread.
The most common way to measure floating plastic in the ocean is to collect it using very fine-meshed nets towed at the ocean surface from a ship. At SEA we have been measuring plastic debris using this method for more than 25 years. To collect data for research projects designed by students in our SEA Semester program, we tow a plankton net at the surface twice a day to collect biological organisms, as well as plastic and any other floating debris. Students sort through the net contents to hand-pick, count, and preserve all plastic samples collected during the tow. Since 1986 more than 6100 plankton net tows have been conducted in the Atlantic Ocean and Caribbean Sea by more than 7000 undergraduate students and scientists at SEA.
The majority of samples we collect are small fragments less than 1 cm in size – no bigger than your smallest fingernail – with a mass less than 0.15 g, or about 1/10th the mass of a paper clip. In most cases it is impossible to know what kind of object the plastic pieces came from. The most recognizable pieces are fragments of fishing line and industrial resin pellets (the “raw material” of consumer plastic products). Physical properties of plastic samples collected by SEA in the Atlantic Ocean indicate the collected material is made of HDPE (high density polyethylene), LDPE (low density polyethylene), and PP (polypropylene), which are used to make common household items such as milk jugs, plastic bags, and drinking straws. These materials have a density less than that of seawater, causing them to float on the sea surface. We do not observe other commonly used plastic types such as PET (polyethylene terephthalate), PVC (polyvinyl chloride) and PS (polystyrene solid). These plastics have been observed on U.S. east coast beaches, but the materials are denser than seawater and likely sink before reaching the open ocean. The properties of plastics appear to change during their time at sea, possibly due to sun and sea exposure and to biological growth.
The term “garbage patch” is very misleading – there are no large islands of trash floating in the open ocean. Most of the floating marine debris is not even visible from the deck of a ship because it is so small. There are regions of the ocean where floating debris (natural or man-made) accumulates due to the movement of ocean currents. High concentrations of plastic debris have been observed in these “convergence zones” in the North Atlantic and North Pacific Oceans, where currents driven by the wind converge or come together. No one has been able to accurately measure the full size of these accumulation regions – not only are they are far offshore and very difficult to access, but boundaries may shift in time due to the ever-changing ocean conditions and the varying (and not well-known) sources of debris.
Plastics are present in every major ocean basin, concentrated in regions that should be pristine environments far from sources of pollution on land. Plastic debris can threaten marine organisms through entanglement, especially by large debris such as derelict fishing gear, and by ingestion in organisms ranging in size from zooplankton to fish and larger animals such as sea turtles and seabirds. Additionally, plastics create a habitat for microorganisms and other species and can transport potentially invasive species to new regions of the ocean. Plastics are known to carry organic toxins such as PCBs, PBDEs, and PAHs, and may be responsible for the transfer these and other chemicals to marine organisms.
We don’t know how long plastic remains in the ocean. Most plastics become brittle when exposed to ultraviolet (UV) light and break down into smaller and smaller pieces, sometimes referred to as “microplastics”. No one knows just how small these pieces become – they are very difficult to measure once they are small enough to pass through the nets typically used to collect them. Current research suggests that most commonly used plastics will never fully degrade in the ocean.
Because most of the plastic in the ocean is in very small fragments there is no practical way to clean it up. One would have to filter enormous amounts of water to collect a relatively small mass of plastic – in a typical net tow that filters about 120,000 gallons of water, the plastic pieces collected would fit in the palm of your hand. In addition, using nets would also remove a “by-catch” of microscopic plankton and other organisms that are important to the ocean ecosystem. This could end up causing more harm than good.
Information provided by the NOAA Marine Debris Program
Marine debris is a global problem that is being tackled by organizations at local, national, and international levels through scientific research and educational programs. Scientific research is needed to answer even the most basic questions about marine debris – Where is it? How much is there? What kind of material is it? Where does it ultimately end up? And public education is the best way to prevent debris from entering the ocean now and in the future.
The NOAA Marine Debris Program has supported more than 140 projects to address marine debris across the U.S. (http://marinedebris.noaa.gov/projects/welcome.html), while many other organizations are working to raise awareness, clean up marine debris on beaches and in the ocean, and reduce the input of debris into the oceans through “Reduce, Reuse, and Recycle” campaigns. This is how you can help, no matter where you live:
- REDUCE the amount of trash you produce
- Choose items you can REUSE over disposable products
- RECYCLE items if you must dispose of them