Recent estimates suggest that it will take 450 years for a plastic bottle to completely break down.^[1]However, since plastic bottles didn’t enter into widespread use until the 1960s,^[2] it’s hard to know exactly how long it will take for them to disappear.

Breakdown of plastics is caused by solar UV-radiation and is most intensive in environments like beaches and the sea surface. The rate of degradation depends on a number of factors, including composition and temperature.^[3]Most plastics “are extremely durable. This means the majority of polymers manufactured today will persist for decades and probably for centuries, if not millennia.”^[4]In addition, it is not known when, if ever, full degradation will occur. Larger plastics may fragment into many small microplastics that take longer to break down. And there is no research yet on the degradation of nanoplastics.^[5]In fact, there is actually little evidence showing that plastics will ever fully break down in the marine environment.^[6]

“Biodegradable plastics” that can break down naturally and disappear from the environment without causing harm may sound like the perfect answer to marine litter, but the reality is not so simple.

A UN Environment report on biodegradable plastics concluded that “the adoption of plastic products labelled as ‘biodegradable’ will not bring about a significant decrease either in the quantity of plastic entering the ocean or the risk of physical and chemical impacts on the marine environment, on the balance of current scientific evidence.”^[1]Amongst other factors, the report noted that the “complete biodegradation of plastics occurs in conditions that are rarely, if ever, met in marine environments.”^[2]And unfortunately, biodegradable plastics may even contribute to the problem. Although limited, some evidence “suggests that public perceptions about whether an item is biodegradable can influence littering behaviour; i.e. if a bag is marked as biodegradable it is more likely to be discarded inappropriately.”^[3]That would certainly defeat the purpose of having biodegradable plastics.

Another reason for not putting all of our eggs in the biodegradable basket is because the issue is really how we use plastic products. The main problem is our love and consumption of single-use and disposable plastics.

Collecting floating plastic litter might seem like a good idea but it may divert attention from more cost-effective and efficient measures, such as preventing plastic pollution from entering the ocean in the first place.  And it may cause more harm than good. Plastic in the ocean constantly moves around and is mostly found in low concentrations and throughout the water column.  This makes surface clean-up impractical and ineffective. Due to the scale needed, collecting surface plastics is expected to have very high costs.^[1]Researchers are concerned as well with potential high risks and negative effects on marine life and biodiversity associated with surface clean-up schemes.^[2]That’s because sea life could become attracted to clean-up gear and exposed to more plastic or entangled in.^[3] Among other issues, the surface clean-up equipment itself is expected to become encrusted with biofouling organisms^[4]further complicating this potential solution.

Removing plastic litter from one beach might seem like a mere drop in the ocean when compared to the scale of the problem but clean-ups can be effective when they target ecologically sensitive or economically valuable areas, including places important for fisheries and tourism.

Such efforts can help keep local habitats healthy and keep plastics out of the ocean. They also help raise awareness about the problem of plastic pollution and can spur individual and local action, and help build public support for positive change from producers and governments.^[6]

Plastic debris can accumulate in certain areas in the Pacific Ocean and other seas but there are no islands of trash.^[1]Not only are there is no islands, there is no layer of trash that can be seen from airplanes. This is because much of the debris found in the ocean is in the form of small particles, not easily seen even from a boat.

In reality these areas, or “patches,” of marine litter consist of higher concentrations of small and tiny fragments of plastic rather than large pieces. But people usually envision seas full of plastic bottles, toys and other big items. In these patches, the number of fragments has been “recorded as over 200,000 particles per square kilometre … that equates to less than one microplastic particle per square metre.”^[2]Large plastic pieces do occur but much less frequently. In general, the material is quite dispersed, like a soup of plastic particles. Since these concentrated areas of plastic are formed by dynamic and constantly changing currents, it is extremely difficult to estimate their size.

Concern has also been raised about a potential plastic patch forming in the Barents Sea,^[3],[4]however even though the problem may be increasing and affecting fish, marine mammals and seabirds,^[5] densities found there are only “slightly higher than those from Antarctica [and] substantially lower than those from temperate waters.”^[6]

There is growing concern about effects marine microplastics may have on people, including toxic chemicals leaching from plastic litter and the fact that “microscopic particles are making their way into the food chain and affecting human health. But are they harmful?”^[1]

It appears that the marine food web is full of plastic. It has been found in the stomachs of deep sea fish in the Northwest Atlantic,^[2]in fish in the English Channel,^[3]in endangered sea turtles,^[4],[5]in giant Bluefin tuna off the coast of Lebanon^[6]and in the stomach of a whale that died off the coast of Norway in 2017.^[7]Concerns include that when ingested, microplastics can affect the feeding behaviours of marine animals and cause weight-loss. Another fear is that when smaller fish are eaten by predators like tuna and swordfish, the plastic moves up the food chain. Chemical pollutants can also bind to microplastics and may increase accumulations of toxins in larger predatory fish – and so particles and toxins can end up on our plates. Such toxins could pass through cell membranes, potentially increasing exposure to harmful chemicals.

However, assessing the risks to human health from marine plastic is complex and there is still much we do not know about its potential to affect human health.^[8]In addition, “the uptake of plastic-associated chemicals in humans due to inadvertent ingestion of microplastics in seafood appears likely to be no more significant than other human exposure pathways of these chemicals.”^[9]

Over the past couple of decades we have learned that plastic pollution is a significant threat to our oceans. According to a 2015 study,^[1] there are 5.25 trillion plastic pieces floating around, equivalent to 720 pieces for every person alive on the planet.  This plastic weighs more than 225,000 tonnes. Another study put the number between 15 and 51 trillion particles, most of which are very small.^[2]But debris of any size – from discarded fishing nets to the tiniest particles – can harm marine life when animals become entangled or mistake it for food.^[3]

However, while plastic pollution is among the most serious threats, a larger problem may be how it compounds all the other stresses on ocean health. These threats include climate change, acidification, ocean warming, overfishing and habitat destruction.^[4]The real problem the ocean faces is the combination of human impacts and our lack of will to address them.

It’s nearly impossible to come up with an exact figure to support this claim. A 2016 report estimated that in a “business-as-usual scenario, the ocean is expected to contain 1 tonne of plastic for every 3 tonnes of fish by 2025, and by 2050, more plastics than fish (by weight).”^[1] The report was quoted widely in the press but the figures really are just a first attempt to address the issue. Questions have been raised regarding the report’s figures and date of 2050. That’s because there is uncertainty over the methods used to estimate both fish populations^[2],[3]and the amount of plastic in the oceans.^[4]

Personal care products include microplastics in the form of abrasive microbeads “in face scrubber cosmetics, or plastic raw material granules used in manufacturing.”^[1] These particles eventually make their way into wastewater systems and, depending on the efficacy of treatment systems, can end up in the ocean.^[2] Much smaller nano-particles are used in sunscreens which can wash off people’s skin at the beach. While there may be a lot of microplastics in a single personal care product – one study estimated from 4,600 to 94,500 microbeads may be released per application of a skin exfoliant^[3] – it is not considered a major source and “is relatively small compared with other sources or primary and secondary microplastics in to the environment, in terms of tonnage involved.”^[4]

Plastic gets into the ocean in many ways.  It is dumped directly or is blown in by the wind.  It comes from ships and lost fishing gear. It is also carried by rivers. One estimate of total plastic input to the oceans from all sources is around 8 million tonnes per year, and about 80% is attributed to land based-sources^[1]. However, it’s not possible at this stage to accurately verify these figures.

In a recent study of the amount of plastic litter transported by 57 river systems, 10 rivers were estimated to be responsible for 90% of it^[2]. In other words, 90% of the plastic coming from rivers is from these 10. It does not mean that 90% of all plastic in the ocean is coming from these 10 rivers. Although there is a great degree of uncertainty with this estimate (ranging from 04. To 4 million tonnes per year), it is a good indicator of the importance of rivers as a source of marine litter. It also helps target regions where better waste management practices are needed.

So, while river-borne plastics are undoubtedly a major source of marine litter, the data is still limited^[3] and we should not ignore marine pollution from other sources. One thing we do know is that the presence of plastics in our ocean is linked to human activity – on land and at sea. “All sectors and individuals contribute to this pollution – from poorly controlled waste sites, illegal dumping and mishandled waste on land to ropes, nets, floats and other debris from fishing, merchant shipping, oil rigs, cruise ships and other sources”^[4].