Pesticides and organic pollutants are consistently found on plastic wastes at harmful concentrations 100 times higher than in sediments, and 1 million times higher than in sea water.
Over five trillion pieces of waste plastic are floating in our oceans, weighing 268,940 tonnes and causing damage throughout the marine food chain, according to data collected by a team of scientists from the United States, France, Chile, Australia and New Zealand.
The team went on 24 expeditions between 2007 and 2013 that surveyed all five sub-tropical gyres: North Pacific, North Atlantic, South Pacific, South Atlantic and Indian Ocean, and extensive coastal regions and enclosed seas including the Bay of Bengal, Australian coasts and the Mediterranean Sea.
Their work included both surface net tows and visual transects for large plastic debris at 1,571 locations in all oceans. This is the most comprehensive survey to-dat - yet it is most likely a gross under-estimate of the scale of oceanic plastic pollution.
In 2012, the world produced 280 tonnes of plastic. Less than half has been consigned to landfill or recycled, and much of the remaining 150 million tonnes not still in use litters continental shelves and oceans.
Global trends suggest that waste plastics are accumulating exponentially in parallel with trends in plastic production - which has increased 560-fold in just over 60 years.
These by-products of the oil industry are icons of the industrial economy built on the over-exploitation of oil and other fossil fuels that's turning the planet literally into a terminal wasteland (see Redemption from the Plastics Wasteland).
Waste plastic an escalating environmental hazard
The estimate from the global survey of plastic pollution on the sea surface for all fragment size classes combined is only 0.1% of the world annual production.
The estimates are "highly conservative", the team acknowledged: they do not account for the potentially massive amounts of plastic washed up on shorelines, submerged on the seabed, suspended in the water column, and inside organisms.
Also, the survey only collected particles larger than 0.33 mm, due to the size of the netting used. Sequestration in the sediment is the likely fate of plastic pollutants after perpetrating numerous impacts on organisms along the way.
Waste plastic in the open ocean is degraded into smaller and smaller fragments through UV radiation, mechanical abrasion, biological degradation, and disintegration. The fragments disperse in the ocean, converging in the subtropical gyres. Generation and accumulation of plastic pollution also occur in closed bays, gulfs and seas surrounded by densely populated coastlines and watersheds.
The impacts through ingestion and entanglement of marine organisms ranging from zooplankton to whales, seabirds and reptiles are well documented, and new studies are showing up harmful effects of nano-size plastic particles that have escaped inventories so far (see Plastic Poisons in the Food Chain).
The data from the global survey showed that during fragmentation plastics are lost from the sea surface . There is a 100-fold discrepancy between the expected microplastics (particles < 4.75 mm) weight and abundance and the actual amounts observed, indicating a tremendous loss of microplastics.
This suggests removal processes are operating, including UV degradation, biodegradation (by microorganisms), ingestion / absorption by organisms, decreased buoyancy due to fouling organisms, entrapment in settled detritus, and beaching.
Fragmentation rates of already brittle microplastics may be very high, breaking them down into ever smaller submicron or nanoparticles, and unrecoverable by the nets.
Numerous studies demonstrate that many more organisms ingest small plastic particles than previously thought, either directly or indirectly via their prey organisms. These are then packaged into faecal pellets which sink to the bottom. Further, there is evidence that some microbes can degrade microplastics.
Plastics at sea the cause of ecological havoc
A team of scientists led by Chelsea Rochman at University of California Davis and Mark Anthony Browne at University of California Santa Barbara in the United States wrote a Commentary in the journal Nature in 2013 calling for the need to classify plastics hazardous waste.
They point out that plastic debris can physically harm wildlife. Many plastics may be chemically harmful either because they are themselves potentially toxic or because they absorb other pollutants.
Waste plastics can kill or damage ecologically and commercially important species including mussels, sea-marsh grasses and corals. Mammals, reptiles and birds can be harmed through ingesting plastic or becoming entangled in it.
In 2012, the secretariat of the Convention on Biological Diversity in Montreal Canada reported that all sea turtle species, 45% of marine mammal species and 21% of seabird species can be harmed in that way.
Yet in the US, Europe, Australia and Japan, plastics are classified as regular 'solid waste' and treated like food scraps or grass clippings. Policies for managing plastic debris are outdated and severely threaten the health of wildlife.
As plastic breaks into smaller pieces, it is more likely to infiltrate food webs. In lab and field studies, fish, invertebrates and microorganisms ingest micrometre sized or smaller particles, which also come from synthetic (polyester or acrylic) clothing and cleaning products containing plastics.
Studies in humans and mussels have found that ingested and inhaled microplastics get into cells and tissues where they can cause harm. In patients who have had their knee or hip joints replaced with plastic implants, such particles can disrupt cellular processes and degrade tissues.
Toxicities of plastics
Plastics are made up of repeating units or monomers that join up to form long chains or polymers. These chains are thought to be generally inert - yet unreacted monomers and other harmful ingredients can be found in plastics.
According to United Nations' Globally Harmonized System of Classification and Labelling of Chemicals, the chemical ingredients of more than 50% of plastics are hazardous. Studies investigating the transfer of additives in polyvinylchloride (PVC) from medical supplies to humans indicate that these chemicals can accumulate in the blood.
In lab tests, monomers and other ingredients of PVC polystyrene, polyurethane and polycarbonate can be carcinogenic and can affect organisms in similar way to the hormone oestrogen.
The monomers making up some plastics such as polyethylene (used for carrier bags) was thought to be more benign. Yet these materials can still become toxic by picking up other pollutants. Pesticides and organic pollutants such as polychlorinated biphenyls are consistently found on plastic wastes at harmful concentrations 100 times higher than those found in sediments, and 1 million times those occurring in sea water.
Many of these are 'priority pollutants' - chemicals regulated by government agencies, including US Environment Protection Agency (EPA) because of their toxicity or persistence in organisms and food webs. These chemicals can disrupt processes such as cell division and immunity, causing disease or reducing the organisms' ability to escape from predators or reproduce.
In an unpublished analysis, the authors found that at least 78% of priority pollutants listed by the EPA and 61% listed by the EU are associated with plastic debris. Seabirds that have ingested plastic waste have polychlorinated biphenyls in their tissues at 300% greater than those that have not eaten the plastic.
Classify the most harmful plastics as hazardous!
Governments have struggled for decades to reduce plastic debris. The International Convention for the Prevention of Pollution from Ships (MARPOL) was signed in 1973, although a complete ban on the disposal of plastics at sea was not enacted until the end of 1988.
Despite 134 nations agreeing to eliminate plastics disposal at sea, ocean sampling suggests that the problem has persisted or worsened since MARPOL was signed.
The scientists wrote: "We feel that the physical dangers of plastic debris are well enough established, and the suggestions of the chemical dangers sufficiently worrying, that the biggest producers of plastic waste - the United States, Europe and China - must act now.
"These countries should agree to classify as hazardous the most harmful plastics, including those that cannot be reused or recycled because they lack durability or contain mixtures of materials that cannot be separated."
Focusing on the most hazardous plastics is a realistic first step. Currently, just four plastics - PVC, polystyrene, polyurethane and polycarbonate - make up roughly 30% of production. These are made of potentially toxic materials and difficult to recycle.
PVC is used in construction, such as pipes that carry drinking water. Polystyrene is used for food packaging; polyurethane in furniture; and polycarbonate in electronics. Health-care and technology industries are already replacing PVC components in intravenous-drip bags and in computers with materials that are safer, more durable and recyclable, such as polypropylene and aluminium.
With the proposed change in plastics classification, many affected habitats could immediately be cleaned up under national legislation with government funds.
In the United States, for instance, the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 would enable the EPA to clear the vast accumulations of plastics that litter the terrestrial, freshwater and marine habitats under US jurisdiction.
Ultimately, the scientists want changes in regulation to drive the development of a closed-loop system in which all plastics are reused and recycled, instead of ending up in landfills where chemicals leach from the plastic into surrounding habitats.
"If current consumption rates continue, the planet will hold another 33 billion tonnes of plastic by 2050. This would fill 2.75 billion refuse-collection trucks, which would wrap around the planet roughly 800 times if placed end to end", the scientists wrote.
"We estimate that this could be reduced to just 4 billion tonnes if the most problematic plastics are classified as hazardous immediately and replaced with safer, reusable materials in the next decade."
Dr Mae Wan Ho is the director of the Institute of Science in Society (ISIS), which campaigns against unethical uses of biotechnology.
Action: Beat the Microbead!
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