The world’s oceans and all marine life are on the brink of total collapse
Along with the tiny beads of plastic deliberately added to products such as face scrubs and toothpaste, and the billions of tiny filaments produced by artificial fibres, these microplastics have invaded the ocean’s food chain, gathering in higher and higher concentrations as one moves upward through the layers of predation. In the eastern Pacific, microplastics are now ubiquitous in the host of species of tiny free-swimming or floating animals known as zooplankton. These creatures fill the oceans’ waters and act as a foundation of the oceans’ ecosystems. In some parts of the ocean there is now more plankton-sized plastic than plankton, meaning organisms that rely on plankton for food, such as whales, are consuming it in extremely large quantities.
The long-term effects of this are not yet well understood, but there is no doubt ocean microplastics are also being consumed by humans: studies have detected them in fresh and tinned fish, while a study published earlier this year found that mussels in Britain contained up to 700 pieces of microplastic per kilogram, and other studies have found them in both fish and sea salt, while a study in California found a fifth of fish in local markets contained fibres from artificial fabrics (one study found a single load of polyester or acrylic clothing can release more than half a million microfibres). Their prevalence is made even more disturbing by the growing evidence that microplastics absorb pollutants such as DDT from seawater, as well as organic molecules such as oestradiol, which is used for birth control. Other studies have found that microplastics contain high levels of chemicals that are known to disrupt the endocrine system and affect reproduction in many species.
Plastic pollution is far from the only form of oceanic pollution. Eelco Rohling from ANU, for instance, points to the largely unreported threat of poly-chlorinated biphenyls, or PCBs. Originally used in the 1920s for cooling and insulation, PCBs were quickly incorporated into paints, adhesives, the PVC coatings on electrical wires and many other products. While their widespread use meant large quantities were released into the environment, it was not until the mid 1960s that Sören Jensen, a Danish scientist looking for evidence of DDT in fish, found traces of PCBs in pike caught in Sweden. Over the next two years he found traces of them everywhere: in fish, in birds, even in the hair of his wife and daughter.
In the years since Jensen’s discovery, PCBs have been banned or regulated in many countries. But PCBs have not gone away. Quite the opposite: studies show PCBs have permeated marine environments around the world, so much so that one recent study found high concentrations of them in the bodies of shrimp-like crustaceans called amphipods living almost 10 kilometres beneath the ocean’s surface.
The presence of PCBs in the ocean is extremely concerning. Highly toxic in even small doses, they cause cancer, liver damage, reproductive problems and deformities in many species, including humans, as well as disturb hormonal balances in fish, birds and mammals, and cause neurological disorders in birds. Because they collect in fatty tissues they also become more concentrated as they move up the food chain, meaning they accumulate in the bodies of long-lived high-level predators such as sharks, seals and cetaceans.
The long-term effects of this are not yet fully understood, but they may well be significant: PCBs have already been implicated in mass die-offs of certain populations of dolphins, and are known to result in increased infant mortality in whales and dolphins, who transfer high concentrations of them to their young in their milk. Worse yet, PCBs break down extremely slowly when kept out of sunlight, meaning they can linger in the deep ocean and in the bodies of animals and fish for decades or even longer, their continued presence a reminder of the way the effects of our actions persist.
The threat posed by plastics, PCBs and other forms of marine pollution may be immense, but it pales into insignificance against that of climate change, something that was made heartbreakingly clear in 2016 and 2017, when the Great Barrier Reef suffered devastating back-to-back bleaching events that killed almost half of its coral.
