Feedstock: Peter Ryan of the University of Cape Town found this great shearwater dead at its breeding colony at Tristan da Cunha. It had ingested 194 bits of plastic. (Peter Ryan)
A staggering 194 bits of plastic. That’s how much marine ornithologist Peter Ryan found in the stomach of a great shearwater after finding its carcass at a remote breeding colony on Tristan da Cunha island in the southern Atlantic Ocean in 2018.
Ryan, the director of the FitzPatrick Institute of African Ornithology at the University of Cape Town, is a co-author of a new study on plastic pollution, which shows how seabirds from Gough Island in the south Atlantic, Marion Island near Antarctica as well as from the coasts of Hawaii and Western Australia eat ocean-floating plastic fragments, mistaking them for prey.
Across the 32 species of seabirds sampled, the international team of authors found that up to 52% of the birds not only ate plastic, but accumulated its harmful chemical components in their bodies.
The researchers analysed oil from the preen gland, located just above the tail, from 145 seabirds in 16 locations for plastic additives and persistent organic pollutants. By examining the chemical concentrations in this oil, they can determine the contaminant burden of the bird’s fat stores.
They detected plastic additives in a range of seabirds. Brominated flame retardants, which are added to some consumer products to reduce the risk of fires, were found in 11% of seabirds while benzotriazole-type UV stabilisers were detected in 46% of seabirds.
High concentrations of additives were found in seabirds that ate large plastic loads, including great shearwaters from Gough Island and blue petrels from the Southern Ocean, south of Africa.
Ryan said it was worrying that species such as the blue petrel, which spend all their lives in the Southern Ocean — which has the lowest concentration of floating plastic — “can find enough plastic to be affected in this way”.
Black-footed albatross and Laysan albatross and petrels, all from Hawaii, and flesh-footed shearwaters from Western Australia, too, had particularly high concentrations of plastic-associated compounds.
Polychlorinated biphenyls (PCBs) and organochlorine pesticides (DDT, DDE and HCHs) were detected in most samples. “High concentrations of PCBs and DDTs were observed in seabird top predators, indicating that these long-lasting legacy pollutants, which have long been banned under the Stockholm Convention, are obtained from seabird prey and biomagnification,” Ryan said.
By comparison, the plastic-associated contaminants were not correlated with these pollutants and were mostly found in species that often consume large amounts of plastic.
UV stabilisers were detected more frequently than flame retardants because they are more widely used to make plastic products.
Ryan said that plastic items are largely immune to biodegradation and gradually break down when exposed to UV radiation. “This is why UV stabilisers are added to plastics used in long-lasting applications such as window frames and car parts.”
Marine plastic debris can contain other hazardous chemicals, with the study confirming that such compounds can be ingested by seabirds. The potential toxicological effect is concerning, Ryan said, because some of these compounds are known to disrupt endocrine functioning.
“We know that some plasticisers and flame retardants are endocrine disruptors, which affect thyroid functioning, for example, as well as potentially affecting fertility. But there are a host of other additives used in plastic manufacture, which are not known.
“The important thing about our paper is that it confirms that plastic ingestion is a significant pathway for some of these compounds to get into birds and that long-distance drift of plastics is likely responsible for the transport of some of these persistent pollutants.”
Seabirds are sentinels for marine health. “The fact that these chemicals are getting into birds through plastic ingestion suggests that they are getting into many other marine consumers, including more critically threatened species such as turtles. It also suggests that we, as consumers of marine products, are being exposed to these compounds,” said Ryan.
Every year, a portion of the 400 million metric tons of plastics produced annually escapes into the environment, eventually reaching the oceans and estimated to run into several million tons a year, according to the study.
When floating on the sea surface or stranded on beaches, plastics are exposed to UV radiation and break down into smaller fragments. Plastic resin pellets are a feedstock of plastic products and enter marine environments through spillages and runoff.
“Consequently, huge amounts of plastics (250 000 tonnes) are available to a suite of consumers in the world’s oceans.”
By 2020, 180 species of seabirds — half of the total number of seabird species — were reported to have ingested plastics, said Hideshige Takada, a professor at the Tokyo University of Agriculture and Technology and a corresponding author. It has been predicted that, by 2050, 99% of seabird species will have consumed plastics.
Takada said that eating plastic can cause physical damage and death, but little is known about the biological consequences of seabirds consuming the chemicals added to bind, stabilise and otherwise improve plastic used in food packaging and fishing gear, for example. Ryan said seabirds face a myriad of threats, linked in part to their complex lifestyle. This includes fishing, invasive species and climate change. “Plastics are just another stressor in the long list of threats. We need to ensure that all plastic waste is disposed of correctly — ideally re-used or recycled, but definitely not littered or dumped illegally in the environment.”