On many beaches around the world, plastic waste is not removed, but simply burned. This creates rock-like plastiglomerate. And this is apparently even more dangerous than regular plastic waste, as researchers have now found out. Accordingly, the plastiglomerate is enriched with carcinogenic substances and also decomposes more quickly into microplastics. It could pose a hitherto underestimated threat to coral reefs and other habitats.
Plastic waste is a global problem and pollutes the oceans in particular. While littered beaches here are subject to strict management and are usually cleaned up within a few weeks, in other countries orphaned plastic waste is often stored on the coast for many months and years. It is often even simply burned, resulting in so-called plastiglomerate. This rock-like mixture consists of melted and solidified plastic and natural components such as sediment and coral fragments.
Plastiglomerate as a microplastic slingshot
Researchers led by Dwi Amanda Utami from the Indonesian Agency for Research and Innovation have now investigated for the first time how plastiglomerate differs from conventional plastic and how dangerous it could be for the oceans. To do this, they analyzed a total of 25 field samples from the Indonesian island of Panjang with regard to their appearance, composition and degree of weathering. They also extracted volatile pollutants from the plastiglomerate using solvents.
It was found: "The unregulated incineration of plastic waste in open pits led to very different degrees of melting and charring, even within a single plastic part," the researchers report. The laboratory analysis also showed that those areas that already looked more burned were also weathered to a greater degree. Normally, the top layer of plastic weathers first because only this is exposed to the oxidizing effects of sunlight. "But the thermal oxidation caused by the incineration of the plastic waste also changes the inner structures of the material considerably," says Utami's colleague Lars Reuning. The charred plastic becomes more brittle and breaks down into harmful microplastics much faster than unburned plastic bags or bottles.
Combustion produces carcinogenic pollutants
But that's not all, because according to Utami and her colleagues, the combustion process also releases dangerous organic pollutants. The researchers were able to determine, among other things, high amounts of polycyclic aromatic hydrocarbons (PAH) in all field samples. PAHs are found in tobacco smoke and car exhaust, for example, and some of them are considered extremely carcinogenic. A sample made of acrylates, polyurethane (PU) and paint was particularly contaminated with five micrograms per gram. The same sample also contained exceptionally high levels of phthalates, which are used as plasticizers and are also classified as carcinogenic.
Since the PAHs and phthalates are grated off the plastiglomerate as microplastics at high speed, they also quickly get into the environment and can be ingested by marine life. Even small amounts of phthalates disrupt the metabolism of sea grass and marine invertebrates such as mussels, they accumulate in mangrove leaves and can probably also pose a threat to coral reefs, explain Utami and her colleagues. All in all, their study results indicate that plastiglomerate is significantly more dangerous for the oceans than the starting plastic from which it is burned. "If the garbage from urban areas on tropical beaches were better disposed of and managed, a serious problem could be prevented," says Utami.
Source: Christian-Albrechts-University of Kiel; Specialist articles: Scientific Reports, doi: 10.1038/s41598-023-37594-z