A single pellet of recycled plastic can contain over 80 different chemicals. A new study seems to show that recycled polyethylene plastic can leach chemicals into water causing impacts in the hormone systems and lipid metabolism of zebrafish larvae.
While the study does not claim that recycled plastics are necessarily worse than virgin materials, in all contexts, it does present strong evidence that recycled polyethylene can pose specific and significant chemical toxicity risks, often due to the unknown and complex mix of substances present in the recycled material.
Recycling is proposed as one of the solutions to the plastics pollution crisis. However, as plastics contain thousands of chemical additives and other substances that can be toxic, and these are almost never declared, hazardous chemicals can indiscriminately end up in recycled products.
Increasing gene expressions
In this new study, the researchers – from the universities of Gothenburg and Leipzig – bought plastic pellets recycled from polyethylene plastic from different parts of the world and let the pellets soak in water for 48 hours. After which zebrafish larvae were exposed to the water for five days. The experimental results show increases in gene expression relating to lipid metabolism, adipogenesis, and endocrine regulation in the larvae.
“These short leaching times and exposure times are yet another indicator of the risks that chemicals in plastics pose to living organisms. The impacts that we measured show that these exposures have the potential to change the physiology and health of the fish,” says Azora König Kardgar, lead author and researcher in ecotoxicology at the University of Gothenburg.
“Never full knowledge”
Previous research has shown similar effects to humans, including threats to reproductive health and obesity, from exposure to toxic chemicals in plastics. Some chemicals used as additives in plastics and substances that contaminate plastics are known to disturb hormones, with potential impacts on fertility, child development, links to certain cancers, and metabolic disorders including obesity and diabetes.
“This is the main obstacle with the idea of recycling plastic. We never have full knowledge of what chemicals will end up in an item made of recycled plastic. And there is also a significant risk of chemical mixing events occuring, which render the recycled plastic toxic,” says Bethanie Carney Almroth, professor at the University of Gothenburg and principal investigator on the project.
Different chemicals
Apart from the study on the impact that recycled plastics have on zebra fish larvae, the researcher also conducted a chemical analysis of the chemicals leaching from the plastic pellets to the water. And they found a lot of different chemical compounds, but the mixture altered between different samples of pellets.
“We identified common plastics chemicals, including UV-stabilizers and plasticizers, as well as chemicals that are not used as plastics additives, including pesticides, pharmaceuticals and biocides. These may have contaminated the plastics during their first use phase, prior to becoming waste and being recycled. This is further evidence of the complicated issue of plastics waste flows, and of toxic chemicals contaminating recycled plastics,” says Eric Carmona, researcher at Department of Exposure Science, Helmholtz Centre for Environmental Research in Leipzig.
“Ban hazardous chemicals”
Representatives from the nations of the world are preparing to head to Geneva, Switzerland, in August, for what is planned to be the final negotiating meeting for a Global Plastics Treaty at the Intergovernmental Negotiating Committee under the United Nations Environmental Program. The authors of the work stress that negotiators and decision-makers must include provisions to ban or reduce hazardous chemicals in plastics, and to increase transparency and reporting along plastics value chains. Plastics cannot be recycled in a safe and sustainable manner if hazardous chemicals are not addressed.
“This work clearly demonstrates the need to address toxic chemicals in plastics materials and products, across their life cycle”, says Professor Bethanie Carney Almroth. “We cannot safely produce and use recycled plastics if we cannot trace chemicals throughout production, use and waste phases.”
Facts: Polyethylene (PE)
Polyethylene, abbreviated PE, is a type of plastic used in a lot of packaging materials like bottle caps, plastic bags, agricultural mulch films, insulation for wiring and cables, pipes, ropes, toys and household items. It is the most widely produced and used polymer. On plastic products made of polyethylene, the number in the recycling code is either 2 or 4.
