Sorry, your browser doesn’t support embedded videos. Stories Project Stories 06.10.2026 All Those Chemicals Inside Microplastics Most of Victor Carrasco Navarro's (left) and Onni Sirkiä's (right) work is done in the laboratory. Photo: Aino Huotari TEXT Sandra Järvenpää Share: What holds plastic together and where does it go when plastic breaks down? And what prevents plastic from burning? Microplastics have been studied for two decades now, but various additives contained in plastics have received less attention. A project funded by the Kone Foundation is investigating the effects of plastic additives on freshwater ecosystems. What is It About? In a four-year project funded by the Kone Foundation called Plastic chemical cocktails: fate and risks in freshwater ecosystems, researchers are studying the toxicity of plastic additives to freshwater ecosystems. The research focuses on five freshwater species: duckweed (Lemna minor), water flea (Daphnia magna), acute bladder snail (Physella acuta), non-biting midge (Chironomus riparius) and blackworm (Lumbriculus variegatus). Plastic additives have been found in both marine and freshwater ecosystems, but their transport and accumulation in various aquatic organisms has received little research attention. The grant recipients are project researcher Victor Carrasco Navarro, PhD, and doctoral researcher Onni Sirkiä. Six years ago, researchers in Washington State, USA, finally discovered the reason why Coho salmon have been dying in vast numbers for some time. The culprit turned out to be 6PPD-quinone, an extremely toxic chemical for salmon: just one drop in an Olympic-sized swimming pool is capable of killing half the fish in it. In Washington, over 90 per cent of the salmon population returning to spawn died before reproduction. In the late 1960s, tyre manufacturers discovered that adding the chemical 6PPD to tyres kept the rubber in good condition seven times longer than previously. However, as tyres wear down over time, along with the rubber, all other substances added to the tyres are released into the environment. And when 6PPD reacts with ozone that is present in the air, it transforms into the toxic 6PPD-quinone. “Tyre rubber is a complex material with many additives,” says Victor Carrasco Navarro, the project’s principal investigator. Carrasco Navarro is researching, together with doctoral researcher Onni Sirkiä, the toxicity and fate of plastic additives and their effects on freshwater ecosystems. Microplastics are not simple, homogeneous or particles made from just a polymer, Carrasco Navarro points out. They come in different sizes and shapes, are formed in different ways, and originate from both virgin and recycled plastics. There are also nearly two hundred polymer types: polyester used in clothing, PET plastic used in drink bottles, and tyre rubber, amongst others. “Depending on the polymer and its intended use, various additives have been added to the plastic to give it certain properties. They provide, for example, flexibility, protect against UV radiation and degradation, or act as flame retardants. However, the problem is that these substances are not bonded to the plastic matrix; rather, they leach out and end up in the environment.” There are roughly 16,000 different plastic additives, and a single product contains anywhere from a few compounds to several dozen. Sirkiä notes that they are most prevalent in industrial plastics and electronics. “If you think of an electronics fire, the smoke is often very black. A significant group of additives in electronics plastics are flame retardants, whose job is to prevent the material from igniting and burning. If a fire does break out, however, the burning is often very impure because of them.” “When we exposed snails to chemicals leaching from tyre rubber, they changed their behaviour. They moved more slowly and over a smaller area than the control group.” Photo: Aino Huotari Why Did the Salmon Get Attention? Coho salmon in Washington’s lakes and rivers may have attracted major media attention because it is a species important to humans. People are often most interested in what concerns them directly. “Plastics are now used everywhere, and the ones that attract the most attention are those connected to humans. For example, food packaging has been studied since the 1950s to prevent chemical exposure in people. However, increasingly more plastic ends up in the environment, yet this is not seen as quite such a high priority matter. It is becoming an ever-larger problem, as we produce more plastic every year,” says Sirkiä. Plastic production is indeed growing. Despite the climate impact of using fossil raw materials, or despite worrying research findings concerning microplastics travelling to the brain, humanity produces 450 million tonnes of plastic annually, and this figure continues to rise steadily. However, microplastics and their additives also end up in the wider natural world and affect its tiniest inhabitants. Five species have been selected as research subjects: duckweed (Lemna minor), water flea (Daphnia magna), acute bladder snail (Physella acuta), non-biting midge (Chironomus riparius) and blackworm (Lumbriculus variegatus) – largely for practical reasons. “Most of them are common species and easy to culture in the laboratory. Additionally, they are important to aquatic ecosystems.” According to Carrasco Navarro, they also broadly represent different parts of the underwater world. Water fleas swim in the water, worms live within bottom sediment, and snails move across the bottom. Duckweed floats on the water’s surface, and after spending its larval stage on the bottom, the non-biting midge takes to the air in search of suitable waters for the next generation. So, what effects do plastic additives have on these animals? That depends on what is being studied at any given time, says Sirkiä. “If we are studying acute toxicity—that is, immediate effects on an animal—we study its survival. If we are studying longer-term, chronic effects, we examine, for example, reproduction. That is, how many offspring they produce or how large they are.” Not much can be said at this stage about unpublished research results, but there is something to report about snails. “When we exposed snails to chemicals leaching from tyre rubber, they changed their behaviour. They moved more slowly and over a smaller area than the control group. We still need to find the link that connects stable laboratory conditions to the changing ecological environment,” says Carrasco Navarro. Photo: Aino Huotari “Each company has its own cocktail, so you can never know exactly what added chemicals are in, say, a plastic bag.” Manufacturers’ Chemical Cocktails Are Trade Secrets What makes the research challenging is the fact that the additives used by companies in their products are not public knowledge. In most cases, they do not disclose the names of chemicals, and the same type of plastic can contain a different mixture of additives depending on its intended use. “It’s rather like a trade secret. Each company has its own cocktail, so you can never know exactly what added chemicals are in, say, a plastic bag,” says Sirkiä. “However, this is a problem for every stakeholder, and everyone should participate in solving it, including companies,” adds Carrasco Navarro. The ultimate goal of Carrasco Navarro and Sirkiä’s research is to succeed in influencing legislation so that compounds harmful to ecosystems cannot enter the natural environment uncontrollably. Although the creation of legislation to ban chemicals is a long process that can take decades. However, testing just one species—or even five—in one location is not enough for this; more research is needed. “To influence legislation, the narrative must be constructed using many different species. Many research groups around the world are conducting research on this topic,” says Carrasco Navarro. However, systemic change occurs slowly. For example, the use of recycled tyre rubber in new artificial turfs will be prohibited in 2023 but it is not clear what will happen with the old artificial turfs with rubber. “It’s a good thing that the EU banned its use, but things move slowly. It will still take five years before the ban comes into force,” Carrasco Navarro notes. Contact Project researcher, PhD Victor Carrasco Navarro, victor.carrasco.navarro@uef.fi The term “additive” refers to compounds that are added to a product or material to improve its desired properties. For example, flame retardants reduce the flammability of plastics used in electronics. However, when plastic material ends up in the environment, the chemicals in additives can leach out and wreak havoc to the surrounding biota. Furthermore, environmental factors can chemically alter additives, which may make them even more harmful to living organisms. It is critical to understand how varied and difficult to detect the chemical threats posed by additives can be, so that we can promote cleaner and safer environments for both people and wildlife.