As the world faces the consequences of its own production, the fight against plastic pollution, highlighted as the central theme of yesterday's World Environment Day under the global motto #BeatPlasticPollution, is becoming increasingly urgent. At a time when staggering figures show that more than 11 million tons of plastic end up in aquatic expanses each year, and an additional 13 million tons contaminate the soil, the scientific community is taking on a key role. In Croatia, one of the leaders in this fight is the Ruđer Bošković Institute (IRB), where experts, through innovative projects and interdisciplinary research, strive to shed light on and offer solutions for one of the greatest environmental challenges of our time.

Research is being conducted with great intensity within the Division for Marine and Environmental Research (DMER) located in Zagreb and at the Center for Marine Research (CMR) in Rovinj, ensuring a comprehensive approach to the problem, from continental waters to the Adriatic Sea.

An invisible threat that pervades the planet

Plastic, once celebrated as a revolutionary material, is now showing its dark side. The problem goes beyond the visible waste floating in the oceans or lying in landfills. The real danger lies in what is invisible to the eye. Through long-term degradation processes under the influence of the sun, water, and mechanical forces, larger pieces of plastic break down into microplastics (particles smaller than 5 millimeters) and nanoplastics. These tiny fragments have become ubiquitous and have been found on the highest peaks of the planet and in the deepest ocean trenches. Their infiltration into food chains is systematic and alarming. We ingest them through the water we drink, the food we eat, and even the air we breathe. Recent studies have confirmed their presence in human blood, lungs, and even in breast milk, raising serious questions about the long-term consequences for human health. Their danger lies not only in their physical presence but also in their chemical nature. They act like sponges, binding other hazardous pollutants from the environment, such as heavy metals, persistent organic pollutants, and pesticides, and thus introducing them into organisms in a concentrated form.

The IRB's scientific response: Modeling the ecological cost of plastic

To quantify the real damage that plastic causes, a series of advanced research projects are being conducted at the Ruđer Bošković Institute. "Today, plastic is not just waste; it is a pollutant that lives a long life," vividly explains Dr. Nina Marn from the Laboratory for Informatics and Environmental Modelling. She heads the QPlast project, funded by the Croatian Science Foundation (CSF), which aims to precisely measure the physical, chemical, and behavioral consequences of exposure to plastic on living organisms.

As part of this project, scientists apply sophisticated computer models known as DEB (Dynamic Energy Budget) models. These tools allow for the simulation and prediction of how the presence of microplastics affects the fundamental life processes of organisms – from energy intake and distribution, through growth and development, to reproductive capacity and changes in behavior. "With this project, we want to show that it is possible to connect the different effects of plastic in nature, but also that we need interdisciplinary tools to truly understand the damage that plastic causes," points out Dr. Marn. In this way, science is moving away from merely recording the problem and moving towards a predictive understanding of the ecological price we as a society pay for plastic pollution.

The Krka River as a research hotspot: From trout to parasites

One of the most valuable natural laboratories in Croatia, the Krka River, has become the central location for another key IRB project called PlastOrgAnoTox. Within the unique karst landscape, scientists are investigating the complex interaction of microplastics and organisms. The project, led by Dr. Vlatka Filipović Marijić from the Laboratory for Biological Effects of Metals, covers the entire course of the river – from brown trout in the clean source areas to gilthead seabream and mussels at the estuary. This approach provides insight into the fate and impact of plastic in different freshwater and brackish ecosystems. The many tourists who visit this area are often unaware of the scientific efforts being invested in preserving its beauty.

"As part of the project, we will analyze organisms from the natural environment and those from farms, but we will also conduct experimental exposures to determine how microplastics and other pollutants they carry affect the biochemical and physiological changes in aquatic organisms, and thus indirectly human nutrition," explains Dr. Filipović Marijić. A particularly innovative segment of the research is the analysis of fish intestinal parasites as potential bioaccumulators of microplastics. "This opens up a completely new perspective in research to prove whether there is a transfer of microplastics within the organism itself, that is, from the host to the symbionts that inhabit its internal microecosystems," adds the scientist. The research conducted in Krka National Park is of vital importance for understanding the fate of plastic in karst rivers.

The tiny water flea in the service of science

In the same laboratory, the research of Dr. Tatjana Mijošek Pavin focuses on one of the smallest but ecologically extremely important organisms – the water flea (Daphnia magna). This freshwater crustacean is a key link in aquatic food chains, connecting the algae it feeds on with the fish that feed on it. Due to its extreme sensitivity to changes in the chemical composition of water, the water flea is an ideal model organism for ecotoxicological testing.

The research is focused on the combined, synergistic effects of microplastics and other chemical pollutants. "It is particularly worrying that plastic in the environment often does not act alone, but binds hazardous chemicals, such as polycyclic aromatic hydrocarbons (PAHs), which are known carcinogens," emphasizes Dr. Mijošek Pavin. Her team conducts immobilization tests, which monitor how the combination of microplastics and PAHs affects the mobility of water fleas. "These tests show the extent to which the combined effects deviate from the individual ones – that is, whether their joint action is additive, synergistic, or antagonistic," she explains. The results are crucial for assessing the real risk in ecosystems, including protected areas like Krka National Park.

Plastic in the environment is more than a waste problem

Scientific research at the Ruđer Bošković Institute unequivocally confirms that plastic is not inert waste, but a chemically and biologically active agent that fundamentally changes the environment. Given that only nine percent of the plastic produced globally is recycled, huge quantities end up in nature, where, due to their persistence, they remain for centuries, gradually fragmenting and entering every pore of life on Earth. The initiatives carried out by IRB scientists, financed through programs such as those of the Croatian Science Foundation, are necessary to create the basis for future environmental protection policies and for making decisions based on verified scientific data. It is precisely this synergy of science, policy, and the public that is key to winning the fight against plastic pollution, which is why the Institute has issued a call for joint action to all stakeholders in society.