Microplastics are found in all water systems and in fish, bivalve molluscs and benthic fauna. Microplastics cause stress to the aquatic organisms and may expose them to harmful substances.
These were the results of a recently completed project by the Finnish Environment Institute (Suomen ympäristökeskus; SYKE) and the University of Eastern Finland wherein the behaviour of microscopic plastic pollution in water systems were studied and research methods focusing on microplastics were developed.
The new results and methods will be utilised in, for example, monitoring and conservation in the Baltic Sea and in research on the health impacts of microplastics.
Microplastics were found in all of the studied groups of organisms. The largest number of microplastics were found in blue mussels that filter water in order to feed.
Fewer quantities were found in the most common benthic fauna, that is, Baltic clam, Marenzelleria polychaetes and chironomid larvae.
Microplastics most likely end up in aquatic organisms when they feed. Exposure is affected by the habitat, prey and feeding method.
Major differences were found in the quantities of microplastics in fish, both regionally and among fish species. In the study, only a very small quantity of plastics was found in Baltic herring, Baltic sprat and three-spined stickleback in the open sea.
Microplastics were remarkably more frequent or abundant in European perch, common bleak and three-spined stickleback on the Finnish coast as well as in European perch and vendace in Lake Kallavesi.
The method developed over the course of the project improved the accuracy of analysis, enabling the identification of smaller particles than before.
In surface waters, microplastics were found in similar concentrations both in Finland's coastal waters and in Lake Kallavesi close to the city of Kuopio. This is probably due to the fact that the sources of microplastics ending up in water systems are mostly located on land.
In the Baltic Sea, stratification seems to affect the concentrations of microplastics in the different layers of water.
The sediment at the bottom of the Baltic Sea contains higher concentrations of microplastics than the water in the area. Relatively high local concentrations of microplastic particles were observed in coastal sediments.
The quantities reach the same levels as in Norway's coastal sediments and in the southern Baltic Sea, for example.
Laboratory tests indicated that plastic and recycled rubber causes stress in plankton and Baltic clam. Small planktonic crustaceans died or had higher stress levels when exposed to rubber used in car tyres and frozen vegetable bags (light PE) containing food residues.
Harmful substances, such as metals and PAHs, were also observed in Baltic clam exposed to car tyre rubber.
Spectroscopic analysis methods for examining the plastic types of particles found in environmental samples were developed in the project.
Arto Koistinen, director of SIB Labs, said that the most common types of plastic found in the samples were the same in both the Baltic Sea and Lake Kallavesi as well as in fish and benthic fauna.
Polyethylene (PE) was often the most abundant type of plastic in the samples. This is understandable as the various forms of polyethylene are the world's most used raw materials of plastic.
Polypropylene (PP) was also found in all samples examined.
Another type of plastic commonly found in the samples was polyethylene terephthalate (PET). PP and PET are plastics widely used in consumer products, including packaging.
In environmental samples, fibres were more common than particles. Because plastic fibres and particles are found everywhere in the living environment, sampling and laboratory work require special care and quality assurance to ensure the reliability of results.
The research project Microplastics in Finnish Waters (MIF), funded by the Academy of Finland, combined extensive field studies, experimental food web research and advanced material identification methods. The aim of the project was to develop methods and produce national information on the behaviour of microscopic plastic waste in aquatic environments and to assess possible adverse impacts.
Over the course of the project, the methods of microplastics research have improved significantly both in Finland and internationally, and the information on microplastic concentrations and microplastic materials has become considerably more accurate.
The Finnish Environment Institute will continue conducting research on the impacts of microplastics on marine ecosystems, and researchers at the University of Eastern Finland will assess the impact of microplastics on human health.