Finnish waterbodies, lake and sea beds, fish and molluscs are contaminated with microplastics, according to a recently concluded four-year research project conducted by the Finnish Environment Institute (SYKE) and the University of Eastern Finland.
"The smaller the microplastics studied, the higher concentrations were observed because plastics constantly fragment into smaller particles in the environment," explained Maiju Lehtiniemi, research professor at the Institute.
According to the report, most microplastics were found in mussels, which filter water to obtain food.
Relatively high concentrations of microplastic particles were observed in local coastal sediments. The quantities match the levels found in Norway’s coastal sediments and in the southern Baltic Sea.
The research was primarily conducted in the Baltic Sea and Lake Kallavesi in Eastern Finland.
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Results observed significant differences in the amounts of microplastics found in fish, both regionally and among different species.
Only a small quantity of plastic was found in Baltic herring, Baltic sprat and three-spined stickleback in open sea waters. However, microplastics were remarkably more abundant in the European perch, common bleak and three-spined stickleback on the Finnish coast as well as in European perch and vendace in Kallavesi.
About nine percent of sea fish were contaminated with plastic. In Kallavesi, 17 percent of the perch and one in four vendace had consumed plastic.
However, Lehtiniemi assured that it is still safe to eat the fish.
"Some fish had no plastic at all, some had a lot. You don’t have to think about this when consuming fish. The fish is healthy — the amounts of microplastics found do not change it," he said.
The study also performed laboratory experiments on small planktonic crustaceans. They died or their stress levels increased when they were exposed to car tyre rubbers and frozen vegetable bags containing food residues.
Stormwater transports plastics
The largest microplastic discovery of sediment was made on the outskirts of the Kilpilahti area in Porvoo — 22 microplastic particles per gram of dry sediment. In the other coastal areas scientists recorded less than 10 particles per gram of dry sediment.
On an average 16 particles per cube of seawater were found at coastal sampling stations.
Microplastics end up in water systems from land especially through flowing water from urban environments, according to SYKE.
"One of the most important pathways is stormwater — rain and meltwater from built-up areas. We need more research in particular on microplastics emissions from transport," researcher Julia Talvitie said.
Polyethylene most common in water bodies
The project researchers developed special methods to examine the plastic types found in samples.
Polyethylene (PE) was often the most abundant type of plastic in the samples. PE’s various forms are among the world’s most used raw materials of plastic.
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," said Arto Koistinen, Director of SIB Labs and the University of Eastern Finland’s sub-project.