Human activities pollute the environment. About 80% of the litter floating in the ocean comes from the land. Most of the litter in the sea is plastic. The most common single-use plastic rubbish is from cigarette butts.

Marine litter is generated from many sources, e.g. construction, industry, illegal dumping of rubbish, leisure, transport, and fishing. The origin of the rubbish is not always even clear. The same type of rubbish can come from many different sources, and some decays over time to become unrecognisable. Besides littering, we can add people's thoughtlessness, as well as poor waste management.

The size of marine litter ranges from large debris to small micro fragments, while the variety of materials is vast. The quantity and quality of the rubbish are measured, for example, by mapping the litter found on the shores. At the seaside, you will notice the popularity of disposable materials: a large part of the rubbish is made up of plastic packaging, bottle caps, crockery, and cutlery.

Plastic is used extensively around the world because it is easy to shape, durable, lightweight, and cheap. Plastic consists of man-made polymers (chemical compounds with molecules bonded together in long, repeating chains) and additives used to improve the properties of the finished product. Plastics are still mainly made from fossil oil.

Most of the plastics produced in Europe are used in the packaging and the construction industries. In third and fourth places are the automotive and electronics industries while household consumption comes in fifth. The most commonly produced types of plastics are also those most commonly found on the shore and at sea. Among the most commonly produced types of plastic in Europe are packaging films, pipes, containers, toys, and drinking bottles.

Since plastic is long-lasting and can float, it can be transported long distances by water currents, wind, or animals.

It can take hundreds of years for plastic to break down in the sea.

Large pieces of plastic become fragile and gradually become tiny microparticles, which continue their journey in the marine food web.

A microplastic is a fragment of plastic less than 5 mm in size. Some plastic fragments are already very small when they enter the sea and are known as a primary microplastics. Primary microplastics are used, for example, in industry, as well as in cleaning and cosmetic products.

Secondary microplastics, in turn, detach from washing clothes made from synthetic fibres, from vehicle tyres on roads, and when the plastic becomes brittle.

The best way to prevent microplastics from getting into the water is to find out its sources and transport routes. Once microplastics reach a water body, it is practically impossible to remove them.

According to surveys carried out in both Finland and Sweden, most of the microlitter less than five millimetres entering wastewater treatment plants is removed during the treatment. However, it is difficult to study the number and quality of the smallest litter fragments, especially when some can even be measured in nanometres. As a result, little is known about the sources, pathways, and entry into the waterways of these "nano-particles". Fun fact! A nanometre is a unit of length in the metric system, equal to one billionth of a metre!

Plastic litter is a danger to marine organisms. A seal or seabird entangled in a fishing net or plastic bag may die. When plastic floats in the sea for some time, it starts to accumulate various organisms upon it. This covering of animals and plants attracts other marine animals who then eat the plastic waste.

Over time, plastic litter breaks into small fragments, which continue their journey in the marine ecosystem. The smaller the fragment, the more likely an animal will think of it as food and try to eat it. In this way, microplastics can circulate in food webs almost endlessly.

Laboratory experiments have shown that planktonic crustaceans, molluscs, as well as many fish, eat microplastics. They have also been found inside wild animals.

Some additives that improve the properties of plastics, such as phthalates and PCBs, are harmful to the environment. Also, plastic can absorb harmful substances already present in water. This means that eventually, their concentration within the microplastic can be higher than in the surrounding water. These toxic substances are then carried to organisms within the tiny plastic fragments. However, more research is needed in the marine environment to understand the risk of plastic contaminants to the Baltic Sea ecosystem.

A littered environment attracts even more littering. An environment with less litter, in turn, raises the threshold to throw rubbish in nature. Everyone can influence the behaviour of others through their example.

Knowledge, awareness, and environmental education reduce the littering caused by pure thoughtlessness. Organisations play an important role in spreading environmental information. Each citizen can also make a difference: if you notice that the waste management in your local community needs to be repaired, suggest improvements to the authorities and decision-makers in your area. You can also write about it on social media and in the Correspondence Sections of magazines and newspapers.

Measures are being taken to reduce littering, e.g. by avoiding the unnecessary packaging of products, charging for plastic bags, making recycling more efficient, and improving waste management. Besides, alternative packaging materials, such as wood, are being developed to replace plastic. It is also important to monitor the effectiveness of these measures 

The monitoring of shoreline litter is directed by the Ministry of the Environment. The organisation known as Keep the Archipelago Tidy (PSS ry), in turn, is responsible for shoreline monitoring in cooperation with the Finnish Environment Institute (SYKE).