Does the perch have a headache?

Compounds that are harmful to the environment have been used for decades and are already found in every corner of the world. The variety of man-made chemicals found in the Baltic Sea is larger than ever and some cause harm to marine animals and plants.

Toxic substances disturb marine organisms

Perch (Perca fluviatilis).

In the cold Baltic Sea, toxic substances break down slowly and can remain for long periods in the seabed and the food web. Also, the slow water exchange rate in the Baltic Sea increases the stress on organisms because pollutants are poorly diluted, and their effects last a long time.

Harmful substances end up in the sea from households, agriculture, and industry. Some are created as a by-product of processes while others are deliberately manufactured. Placing prohibitions and restrictions on the use of the most hazardous substances have helped fish-eating animals in marine ecosystems, especially sea eagles and seals.

Examples of the sources of harmful substances that end up in the sea. These sources include industry, energy production, traffic, and the household. .

Where do these toxic substances come from?

Chemicals can have positive uses. They are used in all kinds of products to improve their properties. However, when released into the environment, these same chemicals can be harmful instead. Pollutants are also produced by emissions from industry and transport and activities like burning coal. There is an increased risk of accidents in the Baltic Sea due to its busy shipping traffic. If an accident happened, it could cause a large oil spill in the sea.

However, it is also important to know that the increasing levels of harmful substances that end up in the sea originally come from households and urban rainwater. Many ordinary household products that we use to make everyday life easier have been found to contain chemicals which are toxic to organisms. These harmful substances occur in household products such as washing and cleaning detergents, glues, paints, lubricants, dyes, and biocides. Besides, plastics, electronics, and textiles also contain toxic surface treatments and flame-retardant chemicals.

Contaminants can be released into the environment throughout the whole life cycle of a household product, from the production of the raw material to the waste disposal of the finished product. People also throw their medicines and hormone drugs in the toilet. From there, they pass through the sewage treatment plant and eventually end up in a water body, like a river, lake or the sea.

Expired home medicine should be returned to a pharmacy for safe disposal.

Tracing chemicals

The dangers of old organic environmental toxins, such as PCB and DDT, as well as heavy metals, are well known. Every day, we gather more and more information about the emissions of fire retardants, surface-treatment agents, anti-fouling paints on ships, and plant protection products. The by-products of combustion are mainly known as dioxins and PAH-compounds, which are also produced in oil spills.

Very little is still known about the releases of medicines, drugs, cosmetics or so-called micro- and nanomaterials. Many drugs pass through wastewater treatment plants unchanged and high concentrations of certain drugs have also been measured in the treated wastewater.

Oil on a rocky shore.

In the European Union, tens of thousands of chemicals are used, and new ones are constantly being introduced. Chemicals are both produced in and imported to Finland, along with their components and products. There are about 20,000 preparations classified as dangerous and these contain more than 5,000 hazardous substances. The information about the properties of many existing and some new chemicals is incomplete.

Many toxins accumulate at the top of the food chain

The plants and animals in the sea are almost always exposed to mixtures of different compounds, not just a single one. Water temperature and salinity also influence how toxic these substances can be. There is a need for more information on both existing, as well as new chemicals, and in particular, about their interactions in the sea.

Toxic substances that break down slowly in nature build up in the bodies of marine organisms and cause suffering especially for those animals at the top of the food chain, i.e. birds, mammals, and even human beings. In particular, persistent toxic organic compounds, such as flame retardants and surface treatments which use bromine and fluorine, interfere with the reproduction of organisms.

Although the use of TBT, an organic tin-based compound used in anti-fouling primer paints for ship hulls, is prohibited, past emissions are still circulating in the food web. TBT acts as a hormone disruptor and has destroyed entire populations of aquatic snails.

When attached to the bottom of a boat, the bay barnacle (Amphibalanus improvisus) becomes a nuisance for boat owners; also visible are colonies of bryozoans (Einhornia crustulenta).

Medicinal drugs and hormones interfere with the cellular function of organisms and thus with their vital functions, such as breathing, circulation, and metabolism. Low levels of toxins are difficult to trace in the tissues of organisms. However, the early effects of stress-causing toxins can be measured by monitoring the biological changes in the organisms themselves, i.e. through what is known as an organism response. When an organism response or biomarker sets off an “alarm”, swift action can be taken to prevent more serious disturbances to the ecosystem.

Blue mussels are excellent biomarkers: they are highly effective at filtering seawater. Blue mussels are kept in a cage in the sea for a certain time period, after which their response to environmental stress is examined from cell samples.

How can marine pollutants be reduced?

For decades no-one seemed to be very worried about pollutants ending up in the sea. Fortunately, attitudes have since improved. International agreements have been established to legally restrict or completely ban the use of substances found to be harmful. Indeed, the levels of contaminants in nature have decreased.

The number of oil spills in the Baltic Sea have been brought under control through air surveillance, strengthening the structures of ship hulls, and by spreading environmental information. Finland was the first country in Europe to draw up an action plan that also prepared for the ecological impact of an oil spill accident.

Today, contaminated sites and wastewater are being treated with more efficient methods, such as activated carbon and ozone. Combustion processes have also been made cleaner. A good exchange of information between the public authorities, different agencies, and consumers is the most effective way of preventing the creation and release of harmful substances.

Even the choices and needs of the individual consumer can also influence the levels of pollutants that burden the environment. An eco-labelled product puts less strain on nature. Delivering unnecessary medicines and hazardous chemicals to the correct collection points is also an important environmental act.

A cartoon, in which we see a flushing toilet leading directly to a dirty surface splash in a watercourse.
If thrown in the toilet, harmful substances, such as medicines, end up in the sea. Instead, unneeded medicines should be taken to the pharmacy while the proper destination for the lavatory water must be, of course, through the treatment plant!


Biomarkers are indicators of biological changes in organisms caused by various stress factors. They act as early warning signs, among other things, of the negative effects of chemicals, before these changes appear at higher levels within the ecosystem. Biomarker measurements have been carried out in the Baltic Sea on, for example, molluscs, fish, and amphipod crustaceans.


A biocide is a chemical or micro-organism whose purpose is to destroy and deter harmful organisms and to prevent or limit their influence and occurrence. Biocides include, for example, disinfectants, pesticides, industrial and wood preservatives, as well as anti-fouling paints on ships.


Although dioxins are neither produced nor used, they are still formed as an impure by-product in combustion processes. Most of the dioxins entering the Baltic Sea come from long-distance transport. In the past, they were present, for example, as impurities in wood preservatives, such as chlorophenol. Dioxin concentrations in the sediments from the Kymijoki River still pose a risk to the marine ecosystem. Dredging can even move harmful substances to new areas.

Hormone disruptors

A hormone disruptor interferes with an organism’s hormone function and has other undesirable effects. In the European Union, if a substance is proven to be a hormone disruptor, its use will be severely restricted.


Persistent Organic Pollutants (POPs) are long-lived and toxic organic substances that build up in living organisms. They can even cause environmental damage at low concentrations. POP compounds include DDT, PCB, HBCDD, PBDE, PFOS, chlorophenol, and dioxins. The use of POP compounds is forbidden or restricted by the so-called Stockholm Convention. However, there are still such substances used in the products and waste of both flame retardants and surface finishes.

Heavy metals

Of the various heavy metals, mercury is the biggest burden in the Baltic Sea. Its use in products has been severely restricted. Most of today's emissions come from burning coal and airborne deposition by the metal industry, either released directly into the sea or from the ground through rivers.


PAH-compounds (polycyclic aromatic hydrocarbons) in oil spills are among the most harmful substances. Not only ship accidents but also persistent low emissions, such as oil carried in run-off and wastewater, pose a risk to the marine ecosystem. In some ports and shipping lanes, the concentrations of PAHs are harmful to higher organisms, e.g. birds and mammals.

A mallard duck swims in oily water.