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The concentrations of harmful substances are measured in water, sediments, and organisms

The monitoring of harmful substances in the Baltic Sea has traditionally focused on assessing the concentrations of harmful substances in water, the seabed, and organisms.

Estimates of the effects of harmful substances on the biota of the Baltic Sea are mainly based on individual research projects. Thus, much of the actual effects of chemicals on biotic communities and ecosystems remain completely unknown. Besides, the interactions between different substances on marine organisms are also not sufficiently known.

The effect of harmful substances is based on many different factors

The effects of toxic substances on biota are the result of a variety of processes. They depend on the physicochemical properties and concentrations of the substances, environmental factors, such as pH and oxygen content, as well as the biology of the organism.

In the marine environment, organisms are almost invariably exposed to mixtures of different compounds and not just to individual toxins. Such exposure and its effects can be observed at many different levels, such as molecular, cellular, tissue, individual, population, and community.

The EU monitors the effects of harmful substances on the marine environment

In accordance with the obligation of the Marine Strategy Directive of the European Union, the effects of harmful substances are also monitored in Finnish sea areas.

Monitoring has traditionally focused on apex predators at the top of the ecosystem. The concentrations of the substances accumulating in such animals are the highest due to their enrichment in the food web.

However, the monitoring of impacts in the Baltic Sea as a whole is deficient compared to other EU maritime regions. For example, this is one of the improvements proposed by the HELCOM Baltic Sea Action Plan.

Bird populations have recovered with reduced exposure

The contribution of harmful substances to the deterioration of the health status of seabird populations in the Baltic Sea is not fully known. However, as concentrations of certain substances decline, bird populations have also recovered.

Sea eagles suffered from exposure to insecticides

From the 1960s to the 1980s, populations of the white-tailed sea eagle, i.e. Haliaeetus albicilla, in the Baltic Sea suffered from an accumulation of organochlorine compounds. The commonly used insecticide dichlorodiphenyltrichloroethane, or DDT, accumulated in birds. It caused the eggshells to become too thin and chick production collapsed.

Since the ban on the use of DDT came into force, its concentrations in the environment have decreased since the beginning of the 1990s. Today, the sea eagle population in the Baltic Sea is again stable.
 

PCBs and DDEs caused chick deaths in lesser black-backed gulls

Fluctuations in the numbers of chicks of the lesser black-backed gull, i.e. Larus fuscus, in the Gulfs of Finland and Bothnia have clearly been affected by polychlorinated biphenyls (PCBs), as well as dichlorodiphenyldichloroethane (DDE).

The concentrations of these chemical compounds measured in the environment have been shown to correlate with the levels measured in the chicks’ livers. The harmful compounds that pass from the mother through the yolk sac to the chick damage its liver while it is still a foetus. As a result, the chicks die soon after birth.

In the 1990s, chick mortality was particularly common. However, in the first decade of the 21st century, exposure appears to have decreased, in particular to DDT. Indeed, the survival rate and the number of chicks of the lesser black-backed gull have risen to a level at which the population can be expected to remain stable or even increase.

Eider ducks suffered from lead poisoning

Lead poisoning in eider duck individuals, i.e. Somateria mollissima, has been observed in their nesting areas. Exposure to lead has decreased in the Baltic Sea region since the ban on lead shot in shotgun cartridges came into force in 1996. The adoption of unleaded fuel has also reduced the exposure to lead. Other sources of lead are still found in, among other things, industry and boat paints.

Environmental toxins disrupted seal reproduction

In the 1960s and 1970s, very high levels of heavy metals and organochlorine compounds were measured in the tissues of Baltic seals. These toxins disturbed the biological functions of seals, in particular causing reproductive disorders.

The concentrations of environmental toxins accumulated in Baltic Sea seals have since decreased. However, they are still many times higher than in less polluted areas. As concentrations decrease, the reproductive capacity of seals has improved, and populations have grown.

The effects of harmful substances on fish and invertebrates are difficult to verify

The effects of harmful substances on fish and invertebrate communities are difficult to verify. For example, benthic communities naturally have only relatively few different species. This is especially true in the low salinity northern areas of the Baltic Sea.

Also, the effects of eutrophication, such as oxygen depletion, may partially mask the effects of toxic substances. At the same time, the harmful substances may also amplify the effects of eutrophication on biotic communities.

If the effects of toxins cannot be detected at the population and community levels and the effects of harmful substances on individuals cannot be measured, it is difficult to assess the exposure and health status of the organism.

Soil and water acidity have affected fish stocks

The loading from acidic sulphate soils has been estimated to have destroyed or severely weakened many locally and regionally important fish stocks on the west coast of Finland. In particular, salmonid (trout, salmon, grayling) and cyprinid (roach, bream, etc.) fish are sensitive to water acidity.

Due to human activities, both soil tillage in acidic sulphate soils and its effects have intensified in recent years. This increases the risk of harm to aquatic organisms.

Moreover, in the Bay of Bothnia, it has been observed that the bottom-dwelling fish known as burbot (Lota lota) has been unable to spawn. This inability is thought to have been related to the adverse effects of wastewater from the pulp industry. However, the specific cause for the observed inability to spawn could not be definitively identified.

The future effects of harmful substances are difficult to predict

The almost uncontrolled pollution of the Baltic Sea by harmful substances has largely been brought under control in recent decades. Although the problems caused by harmful substances are still significant, they have not worsened recently. Quite the opposite, in fact.

Chemical loading must be considered in certain activities such as dredging

As external loading decreases, harmful substances are slowly stored in the deeper bottom sediment layers of the Baltic Sea. In this way, they leave the cycle of nature.

However, human activities, such as the dredging and dumping of bottom sediments, can release harmful substances back into the water. Once they are in the water column, they can transfer back into marine biota. Therefore, it is important that large-scale offshore construction works consider the chemical consequences of their project.

There is no certainty about the potential threat of new chemicals

The changes regarding the transport of banned and restricted substances into the environment will no longer be as large as they were between the 1970s and 1990s. Emissions have already been reduced across Europe and the rest of the world.

However, such bans and restrictions on the use of harmful substances will continue to be important in the future. It is only with such legislation that the amounts of harmful substances in the environment can be further reduced.

Although environmental standards have tightened and the situation is better than before, the problem is not entirely behind us. While the manufacture and use of many known harmful substances are currently banned, they are persistent in the environment and continue to have an impact.

There are tens of thousands of chemicals already in use in the European Union and new ones are constantly being developed and introduced. In Finland, chemicals are both produced and domestically and imported. In addition, they come with their chemical components and products. There are almost 20,000 products classified as dangerous. These contain more than 5,000 different hazardous substances.

We are unaware of the effects of new synthetic compounds released into the environment, let alone the many chemicals already in use. Nor do we know the effects of their degradation products or their interactions with other substances. As a result, it is impossible to say directly whether a future cocktail of harmful substances poses a lesser or greater threat to the marine ecosystem than the current one.