Environmental toxins and litter

Levels of many environmental toxins have fallen considerably since the 1970s, but society’s massive use of chemicals is still a threat to the marine environment.

Environmental toxins

Virtually all toxic substances that end up in nature can be classified as environmental toxins. Some contaminants can harm living organisms even at low levels, at least if they are able to act over a longer period of time. As a result, contaminants that are stable and persistent are particularly liable to act as environmental toxins. Their stability means not only that their effect can be long-term but also that the substances in question can be spread across large areas before they are broken down.

Excessive levels of many metals are harmful to plants and animals. Of course, these elements occur naturally in the environment, but they are now present at unnaturally high levels because mankind has released them into circulation. Mercury in seeds, lead in petrol, copper in antifouling paint and cadmium in batteries are examples of heavy metals that have – or have previously had – a significant impact on the marine environment.

DDT, PCBs, dioxins, similar toxins and persistent organic substances can easily build up in living organisms, and can reach harmful levels especially in predators and other species high up the food chain. These substances are like hormones, and can therefore have an effect even at low levels. Some of the ‘classic’ environmental toxins are insecticides such as DDT, toxaphene, chlordane and hexachlorocyclohexane (HCH). These have been intentionally spread across agricultural land, for example, but in industrial nations such as Sweden their use has been gradually phased out.


One of the challenges faced by the Baltic Sea is litter in the form of plastic. This is likely to remain in the sea for the foreseeable future.

Plastic is broken down very slowly in nature, and the amount of plastic ending up in the sea as rubbish has risen dramatically in recent decades. It takes a particularly long time for plastic to break down in the Baltic Sea, because the water is cold and the sunlight is less strong compared with many other seas. The lack of oxygen on the seabed means any plastic waste that ends up there is broken down extremely slowly. This, combined with the slow water exchange, results in plastic staying in the Baltic Sea for a long, long time. For example, an ordinary plastic cup can last for a hundred years.

Microplastics Plastic that ends up in the marine environment is broken down into small pieces, which eventually become tiny particles known as microplastics. The problem of microplastics has attracted attention in recent years, and scientific studies show that they can harm the marine environment and its organisms. Microplastics are also created as materials such as tyres, clothing and other plastic materials gradually wear out. They can also be produced when we do not reuse, recycle or dispose of plastic materials correctly. Plastic pellets – the raw material from which other plastic products are made – are unintentionally released into the environment during manufacturing processes and transportation. Plastic is also intentionally added to a variety of products such as cosmetics, body care products and detergents – known as primary microplastics – which end up in the sea via waste water.

Plastic, plastic everywhere Microplastics make up the largest proportion of all plastic waste in the oceans in terms of number of particles, and are now found in all the planet’s marine environments. They are present in water, in seabed sediments and in living organisms. Microplastics can now even be found in Arctic ice and the depths of the oceans.

Plastic instead of food One major problem is that the small inhabitants of the sea and certain sea birds mistake plastic particles for food. These plastic particles are not broken down in the gastrointestinal tract, and can remain there and cause problems. However, small particles probably quickly pass through the gastrointestinal tracts of many of the creatures that ingest plastic. Another fear is that these plastic particles may contain or attach to environmental toxins, potentially affecting both the creatures that eat them and those higher up the food chain. However, microplastics probably bind with relatively small amounts of environmental toxins compared to what these creatures ingest via their food.

These pages include factual information from havet.nu - a site run by Stockholm University, Umeå University, the University of Gothenburg and the Swedish University of Agricultural Sciences (SLU) within the collaborative framework of the Swedish Institute for the Marine Environment, and in cooperation with the web agency Azote.

Baltic Sea Science Center