Fish are among Norway’s most important resources and clean waters are a prerequisite for good, sustainable management. Unfortunately, human activities over the last few centuries have had an adverse effect on all parts of the environment, including the ocean. This is where a large number of chemicals used for various purposes end up. If we are to grasp the scope of the problem, we must know what types of pollution exist, where, and how much. The surveying programme of the Institute of Marine Research has been running for more than 20 years in the North Sea, the Norwegian Sea, and the Barents Sea. We have gathered extensive data about manmade contaminants in fish (16 species) and crustaceans (three species).
Among many hundreds of chemicals identified as contaminants, we have chosen to focus on chlorinated contaminants (such as PCB and some pesticides), in fish and crustaceans. These substances are industrially produced and decompose slowly in nature. This is why traces of them remain in the environment even many years after their release. They are among the most harmful chemicals released into the environment. The potential to cause damage varies from substance to substance: some of them may be hormone disruptors or have carcinogenic effects; others may be acutely toxic even in small concentrations. The United States prohibited production of PCB in 1979, and PCB was later included with several pesticides in the list of persistent contaminants prohibited by the Stockholm Convention in 2001.
Other groups of contaminants are also included in our surveys. These substances are different from chlorinated contaminants and require a separate analysis. We also analyse brominated flame retardants, which have not been used for as long as PCB but also decompose slowly and represent an environmental problem because they are so widespread. They are widely used all over the world as additives to technical equipment, furniture, textiles, and other household goods, as they are efficient at preventing fire. Some types of brominated flame retardants are also on the list of substances that are to be phased out pursuant to the Stockholm Convention.
Another important group of substances is polycyclic aromatic hydrocarbons (PAHs), which can come from a variety of sources and also occur naturally in the environment. PAHs form during combustion of organic material and are given off in smoke (for instance in exhaust from cars, burning coal, and wood). They are also found in oil and other fossil fuels. Fish are able to
excrete these contaminants quite efficiently – at least in small amounts – but crustaceans do not have the same enzyme system for metabolism and excretion
of PAHs. PAHs can also accumulate in sediments. Our project therefore analyses sediments from the seabed to examine PAH levels there.
Levels in the ocean today
Our results from 20 years of environmental surveys vary quite a lot. Levels of some types of contaminants are low or undetectable, whereas others are clearly present. We see, for instance, low levels of brominated flame retardants, while there often are higher levels of PCB and the pesticide DDT than of other substances.
The higher we get in the food chain, the greater the concentrations of contaminants. This is as we expected. Concentrations also increase with age in fish.
Generally speaking, the highest levels are found in the North Sea (especially near the coast and in Skagerrak) and the lowest levels in the Barents Sea, but large variations have also been observed.
Although some of the contaminants are present at higher concentrations than others, even the higher levels are usually below the maximum limits for nutritional safety (200 g/kg wet weight for the sum of six PCB congeners in liver). However, individual fish may on occasion deviate markedly from the average (see figure).
Some decrease found
Several species have been sampled consistently over time, whereas others have been sampled more sporadically. For the species under regular surveillance, we can present time series describing changes in the contaminants over time. Levels of some substances have decreased significantly in the past 15-20 years. An example is the pesticide HCH in liver from cod in the Barents Sea. Levels of some other substances seem relatively stable, for instance PCB in liver from the same cod. Our surveys show that it is still important to monitor organic contaminants in the marine food chain and in sediment. The contaminants are transported over great distances from their original sources, and background levels are clearly detectable even in the Arctic, where there are few local pollution sources. Despite having been prohibited for several decades in many countries, some of these contaminants persist in the environment.
For some groups of substances, levels in open waters are slowly but surely decreasing, while others are maintaining stable low levels. It is important to document this development, too, and thus continue the time series established through two decades of surveys.