Industrihamn med rykande skorstenar
PAHs from industrial processes often reach the marine environment via air pollution. Photo:

The study, published in the Science of the Total Environment, combines information from several environmental monitoring programs to find out how levels of Polycyclic Aromatic Hydrocarbons (PAHs) have changed in the Baltic Sea’s blue mussels since the late 1980s.

Ecotoxicologist Agnes Karlson
Agnes Karlson

PAHs are formed during incomplete combustion of organic material and petroleum products and can be endocrine disruptive and carcinogenic in animals and humans. They often reach the marine environment via air pollution and several efforts have been made to reduce the emitting sources. To be able to see if measures, such as legislation, translates into reduced concentrations in the marine environment, environmental monitoring is a crucial tool.

- Long term data is our only opportunity to detect changes over time. How quickly you are able to detect a change depends on how much variation you see between years, says Agnes Karlson, researcher at the Department of Ecology, Environment and Plant Sciences, Stockholm University, who initiated the study.

Environmental factors mask
development in contaminants

Porträtt av miljögiftsforskare Caroline Ek
Caroline Ek

Unfortunately, the concentrations in PAHs in biota depends not only on the actual concentrations in the environment that we want to measure, but also on background noise from various biological and environmental factors.

- For PAHs in blue mussels in particular, the variations in concentrations have been large, high one year, low the next and then high again, and we have focused on finding a statistical method to reduce the variation and increase the reliability of the environmental monitoring data, says Caroline Ek, lead author and researcher in contaminant science, who has previously worked with coordination of contaminant monitoring at the Swedish Museum of Natural History.

Could detect trends faster

In the case of blue mussels, body size, metabolism, water temperature, amount of plankton or runoff from land can affect how much PAHs they are exposed to, to varying degrees. The study identified the factors most important for PAH levels in the mussels.

- We noticed, among other things, that the amount of benthic fauna that stirs the sediment had an important impact on the PAH levels in mussels. Hence, it can be old sins in the sediments that explain extremely high levels in a certain year when there is a lot of benthic fauna present, rather than the emissions being particularly large that year, Agnes Karlson explains.

- It also seems that the mussels enrich more PAHs when there are large algal blooms in the spring. PAHs probably stick to the algae particles. That is why it is really important to continue with frequent monitoring of plankton, for instance. Not only to understand the state of the sea but also to understand how organisms in the ecosystem are exposed to environmental toxins, she says.

Irreplaceable time series

The costs of measures for reducing pressures on the marine environment are often extensive. It is therefore desired that the time required to determine whether measures are effective, or need to be implemented at all, is reduced as it can be of great importance from an economic perspective.

- By adjusting the time series for the most relevant factors, we reduced the number of years required to detect a change by several years in almost all PAH time series examined. The faster we are able to observe and react to changes in the environment, the better we can protect it and act cost-effective, Caroline Ek concludes.

About the study: