Contaminated wood fiber-sediments: dispersal of persistent organic pollutants, release of greenhouse gases and sustainable remediation solutions

The Swedish national database for contaminated sites contains several thousands of objects classified as having high risk to the environment and human health. Most of the pollution comes from the period when Sweden underwent major industrialization, while there were neither environmental laws nor much knowledge about the risks of chemicals to the environment.

There is a societal need to find improved methods for assessing the risk of contaminated sites and to use efficient remediation techniques that are environmentally and economically sustainable. This forms the core of my research at SLU, with a special focus on contaminated sites linked to the forest industry.

The forest industry have historically been associated with the release of persistent organic pollutants (POPs) due to the use of insecticides at forest plant nurseries, wood preservation and formation of unwanted by-products in the pulp and paper making process. Many industries, such as sawmills and pulp and paper mills, have been located along rivers and the coast, which has contributed to pollution of POPs in the aquatic environment.

These industries have also discharged large amounts of contaminated cellulose material with their wastewater. Organic material that have accumulated and formed meter thick fiber-deposits (so called fiberbanks) on the seafloor in lakes and coastal areas. Lately, contaminated fiberbanks have been identified as national priority objects because of the lack of knowledge on the characteristics of this unique type of sediment and their risks posed to the aquatic environment.

In my lecture, I will provide an overview of my work on how to better assess the risk of dispersal of POPs from fiberbanks to the surrounding aquatic environment. This includes field measurements to quantify different dispersal pathways such as sediment-to-water fluxes, particle resuspension and uptake in benthic organisms. Furthermore, my research findings show that degradation of the fiber-sediment under anoxic conditions leads to extensive biogenic production of greenhouse gases (GHG).

A novel flux sampling device was therefore developed to allow, for the first time, in-situ measurement of greenhouse gas fluxes, gas-mediated contaminated transport and gas ebullition facilitated particle resuspension from the sediment. Being able to measure various environmental contaminants in different matrices forms the basis of my research. In my lecture, I will therefore give example of the analytical methodology used to measure POPs at trace levels using gas chromatography coupled to mass spectrometry (GC-MS/MS).

Finding effective remediation techniques for fiber-contaminated sediment is urgently needed. Traditional remediation methods involves excavation/dredging and landfilling. However, placing large volumes of fiberbank sediment in landfill is not sustainable, and without pretreatment, it risks to generate unacceptable GHG emissions.

In my lecture, I will present example of potential in-situ and ex-situ remediation methods for fiber-contaminated sediments and present results from a large-scale laboratory column experiment that aimed to determine the effectiveness of in-situ capping of fiberbank sediments. Climate change can cause other spreading conditions from contaminated sites, which needs to be accounted for when assessing risk and choosing remediation measures. With increasing temperatures, GHG emissions from fiber-contaminated sediments are expected to increase, with a risk of increased contaminant dispersal.

In my new research project, we are therefore investigating which parameters affect methanogenesis in this unique type of sediment and how the GHG production differs in various aquatic environments in Sweden. In general, the implications of climate change on contaminated sites needs much further research. To fulfill the Swedish environmental quality objectives of “a non-toxic environment”, it is important that the society better manages and remediates contaminated sites in order to achieve a sustainable future.