Contaminated Aquatic Sediments Can Be Remediated On Site Using New Methods

Contaminated Aquatic Sediments Can Be Remediated On Site Using New Methods

March 25, 2026
By Marianne Mustonen, University of Eastern Finland

Aquatic sediments serve as a chronological record of human impact on water bodies, acting as both a reservoir of essential nutrients and a repository for harmful substances. "Many lakes undergo remediation primarily due to issues related to eutrophication. However, remediation efforts concerning the presence of hazardous substances occur much less frequently," notes Jarkko Akkanen, Research Director at the Department of Environmental and Biological Sciences.

The sediment layers of a lake can provide insights into its environmental history. For instance, the cesium deposits from the Chernobyl nuclear disaster can indicate whether a specific sediment layer was formed at or subsequent to the event.

While sediment can store harmful substances, it also has the potential to release these toxins back into the water, even after the original contamination source has been eliminated. The presence of these harmful substances in sediments can significantly impact both the aquatic environment and its organisms.

Akkanen elaborates, "The release of toxins from sediment poses risks to benthic organisms and may contribute to bioaccumulation in the food chain, ultimately affecting human health. Fishing in these affected areas may need to be restricted."

In Finland, the management of environmental issues is generally robust. If an area has a history of industrial usage, it is possible to investigate the pathways of pollution from that activity. Nonetheless, a pressing question remains: are we fully aware of all potential sources of emissions? With shifting climate patterns, water currents may change, causing sediments to redistribute.

Currently, Finland and the EU lack threshold values for hazardous substances in sediments, similar to those established for contaminated soil. Areas of contamination are addressed on a case-by-case basis, often prompted by the transition of former industrial sites into residential zones.

It is important to recognize that contaminated sediment cannot simply be excavated and placed on land without proper treatment. When substances in the sediment exceed safety thresholds, they cannot be returned to the aquatic environment. In the land disposal process, it is crucial to mitigate risks by effectively sealing these hazardous substances within a mound.

The research group led by Akkanen has conducted sediment remediation studies at various sites, including Lake Kernaalanjärvi in southern Finland. The historical monitoring of PCB emissions from the Tervakoski paper mill since the 1980s has resulted in consumption advisories for fish from this lake.

"PCB levels in fish are gradually declining, with the most recent consumption advisories issued in 2010," states Akkanen.

"This decline may be attributed to layers of clean sediment covering the contaminated strata, naturally capping the harmful substances. However, as these substances are persistent, the feasibility of remediation must be thoroughly evaluated. For instance, the decision was made not to dredge the dioxin-contaminated sediments in the River Kymijoki, meaning no remediation has occurred there."

High concentrations of PCBs have also been detected in Viinikanlahti, located in central Tampere. As this site transitions to residential use, sediment removal is anticipated. "Given that Viinikanlahti is an old industrial site, sediment removal is likely necessary — a wastewater treatment facility is also situated nearby," Akkanen explains.

In contrast, central Joensuu, previously home to the Penttilä sawmill, underwent a significant remediation effort involving the soil and sediment of the log pond, whereby some contaminated material was safely encapsulated on-site in a landscaped mound.

The latest investigation by Akkanen's team focused on the water bodies surrounding the Paukkajanvaara uranium mine in Eno, eastern Finland. "Although the mine, which was operational in the 1950s and 1960s, has been remediated, uranium levels in the downstream ponds are among the highest globally," Akkanen reveals.

Despite the presence of high uranium levels in benthic organisms and fish, anglers continue to frequent the area. "No remediation has occurred concerning these ponds. It remains unclear how widely this concern is recognized; perhaps anglers are simply not consuming the fish," Akkanen speculates.

"Our research prioritizes understanding the toxicity of uranium and its transfer through the food chain rather than focusing solely on its radiation. Our upcoming doctoral dissertation will delve deeper into the uranium data specific to Paukkajanvaara."

Materials That Bind Harmful Substances Can Be Used in Sediment Remediation

Dredging contaminated sediment is a significant intervention; therefore, exploring alternatives is crucial. Akkanen’s research group has investigated various on-site remediation methods. "One potential approach is to cover contaminated sediment with clean soil. This can involve placing a geotextile fabric over the sediment to retain it, followed by a layer of clean soil, though this method is still quite resource-intensive," he notes.

Fundamentally, a geotextile serves as a filter fabric that helps retain soil or sediment while allowing water to flow through.

"Introducing binding materials to the sediment can prevent the diffusion of harmful substances. Activated charcoal is a promising candidate, although it could be detrimental to benthic organisms. Our research has explored activated charcoal in pellet form, which might be less harmful. Layering geotextiles, activated charcoal, and heavier soil materials atop the sediment could facilitate remediation."

Securing funding for sediment remediation initiatives presents challenges, particularly when the original source of contamination or responsible entity is no longer present, inadvertently shifting the financial burden to taxpayers.

"It is advantageous to identify the most contaminated locations before initiating any construction projects. Much of this knowledge is built on informed hypotheses, and unfortunately, there may be a lack of data regarding specific sites.

"While remediation of organic contaminants has demonstrated satisfactory results, efforts to manage metals such as uranium have proven more complex. The intricate chemistry of metals in aquatic environments necessitates further investigation to enhance remediation strategies."