Microbial communities in coastal sediments sustain key biogeochemical processes but face growing pressures from metal contamination and oxygen depletion. In this study, we derived the quantitative thresholds for effects of sediment pollutants on microbial diversity and their functions using the pollution-induced community tolerance (PICT) concept. Ecotoxicological EC10 thresholds for sediment microbiomes were calculated based on both biodiversity loss and functional gene expression measured through metatranscriptomics. A 10-day mesocosm experiment was conducted with sediments from a historically Cu-contaminated harbour (Oskarshamn) and a pristine reference site (Askö) in the Baltic Sea, exposed to five Cu doses (50–700 mg L⁻¹) under oxic and hypoxic conditions. Communities from Oskarshamn showed consistently higher EC10 threshold values for both diversity and Cu resistance/efflux gene expression, indicating functional pre-adaptation to long-term contamination. Under hypoxic condition, gene-based EC10 values were up to five times higher than under oxic conditions. Random Forest modelling further identified porewater Cu and dissolved oxygen as dominant predictors of Cu partitioning and microbial sensitivity. This study establishes, for the first time, a microbial species sensitvity distribution (SSD) framework linking geochemical drivers with molecular and community responses to derive site-specific EC10 thresholds for improved sediment risk assessment.

The energy sector is the most influential industry for the successful functioning of the states’ economy and general daily life maintenance. One of the future targets of the Baltic states is reaching the continental European energy network integrity and securing it. Furthermore, regional independence of the energy networks apart from eastern neighboring countries is of the most significant importance as the existing electricity grid is still synchronized with the supply systems of Russia and Belarus. During a tense geopolitical situation, it is crucial to search for alternative energy production options in terms of environmentally friendly and sustainable energy sources and economically viable alternatives. The Baltic states already have hydropower capacity, and Latvia is a leading country in this regard. Also, the energy production sector based on wind power use is developing significantly, and in this niche, the dominant one is Lithuania. Another alternative mentioned at the interstate level is the construction opportunity of a small modular reactor for nuclear fission, where Estonia has taken the first assessment step. In any case, but most significantly for the latter option, the regional geological and environmental situation determines where such strategic energy objects can be safely situated. The dynamic progression of climate change in boreal regions, including the Baltic states, may endanger the structural integrity of energy production infrastructure objects; therefore, geotechnical investigation serves as a key stage in the objects’ construction planning.

The surge in industrialization has led to a significant increase in contaminants deposited into marine sediments, transforming them from sinks into secondary sources of pollutants that may affect sediment-living biota and expose pelagic organisms through the food chain or through diffusive fluxes and particle resuspension, in turn affecting the sustainability of the blue economy. Hence, to combat environmental risks due to contaminated sediments, remediation operations through, traditionally dredging and isolation capping methods have been employed. These methods are not only costly affairs but also have disadvantages such as increasing the resuspension of particle-bound contaminants and increasing the risks of spreading the contaminants to other areas. Moreover, dredging and deposition of contaminants on a landfill only displaces the problem from one place to another and also adds a burden to landfills. Recently, in situ treatment methods like thin-layer capping with reactive sorbents [such as activated carbon (AC)] have been implemented as a more cost-effective and environmentally sustainable alternative to dredging for remediation. These treatment methods are often selected solely based on total contaminant concentrations in the sediments, rather than on the potential toxicity of the contaminants. As a large part of the sediment-associated contaminants are often strongly bound to the sediment and not readily available to the benthic organisms, the environmental risks of contaminated sediments are often overestimated, which may lead to unnecessary remediation decisions. Given this perspective, employing a triad-based risk assessment for contaminated sediment can play a crucial role in determining the most appropriate treatment method. This approach considers all three elements – chemistry, toxicity, and ecology – and facilitates a systematic process for the comprehensive evaluation and management of contaminated sites, drawing upon multiple lines of evidence. This cumulative approach will further lay down the criteria for deciding the feasibility of remediation methods for marine contaminated sediment. This, in turn, will help in paving the way towards more sustainable development goal targets. In essence, this chapter offers readers the opportunity to delve into a study that builds upon prior research to enhance the precision of risk assessments for the purpose of environmental management.

Microplastics (MPs) have become a critical pollutant, accumulating in aquatic ecosystems and posing significant environmental and human health risks. Approximately 5.25 trillion plastic particles float in global oceans, releasing up to 23,600 metric tonnes of dissolved organic carbon annually, which disrupts microbial dynamics. MPs arise from the breakdown of larger plastics, degraded by photodegradation, thermal degradation, and biological processes, which are influenced by polymer type and environmental factors. As carriers, MPs absorb and transport contaminants such as heavy metals, per- and polyfluoroalkyl substances (PFAS), and persistent organic pollutants (POPs) across trophic levels, thereby increasing toxicity within food webs. Key aquatic organisms, including microalgae, molluscs, and fish, experience cellular toxicity, oxidative stress, and disruptions in essential functions due to MP ingestion or adhesion, raising concerns about their bioaccumulation in humans through ingestion, inhalation, and dermal contact. The complex surface chemistry of MPs enhances their pollutant adsorption, a process modulated by environmental pH, salinity, and contamination levels, while aging and structural attributes further impact their bioavailability and toxicity. This review consolidates knowledge on MPs’ occurrence, transformation, pollutant interactions, and methodologies for sampling and analysis, emphasizing advancements in spectroscopy and imaging techniques to improve MP detection in aquatic environments. These insights underscore the pressing need for standardized analytical protocols and comprehensive toxicological research to fully understand MPs’ effects on ecosystems and human health, informing future mitigation strategies and policy development.

Sediments contaminated with hazardous metals pose risks to humans and wildlife, yet viable management options are scarce. In a series of laboratory experiments, we characterized Polonite® – an activated calcium-silicate – as a novel sorbent for thin-layer capping of metal-contaminated sediments. We tested a fine-grained by-product from the Polonite production as a cheap and sustainable sorbent. First, Polonite was reacted with solutions of Cu, Pb, and Zn, and the surface chemistry of the Polonite was examined using, e.g., scanning electron microscopy to investigate metal sorption mechanisms. Batch experiments were conducted by adding Polonite to industrially contaminated harbor sediment to determine sorption kinetics and isotherms. Importantly, we measured if the Polonite could reduce metal bioavailability to sediment fauna by performing digestive fluid extraction (DFE). Finally, a cap placement technique was studied by applying a Polonite slurry in sedimentation columns.

The results showed rapid metal sorption to Polonite via several mechanisms, including hydroxide and carbonate precipitation, and complexation with metal oxides on the Polonite surface. Isotherm data revealed that the sediment uptake capacity (K_f) for Cu, Pb, and Zn increased by a factor of 25, 21, and 14, respectively, after addition of 5% Polonite. The bioavailability of Cu, Pb, and Zn was reduced by 70%, 65%, and 54%, respectively, after a 25% Polonite addition. In conclusion, we propose that sediment treatment with low doses of the Polonite by-product can be a cheap, sustainable, and effective remediation method compared to other more intrusive methods such as dredging or conventional isolation capping.