Millions of tons of bottom sediments are dredged annually all over the world. Ports and bays need to extract the sediments to guarantee the navigation levels or remediate the aquatic ecosystem. The removed material is commonly disposed of in open oceans or landfills. These disposal methods are not in line with circular-economy goals and additionally are unsuitable due to their legal and environmental compatibility. Recovery of valuables represents a way to eliminate dumping and contributes towards the sustainable extraction of secondary raw materials. Nevertheless, the recovery varies on a case-by-case basis and depends on the sediment components. Therefore, the first step is to analyse and identify the sediment composition and properties. Malmfjärden is a shallow semi-enclosed bay located in Kalmar, Sweden. Dredging of sediments is required to recuperate the water level. This study focuses on characterizing the sediments, pore water and surface water from the bay to uncover possible sediment recovery paths and define the baseline of contamination in the water body. The results showed that the bay had high amounts of nitrogen (170–450 µg L−1 ), leading to eutrophication problems. The sediments mainly comprised small size particle material (silt, clay and sand proportions of 62 %–79 %, 14 %–20 %, 7 %–17 %, respectively) and had a medium–high level of nitrogen (7400–11 000 mg kg−1 ). Additionally, the sediments had little presence of organic pollutants and low–medium concentration of metals or metalloids. The characterization of the sediments displays a potential use in less sensitive lands such as in industrial and commercial areas where the sediments can be employed as construction material or as plant-growing substrate (for ornamental gardens or vegetation beside roads).

Contamination associated with metals is a critical concern related to their toxicity, persistence, and bio-accumulation. Trace elements are partitioned into several chemical forms, which some are more labile during fluctuations in the environment. Studying the distribution of metals between the different chemical fractions contributes to assess their bioavailability and to identify their potential risk of contamination to surrounding environments. This study concerns the speciation of metals (Pb, Cr, Ni, Zn and Fe) from sediments coming out from Malmfjärden bay, Sweden. The aim was to assess the potential risk of metal pollution during present and future dredging as well as while using dredged sediments in beneficial uses. The Tessier speciation procedure was chosen, and the results showed that low concentrations of metals were associated with the exchangeable fraction. In contrast, the major concentrations were linked to the residual part. The risk indexes (contamination factor and risk assessment code) showed that, during dredging activities, there is a low concern of pollution for Cr, Ni and Fe and a medium risk for Pb and Zn. Additionally, in all elements, the sum of non-residual concentrations was below the Swedish limits for using dredged sediments in sensitive lands. The findings suggested that the investigated metals in Malmfjärden sediments are related to low risks of spreading during using in beneficial uses.

Worldwide, sediments are dredged from water bodies to guarantee proper water levels and remediate aquatic ecosystems. Dredged sediments contain metals that could interfere with recycling if the concentrations overpass permissible limits. Washing of elements from sediments represents a technique to decrease the concentration of metals, and it could introduce a new source of elements. The current study aimed to employ ethylenediamine-tetraacetic acid (EDTA) and ethylenediamine-disuccinic acid (EDDS) and investigate the effect of operational parameters (concentration and pH) on the chemical extraction of metals from dredged sediments. Core sediments were extracted from sampling stations around Malmfjärden bay, Sweden. The results suggested that lead, zinc and copper were the elements with higher extraction rates, followed by arsenic and nickel. Chromium was poorly extracted. EDTA was more efficient than EDDS in dissolving the elements. Moreover, acidic conditions offered higher extraction rates for As using both chelators and for Pb employing EDTA. The 0.05 M concentration presented a higher mean extraction rate than 0.01 M for Cu, Cr and Ni for EDTA and EDDS. The findings in this study suggest that sediment washing is a promising technique to decrease metal concentrations in sediments and enhancing the feasibility to use the material for beneficial uses.