Baltic Sea sediments : Source and sink for metal contamination

Sammanfattning: The Baltic Sea sediments record spatial and temporal information about metalsand metalloids (hereafter referred to as metals), which could help to understandthe past and present contamination sinks in different basins. In addition, giventhe expanding anoxic zones in the Baltic Sea, the response of metals to artificialreoxygenation is poorly understood. This thesis calculated background valuesfor As, Cd, Co, Cu, Pb, U, and Zn and measured their concentration in sedimentsfrom pre-industrial to recent times. Metal concentration peaks during the1970—1980s and clearly decline till present-day, possibly owing to effectivepollution control measures. Furthermore, anoxic Baltic Proper sedimentssubjected to reoxygenation experiments showed that As, Ba, Co, K, Mn, Rb, U,Sr, and Mo are released to bottom waters, suggesting possible aggravation ofmetal pollution if such mitigation option is applied.During previous coastline transgression (5000 years before CE), rich sulfidicsediments (known as potential acid sulfate soils) were deposited and laterexposed to air by natural processes and/or by artificial drainage systems ofcoastal areas of the present-day Baltic Sea. Oxidation of sulfidic phases resultedin the formation of acid sulfate soils, which are a potential source of metalcontamination to drainage areas. This thesis investigated an area in Kristianstad,southern Sweden, in which metal contamination is sourced from acid sulfatesoils. From the acid sulfate soil site, the dispersion showed enrichment of Fe inthe adjacent wetland in the form of akaganeite/schwertmannite, identified usingX-ray absorption spectroscopy. Furthermore, Be, U, rare-earth elements, and Alwere enriched in the drain sediments. Simultaneously, metals such as Mn, Co,Ni, Zn, and Cd were not or only marginally enriched in the drain sediment. Aremediation experiment to remove metals from the drainage water using spentcoffee-grounds and dissolved humic acid was performed. The spent coffeegroundsefficiently removed Al, Ca, Co, Fe, Mn, Ni, and Zn via adsorption, butfail to remove S from the acid sulfate soil drainage. However, the dissolvedhumic acid removed up to 25% of the S from the drainage.