ARSENIC IN STREAMS AND LAKES IN NORTHERN SWEDEN

Arsenic is present in elevated amounts in the Västerbotten county in Northern Sweden. The source is from sulfide ores and mineralisations but also to a large extent from metamorphic sediments containing up to 1 % sulfur. Weathering since glacial times has oxidized sulfides disseminated in the tills and this weathering has been accentuated through extensive forest drainage in recent decades amounting to as much as more than 10 km per km². B-horizons in the till show elevated arsenic contents and in wetlands a remobilization of arsenic occur releasing ferrous iron and arsenic into groundwater discharges. A re-oxidation of the ferrous iron forming ferric oxyhydroxides act as efficient sinks for the arsenic forming precipitates with as much as 0.5 % As and sandy sediments with a few hundreds of mg/kg As. Lakes have moderate amounts of arsenic generally below 10 mg/l but with an extreme at 18 mg/l As. This arsenic tends to be well correlated with iron in lake water (r² up to 0.97) which in turn is correlated to organic carbon (DOC and TOC). In situ dialysis in lakes (10 kDa and 1 kDa) show that arsenic is largely found in the larger molecular sizes indicating low bioavailability. Speciation of arsenic in a few pikes and brown trout indicate slightly elevated amounts of organic As-species like arsenobetaine but background values of inorganic arsenic. Thus while the total arsenic levels in lake water are elevated this does not appear to be of public health concern.