Arsenic in Lake Lansing, michigan

Abstract

Lake Lansing was treated with sodium arsenite for macrophyte control in 1957. Two 2.5-m cores from deep portions of the basin showed the historical consequence of this treatment. Maxima of 330–340 μg As g⁻¹ dry weight occurred at a depth interval of 0.15–0.30 m; background was 17–20 ppm As. An arsenic mass balance budget for the lake for June 1978 to June 1979 showed it lost more arsenic than it received. Internal loading of the water from the sediments was occurring; > 85% of the area of surficial sediments had concentrations two to six times background. From laboratory experiments, we hypothesize Fe³⁺ controls arsenic concentration over aerobic sediments; As(III) increases in anoxic water with conversion of Fe³⁺ to Fe²⁺ and As(V) to As(III) at the sediment surface. As(III) in water diminishes during prolonged anoxia by reaction with S²⁻. As(III) and Fe²⁺ are oxidized upon aeration of anoxic water, and As(V) is taken out of solution with ferric iron in a manner similar to phosphate. Arsenic concentrations observed in the lake over an annual cycle fit these expectations.