Bioaccumulation of microcystins in the food web: A field study of four Swedish lakes

Abstract

The transfer of microcystins (MC) up the food chain was measured in 4 lakes in central Sweden; Ekoln, Lilla Ullfjärden, Valloxen, and Storsjön. In lakes Ekoln and Valloxen, Microcystis aeruginosa was the dominant cyanobacterium, while the oscillatorian species Planktothrix prolifica form dense blooms in Lake Lilla Ullfjärden. The cyanobacterial composition in Lake Storsjön was more diverse with several Microcystis and Dolichospermum species. All dominant taxa are well-known producers of hepatotoxic MC. The highest recorded MC in the water samples from Lake Lilla Ullfjärden was measured in the bloom of P. prolifica (35 μg L-1). The highest MC content was measured in invertebrates; however, the MC concentration was usually low in fish. Maximum levels were 9 μg g-1 dry weight (dw) in zooplankton, 10 μg g-1 dw in benthos, and 2.7 μg g-1 dw in fish (smelt) liver. In fish muscle the highest recorded levels were 0.10-0.18 μg g-1 dw in bleak and smelt from Lake Lilla Ullfjärden and in pike-perch and roach from Lake Storsjön. Based on the World Health Organization's tolerable daily intake value of 0.04 μg kg-1 body weight, we conclude that any risk related to MC from human consumption of fish from these lakes is minimal.