Temporal variabilities of the concentrations of intra- and extracellular microcystin and toxicMicrocystis species in a hypertrophic lake, Lake Suwa, Japan (1991-1994)

Abstract

Temporal variability in the concentration of toxic heptapeptide microcystin was studied during the warm season of four years (1991–1994) in a hypertrophic lake (Lake Suwa) in central Honshu, Japan. Lake water samples (ca. 5 L) were filtered to separate intracellular microcystin (cell fraction) from extracellular microcystin (filtered lake water fraction). These fractions were analyzed to measure the total quantity of microcystin in lake water. Total amounts of extra- and intracellular microcystin were measured with high performance liquid chromatography. Concentrations of intracellular microcystin usually exceeded concentrations of extracellular microcystin (24 out of 26 times). High concentrations of intracellular microcystin were found during the exponential growth phase of the blooms, whereas concentrations of extracellular microcystin were highest at the end of the blooms. However, concentrations of extracellular microcystin remained very small (<4μg/L) compared to the levels of intracellular microcystin. The relatively higher percentages of microcystin in filtered lake water ( > 20%) at the end of blooms suggests that release of microcystin from cells occurs during senescence and the decomposition period of Microcystis cells. © 1998 John Wiley & Sons, Inc. Environ Toxicol Water Qual 13: 61–72, 1998