Concentration and toxicity of microcystin-LR in compartments and organisms of aquatic food webs.

摘要

Microcystin-LR (MC-LR) is one of the most commonly-occurring of more than 50 toxic peptides produced by cyanobacteria in eutrophic lakes worldwide. In this thesis, I studied the concentration of MC-LR in water and organisms of lakes, relationship of MC-LR concentrations to environmental variables, and the toxicity to fish (rainbow trout), in comparison to mammals (mice).;Over the five years of study, MC-LR (detected by high performance liquid chromatography) was found in 24 of 28 Alberta lakes, 6 of 11 farm dugouts and one of three storm water retention ponds located in the City of Edmonton.;MC-LR concentration in the phytoplankton was most variable within and between years in lakes, and to a lesser extent, spatially within a lake. This variability was associated with changes in the abundance and biomass of the cyanobacterium Microcystis aeruginosa (r up to 0.77).;MC-LR concentrations in water (;In laboratory toxicity trials, an intraperitoneal (i.p.) dose of ;Lesions were evident in both the liver and kidney in fish. The main lesion observed in the livers of fish was liquifactive necrosis (rupture of the plasma membrane leaving organelles floating in a milieux of cellular debris). Plasma activities of lactate dehydrogenase, and aspartic acid and alanine aminotransferases were significantly higher in MC-LR-exposed fish than control fish in i.p. and oral exposure trials, indicative of hepatic injury. Lower plasma enzyme activities and a reduced extent and severity of liver damage in fish from the oral relative to the i.p. trial suggested a low efficiency of transport of the toxin from the digestive tract. Kidney lesions in the fish at the highest doses consisted of dilation of Bowman's space and necrosis of tubular epithelium of the kidney. Additionally, necrosis of the villi of pyloric caecae and the intestine was observed in fish in the oral trial.;My studies indicate that MC-LR is much more prevalent in eutrophic lakes than is suggested by the limited number of published studies, and that the concentration of toxin may be regulated by the concentrations of the nutrients phosphorus and nitrogen. Concentrations of MC-LR detected in aquatic invertebrates, accumulated by grazing on phytoplankton from the hypereutrophic lakes, may be sufficient to cause adverse health effects including damage to the liver, kidney and gastrointestinal tract in fish. (Abstract shortened by UMI.).