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Atrazine toxicity in microalgae : differential sensitivities, predictive cellular characteristics, and subcellular alterations in macromolecular constituents

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Title	Atrazine toxicity in microalgae : differential sensitivities, predictive cellular characteristics, and subcellular alterations in macromolecular constituents
Author	Weiner, Jeannette Anne
Date	2002
Affiliation/College	College of Graduate Studies
Department	Molecular and Cellular Biology and Pathobiology
Extent	viii, 143 leaves : ill.; 29 cm
Source	WA 240 W423a 2002
Subject.MeSH	Academic Dissertations Academic Dissertations--South Carolina Atrazine--toxicity Microalgae--cytology
Collection	MUSC Theses and Dissertations
Contributing Institution	Waring Historical Library (MUSC)
Rights	Copyright is held by the author.
Language	English
Type	Text
Format	application/pdf
Media Type	Manuscripts
Resource Identifier	mtd2002_weiner_ja
Abstract	Atrazine is a widely used selective herbicide that often enters aquatic ecosystems as a result of agricultural non-point source runoff. This research addresses the central hypothesis that microalgal species are differentially sensitive to atrazine exposure. Specifically, the following hypotheses are investigated: 1) sensitivity to atrazine varies among microalgal species; 2) differential sensitivities of microalgae are correlated with differing cellular characteristics; and 3) atrazine causes species-specific alterations in the subcellular macromolecular content of individual microalgal cells. In this project, the effect of atrazine (a triazine herbicide) on microalgal growth and productivity is established. Five phytoplankton species are used to assess atrazine toxicity on a range of algal species representing different taxonomic groups and habitat requirements: Pseudokirchneriella subcapitata (freshwater chlorophyte), Dunaliella tertiolecta (marine chlorophyte), Phaeodactylum tricomutum (marine diatom), Synechococcus sp. (marine cyanobacterium), and Isochrysis galbana (marine prymnesiophyte). Growth rate and productivity are used as functional endpoints to calculate 96-hour ECso values for each species, ranging from 37.20 Jlg/L to 122.08 Jlg/L atrazine. Synechococcus sp. was the most sensitive species followed by P. subcapitata, P. tricomutum, D. tertiolecta, and 1. galbana. Although functionally impaired by atrazine, vital staining revealed that atrazine does not cause significant mortality in any of the species tested. Microalgal sensitivities to atrazine are also examined in terms of cell SIze attributes and atrazine uptake capacity. Each species was exposed to 14C-atrazine at its growth rate EC50 concentration and correlations between algal species sensitivity to atrazine and compound uptake, cell dry weight, cell volume and cell surface area were examined using linear regression analysis. Results reveal a significant correlation between atrazine uptake and species sensitivity to atrazine. Cell size measurements (based on dry weight, biovolume and surface area) are not significantly correlated with atrazine sensitivity, but are significantly correlated with atrazine uptake. Additionally, this research characterizes inorganic carbon allocation into microalgal macromolecules and examines how this allocation is altered by atrazine exposure. Following atrazine exposure, inorganic 14C uptake and percent of inorganic 14C assimilated into low molecular weight (LMW) molecules, lipids, polysaccharides, and protein are determined. Despite decreased growth rate in all species, total carbon uptake varied. Total carbon uptake was unaffected in P. subcapitata and 1. galbana but increased in Synechococcus sp. In contrast, atrazine exposure caused a decrease in D. tertiolecta and P. tricomutum carbon uptake per cell. In P. subcapitata and D. tertiolecta, carbon allocation into LMW molecules increased and carbon allocation into protein decreased with increasing atrazine concentrations. D. tertiolecta also increased carbon allocation into lipids and polysaccharides in the highest atrazine treatment. Synechococcus sp., contrary to the chlorophytes, decreased carbon allocation into LMW molecules and increased carbon allocation into protein with atrazine exposure. P. tricomutum decreased carbon allocation into protein at the highest atrazine concentration tested. No significant macromolecular changes were found in 1. galbana exposed to atrazine. In addition, there was a significant correlation between total cellular carbon uptake and carbon allocation into protein. These changes in the macromolecular content of individual microalgal cells can be used to indicate cellular health and to further investigate secondary effects of atrazine. Tools developed by these experiments have the potential to identify, assess, and predict the effects of contaminants on microalgal communities. Because of atrazine's widespread use and persistence in the environment, we need to have a clear understanding of its effects in aquatic ecosystems. The current study shows a wide range of atrazine sensitivity among microalgal species. Thus, a battery of species is recommended for testing to assess potential impacts to algal communities. Additionally, in natural habitats algal communities exposed to atrazine, effects are likely on both population size and productivity. Alterations in the macromolecular composition of microalgal species may cause a nutritional problem for higher trophic levels. The current study shows that the presence of atrazine causes microalgal cells to reduce in population size (i.e. growth) and productivity and causes a reduction in cellular size (biovolume, surface area, and dry weight) and macromolecular, or nutritional, composition. Therefore, those species feeding on microalgae have fewer, smaller, nutritionally altered cells now making up their diet. Thus, their energy per mass uptake is reduced. Clearly, understanding its effects at the microalgal level is crucial to the protection and maintenance of aquatic ecosystems.

Atrazine toxicity in microalgae : differential sensitivities, predictive cellular characteristics, and subcellular alterations in macromolecular constituents

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