Honors College Theses

Publication Date



Biology (B.S.B.)

Document Type and Release Option

Thesis (open access)

Faculty Mentor

Dr. Risa A. Cohen


Industrial discharge, such as textile effluent, is a major source of chemical mixtures to surface waters. The effects of these mixtures on interacting aquatic organisms can be difficult to predict. We hypothesized that individual chemical effects on phytoplankton and a zooplankton grazer are altered by the presence of other chemicals in mixtures. Microcosms containing a phytoplankton food source (Chlorella sp.) and a zooplankton grazer (Daphnia magna) were exposed to THPC, ammonium, and hydrogen peroxide in a fully crossed design in a greenhouse for one week. Phytoplankton abundance was quantified and zooplankton response was measured as mortality and stress. THPC increased D. magna mortality by >90%, regardless of whether it was alone or in mixture. In contrast, D. magna stress increased only in the treatment with all three chemicals. Abundance of Chlorella sp. was highest in the presence of THPC alone, but the increase was likely due to the absence of D. magna grazers rather than growth stimulation by THPC. In mixtures with THPC the Chlorella sp. cell densities decreased despite high D. magna mortality, suggesting mixtures were more toxic to the algae. Thus, while the chemical mixtures generally decreased Chlorella sp. density relative to each chemical individually, the presence of THPC was responsible for the nearly complete loss of D. magna. This differential sensitivity of planktonic organisms to textile chemicals indicates a clear need for community-level approaches to elucidating mixture effects on species composition and energy transfer in aquatic systems.