State Changes in Laboratory Microecosystems in Response to Chemicals from Three Structural Groups

Generic mixed-flask culture microecosystems derived from small lake and pond planktonic communities were used to evaluate the effects of selected alcohols, aniline derivatives, and aromatic amides on pH and dissolved oxygen—ecosystem state variables which reflect energy flow and nutrient cycling processes within the systems. Using changes in these variables as indicators of effect, the relative toxicity rankings of compounds within each group were determined and compared with the toxicity rankings established by fathead minnow acute toxicity tests. The ecosystem-level relative toxicity of three alcohols agreed with the toxicity rankings based on fathead minnow 96-h lowest-observed-effect levels (LOELs). The toxicity rankings of aniline and three of its derivatives were similar to those for the alcohols. For both alcohols and anilines, the ecosystem state variables were more sensitive than the fathead minnow lethality for the least toxic members of the group. A group of aromatic amides, which included an inhibitor of photosynthesis and an uncoupler of oxidative phosphorylation, showed the most departure from the fathead minnow toxicity ranking. The amide compound that was least toxic to fathead minnows was most toxic at the ecosystem level. These examples can be considered representative of situations that might be encountered in an early stage of ecosystem-level testing. For less well known toxicants, microcosm functional testing could assist in identifying chemicals that require more elaborate test procedures.