About the Selenastrum capricornutum Algal Test

The protocol used in tests with the green algae Selenastrum capricornutum, in the Aquatox Research facility, is drawn from SHORT-TERM METHODS FOR ESTIMATING THE CHRONIC TOXICITY OF EFFLUENTS AND RECEIVING WATER TO FRESHWATER ORGANISMS (EPA-600-4-91-002; July 1994). The test is designed to assess the effects of chemical products or environmental samples on the growth of the green algae after a 96-hr incubation period. Growth can be measured by any one of three different approaches; automated or manual cell counts, chlorophyll content, or turbidity (absorbance).

Aquatox Research has adopted the turbidity approach to assessing growth of Selenastrum capricornutum. Turbidity is determined through absorbance readings at 750 nm on a standard spectrophotometer. The relationship between turbidity and cell counts, in the Aquatox Research facility, was established through the generation of a standard curve comparing manual microscopic cell counts and absorbance as illustrated in the figure below. Each point on the graph represents the mean of cell counts on three subsamples of Selenastrum capricornutum from the same flask.

absorbance/algal counts standard curve thumbnail

R2 for the relationship between absorbance and cell counts is 0.988 illustrating the potential for a high degree of confidence in predicting cell counts from green algal culture absorbance readings over the range of the curve.

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