The biodegradability of linear alkylbenzene sulfonate (LAS) was studied in water samples collected from a receiving stream at locations above and below the discharge of a municipal wastewater treatment plant. Rates of primary biodegradation were determined for a commercial LAS mixture by a modified methylene blue-active substance method. Rates of LAS ultimate degradation were determined by radiochemical methods, using a C12 LAS homolog uniformly labeled with "4C in the benzene ring. The C12 LAS was tested at low concentrations (50 and 500 ,tg/liter) comparable to those existing in the receiving stream. Loss of methylene blue-active substance response over time occurred rapidly in water samples containing sediment collected from below the treatment plant, with an estimated half-life for LAS of 0.23 days. Evolution of 14CO2 during mineralization of the benzene ring occurred rapidly in the same samples, with a half-life for the benzene ring of 0.73 day. Mineralization of the benezene ring was also observed in river water containing no sediments and in river water and sediment samples collected from above the treatment plant. However, the rate of degradation was reduced in these cases, with half-lives for ring carbon ranging from 1.4 to 14 days. Although LAS degradation was enhanced in the presence of sediments, adsorption of LAS to the clay-silt fraction of river sediments was low, and most of the radioactivity was bound to biomass.

An algal toxicity test has been developed specifically for use in the environmental safety assessment of new chemicals. The test is based on the Algal Assay Procedure (Bottle Test) but has been modified in order to make the procedure useful for toxicity assessment. A five-day exposure of freshwater or marine unialgal cultures to a range of test material concentrations is followed by a nine-day recovery period in the absence of the test material. Cell counts or in vivo fluorescence measurements made during the study allow the quantification of toxic responses ranging from reduced growth, through the algistatic response, to the algicidal response. The primary toxicity effect sought in this method is the algistatic response, which is both easily determined and environmentally meaningful. The algistatic concentration of a test material, as derived by this method, is the concentration that causes no net change in cell number after chronic exposure but permits regrowth when the cells are resuspended in fresh media without the test material. The environmental significance of this type of measurement relative to other measurements of algal toxicity is discussed.

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