Algal growth inhibition test in filled, closed bottles for volatile and sorptive materials

Exposure concentrations of many hydrophobic substances are difficult to mai ntain in algal growth inhibition tests performed in open agitated flasks. T his is partly because such compounds tend to volatilize from aqueous soluti on and partly because of sorption to the algal biomass as well as to the re st container. A simple filled closed bottle test with low algal densities a nd bicarbonate enrichment is described here as an approach to minimize the loss of test material from solution. The algal medium was enriched with 300 mg NaHCO3/L, the pH was adjusted to 7.0 by addition of HCl, and the result ing dissolved CO2 concentration supported maximum algal growth rates withou t pH drift for algal densities up to 4 mg dry weight/L. Two-day toxicity te sts with kerosene were performed with this new test design and compared wit h an open bottle test and with a closed bottle test with headspace. Exposur e concentrations of the volatile fraction of kerosene decreased by 99% in t he open test, by 77% in the closed flask test with headspace, and by 16% in the filled closed bottle test. Algal growth inhibition was observed at muc h lower additions of kerosene in the new test design because of the improve d maintenance of a constant exposure.