Algal tests with soil suspensions and elutriates: A comparative evaluation for PAH-contaminated soils Anders Baun * , Kasper B. Justesen, Niels Nyholm Environment and Resources DTU, Building 115, Groundwater Research Centre, Technical University of Denmark, DK-2800 Lyngby, Denmark Received 13 October 2000; accepted 26 March 2001 Abstract An algal growth inhibition test procedure with soil suspensions is proposed and evaluated for PAH-contaminated soil. The growth rate reduction of the standard freshwater green alga Pseudokirchneriella subcapitata formerly known as Selenastrum capricornutum) was used as the toxicity endpoint, and was quanti®ed by measuring the ¯uorescence of solvent-extracted algal pigments. No growth rate reduction was detected for soil contents up to 20 g/l testing ®ve non- contaminated Danish soils. Comparative testing with PAH-contaminated soil elutriates and soil suspensions showed that the suspensions had toxicity endpoints 2.5±3000 times lower than tests with the corresponding elutriates. Algal growth inhibition tests with soil suspensions are recommended for screening purposes as a supplement to elutriate testing. Experiments with a phenanthrene-spiked soil, showed that the sorbed compound did not contribute to the toxicity. However, the soil did act as a reservoir for phenanthrene, allowing desorption to occur continuously during the algal test which maintained higher concentrations of phenanthrene in the dissolved phase. Phenanthrene-spiked soil incubated for 90 days before algal testing, resulted in a reduction of the toxicity to P.subcapitata by a factor of 76 from EC 10  0:3 to 23.6 g soil/l). However, during this 90-day period the total concentration of phenanthrene in the soil decreased by 38% from 322 to 199 mg/kg) indicating that phenanthrene in the aged soil had become less bioavail- able. Ó 2002 Elsevier Science Ltd. All rights reserved. Keywords: Algal test; Bioavailability; Contaminated soil; Selenastrum capricornutum; PAH; Phenanthrene; Pseudokirchneriella subcapitata 1. Introduction Complex samples from polluted environments, such as contaminated soil, are often characterized by labori- ous and expensive chemical analysis that may provide limited information for evaluation of environmental risks. Chemical analysis cannot assess directly the bio- availability or the combined eects on organisms of all identi®ed chemicals present. Several studies have shown that data on commonly found and analyzed pollutants are often a doubtful basis for predicting the toxic po- tential of samples of complex composition e.g. Miller et al., 1985). Generally speaking, identi®ed pollutants can often account only for a small fraction few percent) of the full toxic potential of a sample and information on the bioavailability of the pollutants, which can be crucial in a risk assessment, is usually not available. Simple bioassays, on the other hand may provide a direct quantitative measure of actual environmental toxicity of contaminated soils. The toxicity tests of soils and sediments determined with aquatic organisms are usually carried out with aqueous elutriates Miller et al., 1985; Thomas et al., 1986; Athey et al., 1989). Elutriate Chemosphere 46 2002) 251±258 www.elsevier.com/locate/chemosphere * Corresponding author. Tel.: +45-4525-1567; fax: +45-4593- 2850. E-mail address: ab@imt.dtu.dk A. Baun). 0045-6535/02/$ - see front matter Ó 2002 Elsevier Science Ltd. All rights reserved. PII:S0045-653501)00097-2