Toxicological Investigation of Soils with the Solid-phase Flash Assay: Comparison with Other Ecotoxicological Tests

A new direct-contact toxicity test, the solid-phase flash assay, which utilises photobacteria in direct contact with soil particles during the exposure, was evaluated on four soil samples. Samples HTNT1 and HTNT2 originated from former military sites in Germany, and were highly contaminated with nitroaromatics (approximately 20g/kg), lead and polycyclic aromatic hydrocarbons. Samples LMKW1 and LMKW2, from bioremediation stacks in Germany, were mainly contaminated with mineral oils. The solid-phase flash assay was applied to soil-water slurries, and the results were compared with the toxicity data for soil-water extracts obtained by using various conventional ecotoxicological tests, in which photobacteria, crustaceans, protozoa and algae were used as test organisms. The LMKW1 and LMKW2 samples were not toxic (EC20 > 12.5%) according to all the tests applied, except for the Photobacterium phosphoreum conventional luminescence-inhibition test for LMKW1 (15-minute EC20 = 5.4%(. The HTNT1 and HTNT2 samples were toxic according to all the tests applied, with the majority of EC20 values being lower than 1%. The solid-phase flash assay (1 minute of extraction and 30 seconds of exposure time) gave comparable results to the conventional tests. Therefore, this flash assay could be applied as a fast screening test in parallel with conventional toxicity tests that use soil 24-hour extracts. The flash assay results will be ready by the start of the conventional assays, and could serve as range-finders for these slower and more expensive tests.