Development and applicability of artificial reference sediments for interpretation of results and evaluation of toxicity with the Microtox Solid-Phase Bioassay

The Microtox® Solid-Phase Test estimates the toxicity of sediments by measuring light reduction in the photoluminescent bacterium, species Photobacterium phosphoreum, upon exposure to the sediment. However, particles less than 45 microns in diameter often remain suspended in the diluent during testing and pass through the filter with the bacteria, scattering the luminescence of the bacteria and giving the illusion of toxicity. In order to determine the extent of this scattering effect, site-specific artificial reference sediments can be constructed from non-toxic components to provide a baseline of light inhibition by clay. As the concentration of clay in the sediment increases, the measurable light output decreases. From this relationship and the baseline light inhibition as determined from artificial sediments, the actual toxicity of the test sediments due to contaminants can be measured.