Testing of coloured samples for toxicity by the algal-ATP bioassay microplate technique.

Algal-ATP bioassay is a relatively simple, inexpensive, reliable and fast testing procedure for toxicity assessment. This algal growth inhibition bioassay technique using Selenastrum capricornutum was used to assess the toxicity levels in pulp and paper mill and thermomechanical mill effluent samples. Pulp and paper mill and thermomechanical mill effluent samples contain a wide range of colours due to certain physico-chemical properties of the test samples. The optical densities of the samples ranged from 0.27 to> 2.0 (a 600 nanometer). The colour variations in the test samples may interfere with ATP measurements. This paper presents data on the nature of interferences due to certain physico-chemical properties of the test sample and the usefulness of developed controls to overcome the problems for a more realistic toxicity assessment of coloured waste samples.