title: Combination effect of light and toxicity in algal tests.
abstract: The sensitivity of Scenedesmus subspicatus against potassium dichromate is positively correlated to the photon flux density during the algal growth inhibition test. Low photon flux densities led to significantly reduced maximum effects and higher EC50 levels. To improve the testing of colored substances, we distinguished between the toxic effect (chemical part, represented by potassium dichromate) and the shading effect (physical part, simulated by reduced light intensities during the test) of a hypothetical light absorbing substance. The contribution of these single effects to the total inhibition varied greatly. At high concentrations of potassium dichromate (1.6 and 3.2 mg L(-1)) the physical part never exceeded 25% of the total inhibition, not even at strongest light reduction, while at low concentrations (0.2 and 0.4 mg L(-1)) the physical effect became more prominent when halving the amount of available light. Further, the combination effect of the chemical and the physical effect could be calculated well only by using the concept of independent action. Thus, if chemical and physical effects are measured in combination, as is the case in tests with dye-stuffs, the current test protocol for the algal growth inhibition test may lead to incorrect estimations of the toxic potential.
authors.affiliation: Department of General Biology, Aachen University of Technology, Germany. cleuvers@bio2.rwth-aachen.de
authors.forename: Michael
authors.initials: M
authors.lastname: Cleuvers
authors.forename: Rolf
authors.initials: R
authors.lastname: Altenburger
authors.forename: Hans Toni
authors.initials: HT
authors.lastname: Ratte
mesh_terms: D000460:Chlorophyta; D004396:Coloring Agents / Q000633:toxicity*; D007928:Lethal Dose 50; D008027:Light; D011192:Potassium Dichromate / Q000633:toxicity*; D015203:Reproducibility of Results; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D004396:Coloring Agents; D014874:Water Pollutants, Chemical; D011192:Potassium Dichromate