Ecological Systems and Devices Annotation << Back INFLUENCE OF PHOSPHORUS ON A PLANT TEST OBJECT WHEN CULTIVATED ON NATURAL WATER A.M. Lazareva, V.I. Ipatova The effect of sodium phosphate on the number of cells of the algae Scenedesmus quadricauda was tested on natural water from the Belaya River and water from the lake M. Vudyavr The tasks of the work included the study of the dynamics of development of the test object in the norm and under the influence of sodium phosphate, and the determination of the sensitivity of the culture to sodium phosphate when grown on river and lake water. The maximum allowable concentration of phosphates (in terms of phosphorus) was established, which for algae was 5 mg P/l, and taking into account the background content of phosphates in natural water, 5,016 mg P/l. Comparison of the growth of the plant test object S. quadricauda on water from the Belaya River and water from the lake M. Vudyavr showed that in both cases the maximum allowable concentration of phosphate (calculated as phosphorus) for cell abundance was 5 mg P/l, and the threshold minimum effective concentration was 10 mg P/l, although acute toxicity in terms of EC50 for 72 hours on lake water was an order of magnitude higher than on river water. The obtained data on the effect of phosphates on the test object S. quadricauda indicate that algae can withstand high concentrations of phosphates and are not a limiting link in establishing the MPC of phosphates in the study region. In accordance with the accepted classifi cation according to the degree of acute toxicity for S. quadricauda, phosphorus can be classified as a non-toxic substance (EC50 over 1000 mg/l). For the purpose of establishing regional maximum allowable concentrations of toxic substances in a certain region of water basins, bioassay should be carried out on natural water from this region with a minimum anthropogenic load. Keywords: Scenedesmus quadricauda, bioassay, phosphates, toxicity, natural water. DOI: 10.25791/esip.4.2023.1365 Pp. 58-66.