KINETIC STUDIES ON THE EFFECTS OF ORGANOPHOSPHORUS PESTICIDES ON THE GROWTH OF MICROCYSTIS A. AND ITS UPTAKE TO PHOSPHORUS

Organophosphorus pesticides (OPs) are widely used in agriculture and they do not only kill target organisms but also extend to some nontarget organisms. Major portions of some nontarget organisms are algae cells. The objective of this work was to study the effects of low concentration methamidophs(MAP) and phoxime on the growth of Microcystis aeruginosa. Meanwhile, the kinetic mechanism of uptake of three kinds of phosphorus forms-total soluble phosphorus (TSP), soluble reaction phosphorus (SRP) and dissolved organic phosphorus (DOP) by Microcystis were also studied. The concentration of total phosphorus was 6.95 mg/L in each medium. Methamidophs and phoxime were diluted with sterile distilled water and added into the sterile modified HGZ medium at various phosphorus concentration ratios of methamidophs and phoxime to K2HPO4. Microcystis cell density measured by spectrophotometer every 24hr at 663nm after inoculation. And adopted ammonium molybdate spectrophotometric methods to determine the phosphorus forms concentration. Compared with no MAP and phoxime in medium, when MAP, phoxime and K2HPO4 combined in concentration ratio (1:11 and 1:9, 1:349 and 1:114) was treated, the growth of Microcystis was stimulated. And the algal cells in MAP, phoxime:K2HPO4 ratio 1:9,1:114 treated medium grew faster than that of in MAP:K2HPO4 ratio 1:11,1:349 treated medium. The growth of Microcystis significantly inhibited by MAP when no K2HPO4 in medium and MAP as unique P source of algal growth. The kinetic curves of change of phosphorus forms concentration in each medium were fit to logistic model. The SRP could be assimilated by algae at higher velocity than that of other phosphorus forms, and few DOP used by algae. The algal grew faster, the values of uptake velocity of the SRP by Microcystis were bigger. All these results showed that the MAP and phoxime could stimulate growth of Microcystis when they and inorganic phosphorus combined in certain ratio, but the point of the certain ratio for MAP is higher than that for the phoxime. The growth rate of Microcystis was dependent upon the concentration of intracellular phosphorus, and SRP was the preferential phosphorus form used by algae. The cause of stimulation might be the MAP and phoxime could accelerate the velocity of SRP uptake by the algal at the low concentration.