The kinetics of the radioactive isotope P³² uptake by the fresh water algae, chlorella, have been investigated in soil-water cultures, natural systems, and synthetic culture media. These laboratory investigations were done at three different pH values, 4, 7 and 10, and maintained at constant temperature of 20 ± 2° C.

Portions of reagent grade sodium pyrophosphate were irradiated with a fast neutron flux converting a portion of the sample into the radioisotope P³² (P³²emits a 1.7 MeV beta with a half-life of 14.31 days.) Tagging was done at a rate sufficient to produce an activity of 0.03 microcuries/gram. Solutions were then prepared containing the tagged pyrophosphate. These phosphate solutions were used to spike chlorella cultures. The uptake of the isotope was then monitored as a function of time. After various times the cultures were samples, filtered and counted for P³² activity.

The data show that the kinetic interpretation of P³² uptake must allow for first order kinetics with respect to P³² at a pH of 10, and a second order kinetic scheme at pH 7 and 4. This evidence indicates that algal systems only utilize phosphorus in the orthophosphate form. These data also give phosphorus exchange rates with soil and give additional information about degradation pathways.

Two experiments, one with an oxygen rich environment and the second with a carbon dioxide rich environment, were carried out with sodium pyrophosphate-chlorella, soil-water and chemical cultures. In the first case, the oxygen experiment, P³² removal was eliminated in the chemical cultures; removal was slowed for the soil-water cultures. CO₂ enrichment greatly accelerated the removal.

Project NO. A-035-NMEX