[en] The behavior of ²³⁸Pu oxide particles (20 to 74 μm in diameter) deposited on a soil surface was studied by using an environmental test chamber. The soil was obtained from Florida orange groves, and the chamber was set up to simulate a Florida climate. After more than 9 months and more than 60 simulated rainfalls, the plutonium oxide particles remained on top of the soil and showed no evidence of having moved down into the soil column. Plutonium was released into the soil drainages at the rate of 18 ng/m²/L. This release, which represents a minute portion of the source, appears to correlate with the volume of the drainage rather than with time and probably consists of plutonium attached to very fine soil particles. The average concentration of plutonium observed in the air was 7 fCi/L, which on an absolute basis, represents 8 x 10^-12% of the source material. Thus the generation of airborne plutonium constitutes an insignificant release pathway in terms of the original source. However, the air concentration during, and especially at the beginning of, a rainfall was typically much higher (1400 fCi/L). This concentration decayed rapidly after the end of the rainfall. These results are compared with those from past experiments, and their implications are discussed