The resuspension and redeposition of 137Cs in an urban area: The experience after the Goiânia accident

Abstract

In Goiânia, Brazil, the accidental opening of a 137Cs teletherapy source led to the contamination of an urban area of approximately 1 km 2. The restricted, local contamination patterns without any significant influence from previous contaminations (Chernobyl reactor accident and atmospheric atomic bomb test fall-out) provided a unique opportunity to study the resuspension and redeposition mechanisms in an urban area under tropical climate characteristics. Air, total deposition, rainwater, surface soil and street dust were sampled over 2 years at a garden of a house and the surroundings and analysed for 137Cs. The local meteorological conditions were recorded. In addition, some size fractionation measurements were performed. The data show a significant seasonality and a very slow long-term decrease with time for the activity concentration in air and deposition rate. Resuspension factors in the order of 10 −8 to 10 −9 m −1 (based on the air activity data) were derived. A wide range of values for nominal deposition velocities were found, averaging at 5–6 cm s −1. Impactor measurements indicate that about 30–60% of the total particulate matter in air is due to aerosol particles above 15 μm diameter. The data as a whole suggest that in Goiânia resuspension and deposition are mainly local phenomena and no evidence was found for a significant spreading of 137Cs from the place of primary contamination.