Spreading of 137 C in the Goiania urban area by resuspension and transport of surface soil

The resuspension of surface soil was considered the mechanism responsible by the spreading of 137 Cs after the Goiania accident, which affected an urban area of about 1 km2. Studies on the transport of 137 Cs associated to the surface soil were performed in a house located at 57th Street, close to the main focus of contamination, from 05/89 to 07/00. Periodically, samples of surface soil and soil profile were collected at the house yards and street dust sampling at representative locations was performed in order to know the extension of the contamination in the city. The soil profile samples have shown the low mobility of 137 Cs in deep layers of the soil, although a slight long-term decrease of the 137 Cs activity concentration in the surface soil were observed. The 137 Cs activity concentration in the street dust samples also decrease with time, suggesting a natural dilution of the contamination in those samples; higher values were only found in few locations close to the foci of primary deposition and no additional spreading of the radionuclide is expected to occur from that area. Street dust sampling is a suitable method to assess the spreading of caesium in urban environment. (author)