Cesium-137 in the Goiânia waterways during and after the radiological accident.

The main contamination areas in Goiânia were exposed soil surfaces, and with the first rainfalls, 137Cs quickly reached the Meia-Ponte River, the main local waterway. Regular measurements of bottom sediment, surface water, and fish were begun 3 wk after the accident. In the first survey, 137Cs was detectable in sediments up to 12 km downstream from the accident area. Maximum 137Cs concentrations found in sediments of the Meia-Ponte River were 1.3 kBq kg-1 dry weight and 200 Bq kg-1 fresh weight for fish. Cesium-137 was always less than 10 Bq L-1 in surface waters plus suspended particulates, even in the most contaminated creeks. Because it was the beginning of the rainy season, downstream sediment transport was enhanced. This resulted in a decrease of 137Cs concentrations in sediments of the urban area by a factor of approximately 20, 5 wk after the accident. The main sedimentation area for suspended sediments in this portion of the river is the Rochedo Reservoir, which is 80 km downstream from the accident area. In a survey performed 10 mo after the accident, 137Cs concentrations in the reservoir were up to 14 Bq kg-1 for fish, 1 Bq kg-1 for aquatic plants, and 100 Bq kg-1 dry weight for bottom sediments.