Enhancement of natural radioactivity in the surrounding of a phosphate fertilizer complex in Santos basin, Brazil

Instituto de Pesquisas Energéticas e Nucleares, Departamento de Radioproteçao Ambiental, Caixa Postal 11049, Sao Paulo, Brazil

Abstract

Phosphate deposits are generally characterised by enhanced radionuclides concentration compared to average natural levels. Mining and processing of phosphate ore redistribute radionuclides into final products, by-products and solid waste (phosphogypsum). The phosphate fertiliser complex located in Santos Basin, Southwest Brazil, produces approximately 2000 tons of phosphogypsum per day, which are stockpiled and presents a potential threat to the environment. The radiological environmental impact is mainly due to the presence of ²²⁶Ra, ²²⁸Ra and ²¹⁰Pb. This study aims to determine these radionuclides in 13 sediment samples from Santos estuarine system in the surrounding of phosphate plants. As the organic debris is a good adsorbent of radionuclides, total organic carbon was also determined. ²²⁶Ra, ²²⁸Ra and ²¹⁰Pb were measured by gamma spectrometry using a hiperpure Ge detector. The activity concentrations varied from 6±2 to 44±5 Bq/kg for ²²⁶Ra, from 8±3 to 77±6 Bq/kg for ²²⁸Ra and from <13 to 114±21 Bq/kg for ²¹⁰Pb. Statistical analyses of the results showed that three samples collected near the industries presented anomalous activity concentrations, above average values of the region. A good correlation was observed between the activity concentration and the total organic carbon in all samples analysed, exception made for the three already mentioned.