Anthropogenic source assessment of 226Ra and 210Pb in a sediment core from the Cubatão River estuary (SE Brazil)

A sediment core from an estuarine area receiving drainage from the highly industrialized Cubatão River basin (SE Brazil) showed ²²⁶Ra and ²¹⁰Pb activities up to 80 and 213 Bq kg⁻¹, respectively, which are greater than activities considered as regional background levels. Radionuclides and the elevated phosphorus concentrations (up to 0.3% sediment dry weight) found along the sediment core were significantly correlated with each other, indicating source similarity. These results indicate that ²²⁶Ra and ²¹⁰Pb activities are affected by fertilizer industry-derived inputs in addition to natural sources. This interpretation was supported by ²¹⁰Pb/²²⁶Ra ratios (found to be between 2.6 and 3.9) that indicate disequilibrium between ²²⁶Ra and its decay product ²¹⁰Pb, as expected for phosphogypsum-affected sediments.