Self-cleaning in an estuarine area formerly affected by 226Ra anthropogenic enhancements

Coupled anthropogenic anomalies of radionuclides and major elements in estuarine sediments

“…These authors evidenced a strong anthropogenic influence on 210 Pb distribution only in the inner, northern area of the system. In the present study, higher radionuclide levels are recorded, reaching the magnitude found in estuaries strongly affected by fertilizer industries, which have caused, for example, 210 Pb levels up to 1580 Bq kg À1 in the Tagus River estuarine sediments (Carvalho, 1995) and 226 Ra levels up to 961 Bq kg À1 in sediments from the Tinto and Odiel Rivers estuary (Absi et al, 2004).…”

“…However, a depletion in all contaminant levels within the upper layers (Fig. 2) suggests a substantial decrease in the anthropogenic input, as observed in sites where industrial inputs were attenuated or avoided (e.g., Absi et al, 2004).…”

Calibration and measurement of using two independent techniques

“…T3 was collected in an area containing enhanced levels of natural radionuclides due to leaching from the phosphogypsum piles located in the vicinity; in contrast, OT5 is a sediment sample collected from open sea with natural radionuclide levels typical of unperturbed environments (Absi et al, 2004).…”

“…The analysed riverbed sediments have enhanced 210 Pb activity concentrations because they have been collected in an estuary affected by past phosphogypsum discharges, released by direct discharges from the phosphoric acid factories and also from piles close to the rivers where the phosphogypsum was stored (Martínez-Aguirre and García-León, 1996). Direct phosphogypsum discharges ceased in 1998, and the phosphogypsum piles have since been better isolated using a closed water circuit (Absi et al, 2004).…”

The Role of Suspended Particles in Estuarine and Coastal Biogeochemistry

“…In particular, 226 Ra, and other radionuclides such as 210 Pb and 210 Po, can be present with activity concentrations of up to 1000 Bq kg −1 . The rivers Odiel and Tinto, in south west Spain, have been seriously affected by direct and uncontrolled industrial discharges of phosphogypsum to their waters over several decades (Absi et al, 2004). The activity concentrations in the sediments in 1998 were relatively high but, in general, they have declined in 2001 and 2002 because of improved control of the discharges plus the effects of a process that Absi et al (2004) described as natural 'self-cleaning'.…”