Measuring and modelling temporal trends of 226Ra in waters of a Spanish estuary affected by the phosphate industry

The presence and temporal evolution (1990-2001) of 226Ra in a tidal estuary affected by the phosphate industry has been investigated. Water samples collected in the course of four separate sampling campaigns were analysed for 226Ra content using a gas flow proportional counter following Ba coprecipitation. Two 226Ra sources have been identified: direct discharges from the industrial complex and run-off from a phosphogypsum pile. Although activity levels are similar, or even higher, than those found in other environments affected by the phosphate industry, there has been a general decrease in contamination since direct discharges ceased in 1998 due to new regulations from the EU. However, sediments are now acting as a source of Ra to the water column due to redissolution processes. A numerical model of the estuary has been developed to describe quantitatively the experimental results. The model solves the hydrodynamics and the dispersion equation of 226Ra including interactions with sediments. Model results are, in general, in good agreement with observations.