Water samples were collected along the Guadiamar River and in Doñana Park in December 1998, December 1999, and June 23000 following a 5 X 10-6m3 release of acid sludge on April 25, 1998 from the Boliden-Apirsa zinc mine near Aznal—llar. Together with results of previously collected samples (May 2 and May 25, 1998), we present here a two-year time series of dissolved Zn in the spill affected area. Our findings suggest different degrees of attenuation between sites that received both pyrite slurry and acid water (within ~40 km from the breached tailings pond) and those farther downstream that received only acid waters (between ~40 and ~95 km from the pond). Maximum Zn levels of 10-3 M were still observed in sites closest to the pond on the December 1999 and June 2000 dates. These sites showed high temporal variability in Zn concentrations, sometimes increasing or decreasing by almost three orders of magnitude. Zn levels in the lower reaches of Guadiamar , including those in Doñana Park had decreased to ~10-7 M by December 1998, and remained below this level on the two subsequent sampling dates. The lowest concentration observed here was 2 X 10-8 M, which was similar to levels found at nearby sites unaffected by the spill. Limited pre-spill data on [Zn] in the Guadiamar shows levels at a station ~4 km downstream of the tailings pond to have been `10-4 M in the three years preceding the accident. Based on this, we conclude that although clean-up efforts have allowed Zn levels in the vicinity of the mine to return to pre-spill conditions, these conditions indicate a heavily and chronically impacted river, even when compared to other industrially-influenced rivers around the world.
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Last updated: 7 May 2001, KAK.