Biogeochemistry of arsenic following release of mine wastes into DonÌƒana, SW Spain
In April 1998 millions of m3 of toxic, metal rich acid mine waste poured from a failed storage lagoon in Spain and had a significant impact on the Coto Doñana World Heritage Site. The monitoring data presented here, shows that whilst ‘clean-up’ operations were partially effective in the spill affected areas, a significant quantity of residual As remained in affected soils/sediments. Also, just 2-3 months after the spill, both As and Cu appeared to be elevated in livers of waterbirds found dead in affected protected areas. Arsenic mobility in sediments is assessed as being relatively low, but evidence suggests that this may increase with time. Arsenic is found in association with iron sulphide and/or oxide phases in contaminated sediments, but it may also be becoming increasingly re-distributed and then reassociated with macrophyte roots. Such roots tend to form extensive surface iron plaques in saturated sediments, and these may be acting as arsenic accumulation sites in the Doñana wetlands. This may have very important ecotoxicological implications, as certain waterbirds in Doñana feed extensively on subsurface macrophyte material. This is however, an as yet, completely unstudied potential food chain transfer pathway for As and a range of other toxic metals (such as Pb, Cu, Zn, Cd). Levels of As on macrophyte roots are as high as >100 mg kg-1, and up to >11 times higher than they are in the bulk sediments from which they were sampled. Arsenic speciation has been identified as inorganic, and whilst predominantly as AsV (arsenate), it has also been noted as the more toxic/mobile AsIII (arsenite) on certain roots morphologies. Data on geese strongly suggests that avian species potentially feeding on such roots may be exposed to elevated levels of As (and Pb, Cu, Zn) in spill contaminated areas of Doñana.