PARENT SESSION
WA3 SPECIAL SYMPOSIUM: Effect assessment in marshlands and areas of high eocological value: the "Aznalcollar accident, Spain" case study
9:00 AM to 12:30 PM, Wednesday, 09 May 2001
Session Chair: J. Blasco
Room 3

(307) Sediment Toxicity in the Rio Guadimar (Spain), after a mine tailings spill.

Reynoldson, Trefor¹, Milani, Danielle¹, Gillis, Patti^1,2, ^{1 2}

ABSTRACT- Sediment toxicity tests in combination with chemical analysis and benthic community data are required in the assessment of sediment contamination. In April 1998, the Los Frailes zinc mine experienced a failure at the tailings impoundment, which resulted in a flow of tailings into the Rio Guadiamar. To determine the extent of contamination of the sediment of the Rio Guadiamar, the toxicity at 5 sites was examined. Four sediment toxicity tests and guidelines developed by Environment Canada were used to provide an initial assessment of sediment quality in the area of tailings deposition. These tests are: Hyalella azteca 28-day survival and growth test; Chironomus riparius 10-day survival and growth test; Hexagenia spp. 21-day survival and growth test; and Tubifex tubifex 28-day reproduction and survival test. Toxicity tests were performed on sediment from five sites located along the river. Additionally, the sediments were also analyzed for metals, particle size, total organic carbon. The results showed severe toxicity to be evident in three out of the five sites, as evidenced by poor survival, depressed growth and poor reproduction relative to the criteria derived for the Great Lakes. There is a progressive degradation in sediment quality observed along Rio Guadiamar from the impoundment to site 1, after which there is a recovery by site 3. The sites which elicited poorest growth or reproduction had the highest concentrations of zinc, copper, and lead, and other metals. These sites also had the highest percentage of fine material, which may alter the bioavailability of the metals to the organisms. Recovery is noted at the site furthest away from the impoundment and metal concentrations and the particle size are similar to those at the upstream site. Elevated ammonia concentrations and/or low pH may have contributed to the observed toxicity in sites 1, 2, and 5. Sites 1, 2, and 5 fall outside the normal range of variation observed for reference sites in ordination space, and thus are considered toxic.

Key words: sediment, toxicity, mining, Guadiamar