The first peer-reviewed paper (as far as I can tell) related to the Animas River, Colorado, was recently published. If you don’t remember, about 15 months ago, an estimated 3 million gallons of toxic acid mine drainage water was released into a small tributary of the Animas River due to the failure of a dam containing the waste. What I hadn’t realized, and is cited in this paper, is that there were two other major spill accidents, in 1974 and 1978, which released hundreds of thousands of acid mine drainage into the river.
The study by Rodriguez-Freire et al. collected both water column and sediment samples from throughout the watershed 13 days after the spill, going downstream about 100 miles from the mine. Their primary focus was metals (lead, copper, zinc, iron, and others).
Because of the long legacy of contamination in the Animas River, they found plenty of metals in the sediments. The metals were mainly adsorbed to iron minerals, mainly jarosite (KFe3(OH)6(SO4)2) and goethite (FeO(OH)), and clays. They found evidence of metals associated with both naturally occurring minerals and phases produced by mining activities. They note that these metals remain bioavailable, especially when associated with jarosite, and that high flow events could re-suspend toxic metals. They also reported that high nutrient loads (nitrogen and phosphorous) enter the river in an intensely farmed region about 100 miles downstream of the mine. The presence of excess nutrients can contribute to oxygen depletion and affect redox sensitive metals, possibly causing them to be dissolved.
Rodriguez-Freire et al. Environ. Sci. Technol. 2016, 50, 11539−11548.
