Heavy metals pollution of aquatic ecosystems in the vicinity of a recentlyclosed underground lead-zinc mine (Basque Country, Spain)

A presentation is made of the study of an underground polymetallic sulphide mine and the pollution caused by this in the adjoining aquatic ecosystems. Troya Mine is in the Basque Cantabrian region (northern Spain). The annual production of the ore deposit of over 3.7 million tons of Pb (0.9%), Zn (1 1.2%) and Cu (0.2%) was 300,000 t. It was open and producing from 1986-1993 . The mineralization was made up of pyrite, marcasite, sphalerite, galena, chalcopyrite and arsenopyrite. Only the Zn and the Pb were mined. We studie d the distribution and behaviour of the heavy metals Zn, Pb, Fe, Mn, Cu, Cr and Cd in the water column, dissolved and suspended fractions, and in the sediments of Estanda Stream and of Gezala Creek. Zn, Cd and Mn tend to be f ound in the water; Fe, Pb, Cu and Cr appear as an adsorbed fractionin the s olid phases. Those of the second group are significantly linked to the fluv ial sediments and present very high levels. The concentrations of the metal s are conditioned by the waters from the mine galleries, by the leached was te, by the surface runoff, and by overflow from the spillway of the tailing s pond. Our observations provide knowledge on the extent of the polluting p ower of the metals, the physico-chemical effects in play and the subsequent chances of recovering these highly affected environments.