Natural Decrease of Dissolved Arsenic in a Small Stream Receiving Drainages of Abandoned Silver Mines in Guanajuato, Mexico

Arsenic release from the abandoned mines and its fate in a local stream were studied. Physicochemical parameters, metals/metalloids and arsenic species were determined. One of the mine drainages was found as a point source of contamination with 309 μg L −1 of dissolved arsenic; this concentration declined rapidly to 10.5 μg L −1 about 2 km downstream. Data analysis confirmed that oxidation of As(III) released from the primary sulfide minerals was favored by the increase of pH and oxidation reduction potential; the results obtained in multivariate approach indicated that self-purification of water was due to association of As(V) with secondary solid phase containing Fe, Mn, Ca.