The river Topolniza in Sredna Gora Mountain, Bulgaria, is passing near the facilities of the gold mine Chelopech, which is owned by Dundee Precious Metals. Pollution of the river with nitrite nitrogen and sulphate ions coming from the tailing pond of the mine has been recorded and reported. The electrical conductivity of the waters coming from the tailing pond to the river and their pH amplitude are very high. This is sign for heavy metals in the waters. The ore of the mine contains high concentration of arsenic.

According to the Regional Inspectorate of the Ministry of Environment and Waters, Plovdiv, Bulgaria, on 25 November 2008 the amount of lead in the River Chepelarska was 0.48mg/l, which is 9.6 times higher than the allowed amount (0.05mg/l). Even dead fish have started to appear along the river bed. The main dangers to human health after such disasters are related to soil pollution in fertile territories that may be flooded or irrigated with poisonous water and the pollution of underground waters used for drinking.