Efficiency of the Chiprovtsi mining site remediation with regard to heavy metal and arsenic environmental pollution

A Program for the liquidation of the inefficient ore-mines in Bulgaria was started by the government in 1992. One of the main goals of the program is to eliminate the negative consequences of the mining industry to the environment. Restoration and remediation measures are envisaged for the mining sites only but not for the affected areas outside as the heavy metal polluted rivers and their floodplains. Evaluation of the efficiency of the environmental recovery of the mining affected landscapes in the upper part of the Ogosta River basin, NW Bulgaria, is the overall purpose of this study. Three mines (Au; Fe; Pb-Ag) operated in the region from 1951 to 1999 and the remediation activities ended in 2004. The levels of As, Pb, Zn, Cu and Cd were determined in the river water (109 samples), floodplain ground water (3 samples), river channel (97 samples) and floodplain sediment (44 samples), haplic Luvisols, LVh, FAO, 1998 (16 samples), grass vegetation (25 samples), sheep’s milk (6 composite samples from 800 animals) and goat’s milk (1 composite sample from 19 animals). Seven sampling campaigns were carried out in the period 2005-2007. The studied trace elements were measured with the means of ААS-GF, ICP-AES/OES/MS and XRF in the laboratories of the University of Mining and Geology of Sofia, Humboldt University of Berlin, Acme Laboratories (Canada) and the Ministry of agriculture and food of Bulgaria. The results show As and Pb as the main contaminants in the local environment, associated mostly with the river channel and floodplain sediments along the Ogosta River and its initial tributary Chiprovska River. The mean As value (median) for the channel sediment is 1170 mg/kg (min 16 mg/kg; max 80390 mg/kg) and 1117 mg/kg for the floodplain sediment (min 43 mg/kg; max 26946 mg/kg). The mean Pb levels for the same media are 178 mg/kg (min 10 mg/kg; max 15205 mg/kg) and 282 mg/kg (min 43 mg/kg; max 2982 mg/kg), respectively. The mean As value exceeded the Dutch intervention value 21 times for channel sediment and 20 times for floodplain sediments. The same quantities for Pb were 0.3 and 0.5 times, respectively. Levels above the imperative values of the EU directive 75/440/EEC were detected in river water mostly for As, which ranged between 0.002 mg/l and 0.621 mg/l, with mean value of 0.053 mg/l. Two general patterns of vertical metal and arsenic distribution were revealed in the polluted floodplains. Type 1 is typical for the floodplain sections lower than 1m where the contaminants increase in depth and ground water pollution with As is established. Type 2 is the common one for the floodplain between 1-2.5 m above the usual river level. Trace element accumulation in the upper sediment layers is typical in these areas. Lead concentrations above the EU threshold of 0.02 mg/kg were established in 5 samples from sheep’s milk (min 0.0036 mg/kg; max 0.077 mg/kg), as well as in the goat’s milk (0.052 mg/kg), produced in the Chiprovtsi mining area. As the studied grass samples from the grazing areas were not rich in Pb, other paths of lead transfer to the milk should be suggested. Though some of the remediation measures were successful, it can be concluded that the negative environmental legacy from the mining is still present in the Ogosta River basin. Better results can be expected if all the contaminant accumulation zones and the path-ways of the pollutant dispersal in the mining affected area are taken in account when environmental recovery measures are designed.