Metal phytotoxicity thresholds in copper smelter-contaminated soils

Abstract

Environmental problems associated with non-ferrous smelter operations are a problem in many countries around the world. Copper production in Armenia has resulted in metal contamination of soils and general degradation of environmental quality. In this study we attempted to determine the thresholds of phytotoxicity of metals in soils contaminated by a copper smelter in Armenia. The studied soils were sampled in the Alaverdi valley, located ~200 km north of Yerevan. The range of metal concentrations in the studied soils was very wide, e.g., total copper in the soil was 87-5885 mg kg-1. Most soils had nearly neutral pH (6.9 士 0.57), and average organic matter content (6.3 士 1.9). Some soils were saline. Perennial ryegrass root elongation was used as an operational method to assess phytotoxicity. We calculated a contamination index for each soil studied and plotted root length as a function of soil contamination index. Root growth was mainly affected by the contamination index based on total metal concentration, while the contamination index based on extractable metal concentration proved to be a weak predictor. Soil organic matter had a stimulatory (positive) effect, whereas electrical conductivity had a toxic (negative) effect on root growth. Despite these confounding factors, we were able to derive phytotoxicity thresholds for metals (EC10, EC25, EC50) based on the contamination index. In conclusion, we discuss the practical importance of this study and future research needs concerning contaminated soils in the Alaverdi Valley.