No abstract

Ecotoxicological studies on soil metal toxicity often rely on artificially contaminated soils. A major difficulty in using soils contaminated by anthropogenic activities (e.g., mining and agriculture) is the presence of multiple metals, which can make it impossible to distinguish the toxic effects of a particular metal. Therefore, sites with monometallic pollution have great potential for ecotoxicological research. One such site is an agricultural field in Kargaly, Orenburg region, Russia, where copper mining and smelting activities were carried out during the 18th–20th centuries. Samples of Mollisols (chernozems) were collected in the studied field. At several sampling points there were copper ore rocks on the surface, containing malachite (CuCO3 · Cu(OH)2). The soil samples had a high copper content, up to approximately 10 g kg−1, compared with 75 mg kg−1 in the background soil. Importantly, the content of other elements in all soil samples was similar to that in the background soil, highlighting the uniqueness of the monometallic contamination in the study area. Despite the extremely high total copper content, exchangeable copper was relatively low, with a maximum of approximately 0.5 mg kg−1. We performed a short‐term (21‐day) ecotoxicity assessment using perennial ryegrass as an indicator of copper toxicity. Contrary to expectations, plant growth was not affected by the high copper content in the studied soils. The low copper phytotoxicity may be explained by the low solubility of malachite. However, future long‐term experiments may be warranted to determine copper toxicity thresholds for plants under field conditions. The site discovered in the present study could potentially acquire the same significance as the Danish Hygum site for the study of monometallic soil contamination. Environ Toxicol Chem 2023;42:707–713. © 2023 SETAC

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 ± 0.57), and average organic matter content (6.3 ± 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 (EC 10 , EC 25 , EC 50 ) 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.