Assessment of Copper Toxicity to Sunflower under Monometallic Soil Contamination Conditions

Abstract: Ecotoxicological studies on metal toxicity are commonly conducted using artificially contaminated soils, whereas investigations of naturally or industrially contaminated soils remain limited. Industrially contaminated soils often contain elevated concentrations of multiple elements, complicating the interpretation of toxic effects. This underscores the exceptional value of sites with monometallic pollution. One such site is the Kargaly copper mining district in the Orenburg Region of the Russian Federation. This study assessed copper phytotoxicity to sunflower (Helianthus annuus L.) grown under field conditions in soils historically contaminated by copper mining during the 18th–19th centuries. Total copper content in the studied soils reached up to 10 000 mg/kg, while the content of other elements remained close to the background levels, confirming the monometallic nature of the pollution. The effective concentrations of copper causing 25 and 50% reductions (EC₂₅ and EC₅₀) in sunflower shoot growth were 9.8 and 12 mg/kg, respectively. Corresponding EC₂₅ and EC₅₀ values for total soil copper were 706 and 929 mg/kg, respectively.