Nickel phytotoxicity thresholds for ryegrass: Insights from historical copper smelting sites in Bashkortostan, Russia

Environmental degradation due to the operation of non-ferrous metal smelters is a significant issue in many countries worldwide. In particular, copper smelting in the Ural Mountains has led to metal contamination of soils. This study conducted an ecotoxicity evaluation using ryegrass (Lollium perenne L.) as a bioindicator in 25 soils collected in Kananikolskoe and Zilair villages, Southern Urals, Republic of Bashkortostan, Russia. These study sites were former copper smelters, active during the 18^th-19^th centuries and, thus, copper phytotoxicity was anticipated in the soils under investigation. However, the effect of shoot copper concentrations on plant growth was statistically insignificant. Among all metals, nickel was the primary determinant of phytotoxicity, echoing the findings of other studies on copper-nickel contaminated soils. The obtained 25% and 50% effective concentrations (EC₂₅ and EC₅₀) for shoot nickel concentrations were 44 (28-59) and 52 (39-64) mg kg^-1, respectively, with values in parentheses representing the 95% confidence intervals. It is important to note that there are limited reports on nickel phytotoxicity thresholds for ryegrass, making this study a valuable contribution to ecotoxicological research. Furthermore, the reported critical nickel concentrations in ryegrass shoots vary widely, from 14 to 90 mg kg^-1. The EC₂₅ and EC₅₀ values derived in this study fall within the reported range, underscoring the reliability of the results obtained.