Copper toxicity thresholds in Chinese soils based on substrate-induced nitrification assay

Area of Science:

• Environmental Chemistry
• Soil Science
• Ecotoxicology

Background:

• Copper (Cu) is an essential micronutrient but can be toxic at elevated levels.
• Understanding copper toxicity is crucial for soil health and environmental risk assessment.
• Terrestrial biotic ligand models (tBLMs) aim to predict metal toxicity based on bioavailability.

Purpose of the Study:

• To screen copper toxicity in diverse Chinese soils using a substrate-induced nitrification assay.
• To investigate the influence of leaching on copper toxicity thresholds.
• To inform the development of a terrestrial biotic ligand model (tBLM) for copper.

Main Methods:

• Substrate-induced nitrification assay was used to determine copper toxicity.
• Median effective concentration (EC50) values were measured for total and solution copper.
• Linear stepwise multiple regression analysis identified key soil predictors.
• The effect of leaching on copper toxicity was quantified using a leaching factor.

Main Results:

• Substantial variation in total and solution copper EC50 values was observed across 17 Chinese soils.
• Soil pH, calcium, and electrical conductivity were significant predictors of copper toxicity in unleached soils.
• Magnesium concentration explained a large portion of the variation in solution copper toxicity, indicating a protective effect.
• Leaching altered copper toxicity differently across soils and decreased the predictability of empirical models.

Conclusions:

• Copper toxicity thresholds are highly soil-specific and influenced by various soil properties.
• Magnesium plays a significant role in mitigating copper toxicity in soils.
• Leaching effects complicate copper toxicity predictions and require further mechanistic investigation.
• The findings provide valuable data for refining terrestrial biotic ligand models for copper.