Copper bioavailability and phytotoxicity in Chilean agricultural soils: implications for sustainable fruit production

Central Chile's lowland valleys constitute a major fruit-producing region, but they face soil copper (Cu) contamination originating from Cu mining in the nearby Andes Mountains as well as the historical and ongoing use of Cu-based pesticides. This study investigated the potential toxicity of Cu to plants (phytotoxicity) in a representative fruit-growing valley. To assess this risk, soil samples were collected from 12 agricultural sites with documented Cu contamination and one uncontaminated site to serve as a baseline. A short-term bioassay was conducted using perennial ryegrass (Lolium perenne) to evaluate the effects of Cu on plant growth. The results demonstrated that elevated Cu levels significantly reduced both the shoot length and dry mass of the ryegrass plants. However, other soil properties, such as the presence of soluble zinc, organic matter, available nitrogen, and clay content, could mitigate these negative effects. Interestingly, the estimated concentration of Cu causing a 50% reduction in plant growth (EC50) was greater than the values reported in previous studies. This may be because Cu binds to soil organic matter (SOM), which reduces its bioavailability and immediate toxicity to plants. While this binding to SOM can initially reduce the negative effects of Cu, the eventual breakdown of SOM over time may release Cu back into the soil, posing long-term risks to both crops and the wider soil ecosystem. To fully understand these potential long-term impacts, further research is needed and should include studies with other soil organisms, such as earthworms and microorganisms, to gain a more comprehensive understanding of the ecological consequences of Cu contamination in these vital agricultural systems.