Optimal soil Eh, pH for simultaneous decrease of bioavailable Cd, As in co-contaminated paddy soil under water...

Area of Science:

• Environmental Science
• Soil Science
• Agricultural Chemistry

Background:

• Paddy soils in China frequently suffer from co-contamination with cadmium (Cd) and arsenic (As).
• Decreasing the bioavailability of both Cd (cation) and As (anion) simultaneously is difficult due to their opposing ionic forms.

Purpose of the Study:

• To determine optimal soil redox potential (Eh) and pH conditions for reducing Cd and As bioavailability in the soil-rice system.
• To investigate the impact of water management strategies on toxic element bioavailability and uptake by rice.

Main Methods:

• Conducted soil culture and rice pot experiments.
• Implemented various water management strategies.
• Monitored soil Eh, pH, and concentrations of Cd and As in soil and rice grains.

Main Results:

• Long-term flooding led to near-neutral soil pH (approximately 7.0).
• Soil pH was the primary factor for Cd and As bioavailability in unflooded conditions, while Eh was dominant under flooding.
• Flooding reduced Cd in rice grains (54.5%–95.5%) but significantly increased As concentration (214%–302%).
• Minimal trade-off between Cd and As bioavailability was achieved at soil Eh of -130 mV and pH of 6.8.

Conclusions:

• Water management, particularly flooding, significantly alters soil Eh and pH, impacting Cd and As bioavailability.
• Achieving simultaneous reduction of Cd and As bioavailability requires careful control of soil Eh and pH, with optimal values identified.
• The findings provide critical insights for managing co-contaminated paddy soils to improve rice safety.