Soil pollution by heavy metals may lead to paddy field acidification.
The study looked at how a type of paddy soil from China absorbs and releases copper (Cu2+). They found that the soil can hold over 1,600 mg of Cu2+ per kilogram. At low Cu2+ levels, the soil absorbs the metal in a specific way, but at higher levels, it's more general. As more Cu2+ is absorbed, the pH of the soil solution drops. When Cu2+ is released from the soil using CaCl2, the pH also drops, but not when using HCl. This suggests that heavy metal pollution, like copper and zinc, can make paddy soil more acidic.