Researchers conducted an experiment to see how acid rain affects the release of chromium from red soils. They found that pH 4.5 and 3.5 acid rain caused an increase in chromium release compared to pH 5.6 rain. The release of chromium increased with the amount of leaching liquid. Acid rain makes chromium more soluble and reduces its adsorption to soil. This happens because of the competition between hydrogen ions and chromium ions, the increase in ion strength, and the erosion of soil colloids by acid rain.