Effect of CO₂ exposure on the mobility of heavy metals in submerged soils

Abstract

Increasing atmospheric carbon dioxide (CO₂) concentration can affect CO₂ level in soil, and this, in turn, may cause changes in soil chemical properties. This study investigated the effect of CO₂ exposure on pH and heavy metal mobility in submerged soils. Laboratory-scale batch tests were carried out using two soil samples with different initial pH conditions (A: 5.3; B: 6.3). The changes in the pH values of the soil solutions (i.e., water layer above soil) of the CO₂-affected soil samples and controls with time were not significant (p value > 0.05) with the both soil samples, and this may be attributed to the formation of bicarbonate, which may provide a buffering capacity. The effect on heavy metal mobility was different in the soil samples A and B. With the soil sample A, the soil heavy metal concentrations were generally lower in the CO₂-affected soil than in the controls. Accordingly, the soil solution heavy metal concentrations were changed. With the soil sample B, the soil heavy metal concentrations of the CO₂-affected soil and control did not show a significant difference (p value > 0.05). This can be partially attributed to the dissolution of carbonates that generate bicarbonates, and this is supported by the lower soil Ca concentration in the CO₂-affected soil. Overall, the results suggest that the elevated CO₂ level in submerged soils may have different effects on the soil chemical properties, and this necessitates continuous research efforts in order to manage and conserve soil environment under conditions of increasing atmospheric CO₂ concentration.