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

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.