Changes in soil pH and mobility of heavy metals in contaminated soils

In the present paper, the authors attempt to explain the importance of pH in soil environment studies and show what mistakes to avoid when measuring pH and interpreting the results obtained. The tests conducted (i.e., extraction in aqua regia, buffer capacity determination, and the impact of acidification on the amount of heavy metals extracted from soils) demonstrated how soil pollution and buffer capacity affect the pace of extracting cadmium (Cd), lead (Pb) and zinc (Zn) cations from heavily polluted and unpolluted soils following gradual acidification. It was shown that soil acidification caused a significant increase in metal mobility in the following order Cd > Zn > Pb and that the highest decrease in pH was observed after adding the first portion of acid. Further addition of acid caused a gradually lower decrease in pH. Soils from the polluted area presented a high buffer capacity. The control samples displayed a distinctly poorer resistance to pH changes in the soil environment. Special focus was placed on cadmium due to its high mobility in soils, even with neutral and slightly alkaline pH. The analyses revealed that in areas heavily polluted by long-term industrial activity (I-geo > 5 for Zn, Pb and Cd), it is very important to conduct extensive geochemical studies related to the presence and circulation of particularly toxic elements. This is because every environmental factor, especially pH, may significantly affect their mobility, causing metal ions to become more or less active or increasing or decreasing environmental risk related to their presence. Highlights Soil acidification caused a significant increase in metal mobility in the following order: Cd > Zn > Pb. A special focus needs to be placed on Cd due to its high mobility in soils (up to 70% of total concentration), even with neutral and slightly alkaline pH. A higher pH buffering capacity would lead to a lower increase in percentage of bioavailable pollutants with an increase in acidity.

Automated summary

The study demonstrates that soil acidification significantly increases metal mobility, with the order of mobility being Cd > Zn > Pb. It emphasizes the importance of conducting extensive geochemical studies in areas heavily polluted by particularly toxic elements. High pH buffering capacity leads to a lower percentage increase of bioavailable pollutants as acidity increases.