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

Abstract

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.

Phytoremediation of chromium, iron and nickel by Indian Rice Plant (Oryza sativa L.): An opportunity for management of multi-metal contaminated tannery wastewaterPhytoremediation of chromium, iron and nickel by Indian Rice Plant (Oryza sativa L.): An opportunity for management of multi-metal contaminated tannery wastewater

“…In this study, the pH and organic matter of experimental soil was 6.7±0.15 and 1.52±0.48 %, respectively (Table 2). These results are consistent with Kicińska et al (2022) who suggested that heavy metal mobilization in the soil is a function of pH and organic matter. On other hand, the amount of PTHMs such as Cr, Cd, and Pb in agricultural soil was found to be almost negligible or below the detection limit.…”

Trace Element Contents in Petrol-Contaminated Soil Following the Application of Compost and Mineral Materials

“…A reduction in the pH of the soil subjected to oil-derivative pressure was demonstrated by Akpan and Udoh [ 63 ] and Cheraghi et al [ 64 ]. A reduction in the soil pH to slightly acidic and acidic increases the mobility of trace elements and their availability for plants and soil microorganisms [ 65 ]. In particular, high mobility is exhibited by cadmium, even in soils with a neutral and slightly alkaline pH [ 65 ] and in those accumulated with oil-derivative substances [ 66 ].…”

Ecological Risk Assessment Related to the Presence and Toxicity of Potentially Toxic Elements in Ashes from Household Furnaces

“…The pH value closely determines the physicochemical changes that may occur in the environment due to ash deposition. The larger the deviation from the value of 7 in the pH scale, the greater the changes in the mobility and release of elements in environmental processes, which has been demonstrated in a paper by Kici ńska and colleagues [38].…”

“…d.m., dry mass; AF, alternative fuels based on biomass; C, coals; MW, municipal waste; Av., arithmetical average; * pH values are averaged for 3 measurements; ** means calculated according to Kici ńska et al[38].…”