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.

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The authors present the results of chemical and mineralogical analyses of urban dusts collected in the spring seasons of 2015 and 2016 in three different parks of the Cracow agglomeration. The parks are located in the city centre, in the Nowa Huta industrial district and in a new housing development situated around 9 km west of the city centre. Mineralogical instrumental analyses included the SEM, FTIR and XRD methods and revealed that the dusts of Cracow are highly amorphous and contain significant amounts of hydrocarbons, whereas quartz, feldspars, kaolinite and gypsum are their crystalline phases. Chemical analyses were carried out using the ICP-MS method on aqua regia extracts of the starting samples. The contents of selected toxic elements are: As 5–123; Cd 1–14; Pb 56–258; Zn 486–1891 mg/kg and Fe 0.74–4.02 wt%. The health risk of these elements imposed on the residents of Cracow frequently visiting the three urban parks was assessed on the basis of the health quotient index HQ. At its values exceeding 1, adverse health effects are probable in humans. The HQ values calculated for As and Tl contained in the Cracow Park dusts in the case of adults are 3.42E−01 and 3.00E−01, respectively. They are significantly higher (one order of magnitude) in the case of children 3.19E+00 and 2.27E+00, respectively.