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Page 16 of 21 Artyukhov et al. Carbon Footprints 2026, 5, 8

Figure 7. Spearman correlation matrix of the studied parameters: pH, PCM, MI, Q10, SOC, Zc, and heavy metals concentrations (Figure
was created using Origin Pro 2024 software). PMC: Potentially mineralizable organic carbon; MI: mineralization intensity; SOC: soil
organic carbon.

The influence of soil physico-chemical factors on the MI, calculated from incubation experiments at 10 and
25 °C, was generally similar. The strongest positive correlations were observed with arsenic (Spearman’s r =
0.80-0.95, P < 0.01) and lead (Spearman’s r = 0.59-0.61, P = 0.07-0.08), possibly due to the high toxicity of
these elements and their suppressive effects on microbial activity affecting mineralization. Negative
[68]
correlations were observed with chromium (Spearman’s r = -0.62 to -0.63, P = 0.07-0.08). Other pollutants
exhibited weak negative correlations with MI (positive for strontium: Spearman’s r = 0.22-0.27, P > 0.49;
others: r = -0.10 to -0.28, P > 0.46). Soil acidity showed weak to moderate negative correlations with all
mineralization characteristics (Spearman’s r = -0.47 to -0.31, P = 0.20-0.42), except for Q , which had a weak
10
positive correlation (r = 0.07, P = 0.98).

One possible reason for the weak correlations between heavy metal pollution and mineralization
characteristics is the prevalence of immobile, silicate-bound forms of toxicants that are not bioavailable to
microorganisms, or microbial tolerance to these pollutants [73,74] . Conversely, in mineral soils with lower SOC
content, a different relationship may occur, as metals could be more bioavailable. The complex interplay
between soil properties (pH, SOC, texture), metal type, and bioavailability makes generalized predictions
difficult. Future targeted research, including eco-toxicological assays on microbial communities, is needed to
disentangle these effects. Nonetheless, establishing these baseline concurrent measurements is an important
first step, revealing that areas of highest anthropogenic pressure also store large amounts of PMC, creating
potential hotspots for interactions between pollution and climate-carbon feedbacks.