Catalase activity as a diagnostic indicator of the health of oil-contaminated soils after remediation.

The work objective was to assess the ecological state of soils by changing the residual oil content and restoring catalase activity after remediation. The soils were selected in various ecosystems: a steppe of the Rostov Region (Haplic Chernozem), beech-hornbeam forests in the Republic of Adygea (Haplic Cambisols), and semi-desert of the Caspian province of the Republic of Kalmykia (Eutric Cambisols). Soil samples were polluted with oil at a concentration of 5% of the soil mass. After that, ameliorants (biochar, nitroammophoska, sodium humate, and Baikal EM-1) were introduced into the oil-contaminated soil. The catalase activity of Haplic Cambisols was stimulated only with the introduction of D2 biochar by 11% relative to the control, and in Haplic Chernozem, catalase was most stimulated with the addition of nitroammophoska D0.5 and D1 by 65% and 57% of the control, respectively. Nitroammophoska in all doses significantly stimulated the enzymatic activity, in Eutric Cambisols by four to six times compared to the control. The range of soil stability determined by catalase activity: Eutric Cambisols > Haplic Chernozem > Haplic Cambisols. Thus, it is most effective to apply biochar in doses of D and D2 and D0.5 and D nitroammophoska during the remediation of oil-contaminated Haplic Chernozem. For the remediation of Haplic Cambisols, it is effective to introduce biochar in dose of D2, and Eutric Cambisols-biochar and sodium humate in dose of D0.5 and nitroammophoska (all doses). The results of the study allow using catalase activity as a very informative and statistically significant diagnostical indicator of the health of oil-contaminated soils after remediation.

Assessment of the Health of Soils Contaminated with Ag, Bi, Tl, and Te by the Intensity of Microbiological Activity.

Soil health is the basis of ecological and food security for humanity. Among the informative indicators of soil health are microbiological indicators based on the intensity of the carbon dioxide release from the soil. The reaction of the microbial community of Haplic Chernozem Loamic, Haplic Arenosols Eutric, and Haplic Cambisols Eutric to contamination with oxides and nitrates of Ag, Bi, Tl, and Te at doses of 0.5, 1, 3, 10, and 30 derived specific permissible concentrations (SPC) was analyzed in the conditions of a vegetation experiment (the exposure period was 10 days). One derived concentration is assumed to be equal to three background concentrations of the element in the soil. The carbon content of microbial biomass in Haplic Chernozem varied between the experimental options from 6 to 218 mg/kg of soil; in Haplic Arenosols, from 3 to 349 mg/kg of soil; and in Haplic Cambisols, from 7 to 294 mg/kg of soil. Microbial biomass was a more sensitive indicator of contamination by the studied pollutants than basal soil respiration. A decrease in specific microbial respiration was found when Haplic Cambisols were contaminated with Ag, Bi, Te, and Tl oxides. Te and Tl nitrates had a significant toxic effect on each type of soil. At the maximum dose of Tl and Te nitrate, a decrease in basal soil respiration of 56-96% relative to the control and an increase in the metabolic coefficient by 4-6 times was found. The toxicity series of heavy metals averaged for all types of soils in terms of microbiological activity was established: Bi > Ag > Te > Tl (oxides) and Te > Tl > Ag > Bi (nitrates). Nitrates of the elements were more toxic than oxides. Soil toxicity due to Ag, Bi, Tl, and Te contamination was dependent on soil particle size distribution, organic matter content, and soil structure. A series of soil sensitivity to changes in microbial biomass and basal soil respiration when contaminated with the studied pollutants: Haplic Arenosols > Haplic Chernozems > Haplic Cambisols. When diagnosing and assessing the health of soils contaminated with Ag, Bi, Tl, and Te, it is advisable to use indicators of soil microbiological activity.

Assessment of the Ecotoxicity of Pollution by Potentially Toxic Elements by Biological Indicators of Haplic Chernozem of Southern Russia (Rostov region).

The content of various chemical elements such as metals, metalloids, and nonmetals in the environment is associated with natural and anthropogenic sources. It is necessary to normalize the content of metals, metalloids, and nonmetals as potentially toxic elements (PTE) in the Haplic Chernozem. The soils of the Southern Russia are of high quality and fertility. However, this type of soil, like Haplic Chernozem, is subject to contamination with a wide range of PTE. The aim of the work was to rank metals, metalloids, and nonmetals by ecotoxicity in Haplic Chernozem. To assess the ecotoxicity of chernozem, data for 15 years (2005-2020) were used. Biological indicators used to assess the ecotoxicity of Haplic Chernozem: catalase activity, cellulolytic activity, number of bacteria, Azotobacter spp. abundance, to change of length of radish's roots. Based on these biological indicators, an integral indicator of the state of Haplic Chernozem was calculated. The ecotoxicity of 23 metals (Cd, Hg, Pb, Cr, Cu, Zn, Ni, Co, Mo, Mn, Ba, Sr, Sn, V, W, Ag, Bi, Ga, Nb, Sc, Tl, Y, Yb), 5 metalloids (B, As, Ge, Sb, Te) and 2 nonmetals (F, Se) as priority pollutants. It is proposed to distinguish three hazard classes of metals, metalloids, and nonmetals to Haplic Chernozem: I class - Te, Ag, Se, Cr, Bi, Ge, Sn, Tl, Hg, Yb, W, Cd; II class - As, Co, Sc, Sb, Cu, Ni, B, Nb, Pb, Ga; III class - Sr, Y, Mo, Zn, V, Ba, Mn, F. It is advisable to use the results of the study for predictive assessment of the impact of metals, metalloids, and nonmetals on the ecological state of the soil during pollution.

Impact of Metal-Based Nanoparticles on Cambisol Microbial Functionality, Enzyme Activity, and Plant Growth.

An increase in the penetration of metal-based nanoparticles (NPs) into the environment requires an assessment of their ecotoxicity as they impair the critical activity of plants, animals, bacteria, and enzymes. Therefore, the study aimed to observe the effects of metal-based NPs, including copper (Cu), nickel (Ni), and zinc (Zn), on the Cambisols, which cover a significant part of the earth's soil and play an important role in the biosphere. Metal-based NPs were introduced into the soil at concentrations of 100, 1000, and 10,000 mg/kg. The biological properties of the soil are being investigated as the most sensitive to external contamination. The highest ecotoxicity of the studied pollutants introduced into the soil at the same concentrations was shown by Cu (up to 34%) and Zn (up to 30%) NPs, while Ni NPs showed less (up to 22%). Microbiological (total number of bacteria, Azotobacter sp. abundance) and phytotoxic properties (radish seed germination and length of roots) of Cambisols were more sensitive (22-53%) to pollution by NPs of Cu, Zn, and Ni, while enzymatic activity (catalase and dehydrogenases) showed less sensitivity (14-32%). The present results could be useful for biomonitoring the state of contaminated soils, especially by NPs.

Influence of Silver Nanoparticles on the Biological Indicators of Haplic Chernozem.

In recent years, silver nanoparticles (AgNPs) are increasingly used in various industries due to their antibacterial properties, which lead to an increase in pollution of the environment and soil ecosystems. However, the ecological effects of soil pollution by AgNPs were poorly studied than that with AgNPs of other metal-based NPs. The aim of this study is to assess the influence of AgNPs on the biological properties of Haplic Chernozem. Silver was introduced into the soil in the form of AgNPs with a concentration of 0.5; 1; 5; 10; 50, and 100 mg/kg in laboratory conditions. The influence of AgNPs on the biological properties of Haplic Chernozem was assessed 30 days after contamination. The degree of reduction in biological properties depends on the AgNPs concentration in the soil. This study showed that the sensitivity to contamination by AgNPs in the total number of bacteria and enzymatic activity was more than that in the abundance of bacteria of the genus Azotobacter. The integrated index of biological state (IIBS) of Haplic Chernozem was decreased by contamination with AgNPs. Silver nanoparticles in the concentration of 10 mg/kg caused a decrease in the indicator by 13% relative to the control. It also decreased IIBS by doses of 50 and 100 mg/kg by 22 and 27% relative to the control. All used biological indicators could be used for biomonitoring, biodiagnosis, bioindication, and regulation of ecological condition of soil contamination by AgNPs.