Effect of innovative mineral-organic mixtures on enzymatic activity, ecotoxicity, and microbial communities in contaminated soil

Abstract

The sustainable use of fertilizers to enhance food production while minimizing environmental impact is a pressing global challenge. Soil regeneration is especially critical for soils poor in organic matter and contaminated with heavy metals. This study investigated the effect of mineral-organic mixtures containing zeolite composites and organic additives (lignite/leonardite) on soil enzymes activity, ecotoxicity, and microbiological properties. Various doses of zeolite composites and organic additives were tested in a two-years pot experiment using soil with elevated levels of cadmium, zinc, and lead. Soil enzymes activity (dehydrogenase, urease, phosphatase, and arylsulfatase) were quantified, and soil ecotoxicity was assessed using Microtox®, Phytotoxkit, and Ostracodtoxkit assays. Microbial abundance, diversity, and community structure were analyzed via culturable methods and DNA sequencing. Mixtures containing zeolite-vermiculite composite had the most pronounced positive effect on enzymes activity. Notably, mixture with 3 % zeolite-carbon composite and 3 % leonardite significantly enhanced urease activity after the 2nd year (111 %). Mixtures containing zeolite–vermiculite composite showed an average GMea index about 10 % higher than those with zeolite–carbon composites. The GMea index proved more sensitive than TEI in assessing total enzymes activity and soil quality. Soil microbiological studies showed that the quantity and overall structure of the microbiome remained stable after the application of mineral-organic mixtures. The dominant taxa at the phylum level were Proteobacteria (16.17–18.73 %), Planctomycetota (16.17–18.73 %), Chloroflexi (14.99–18.49 %), and Actinobacteriota (11.28–14.86 %). The mixtures did not affect the diversity of soil microorganisms, suggesting a neutral effect on the soil ecosystem. The greatest reduction in water-soluble Cd, Zn, and Pb was achieved with the mixtures containing zeolite-carbon composite and lignite. The results demonstrate the impact of mineral-organic additives on soil ecotoxicity, which is of significant importance from an environmental and sustainable soil management perspective. The outcomes of this study may prove to be a factor in the formulation of effective remediation strategies for contaminated soils.