Compost and dolomite improve soil conditions and significantly reduce the cytotoxicity and genotoxicity caused by mining waste on Allium cepa

Abstract

Abandoned mines cause environmental and health risks worldwide. Mining waste is characterized by acidic pH and high metal content. This study addressed the combined or individual soil application of dolomite and compost to remediate a soil contaminated with mining waste to evaluate synergistic effects on pH buffering, metal availability, organic complexation, phytotoxicity reduction, and microbial activation. An experimental design was carried out with nine combinations of compost and dolomite doses. Compost increased soil organic matter by 1 and 3 %, and dolomite increased soil pH from 2.6 to 4.5 and 6.5. An incubation test was performed for 69 days and microbial activity was monitored. Physicochemical and microbiological parameters were measured, and Allium cepa tests were conducted. Greater microbial biomass (194.2 ± 31.6 mg C/kg) and CO2 release (176.8 ± 5.6 mg CO2-C) were observed in remediated soils with high dolomite and low compost doses (p < 0.05). Soils with high dolomite dose were associated with a decrease in electrical conductivity (11.18–1.43 mS/cm), redox potential (415–240 mV) and toxicity (RGIC0.8: 0.12 to >100), but an increase in Pb, Cu and Zn immobilization, pH (2.91–7.18) and carbonates (11.41–40.95 %). Therefore, dolomite application generated a dose-dependent improvement in physicochemical and biological conditions and significantly decreased the cytotoxicity and genotoxicity. The combined use of high dolomite and low compost doses (23.63 g dolomite and 4.05 g compost/100 g soil) represents an upper-bound remediation scenario and provides a reference framework for amendment-driven processes in extremely contaminated soils, warranting further validation in small-scale trials before field application.