Changes in Polycyclic Aromatic Hydrocarbons (PAHs) and Soil Biological Parameters in a Revegetated Coal Mine Spoil

Coal mining leads to severe land degradation and creates huge amounts of mine spoil. Coal mine spoil contains toxic polycyclic aromatic hydrocarbons (PAHs) derived from coal, which can be alleviated through revegetation with suitable tree species. The present study was aimed at evaluating the impact of different tree species (Albizia lebbeck, Cassia siamea, Delonix regia, and Dalbergia sissoo) on the quality of coal mine spoil and changes in PAH concentration. Soil samples were collected from the revegetated coalmine overburden dumps of Jharia coalfield, Dhanbad, India and analysed by GC-MS for 16 priority PAHs and soil quality parameters were analyzed by standard analytical protocols. Reclamation improved the biological properties of the mine spoil: microbial biomass (+59–176%), dehydrogenase activity (+46–198%), fluorescein diacetate hydrolase activity (+104–127%), phenol oxidase activity (+150–250%), and peroxidase activity (+93–181%). PAH concentration in revegetated mine spoil ranged from 0 • 51 to 1 • 35 mg kg−1, with a significance reduction in total as well as individual PAHs. For individual tree species, total PAH reduction decreased in the order: C. siamea (81 • 6%) > A. lebbeck (55 • 6%) > D. regia (51 • 9%) > D. sissoo (51 • 5%). Correlation analysis showed significant association between the degradation of PAHs and soil biological properties of revegetated site. Microbial biomass carbon and soil enzymes were negatively correlated with PAH content in the mine spoil. But microbial stress indicators like respiration/microbial carbon ratio were not correlated, which revealed no adverse effect of PAH on soil microbes. Principal component analysis revealed that most of the biological parameters were closely associated with the degradation of low molecular weight PAHs