Biogeochemical networks in the abandoned historical gold mines affecting mobilization and transport of arsenic in Kolar

Enormous water-logging in ancient abandoned mining shafts of Kolar Gold Fields (KGFs), has largely induced the leaching of sulfide-rich gold minerals contaminating the aquifer system with hazardous elements. Transport of these contaminant has posed threat to the health of the urban population of Kolar township. A detailed survey of borewells, covering radius of 10 km of the KGF was carried out during pre and post-monsoon seasons and various parameters were assessed. Almost 80% of the water samples exceeded the regulatory limits of potable water criteria with excess arsenic (As; 12-127 ������g/L), fluoride (F; < 0.005 ������g/L), dissolved salts ( > 500 mg/L). Water Quality Index (WQI) was used to understand the overall urban groundwater quality. At the centre of sam-pling circle core , mineral dissolution was found to be the function of pH, induced by acidophilic sulfur oxidizing bacteria . Modelling of predicted microbial metabolic pathways in metagenomics libraries using PICRUSt, indi-cated complex functional networks. High expression of siderophore proteins (> 2 cm halo in the chrome azurol test) caused Fe-sequestration, secondary Fe-mineral formation and subsequent release of As. Sulfide bearing Au-rich minerals (Arsenopyrite, Scorodite, Jarosite) were bio-weathered leading to release of H3AsO3+ at low pH, resulted in groundwater composition of Ca-HCO3 type and Ca-Na-HCO3 or Ca-Mg-Cl type.

Automated summary

Enormous water-logging in ancient abandoned mining shafts of KGFs has led to the leaching of sulfide-rich gold minerals, contaminating the aquifer system with hazardous elements. This poses a threat to the health of the urban population of Kolar township. A survey of borewells within a 10 km radius of KGF was conducted and the water samples were found to exceed regulatory limits for potable water criteria, with high levels of arsenic, fluoride, and dissolved salts. The quality of urban groundwater was assessed using the Water Quality Index (WQI), indicating complex functional networks and the release of arsenic due to bio-weathering.