Fluoride (F⁻) contamination in drinking groundwater is a significant human health risk in Pakistan. Moreover, high fluoride pollution in drinking water causes a variety of disorders, including dental, neurological, and skeletal fluorosis. The aim of this research was to evaluate the health risk of elevated fluoride in groundwater and its suitability assessment for drinking purposes. The total of (n = 37) samples were collected from community tube wells of Quetta Valley, Balochistan, Pakistan. The results show a mean pH value of 7.7, TDS of 404.6 mg/L, EC of 500 µs/cm, depth of 96.8 feet, and turbidity of 1.7 nephelometric turbidity units. The mean values of HCO₃⁻, Ca²⁺, Mg²⁺, and Na⁺, were 289.5, 47.5, 30.6, and 283.3 mg/L, respectively. The mean values of SO₄²⁻, NO₃⁻, K⁺, Cl⁻, and Fe²⁺, were 34.9, 1.0, 1.6, 25.6, and 0.01 mg/L, respectively. The F⁻ concentration in the groundwater varied between 0.19 and 6.21, with a mean value of 1.8 mg/L, and 18 samples out of 37 were beyond the WHO recommended limit of 1.5 mg/L. The hydrochemical analysis results indicated that among the groundwater samples of the study area, 54% samples were Na-HCO₃ type and 46% were mixed CaNaHCO₃ type. The saturation indices of the mineral phases reveal that the groundwater sources of the study area were saturated with CaCO₃ and halide minerals due to their positive (SI) values. Such minerals include calcite, dolomite, gypsum, and fluorite. The principal component analysis results reveal that the groundwater sources of the study area are contaminated due to geological and anthropogenic actions. The health risk assessment results of the F⁻ concentrations show the ranges of ADD_ingestion for children, females, and males in the Quetta Valley, and their mean values were observed to be 0.093052, 0.068825, and 0.065071, respectively. The HQ_ingestion mean values were 1.55086, 1.147089, and 1.084521 for children, females, and males, respectively. It was noticed that children had the highest maximum and average values of ADD_ingestion and HQ_ingestion in the research area, indicating that groundwater fluoride intake poses the greatest health risk to children. The water quality index (WQI) analyses show that 44% of the samples belong to the poor-quality category, 49% were of good quality, and 8% of the samples of the study area belong to the excellent category.

Since Mn, Fe and As contaminants often coexist in the environment, we hypothesize that the presence of multifunctional bacteria is capable of reducing Mn and Fe oxides and promoting the mobilization and release of arsenic. However, such bacteria have not been reported yet; moreover, the impact of bacteria with the ability to simultaneously reduce Mn and Fe oxides on the formation of high-arsenic groundwater remains unclear. This study aims to address this question. Here, we found that the microbial community in the soils was able to efficiently reduce Mn oxides into Mn(II). An analysis of the microbial community structures of the soil shows that it contained Proteobacteria (41.1%), Acidobacteria (10.9%), Actinobacteria (9.5%) and other less abundant bacteria. Based on this observation, we successfully isolated a novel bacterium Cellulomonas sp. CM1, which possesses both Mn- and Fe-oxide-reducing activities. Under anaerobic conditions, strain CM1 can reduce Mn oxides, resulting in the production of 13 mg/L of Mn(II) within a span of 10 days. Simultaneously, it can reduce Fe oxides, leading to the generation of 9 mg/L of Fe(II) within 9 days when a yeast extract is used as an electron donor. During these reduction reactions, the cells were grown into a density of OD₆₀₀ 0.16 and 0.09, respectively, suggesting that Mn(IV) is more beneficial for the bacterial growth than Fe(III). Arsenic release assays indicate that after 108 days of anoxic incubation, approximately 126.2, 103.2 and 81.5 μg/L As(V) were mobilized and released from three soil samples, respectively, suggesting that CM1 plays significant roles in driving mobilization of arsenic from soils. These findings shed new light on the microbial processes that lead to the generation of arsenic-contaminated groundwater.