Groundwater fluoride concentrations in the watershed sedimentary basin of Quetta Valley, Pakistan.

Litho-geochemical characteristics of low and high fluoride (F-) groundwater along with hydrological processes were investigated to delineate its genesis and enrichment mechanism in a watershed sedimentary basin. In this study, groundwater F- concentration ranged from 0 to 20 mg/L with a mean and standard deviation of 2.8 and ± 3.7 mg/L, respectively. Out of N = 87, 63% of samples exceeded the World Health Organization (WHO) limit of 1.5 mg/L. The order of cationic and anionic dominance in groundwater samples with mean was found in decreasing order as Na+ > Mg2+ > Ca2+ > K+ and HCO3- > SO42- > Cl- > PO43- > NO3- measured in milligrams per liter. Groundwater chemistry changed from Ca-HCO3 to Na-HCO3 type and low to high fluoride as we moved from mountain foot towards the synclinal basin. Low fluoride groundwater reflected weathering, recharge, and reverse ion exchange processes with Ca-HCO3- and Ca-Mg-Cl-type water while high fluoride groundwater revealed base ion exchange, mixing, and desorption as dominant hydrological processes with Na-HCO3 and Na-Cl types of water. Gibb's diagram showed rock weathering and mineral dissolution as the major geochemical processes controlling water chemistry with an insignificant role of evaporation in the semi-arid area. Fluoride was undersaturated with mineral fluorite, indicating fluoride in groundwater is released by secondary minerals. However, due to complex geological features, groundwater fluoride enrichment was affected by a broad-scale process across a wide area such as depth, residence time, and most important geomorphological units hosting the aquifer.

Micro-synteny conservation analysis revealed the evolutionary history of bacterial biphenyl degradation pathway.

Phenolic compounds have been enlisted by the United States Environmental Protection Agency (USEPA) and the European Union (EU) as pollutants of priority concern. The biphenyl degradation pathway plays an essential role in prokaryote polychlorinated biphenyls degradation. Our understanding of prokaryotic pathways and their evolution has dramatically increased in recent years with the advancements in prokaryotic genome sequencing and analysis tools. In this work, we applied bioinformatics tools to study the evolution of the biphenyl degradation pathway focusing on the phylogeny and initiation of four representative species (Burkholderia xenovorans LB400, Polaromonas naphthalenivorans CJ2, Pseudomonas putida F1 and Rhodococcus jostii RHA1). These species contained partial or full concatenated genes from bph gene cluster (i.e. bphRbphA1A2A3A4BCKHJID). The aim was to establish this pathway's origin and development mode in the prokaryotic world. Genomic screening revealed that many bacterial species possess genes for the biphenyl degradation pathway. However, the micro-synteny conservation analysis indicated that massive gene recruitment events might have occurred during the evolution of the biphenyl degradation pathway. Combining with the phylogenetic positions, this work points to the evolutionary process of acquiring the biphenyl degradation pathway by different fragments through horizontal gene transfer in these bacterial groups. This study reports the first-ever evidence of the birth of this pathway in the represented species.