Isotope hydrology tools in the assessment of arsenic contamination in groundwater: An overview.

Groundwater is important for the survival of humanity and the demand for the same is drastically increasing globally. The precious water resources are under constant threat, either as a result of natural processes or due to the influence of the anthropogenic activities. Arsenic contamination of groundwater is one of those threats that have affected approximately over 500 million people in 107 countries globally. Although, many studies (∼1000 Nos.) have been carried out on arsenic hydrogeobiochemistry, only a few have reported, on the use of different isotopes in understanding the arsenic hydrochemistry, and its release mechanism and mobilization. Determination of the isotopic composition of a groundwater sample and its dissolved compounds enable a better insight into the hydrological processes that control the distribution and migration of arsenic in the subsurface hydrological system. The environmental isotopes of water molecules (δ18O and δ2H) have been widely used to assess the groundwater origin, its recharge mechanisms, the rock-water interactions and quality. The stable isotopes of dissolved compounds of water (δ34S, δ15N, δ13C, δ56Fe etc.) give better information on the reaction processes within these elements and thus act as a tracer for contaminants, while the radioactive isotopes, such as 14C, 3H, 81Kr, 36Cl, 39Ar etc., can be used to assess the residence time of groundwater and its renewability. This article reviews the different uses of environmental isotopes as tools for providing critical information on various hydrological processes in the arsenic contaminated regions that can't be obtained through conventional tools for better management of the groundwater resources.

Application of radon (222Rn) as an environmental tracer in hydrogeological and geological investigations: An overview.

Radon (222Rn) is a colourless, odourless, inert, and radioactive noble gas (t1/2 = 3.8 days) that emanates from rocks and soils as a result of the alpha decay of its parent, radium (226Ra) in the decay series of uranium-238, is the focus of this study. Radon is produced in the crystal lattice of the minerals and emanates out through alpha recoil. It dissolves in water, and is also found in soil and air. Its distribution in water is more pertinent for scientific investigations. It can be measured by various methods. Certain properties of radon enable it to serve as an ideal tracer, viz., short-half life, inertness, high abundance in groundwater than surface water, preferential partitioning, sensitivity to sudden changes in subsurface conditions, non-invasiveness etc. This paper reviews the state-of-the-art techniques on the measurement of dissolved radon in water and its potential applications as a tracer and precursor in several hydrogeological and geological applications like understanding the surface water - groundwater interactions, hydrograph separation of streams, estimation of Submarine Groundwater Discharge (SGD), study of hydrodynamics and water balance of lakes, earthquake predictions, locating geological structures (faults/lineaments), geochemical explorations, NAPL contamination studies etc. Among the various applications presented, radon based approach is found to be more reliable in water resources domain than seismic precursory studies. The interpretations based on radon study in the above applications will pave the way for the improved understanding of the hydrological processes, and thus, help the planners and water managers for the sustainable development and management of water resources.

Factors controlling the distribution of radon (222Rn) in groundwater of a tropical mountainous river basin in southwest India.

Studies on occurrence of radon in the environment are receiving growing attention worldwide due to its adverse impact on human health. Despite that, the dissolved radon in water is found to be a useful tracer in many hydrogeological studies. Although, several studies focused on the occurrence of high 222Rn in groundwater, the processes responsible for its variation is still not well understood. Hence, an attempt has been made in the present study to elucidate the underlying factors influencing the abundance 222Rn in hard rock (gneissic) aquifers of Karamana River Basin, southwest India. 222Rn in groundwater was analyzed in 71 dug wells during the pre-monsoon period of 2017. A large variability in 222Rn activities (170-68,350 Bq/m3) was noticed in groundwater and high activities were mainly seen in the khondalite formation. No significant dependencies between 222Rn activity and depth to water table, groundwater temperature and electrical conductivity were observed. However, majority of the presence of high 222Rn activity in groundwater matches with the location of lineaments. Furthermore, radium content in the host rock, degree of weathering and fracturing and the emanation coefficient of the rock were found to have an important bearing on the occurrence of radon in groundwater. The underlying factors influencing the abundance of radon in hard rock aquifers were also conceptualized. Thus, the study highlights the usefulness of 222Rn as a potential tool in delineating the macro-structural features like fractures/lineaments that are significant repositories of groundwater, which could be explored for groundwater development in hard rock terrains.

Evaluation of radiation dose from radon ingestion and inhalation in groundwater of a small tropical river basin, Kerala, India.

A comprehensive study was conducted to understand the radon (222Rn) distribution and associated radiation doses to the public in a small tropical river basin partly set in the western slope of the Southern Western Ghats of Kerala, India. Radon, though detected in all the 71 monitored wells (0.17-68.3 Bq L-1), exceeded the maximum contamination level (MCL) of 11.1 Bq L-1 for drinking water recommended by United States Environmental Protection Agency (USEPA) in eight samples from isolated pockets of highland, midland and lowland of the Karamana River Basin (KRB) and found to be well within 100 Bq L-1, the parametric value suggested by the World Health Organization (WHO) and the European Union (EU). The age-wise total annual effective doses (AEDs) of groundwater radon activity ranged from 0.5-208.4 µSv a-1 for infants, 0.4-172.2 for children and 0.5-189.7 µSv a-1 for adults. The results reveal that effective doses due to groundwater radon pose no potential public health risk in the study region. Since there is no previous background information on radon-induced radiation dose in the KRB, this work is a newfangled attempt from a public health point of view.

Cytomegalovirus and human immunodeficiency virus in semen of homosexual men.

OBJECTIVE: To assess the accuracy of serology to predict the presence of cytomegalovirus (CMV) in semen of homosexual men without and with HIV coinfection. DESIGN: Semen CMV was detected by electron microscopy and by polymerase chain reaction (PCR) amplification; paired serum was tested for CMV IgG/IgM. Semen HIV was detected by reverse transcription-PCR. SETTING: Licensed clinical and research laboratory. PATIENT(S): Sixty-eight men. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): Frequency of CMV and HIV in semen. RESULT(S): Cytomegalovirus was detected by electron microscopy in 3 of 10 specimens examined. Forty-six (89%) of 52 HIV-infected men were seropositive for CMV by combined assay for IgG/IgM; two more (48 of 52, 92%) were seropositive for CMV IgG by separate assay; 25 (48%) of the HIV-infected men had PCR-detectable CMV DNA in at least one semen specimen, 22 of whom (42%) had CMV in all specimens. Nineteen (13%) of the 150 specimens tested positive for HIV, whereas 67 (45%) tested positive for CMV; seven specimens tested positive for both CMV and HIV. Cytomegalovirus, but not HIV, detection in semen correlated with decreased CD4(+) lymphocytes in peripheral blood (<700/µL) but was not accurately predicted by serology, leukocytospermia, or age. CONCLUSION(S): Cytomegalovirus in semen is not accurately predicted by serology. Sperm banking needs to include direct assessment of CMV in semen specimens. Strategies to eliminate CMV from semen specimens are needed to alleviate the risk of virus transmission.