A Review on the Application of Isotopic Techniques to Trace Groundwater Pollution Sources within Developing Countries

Abstract

Owing to a lack of efficient solid waste management (SWM) systems, groundwater in most developing countries is found to be contaminated and tends to pose significant environmental health risks. This review paper proffers guidelines on the application of isotopic techniques to trace groundwater pollution sources from data spanning from 2010 to 2020 within developing countries. Earlier groundwater studies in those countries were mainly focused on using hydrochemical and geophysical techniques. The limitation of these techniques is that they can only monitor the concentration of pollutants in the water bodies and possible leachate infiltration but cannot determine the specific sources of the pollution. Stable isotopes of δ18O, δ2H and δ13C can confirm leachate migration to water bodies due to methanogenesis. The high tritium in landfill leachates is useful to identify leachate percolation in groundwater. The δ15N technique has been used to distinguish between synthetic and organic nitrogen sources but its application is limited to differentiating between atmospheric vs. inorganic nitrogen sources. The use of a dual isotope of δ15N–NO3− and δ18O–NO3− is beneficial in terms of identifying various sources of nitrogen such as atmospheric and inorganic fertilizers but is yet to be used to differentiate between nitrogen pollution sources from dumpsites, sewage and animal manure. The coupling of the 11B isotope with δ15N–NO3− and δ18O–NO3− and other hydrochemical parameters has proven to be effective in distinguishing between nitrate fertilizer, animal manure, seawater contamination and sewage. Therefore, in areas affected by agricultural activities, landfill leachates, domestic or sewage effluent and seawater intrusion, it is incumbent to couple hydrochemical (Cl−, NO3−, B, DO) and isotope techniques (δ18O, 2H, δ13C, δ18O–NO3−, δ15N–NO3−, δ11B and 3H) to effectively determine pollution sources of groundwater in developing countries. The foregoing review will provide guidelines for studies that may aim to critically distinguish between seawater intrusion, dumpsites, sewage and septic leachates.

Integrated Hydrogeological, Hydrochemical, and Isotopic Assessment of Seawater Intrusion into Coastal Aquifers in Al-Qatif Area, Eastern Saudi Arabia

“…Oxygen and hydrogen stable isotopes have been used to identify GW salinization and the effect of seawater intrusion on coastal aquifers in many regions worldwide [ 5 , 62 , 63 ]. Generally, GW affected by SWI has higher values of δ 18 O and δ 2 H than fresh GW [ 64 ].…”

Carbon and Sulfur Isotope Methods for Tracing Groundwater Contamination: A Review of Sustainable Utilization in Reclaimed Municipal Landfill Areas

“…The relatively distinct isotopic ratios or signatures of substances, created through biogeochemical processes, offer great potential for tracing contaminants such as leachates around the landfill [14]. The most frequently used environmentally stable isotopes are as follows: δ 13 C DIC (CO 3 2− and HCO 3 − ), δ 34 S (SO 4 2− ), δ 2 H, and δ 18 O of water molecules; δ 15 N and δ 18 O (NO 3 − ) [14,27,44,46,[60][61][62][63][64][65][66][67][68][69][70][71][72]; and radioactive isotopes 3 H, 14 C, 87 Sr, 36 Cl, and 11 B [73][74][75][76][77][78][79]. Satisfactory results are obtained on the basis of carbon and sulfur isotope tests, which are easy and friendly to use and are characterized by appropriate precision.…”

A Unit‐Concentration Method to Quantify Source Contribution

“…Field measurements for distinguishing water sources include stable isotope analyses (Sankoh et al 2022) and tracer testing (Davis et al 1980). Tracer tests provide data to identify the fate of water arising from a particular source such as a stream, injection well, or area of focused recharge.…”