Heavy Metal Contamination Due to Waste Disposed Zone of Shahbazpur Gas Field in Bangladesh: Environmental and Health Impact Assessment

Abstract

Produced water constitutes the largest fraction of waste generated in the oil and gas extraction industry, while drilling waste represents the second major fraction. Both types of waste are typically discharged into evaporation ponds, which therefore serve as the primary accumulation zones for toxic elements. The study aims to evaluate the extent of elemental contamination associated with hydrocarbon extraction activities at the Shahbazpur gas field in Bangladesh by analyzing elemental abundances in both subsurface reservoir core samples and surface environmental samples (soil and drilling mud). A total of fourteen samples, including three gas reservoir well core samples (depths: 2591.8–3699.0 m) and eleven surface environmental samples (soil and mud from evaporation ponds and surrounding areas), were collected for analysis. In this study, twelve elemental abundances and different environmental contamination indicators were analyzed using the Energy Dispersive X-ray Fluorescence (EDXRF) method. The analysis was conducted on both gas-well core samples and environmental soil and mud-soil samples collected from the Shahbazpur gas field. In the environmental soil and mud-soil samples, Pb concentrations range from 7.3 to 113 ppm, with an average value of 71 ppm, whereas the corresponding Upper Continental Crust (UCC) value is 17 ppm. Similarly, As concentrations range from 10 to 44 ppm, with an average of 27 ppm, compared to the UCC value of 4.8 ppm. These results indicate that the average concentrations of both Pb and as in the soil and mud-soil samples are significantly higher than their respective UCC background values. The calculated enrichment factor (EF), geo-accumulation index (Igeo), and contamination factor (CF) for Pb indicate severe enrichment, moderate geo-accumulation, and considerable contamination in most soil and mud-soil samples.  Overall, the environmental assessment suggests considerable ecological risk, indicating that the soils in the study area are increasingly polluted by toxic elements such as Pb and as introduced through gas production activities. The hazard study of as for children exhibits the existence of chronic non-carcinogenic risk and medium to high cancer risk, though children are more susceptible to heavy metal/metalloid.