Analysing Microbial Risks Associated with Heavy Metal Levels in Groundwater Sources: A Case Study of Werdama, Libya

Abstract

Groundwater is the main source of drinking water for rural and peri-urban communities across the Al-Jabal Al-Akhdar region of Libya, yet its quality has rarely been documented in any systematic way. In this study we assessed the physicochemical and microbiological quality of groundwater drawn from three wells (W1–W3) in the Werdama area, Al-Bayda, Libya, focusing in particular on four priority heavy metals: lead (Pb), cadmium (Cd), chromium (Cr), and iron (Fe), benchmarked against World Health Organization (WHO) maximum contaminant levels (MCL). Physicochemical parameters (electrical conductivity, temperature, pH, dissolved oxygen, turbidity, and total dissolved solids) were measured both in situ and in the laboratory, and metal concentrations were quantified by atomic absorption spectrophotometry following acid digestion; calibration curves showed excellent linearity throughout (R² = 0.9984–0.9999). Pb and Fe exceeded WHO limits in all three wells, Cd exceeded the WHO limit but stayed below the U.S. EPA threshold, and Cr remained within internationally accepted limits. The computed Heavy Metal Pollution Index (HPI) came to 97.99, 120.40, and 128.50 for W1, W2, and W3, placing W2 and W3 in the high-pollution category. Culture-based screening on Nutrient Agar, MacConkey Agar, and Eosin Methylene Blue Agar detected Escherichia coli in all three wells, with colony counts pointing to a low-to-moderate contamination risk (5–40 CFU/100 mL). Together, these results show that Werdama groundwater carries both geogenic heavy-metal enrichment and low-level faecal contamination, and is therefore not consistently safe for direct consumption without treatment. We argue that routine groundwater surveillance, targeted remediation, and better sanitation infrastructure are needed in this water-scarce region.