Tracing enteric pathogen contamination in sub-Saharan African groundwater

Area of Science:

• Environmental microbiology
• Hydrogeology
• Public health

Background:

• Groundwater contamination poses a significant threat to public health, especially in urban areas with inadequate sanitation.
• Quantitative PCR (qPCR) offers a rapid method for detecting fecal bacteria as indicators of groundwater contamination.
• Understanding groundwater vulnerability is crucial for ensuring safe drinking water supplies.

Purpose of the Study:

• To assess the prevalence and seasonality of enteric bacterial contamination in groundwater supplies in Kabwe, Zambia.
• To identify specific bacterial species indicative of fecal pollution using qPCR.
• To evaluate the effectiveness of traditional and emerging fecal indicators in assessing groundwater quality.

Main Methods:

• A microbial DNA qPCR array targeting 45 bacterial species was used on 22 groundwater samples collected seasonally.
• Samples were analyzed for thermotolerant coliforms and tryptophan-like fluorescence.
• Geological context (shallow wells, boreholes in laterite/saprolite and dolomite) was considered.

Main Results:

• Enteric bacterial DNA was detected in 72% of analyzed groundwater supplies.
• Citrobacter freundii (69%) and Vibrio cholerae (41%) were the most prevalent detected bacteria.
• Contamination was highest in shallow wells, but deeper boreholes were also affected, indicating vulnerability of bedrock aquifers.
• Thermotolerant coliforms and tryptophan-like fluorescence confirmed fecal contamination in most positive sites.

Conclusions:

• Kabwe's groundwater is highly vulnerable to fecal contamination, with rapid subsurface pathways facilitating pollution.
• Both shallow and deeper groundwater resources are at risk, challenging the protective capacity of geological formations.
• Peri-urban areas showed less contamination, suggesting limited lateral transport outside the city.
• qPCR and tryptophan-like fluorescence are effective tools for assessing groundwater contamination and associated health risks.