Tracking pollution from a small town in Zambia

James Sorenson (BGS) walked us through his poster presentation for his Catalyst Project: Mapping groundwater quality degradation beneath growing rural towns in Sub Saharan Africa.

The story starts with a pesticide found in slug pellets, which was unexpectedly detected in UK groundwater. This prompted this research to look for similar chemicals in African groundwater, What was found was relatively high levels of DEET, known to many travellers as “Jungle Formula” for keeping mosquitos at bay.

The implications are that these potentially health impacting chemicals are not being tested for. The levels detected were low, but DEET, and similar pesticides break down very slowly, if at all. In larger urban areas, these chemicals could be entering water supply wells and boreholes at potentially harmful levels.

The level of risk is just not known yet, but this research has raised an important warning flag. However, relatively simple measures, such as well protection is critical, especially for shallow self supply boreholes.

A risk that is understood better is that from pathogens coming from sewage-polluted groundwater. This can lead to outbreaks of cholera, typhoid and many other diseases.The challenge is how to map and track this pollution to see where it is coming from and where it is going to.

Pathogens can’t be measured directly. The most common approach is to measure concentrations of faecal coliforms, but doing this has drawbacks: Coliforms are micro-organisms that have to be grown in ‘culture’ so that they can be counted. Coliforms also die more quickly than pathogens so groundwater sample tests may come back showing nothing, but in reality still be potentially harmful to health.

Field measurements of an amino acid, found in sewage, called tryptophan can be used to map and monitor pathogen contamination. Monitoring is done using fluorescence – shining a light through the water sample – so it can be done in realtime and doesn’t need regents. The work demonstraed that this monitoring method is quicker, cheaper and more accurate that than measuring faecal coliforms.

The fieldwork also showed that the drawdown from the supply wells is pulling in contamination from under the city, Kabwe. This has helped the town authority prioritise the control of informal settlements to the west of the town that is encroaching towards the well field for the town’s water supply.

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