Pollutants are Seeping Into Drinking Water From Karst Regions at an Alarming Rate

Scientists have been looking at how easily contaminants can enter groundwater sources in karst areas and how it could impact drinking water safety.

An international team headed by Junior Professor Dr. Andreas Hartmann of the University of Freiburg's Chair of Hydrological Modeling and Water Resources compared the time it takes for toxins to decompose in carbonate rock regions in Europe, North Africa, and the Middle East with the time it takes for water to seep down from the surface to the subsurface.

The findings were presented in the Proceedings of the National Academy of Sciences, a scientific journal (PNAS).

Drinking Water from Karst Areas

Clean water is essential to the planet's environment and to its inhabitants, especially to humans. A significant amount of them came from the Karst regions. Karst regions are created as carbonate rock weathers, and they provide drinking water to around a quarter of the world's population.

Previous applications of continental or global hydrologic models have primarily focused on the occurrence of flooding or droughts and the general supply of drinking water. Water safety, in particular how easily contaminants can seep from the earth's surface into the groundwater by fractures or fissures, has been largely overlooked by scientists as an essential element in the potability of water on these vast scales.

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Pollutants in the Water

The recent research findings of Hartmann and his colleagues indicate that the risk of contamination by degradable contaminants such as pesticides, pharmaceuticals, or pathogens is substantially higher in karst areas, which are marked by an increased incidence of cracks or fissures than previously thought. While contaminants are deemed short-lived, based on the time it takes for them to decompose, up to 50% of them may still enter groundwater.

According to the researchers, rapid seepage mechanisms enable vast volumes of infiltrating water to enter groundwater in a short period of time. During major rain events, contaminants on the surface can seep rapidly and in high concentrations into the subsurface, particularly in regions with thin soils, such as the Mediterranean region. The effects were illustrated by Hartmann's team using the degradable pesticide Glyphosate as an illustration.

Their estimates showed that Glyphosate will surpass its permissive values by a factor of up to 19 due to accelerated transport through groundwater. For regions where agriculture relies on degradable fertilizers and pesticides, the increased risk of contaminants for drinking water or habitats that depend on groundwater is especially important.

What Makes Karst Areas Prone to Pollutants

Limestone aquifers have certain properties that make them especially vulnerable to pollution. Sinking streams and sinkholes enable unfiltered pollutants to travel quickly from the ground surface to the underlying aquifer. This function, combined with rapid groundwater flow in conduits expanded by mineral dissolution (karst aquifers) and the challenge of characterizing and controlling the extremely heterogeneous karst subsurface, raises the risk of water quality deterioration. The karst regions' dependence on groundwater for drinking sources has the potential to have adverse public health consequences.

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