Investigating the dynamics of two herbicides at a karst spring in Germany: Consequences for sustainable raw water management

- Atrazine can almost always be detected in spring water.
- Metazachlor is only detectable after recharge events and not in winter.
- Atrazine, inorganic cations (Ca2 + and Mg2 +) and the electrical conductivity correlate.
- The long-term storage potential of karst aquifers may not be ignored.
- Persistent substances are prone to cause long-term contamination in karst systems.

While karst aquifers are considered as rapid flow and transport systems, their high potential for long-term storage is often ignored. However, to achieve a sustainable raw water quality for drinking water production, the understanding of this potential is highly essential. In this study, the transport dynamics of the two herbicides metazachlor and atrazine as well as a degradation product of the latter (desethylatrazine) were investigated at a karst spring over 1 year. Even 20 years after its ban in Germany, atrazine and its degradation product were almost always detectable in the spring water in the low ng L-1 range (up to 5.2 ng L-1). Metazachlor could only be detected after precipitation events, and the observed concentrations (up to 82.9 ng L-1) are significantly higher than atrazine or desethylatrazine. Comparing the dynamics of the herbicides with the inorganic ions Ca2 +, Mg2 + and electrical conductivity, a positive correlation of atrazine with these parameters could be observed. From this observation, atrazine is concluded to be located within the aquifer matrix. To achieve a sustainable raw water management at karst springs, the rapidness of these systems needs to be highlighted as well as their long-term storage potential. Persistent substances or transformation products are prone to deteriorate the raw water quality for decades.