Supplementary files for: The limitations of nitrate-sensitive zoning for groundwater protection from pesticides in Denmark

Pesticides and degradation products are a major challenge for groundwater management in Europe, and in Denmark where drinking water relies entirely on groundwater. To protect drinking water resources, local Danish authorities must take groundwater-protective measures in areas designated as sensitive to pollution; however, official zonation for pesticides is lacking. Nitrate-sensitive groundwater abstraction areas have been used instead. The goal of our study was to test the appropriateness of this groundwater protection strategy. We used Køge municipality (Denmark) as a focus area and tested how our findings upscale to the national level. The data for Køge municipality included 1070 individual groundwater samples, analysed for at least one of 366 pesticide compounds during the period 2012–2022, which were aggregated at the well-screen level by the median. Four pesticide compounds (2,6-dichlorobenzamide (BAM), desphenylchloridazon (DPC), N,N-dimethylsulphamide (DMS), 1,2,4-triazole) and three pesticide groups (phenoxyalcanoic acids, triazines and dimethachlor and its metabolites) were found with the highest detection frequency in the study area. We found that groundwater pollution with pesticide compounds was not limited to nitrate-sensitive areas in Køge municipality or in Denmark as a whole. Therefore, nitrate-sensitive areas can only be used partially for identifying pesticide-sensitive groundwater abstraction areas. The management implication is that placing protective measures only within nitrate-sensitive areas would be insufficient to fully address the risk of future groundwater pesticide pollution. We identified knowledge gaps and discussed a potential way forward with a more integrated management of groundwater protection in Denmark.

农药及其降解产物是欧洲地下水管理的一大难题，对于完全依赖地下水作为饮用水源的丹麦而言尤为如此。为保护饮用水资源，丹麦地方当局必须在被划定为污染敏感的区域采取地下水保护措施，但目前缺乏针对农药的官方区划，因此转而采用对硝酸盐敏感的地下水取水区域作为替代方案。本研究的目标为检验该地下水保护策略的适用性，以丹麦克厄自治市（Køge municipality）为重点研究区域，并测试研究结果能否推广至全国层面。克厄自治市的数据集包含1070个独立地下水样本，于2012年至2022年间针对366种农药化合物中的至少一种开展了检测，所有数据按井筛层级以中位数进行聚合。研究区域内检出频率最高的四种农药化合物分别为2,6-二氯苯甲酰胺（2,6-dichlorobenzamide，BAM）、脱苯基氯草隆（desphenylchloridazon，DPC）、N,N-二甲基磺酰胺（N,N-dimethylsulphamide，DMS）以及1,2,4-三唑，另有三类农药组：苯氧烷酸类（phenoxyalcanoic acids）、三嗪类以及二甲吩草胺及其代谢物。研究发现，克厄自治市乃至全丹麦范围内的农药化合物地下水污染，并不局限于硝酸盐敏感区域。因此，硝酸盐敏感区域仅能部分用于识别对农药敏感的地下水取水区域。本研究的管理启示在于，仅在硝酸盐敏感区域设置保护措施，不足以全面应对未来地下水农药污染的风险。此外，本研究明确了现有知识缺口，并探讨了在丹麦推行更一体化的地下水保护管理的可行路径。