School of Biological, Earth and Environmental Sciences, University College Cork, Cork, Ireland; Irish Centre for Research in Applied Geosciences, University College Dublin, Dublin, Ireland; Environmental Research Institute, University College Cork, Cork, Ireland.
Environmental Sustainability and Health Institute, Technological University Dublin, Dublin 7, Ireland.
Sci Total Environ. 2022 Sep 20;840:156311. doi: 10.1016/j.scitotenv.2022.156311. Epub 2022 May 27.
Groundwater is a vital drinking water resource and its protection from microbiological contamination is paramount to safeguard public health. The Republic of Ireland (RoI) is characterised by the highest incidence of verocytotoxigenic Escherichia coli (VTEC) enteritis in the European Union (EU), linked to high reliance on unregulated groundwater sources (~16% of the population). Yet, the spatio-temporal factors influencing the frequency and magnitude of microbial contamination remain largely unknown, with past studies typically constrained to spatio-temporally 'limited' sampling campaigns. Accordingly, the current investigation sought to analyse an extensive spatially distributed time-series (2011-2020) of groundwater monitoring data in the RoI. The dataset, compiled by the Environmental Protection Agency (EPA), showed 'high' contamination rates, with 66.7% (88/132) of supplies testing positive for E. coli, and 29.5% (39/132) exceeding concentrations of 10MPN/100 ml (i.e. gross contamination) at least once during the 10-year monitoring period. Seasonal decomposition analyses indicate that E. coli detection rates peak during late autumn/early winter, coinciding with increases in annual rainfall, while gross contamination peaks in spring (May) and late-summer (August), likely reflecting seasonal shifts in agricultural practices. Mixed effects logistic regression modelling indicates that monitoring sources located in karst limestone are statistically associated with E. coli presence (OR = 2.76, p = 0.03) and gross contamination (OR = 2.54, p = 0.037) when compared to poorly productive aquifers (i.e., transmissivity below 10m/d). Moreover, 5-day and 30-day antecedent rainfall increased the likelihood of E. coli contamination (OR = 1.027, p < 0.001 and OR = 1.005, p = 0.016, respectively), with the former also being associated with gross contamination (OR = 1.042, p < 0.001). As such, it is inferred that preferential flow and direct ingress of surface runoff are the most likely ingress mechanisms associated with E. coli groundwater supply contamination. The results presented are expected to inform policy change around groundwater source protection and provide insight for the development of groundwater monitoring programmes in geologically heterogeneous regions.
地下水是一种重要的饮用水资源，保护地下水免受微生物污染对于保障公众健康至关重要。爱尔兰共和国（RoI）是欧盟中肠出血性大肠杆菌（VTEC）肠炎发病率最高的国家，这与对不受监管的地下水源的高度依赖有关（约占人口的 16%）。然而，影响微生物污染频率和程度的时空因素在很大程度上仍不清楚，过去的研究通常局限于时空上“有限”的采样活动。因此，目前的研究旨在分析爱尔兰广泛分布的时间序列（2011-2020 年）的地下水监测数据。该数据集由环境保护局（EPA）编制，显示出“高”污染率，有 66.7%（88/132）的供应水样检测出大肠杆菌呈阳性，29.5%（39/132）的水样在 10 年监测期间至少有一次超过了 10MPN/100ml 的浓度（即严重污染）。季节性分解分析表明，大肠杆菌的检出率在晚秋/初冬达到峰值，与年降雨量的增加相吻合，而严重污染则在春季（5 月）和夏末（8 月）达到峰值，这可能反映了农业活动季节性的变化。混合效应逻辑回归模型表明，与生产力较低的含水层（即渗透率低于 10m/d）相比，监测到位于岩溶石灰岩层的水源与大肠杆菌的存在（OR=2.76，p=0.03）和严重污染（OR=2.54，p=0.037）具有统计学关联。此外，5 天和 30 天的前期降雨量增加了大肠杆菌污染的可能性（OR=1.027，p<0.001 和 OR=1.005，p=0.016），前者也与严重污染有关（OR=1.042，p<0.001）。因此，可以推断，优先流和地表径流的直接进入是与大肠杆菌地下水供应污染最相关的可能进入机制。所提出的结果有望为地下水源保护政策的改变提供信息，并为地质异质性地区地下水监测计划的制定提供参考。
