School of Environmental Studies, Queen's University, 99 University Ave, Kingston, ON, Canada.
Technological University Dublin, Park House, 191 N Circular Rd, Dublin, Ireland.
Sci Total Environ. 2022 Nov 10;846:157478. doi: 10.1016/j.scitotenv.2022.157478. Epub 2022 Jul 20.
A spatiotemporally static total coliform (TC) concentration threshold of five colony-forming units (CFU) per 100 mL is used in Ontario to determine whether well water is of acceptable quality for drinking. The current study sought to assess the role of TC and associated thresholds as microbial water quality parameters as the authors hypothesized that, since static TC thresholds are not evidence-based, they may not be appropriate for all well water consumers. A dataset containing the microbial water quality information of 795,023 samples (including TC and Escherichia coli (E. coli) counts) collected from 253,136 private wells in Ontario between 2010 and 2017 was used. To accurately assess the relationship between E. coli and non-E. coli TC, "non-E. coli coliform" (NEC) counts were calculated from microbial water quality data and replaced TC throughout analyses. This study analysed NEC and E. coli detection rates to determine differences between the two, and NEC:E. coli concentration ratios to assess links, if any, between NEC and E. coli contamination. Study findings suggest that spatiotemporally static NEC thresholds are not appropriate because seasonal, spatial, and well-specific susceptibility factors are associated with distinct contamination trends. For example, NEC detection rates exhibited bimodality, with summer (29.4 %) and autumn (30.2 %) detection rates being significantly higher (p < 0.05) than winter (21.9 %) and spring (19.9 %). E. coli detection rates also varied seasonally, but peaked in summer rather than autumn. As such, it is recommended that these factors be considered during the development of private well water guidelines and that static thresholds be avoided. Furthermore, the authors propose that, because NEC:E. coli concentration ratios change in the context of the aforementioned factors, they may have a role in inferring groundwater contamination mechanisms, with high ratios being associated with generalized aquifer contamination mechanisms and low ratios with localized contamination mechanisms.
安大略省采用每 100 毫升 100 个菌落形成单位（CFU）的时空静态总大肠菌群（TC）浓度阈值来确定井水是否可安全饮用。本研究旨在评估 TC 及其相关阈值作为微生物水质参数的作用，因为作者假设，由于静态 TC 阈值不是基于证据的，因此它们可能不适合所有井水消费者。使用了一个包含 2010 年至 2017 年间从安大略省 253136 口私人井中采集的 795023 个样本（包括 TC 和大肠杆菌（E. coli）计数）的微生物水质信息数据集。为了准确评估 E. coli 和非 E. coli TC 之间的关系，从微生物水质数据中计算出“非 E. coli 大肠菌群”（NEC）计数，并在整个分析中替代 TC。本研究分析了 NEC 和 E. coli 的检出率，以确定两者之间的差异，并分析 NEC：E. coli 浓度比，以评估 NEC 和 E. coli 污染之间的任何关联。研究结果表明，时空静态 NEC 阈值并不合适，因为季节性、空间和特定水井的易感性因素与不同的污染趋势有关。例如，NEC 的检出率呈双峰分布，夏季（29.4%）和秋季（30.2%）的检出率显著高于冬季（21.9%）和春季（19.9%）。E. coli 的检出率也随季节而变化，但在夏季而非秋季达到峰值。因此，建议在制定私人井水指南时考虑这些因素，并避免使用静态阈值。此外，作者提出，由于 NEC：E. coli 浓度比在上述因素的背景下发生变化，它们可能在推断地下水污染机制方面发挥作用，高浓度比与普遍的含水层污染机制有关，低浓度比与局部污染机制有关。
