几年前，加利福尼亚州召集了一个监管机构和 利益相关者制定科学合理的金属最低报告限值（MRL） 在饮用水中。工作组对降低报告级别感兴趣 受监管的金属可在不损害使用能力的情况下最大化发生信息 美国环境保护局（USEPA）批准的饮用水分析方法。为了验证其有效性 在这些决定中，工作组于2006年6月16日进行了大规模的实验室间性能研究 金属使用经批准的饮用水方法。这项研究使用了不同浓度的 两种代表性基质中的每种金属（去离子水和典型的加州饮用水 矩阵类似于州项目水）。样本包括不同位置的空白和盲峰 水平。 在较新的方法中，如314（高氯酸盐）、317和326（溴酸盐）、515.4（除草剂）和 526、528和532（UCMR清单2方法），EPA已经颁布了规定 MRL和空白最大浓度下的精度/准确度要求为基本要求 方法验收标准。根据现有法规，这种方法提供了一种平衡 实验室容量和实验室性能之间的关系。然而，如果一个特定的 金属在非常低的水平上是显著的，需要更仔细的审查以确定 通过进一步限制批准方法的数量，或 规定具体的额外质量控制绩效标准。 本文介绍了砷和钡的案例研究，其中对 关于可实现的最大残留限量，数据导致了不同的结论。 案例研究评估了以下参数，以确定可以实现的最大残留限量 常规地: 每个实验室获得低于标准的未标记空白矩阵结果的能力 目标MRL（评估了33%、40%和50%的目标MRL水平）；每个实验室获得盲试剂水峰（LFB）结果的能力 在规定的目标精度和精度范围内，达到所需的最大残留限量（需要两级LFB 每种金属提供）； 每个实验室获得范围内盲基质峰结果的能力 在所需MRL（5种不同的峰值水平）下指定的目标精度和精度 用括号括住目标MRL范围）； 每个实验室报告MDL的能力与其 准确定量给定目标MRL（例如，如果实验室报告MDL为1 ppb，但 明显无法在1 ppb时准确检测或量化，这被认为是一个问题）；和 对每种批准的方法评估所有这些因素，以确定 MRL可能会受到一系列方法的限制（例如，如果一种方法的结果给出 结果总是比另一个更为严格，这可能会导致MRL的潜在减少 知道这些限制通常是可以实现的）。 其他需要考虑的主观因素包括实验室的潜力 对给定方法实现更严格限制的经验水平。如果之前没有 要求低水平报告，实验室可能没有修改其校准或QC 相应的程序。 砷被用于一个案例研究，因为它在非常低的环境下具有高度记录的健康风险 这导致监管者寻求尽可能低的报告限额，甚至冒着风险 限制可用实验室的数量。另一个案例是钡元素的研究 众所周知，任何批准方法的分析准确度和精密度 足以应对健康风险。因此，在这种情况下，监管方法应该是 基于最大限度地增加可以进行测试的潜在实验室数量。 对于砷，如果研究中的所有实验室都包括在所有批准的方法中，那么 确定MRL会在订单上

Several years ago, the State of California convened a workgroup of regulators and stakeholders to develop scientifically defensible minimum reporting limits (MRLs) for metals in drinking water. The workgroup was interested in lowering the reporting levels for the regulated metals to maximize occurrence information without jeopardizing the ability to use any methodology approved by the US Environmental Protection Agency (USEPA) for drinking water analysis. In order to validate its decisions, the workgroup carried out a large-scale interlaboratory study of performance on 16 metals using approved drinking water methodologies. The study used varying concentrations of each metal in two representative matrices (DI Water and a typical California drinking water matrix similar to State Project Water). Samples included blanks and blind spikes at different levels. In newer methods such as 314 (perchlorate), 317, and 326 (bromate), 515.4 (herbicides), and 526, 528, and 532 (UCMR List 2 methods), EPA has promulgated the concept of specifying precision/accuracy requirements at the MRL and maximum concentrations for blanks as basic method acceptance criteria. Under existing regulations, this approach provides a balance between laboratory capacity and laboratory performance. However, if the health risk of a given metal is significant at very low levels, a closer review is indicated to determine whether a lower reporting limit could be achieved by further restricting the number of approved methods, or by mandating specific extra QC performance criteria. This paper presents case studies of arsenic and barium, in which a close review of the data leads to different conclusions regarding achievable MRLs. The case studies evaluated the following parameters to determine MRLs that could be achieved routinely: the ability of each lab to obtain a result for the unspiked blank matrix that was below the target MRL (levels of 33%, 40%, and 50% of the target MRL were evaluated); the ability of each lab to obtain results for blind reagent water spikes (LFB) that were within specified target accuracy and precision at the desired MRL (two levels of LFB were provided per metal); the ability of each lab to obtain results for the blind matrix spikes that were within specified target accuracy and precision at the desired MRL (5 different spike levels bracketing the target MRL range were used); the ability of each lab to have a reported MDL that was consistent with its ability to accurately quantitate at a given target MRL (e.g. if a lab reported an MDL of 1 ppb, but could clearly not detect or quantify precisely at 1 ppb, it was considered a problem); and, all of these factors were evaluated for each approved method to determine whether MRLs might be limited by allowing a range of methods (e.g. if results of one method gave consistently tighter results than another, this might lead to potential reductions in MRLs, by knowing that such limits were routinely achievable). Other subjective factors that required consideration included laboratories' potential experience level in achieving tighter limits for a given method. If there was no previous requirement to report at low levels, labs might not have modified their calibration or QC procedures accordingly. Arsenic was used for one case study because it has highly documented health risks at very low levels, leading regulators to search for the lowest possible reporting limits, even at the risk of limiting the number of available labs. The other case study is for the element barium, for which the analytical accuracy and precision by any of the approved methods are well known to be adequate for addressing health risks. Thus, in this case, the regulatory approach should be based on maximizing the number of potential labs that can do the testing. For arsenic, if all the labs in the study were included along with all approved methods, the determined MRL would be on the order