Following the publication of the Kolpin et al. (2002) landmark study, the term contaminants of emerging concern (CECs) has become increasingly popular as a catchall for various chemicals measured in the environment that are not regulated and therefore not typically monitored by federal, state, or local environmental agencies. These chemicals are considered “emerging” in the sense that we, as scientists, know very little about most of them, and certainly do not have enough information as to whether some of these CECs are or should be a concern and perhaps regulated. This ambiguity is reflected in how different researchers categorize CECs. In a cursory literature review examining studies over the past 20 yr, we found that between 9 and 40 groups of chemicals have been identified as CECs in individual studies (e.g., Daughton and Ternes [1999] identified 17 groups of emerging chemicals that only included pharmaceuticals and personal care product chemicals). The number of chemicals in each group appears to be growing over time as more chemicals are detected and increasingly finer distinctions are made in chemical groupings by researchers.

The only characteristic that CECs share in common is that they are currently unregulated, and some believe they have the potential to cause adverse effects. Thus, CEC is an artificial classification that doesn't strike us as either meaningful or useful for environmental decision-making. As a case in point, some water utilities, resource agency staff, the public, and even some researchers have been known to request data for “CECs” for a site or a project, as if CECs comprised a standardized list of chemicals. Other researchers have noted similar issues regarding the term CECs (e.g., Sauvé and Desrosiers 2014).

How do we take the thousands of unregulated chemicals (and their degradation products) reported in United States surface waters and identify which of these are truly a concern? To answer this question, it is educational to examine how a chemical arrived at the state of being a real concern. Triclosan, which is used as an antimicrobial agent in various consumer products, was first reported in some treated wastewater effluents and surface waters in the late 1990s (Kolpin et al. 2002) even though it has been in use in hospitals in the United States and elsewhere since the 1970s and has been widely incorporated into consumer products since the 1980s. Triclosan became an emerging contaminant because we could now detect lower concentrations in surface waters than before and it is widespread. The intended use of triclosan as an antimicrobial could have potential effects on biota and people (Bedoux et al. 2011). The widespread incorporation of triclosan into many personal care products used by millions of households and the “down the drain” fate of these products were key considerations in escalating the concern over triclosan. Human health concerns over triclosan, particularly potential cross-resistance to antibiotics, was a major consideration when both the European Union and the United States banned triclosan in certain consumer products. Thus, this CEC had a wealth of supporting data (i.e., a weight-of-evidence) demonstrating several reasons to be a concern.

If in fact, CECs take the path noted for triclosan, in which many years and extensive resources are needed to confirm a chemical is truly a concern, how is it possible to address the thousands of chemicals considered to be CECs? Many assessments have approached this challenge by targeting specific chemical groups (e.g., pyrethroid or nicotinamide pesticides), chemicals with similar intended use (e.g., antimicrobials, synthetic hormones, surfactants), type of source (e.g., agricultural watersheds, wastewater treatment effluents), intended biological effects (e.g., biocide, pesticide), a predetermined list of priority chemicals (e.g., Diamond et al. 2011), or those with alarming chemical characteristics, if known (e.g., high bioaccumulation potential). All these approaches could miss many chemicals that we currently do not recognize as having potential effects on biota or people. Also, currently unknown or undescribed chemicals (such as chemical degradation products) are generally not addressed.

Another less frequently used strategy is linking exposure and effects to determine chemicals of concern. Assessment tools for this strategy target chemical toxicity mechanisms using diagnostic organism and population measures. These tools are also capable of distinguishing the relative effects of chemicals versus other types of stressors (e.g., Brack et al. 2015; Water Environment & Reuse Foundation 2017). Biomolecular tools indicating the presence of other types of mechanisms of action are actively being developed and refined, which will help address a large universe of chemicals (LaLone et al. 2017). Organism and population characteristics along with exposure tools are capable of distinguishing endocrine-disrupting chemical exposure in fish and other types of chemical exposures, some of which may be caused by unregulated chemicals (Water Environment & Reuse Foundation 2017; Kidd et al. 2019). Targeted chemical analysis of water, biota, and other relevant media based on biological results can help identify types of chemicals of concern as well as perhaps the likely candidate chemicals themselves.

These frameworks are mostly retrospective, that is, monitoring and analysis results are fed into the framework, often using a weight-of-evidence approach, to determine whether a concern exists. Many researchers have suggested that there is an even greater need for frameworks and approaches that can be used prospectively as well (Posthuma et al. 2017).

A path forward in the assessment of unregulated chemicals should address mixtures, because chemicals rarely if ever occur singly in aquatic systems. Exposure-effects–driven tools can address mixture effects, and then follow-up chemical analysis can be used to identify the specific chemicals that may be responsible for the observed effects. The path forward should also bundle chemicals by their fate and intended uses, which can help inform where the chemicals are likely to be transported, and how biota or people would be exposed if at all. The intended use of chemicals can in some cases provide useful information as to their fate and transport and therefore their potential concern, as evidenced in the triclosan example.

Figure 1 depicts a framework that groups chemicals by their fate properties coupled with their intended use to help inform which types of chemicals are likely to be transported and available for exposure, and therefore whether there is a potential concern for biota as well as people. The intended uses and fate properties of chemical groups drive the framework, to help identify groups of chemicals that may be of most concern, pending information regarding the potential level of exposure and effects. A similar logic has been reported by other researchers (e.g., Nilsen et al. 2019) to convey how chemicals could be evaluated as groups rather than individually. This framework could work prospectively as well as retrospectively by knowing the intended use and fate of a particular group of chemicals. “Fate” as used in Figure 1 includes probable transport pathways for the chemical group. We believe this is important because it gives us clues as to the likelihood that biota would be exposed to the chemicals. This framework might also help identify those groups of chemicals for which exposure and effects information may be lacking or ambiguous and therefore high priority for further monitoring and research.

We would argue that the use of CECs as a term serves to continue a chemical-by-chemical approach with relatively little attention given to the chemical mixtures that largely occur in aquatic systems. An exposure-effects–driven approach such as we have outlined is likely to be more effective in identifying chemical mixtures of concern, the conditions under which they may be a concern, and the types of aquatic biota that should be targeted as being most at risk so that appropriate management actions can be identified.

在 Kolpin 等人发表之后。( 2002 ) 具有里程碑意义的研究，新出现的污染物术语(CECs) 作为环境中测量的各种化学品的总称越来越受欢迎，这些化学品不受监管，因此通常不受联邦、州或地方环境机构的监控。这些化学物质被认为是“新兴的”，因为我们作为科学家，对其中的大多数化学物质知之甚少，当然也没有足够的信息来说明这些 CEC 中的一些是否是或应该受到关注并可能受到监管。这种模糊性反映在不同研究人员对 CEC 的分类方式上。在对过去 20 年研究的粗略文献回顾中，我们发现 9 到 40 组化学品在个别研究中被确定为 CEC（例如，Daughton 和 Ternes [ 1999] 确定了 17 组新兴化学品，其中仅包括药品和个人护理产品化学品）。随着检测到的化学物质越来越多，研究人员对化学分组的区分越来越精细，每组中化学物质的数量似乎都在增加。

CEC 的唯一共同点是它们目前不受监管，有些人认为它们有可能造成不利影响。因此，CEC 是一种人工分类，我们认为它对环境决策既没有意义也没有用处。例如，一些水务公司、资源机构工作人员、公众，甚至一些研究人员都要求提供场地或项目的“CEC”数据，就好像 CEC 包含标准化的化学品清单一样。其他研究人员也注意到有关 CEC 一词的类似问题（例如，Sauvé 和 Desrosiers 2014）。

我们如何处理美国地表水中报告的数千种不受管制的化学品（及其降解产物），并确定其中哪些是真正值得关注的？要回答这个问题，检查化学品如何达到真正令人关注的状态是很有教育意义的。三氯生在各种消费品中用作抗菌剂，在 1990 年代后期首次在一些处理过的废水和地表水中报道（Kolpin 等人，2002) 尽管它自 1970 年代以来一直在美国和其他地方的医院中使用，并且自 1980 年代以来已被广泛纳入消费品中。三氯生成为一种新兴污染物，因为我们现在可以检测到地表水中的浓度比以前更低，而且它很普遍。三氯生作为抗菌剂的预期用途可能对生物群和人类产生潜在影响（Bedoux 等人，2011）。数百万家庭使用的许多个人护理产品中广泛使用三氯生以及这些产品的“下水道”命运是加剧对三氯生的担忧的关键考虑因素。当欧盟和美国禁止在某些消费品中使用三氯生时，对三氯生的人类健康担忧，尤其是对抗生素的潜在交叉耐药性，是一个主要考虑因素。因此，该 CEC 拥有丰富的支持数据（即证据权重），证明了几个值得关注的原因。

如果事实上，CEC 采取了以三氯生着称的路径，需要多年和大量资源来确认一种化学品确实是一个问题，那么如何解决数以千计被认为是 CEC 的化学品？许多评估通过针对特定化学组（例如拟除虫菊酯或烟酰胺杀虫剂）、预期用途相似的化学品（例如抗微生物剂、合成激素、表面活性剂）、来源类型（例如农业流域、废水处理流出物）、预期的生物效应（例如，杀菌剂、杀虫剂）、预先确定的优先化学品清单（例如，Diamond 等人，2011)，或具有惊人化学特性的那些，如果已知的话（例如，高生物积累潜力）。所有这些方法都可能会遗漏许多我们目前尚未认识到对生物群或人类有潜在影响的化学物质。此外，目前未知或未描述的化学品（例如化学降解产物）通常没有得到解决。

另一种不太常用的策略是将暴露和影响联系起来，以确定关注的化学品。该策略的评估工具使用诊断性生物体和种群测量针对化学毒性机制。这些工具还能够区分化学品与其他类型压力源的相对影响（例如，Brack 等人，2015 年；水环境与再利用基金会2017 年）。表明存在其他类型作用机制的生物分子工具正在积极开发和完善，这将有助于解决大量化学物质（LaLone 等人，2017 年））。生物体和种群特征以及暴露工具能够区分鱼类的内分泌干扰化学物质暴露和其他类型的化学物质暴露，其中一些可能由不受管制的化学物质引起（水环境与再利用基金会2017 年；Kidd 等人2019 年）。基于生物学结果对水、生物群和其他相关介质进行有针对性的化学分析可以帮助确定关注的化学物质类型以及可能的候选化学物质本身。

这些框架大多是回顾性的，即将监测和分析结果输入框架，通常使用证据权重的方法来确定是否存在问题。许多研究人员表示，更需要可以前瞻性使用的框架和方法（Posthuma 等人，2017 年）。

评估不受管制的化学品的前进道路应该解决混合物问题，因为化学品很少单独出现在水生系统中。暴露效应驱动的工具可以解决混合物效应，然后可以使用后续化学分析来确定可能对观察到的效应负责的特定化学物质。前进的道路还应该根据化学品的命运和预期用途将化学品捆绑在一起，这可以帮助告知化学品可能被运输到哪里，以及生物群或人将如何暴露（如果有的话）。在某些情况下，化学品的预期用途可以提供有关其命运和运输的有用信息，因此可以提供有关其潜在问题的信息，如三氯生示例所示。

图 1 描绘了一个框架，该框架根据化学品的归宿特性及其预期用途对化学品进行分组，以帮助了解哪些类型的化学品可能被运输并可供暴露，从而了解生物群和人类是否存在潜在问题。化学组的预期用途和归宿特性驱动框架，以帮助确定可能最受关注的化学品组，等待有关潜在暴露水平和影响的信息。其他研究人员也报告了类似的逻辑（例如，Nilsen 等人，2019) 传达如何将化学品作为整体而不是单独进行评估。通过了解特定化学品组的预期用途和归宿，该框架既可以前瞻性地也可以回顾性地发挥作用。图 1 中使用的“命运”包括化学基团可能的运输途径。我们认为这很重要，因为它为我们提供了生物群暴露于化学物质的可能性的线索。该框架还可能有助于确定暴露和影响信息可能缺乏或不明确的化学品组，因此是进一步监测和研究的优先事项。

我们会争辩说，使用 CEC 作为一个术语是为了继续一种化学方法，而很少关注主要存在于水生系统中的化学混合物。我们概述的暴露效应驱动方法可能更有效地确定关注的化学混合物、它们可能成为关注的条件以及应作为风险最大的水生生物群类型以便确定适当的管理措施。