Updating Water Quality Standards Criteria Considering Chemical Mixtures in the Context of Climate Change

Abstract

Human activity has rapidly impacted the world; however, regulations have not kept pace to protect human life and the environment. Chemical pollution and climate change are consequences of the accelerated development that have not been sufficiently incorporated in regulations regarding water quality. This paper explores chemical pollution and climate change as criteria for water quality regulation updates, and it examines global north–south relations using a thorough literature review including papers and relevant regulations regarding surface water standards in different countries and proposes ways forward for the field of water quality. Water Quality Standards (WQS) definitions are defined by regulatory bodies that primarily consider toxicological assays provided by companies or literature-based research on emerging compounds, primarily conducted in laboratory conditions that differ from realistic environments, where compounds may be co-exposed to other contaminants and under variable temperatures. The research provided evidence that discussions on updating WQS to account for chemical mixtures are advanced in some countries such as the Netherlands, but implementation remains necessary. Furthermore, updates in WQS regarding climate change focus mostly on avoiding the climate crisis by reducing emissions. However, updates are not implemented rapidly enough to enhance protection under realistic scenarios.

1. Introduction

Protecting human life and the environment is the main goal of any environmental legislation around the world [1,2]. However, human activities are rapidly impacting the environment, and corresponding regulatory frameworks have failed to remain current, thus creating a disconnect between legal protection efforts and actual protection [1,2]. This paper has explored two aspects of water quality regulation that could be used as criteria for updating regulatory thresholds: chemical pollution and climate change. Water Quality Standards (WQS) are regulatory thresholds defined by policymakers that pollution-generating activities must follow by monitoring effluent and receiving water bodies to ensure compliance with established value [3,4].

Every year, thousands of new compounds are developed, applied to their intended purpose, and discharged into the environment either through liquid effluent or improper disposal of solid waste [1,5]. Thus, when these compounds are potentially exposed to different life forms, WQS need to be established to ensure environmental safety [6]. Regulatory protection usually uses literature reviews on the effects of existing compounds as the baseline for defining new compounds’ safe concentrations [6]. Information on their toxicity, however, cannot predict the effects on every living species. Therefore, their compound thresholds are defined using a few representative species of each class of organism, such as plants, algae, invertebrates, and fish [6]. Furthermore, toxicological assays that assess the safe concentrations for a new compound are conducted under laboratory conditions (e.g., constant temperature) and aim to assess only the effects of single compounds. Multiple compounds in a mixture could have different interactions, such as additivity in which the observed mixture toxicity consists of the sum of the individual effects, synergism when it exceeds the additivity, or antagonism when it is below the additivity threshold [7].

Since environmental conditions are dynamic, many factors can alter compound toxicity, through either environmental modifications or organismal responses, thus indicating that regulatory bodies must update WQS. Climate change is one of the most impactful environmental phenomena currently occurring, and integrating its effects will challenge policymakers in updating regulations [8]. Water availability is another concern regarding climate change; as droughts and floods become more frequent, water distribution becomes increasingly heterogeneous, which alters pollutant bioavailability and environmental fate [9].

An increase in temperature caused by climate change affects compounds’ characteristics, such as solubility, volatility, and physical state. It could even alter toxicity by interfering with organismal physiology, making them more sensitive to the toxic effects of the compounds [10]. Even a +1.5 °C increase in global average temperature could make compounds more susceptible to volatilization or migration among environmental media [11]. Compounds previously sequestered in permafrost, for example, could become bioavailable to terrestrial and aquatic organisms when released into water bodies through runoff during permafrost thaw [12].

Organisms exposed to temperatures above their optimal physiological range tend to exhibit altered responses to toxicants. Thus, temperature represents a non-chemical stressor and can enhance the toxicity of a given compound that, under normal conditions, would not cause harm [10,13,14]. Most aquatic organisms are ectotherms. Thus, water temperature is crucial for internal biochemical processes [15]. Changes in environmental conditions will similarly affect the effects of contaminants on humans in similar ways to the effects on biota. However, human exposure criteria differ significantly from ecosystem protection standards, particularly when considering socioeconomic disparities among population groups [16,17]. Material conditions such as household income and lifestyle can dramatically impact the exposure duration and composition [16,17]. Decreased environmental quality is directly associated with decreased human health, as evidenced by the incidence of gastrointestinal diseases, cancer, and even diseases such as depression [18].

This paper has discussed the process of updating water quality criteria regarding climate change and chemical mixtures by leading regulatory agencies worldwide, with particular focus on advances needed in the Global South and whether including these discussions affects regulatory validity. First, the primary regulatory agencies will be listed, and their processes for establishing concentration thresholds will be described (Figure 1). The primary focus of this discussion is therefore the procedures used to update these parameters, rather than the specific parameter values themselves.

Surface water and potable water quality standards were selected as the primary focus of this study due to their universal implementation across all analyzed countries and ongoing discussions about integrating mixture effects and climate change considerations into regulatory frameworks. Other water quality standards, including those for irrigation, industrial, or recreational (bathing) purposes, are beyond the scope of this study. Therefore, this study will provide a critical discussion of pathways forward, and methodologies for updating regulatory processes will be proposed, based on feasibility and scientific merit.

2. Review

2.1. Main Actors

Environmental protection agencies are responsible establishing the concentration thresholds for environmental contaminants, either as legally binding standards or as recommended limits [1,3,6]. During the regulatory process, these thresholds can be referred to as WQS, a part of the regulatory framework that define allowable concentrations of specific compounds in water [3]. Regulation and implementation are not homogeneous worldwide, nor are WQS, even when considering the same compounds for the same organisms [3]. Therefore, the following section lists the regulatory bodies and describes their respective criteria for updating WQS regarding climate change and chemical mixtures.

The field of chemical regulation presents challenges in determining which regulatory body is responsible for each compound [19]. Kortenkamp et al. use the term “regulatory silos” for these different areas of regulation of chemicals. Cosmetics, food, medicines, and emissions are all areas that can apply some constraints to the level of a given chemical when in contact with humans or the environment [19]. Because it is difficult to find a single organization responsible for the regulation of all chemicals, this work focuses on the analysis of the regulatory bodies in charge of surface and drinking water, as these represent the most advanced areas of water quality regulation regarding WQS updates.

2.1.1. Regulatory Agencies

The list of the main organizations responsible for establishing WQS across six countries and the European Union is summarized in

Table 1. Primary organizations responsible for updating Water Quality Standard (WQS) for drinking water and surface water and their approaches to addressing climate change or chemical mixtures. Adapted from Van Vickel et al. [3].

Country	Regulatory Agency		Discussions on Adapting to		WQS Updating Criteria Due to:
	Drinking Water	Surface Water	Climate Change	Chemical Mixtures	Climate Change	Chemical Mixtures
Australia	National Health and Medical Research Council—NHMRC National Resource Management Ministerial Council—NRMMC	Australian and New Zealand Environment and Conservation Council—ANZEC Agriculture and Resource Management Council of Australia and New Zealand—ARMCANZ	Yes. Mainly emission reduction and water management [20].	Yes. Australia was involved in OECD guidelines definition for mixture toxicity assessments [21].	No.	No.
Brazil	Brazilian Health Ministry—MS	National Environmental Council—CONAMA	Yes. Mainly emission reduction and water management [22].	No.	No.	No.
Canada	Health Canada	Canadian Council of Ministers of the Environment—CCME	Yes. Mainly emission reduction and water management [23].	Yes. Canada was involved in OECD guidelines definition for mixture toxicity assessments [21].	No.	No.
China	PRC Ministry of Health	PRC Environmental Protection Bureau	Yes. Mainly emission reduction and water management [24].	No.	No.	No.
European Union	European Commission	European Commission	Yes. Mainly emission reduction and water management [25].	Yes. Progress is being made by discussing mixture risk assessment on certain legislations such as Water Framework Directive.	No.	Partially. The Netherlands have started discussions on the TEF and Mixture Assessment Factor (MAF) methods to their regulatory framework [26].
South Africa	South Africa Department of Water Affairs and Forestry—DFF	South Africa Department of Water Affairs and Forestry—DFF	Yes. Mainly emission reduction and water management [27].	No.	No.	No.
United States	United States Environmental Protection Agency—USEPA	United States Environmental Protection Agency—USEPA	Yes. Mostly emission reduction and water management.	Yes. USEPA issues guidelines towards chemical mixtures evaluation and methods updating (such as EPA 630-R-98-002 and 630-R-00-002)	No.	No.

. These countries were selected to represent at least one country per continent. For Europe, the European Union was selected because it has jurisdiction over multiple countries and maintains the most advanced discussions on environmental regulations relevant to this study. The list includes organizations responsible for drinking and surface water standards from Australia, Brazil, Canada, China, the European Union, South Africa, and the United States.

Literature Research Update

A well-established method for updating WQS is literature research, which means that the regulatory bodies use their staff to actively and frequently review threshold limits for their respective regulations [3]. Although the overall method remains consistent, each country has a specific methodology and adapts thresholds to local conditions [5]. Regulators assume that published toxicological tests have been peer-reviewed, which increases regulatory confidence.

All studied countries have methodologies in place to update their WQS based on literature research, including Australia [28], Brazil [29], China [5], Canada [30], the European Union [31], the United States of America [32,33], and South Africa [34]. The frequency of updates is not clearly established, nor is the detailed methodology for these countries. Therefore, discussions are at such an early stage about including climate change and chemical mixture that there are few documents readily accessible for all seven territories analyzed.

Including Climate Change on the Updating Process

All analyzed organizations have assessed how different climate change scenarios could impact their territory and have established general public guidance. However, water availability seems to be the main concern rather than water quality, given that droughts and floods are expected to be more frequent [20,24,27,35]. Thus, water management becomes even more crucial as a strategy to address climate change, and water quality is mentioned briefly without concrete strategies.

Some countries have developed climate change regulatory frameworks that focus heavily on carbon dioxide reduction to achieve the Paris Agreement. However, these emission reductions aim to prevent temperature increases above the +1.5 °C threshold. Arctic regions will experience disproportionately greater temperature increases, leading to predictions that permafrost melting will alter water quality either through the runoff produced by thawing or through the potential ground instability that is already occurring and will intensify in the next few years [12]. The increased temperature could also lead to a decrease in water quality due to enhanced degradation of soil organic matter, which will be transported through runoff to water bodies and become dissolved organic matter [36,37].

Notably, regarding water quality approaches, the evaluated countries have proposed mitigation strategies for the decision-makers and city planners. National or supranational organizations suggest voluntary measures to address the climate crisis rather than implementing mandatory requirements [38]. For example, the United States Environmental Protection Agency (USEPA) suggests that water treatment facilities adjust raw water properties, such as temperature and nutrient levels, to optimize the conventional treatment process [38].

Including Chemical Mixtures on the Updating Process

When discussing climate change, it is common to relate the temperature increase with the solubilization of compounds such as trace metals and polycyclic aromatic hydrocarbons that are present in sediments [39]. Furthermore, increased erosivity is also expected with increased rainfall caused by climate change [39]. These processes could promote enhanced pollutant interactions, potentially increasing effects on the biota [37,39]. Notably, the quantification of these compounds in the environment is related to the limit of detection of the available equipment for a given region; thus, protection could vary depending on the country [40].

On the other hand, discussions of chemical mixtures have recently led to updates in regulatory frameworks (Table 1). Most mixture studies examine their impacts on the biota rather than human cells, thus making the WQS discussion more relevant to surface water than drinking water [41]. Some countries establish a WQS for groups of chemicals, with pesticides or metals being the typical categories [29,42,43]. This grouping approach enables faster regulatory decisions with a reduced need for extensive research on each compound involved in the sample and reduces the need for bioassays for each compound, relying more on toxicity testing for the whole effluent [29,42,43].

Ecotoxicological tests using the whole mixture approach are the most popular among regulatory bodies [44]. Serial dilutions of existing effluents provide an ideal diluting factor (either no effect observed concentration, NOEC, or low effect observed concentration, LOEC) to cause less environmental harm [45]. This methodology enables decision-makers without a mixture toxicity background to easily evaluate the discharge in practical terms. However, in watersheds where multiple effluents are discharged, this situation leads to a co-exposure of different effluents that are individually safe, although the toxicity of the resulting environmental mixture remains unknown.

Different organizations have different priorities regarding chemical regulations depending on their main economic activities. Methods for updating WQS, however, are similar and rely heavily on in vivo test results published in scientific journals. Therefore, climate change and chemical pollution promote a highly dynamic environment requiring frequent updates to WQS frameworks.

When evaluating mixtures of organic and inorganic compounds to define WQS values, policymakers usually treat metals as a single class and apply mixture toxicity methodologies to achieve the regulatory thresholds. WQS for metals are implemented in most countries; however, metal guideline updating criteria have been established in the reference territories of this study: Australia [28], Canada [30], Europe [31], and the United States [32]. China does not have a defined updating system for metals but is at the discussion stages [46]. Some regulatory frameworks have established WQS limits for individual pesticide compounds in water based on their toxic potential, such as carcinogenicity and teratogenicity [47]. Another layer of protection is established by defining a concentration limit to the sum of pesticides, thus limiting, even more, the number of pesticides in the mixture [47].

2.1.2. Actions Toward Updating WQS

As stated in Table 1, most of the main organizations in the cited countries do not have comprehensive discussions regarding updating WQS based on climate change and/or chemical mixtures [2]. This section discusses the most prominent actions being taken worldwide that are implemented to varying degrees in these regulatory discussions. Most advancements are in chemical mixtures, with elaborate methodologies that have been evaluated and approved as efficient and reliable.

As mentioned previously, different regulatory silos have different approaches toward chemical mixture regulations, providing some background as to what methods could be applied in different countries [48]. Chemical production, for example, is a different regulatory silo from water quality but has well-established methodologies for mixture risk assessment. Legislations such as REACH (Registration, Evaluation, Authorization, and Restriction of Chemicals) state that chemicals being produced in Europe should be assessed for their risk. If these chemicals are commercialized as mixtures, such as some pesticides, they should be evaluated as such. Some European Union countries (Denmark, France, Hungary, the Netherlands, and Spain) have established a component-based approach to tackle chemical mixture assessment [49].

Component-based strategies mean that each compound updates its values in a case-by-case scenario. Researchers from the Netherlands have proposed methods to safeguard the environment and human health from mixture effects. Attempting to simplify the mixture approach to a component-based approach, it was noted that the ten most concentrated compounds are the most important to the mixture toxicity, meaning that the ten pollutants with greater concentrations influence the outcome the most [26].

2.1.3. Groups/Projects Discussing Updating Criterion

Aiming to bridge the gap between highly specialized professionals in academia and regulatory bodies, the European Union has developed the Solutions Project [25]. This organization aims to elaborate reports on scientific subjects of interest to regulation and make them more accessible to policymakers. Such a project does not have the power of law nor is it considered a regulation; however, its report provides lawmakers with the necessary tools to make their decisions [50]. It can take the form of a compilation of methodologies described in the literature, support during a management program, or the elaboration of a water management program [25].

In response to the European Union’s request, SOLUTIONS has developed a methodological framework to help update the list of priority compounds on the European Water Framework Directive (WFD), including mixture risk assessment as a significant part of the process [42]. One of the publications generated by this work states that the current WFD is not adequately prepared to adopt the current mixture assessment methodologies already established, discussed, and accepted in academia [42].

Although there have been significant advances in the regulation of chemical compounds, both individually and in mixtures, the advances in climate change regulation appear limited to preventing the worsening of the crisis by reducing carbon emissions, which is indeed the most important issue to tackle [9]. However, studies indicate that the average temperature will exceed current projections, urging all regulatory bodies to prepare for future changes.

3. Results and Discussion

Updating WQS to chemical mixtures and climate change is crucial to tackling the negative environmental impacts. Both subjects have not been widely incorporated in terms of regulation worldwide and could have significant impacts on actual environmental protection. Extending the discussion, current technologies have already been developed towards modeling using data already generated in the literature from in vivo and in vitro testing. This will be discussed in Section 3.2 Perspectives.

Current WQS updating frameworks rely heavily on conducting literature reviews, which is an important way to start the analysis for regulatory purposes. However, action from regulatory bodies and their respective governments should be undertaken to predict the possible impacts. Modeling software and risk assessment methodologies do not require as much time, resources, and live organisms as the in vivo tests, although they require a higher level of knowledge on the subject from policymakers. WQS values determined to be safe for the single compounds in laboratory settings will apply to all other scenarios. Therefore, computational approaches can address this limitation [51].

The rapidly evolving environment due to climate change should be accompanied by rapidly adapting legislation. Changes in laws and regulations are usually slow, labor-intensive, and time-consuming to avoid brutal changes being made without proper leverage. However, the current scenario represents an exceptional period at which big and difficult changes must be made to ensure the well-being of the next generations. In this context, insufficient action is being taken to update the WQS for aquatic environments affected by temperature increases and other consequences of climate change. The WQS updating process focusing on climate change may not be implemented worldwide yet due to the expectations that this is a future problem, something to be dealt with 20 years from now. However, what is being shown worldwide is that climate change will have (and currently has) a significant impact on every aspect of human life.

Given the broad implications of this issue, new considerations are yet to arise, such as new chemicals that could be developed to mitigate the impacts of climate change. The chemical mixture regulations should also cover these new compounds since they add complexity to regulatory considerations and raise questions such as “What chemicals do water treatment facilities need to have an efficient treatment?” or “What chemicals are needed to avoid intense eutrophication of water bodies due to climate change?”

3.1. Integration

Demanding the same highly scientific discussions happening in academia from regulatory bodies seems to deepen the idea of three very separate environments: academia, regulation, and industry [52]. This approach contradicts the notion that academia generates all the knowledge that defines WQS, followed by its enforcement by policymakers, and finally, the application by industries. The proposed framework models aim to bring all interested stakeholders into the discussion, making it easier for newly established WQS to be accepted and followed by industries [42,51].

Industries could be resistant to a new piece of legislation and, by actively participating in the process, could identify logistical and production difficulties to adhere to a more restrictive process. This will lead to a better understanding of the importance of following the guidelines and, more importantly, the environmental and legal consequences of not adhering to them. Bringing all stakeholders to the table enables each group to focus on its strengths, saving time and resources and providing better results.

Additionally, this discussion highlights the importance of reaching out to academia and disseminating information to organizations that are implementing newly developed knowledge. The chances of valuable methodological research being forgotten or unused are reduced when organizations such as Solutions Project (solutions-project.eu) help reconnect academia with the rest of the chain [42]. Not every scientist is an avid science communicator, and by associating themselves with people who can make their knowledge more accessible to non-scientists, the chances of success are even greater.

After discussing the scientific importance of the environmental concentration thresholds, different regulatory bodies that regulate similar compounds should discuss a better way to cover all possible areas with single legislation in countries where there are no regulations established for overlapping responsibilities regarding WQSs [48]. Having the same compounds over different regulations with different concentration limits brings additional confounding factors to industries and the public. Even though compounds could be presented in different exposure scenarios to different organisms, there should be a way to summarize all relevant information on an isolated compound or a group of compounds in a more comprehensible and easily accessible law.

Defined WQS for surface waters are also intended to reduce risk to aquatic organisms; however, terrestrial organisms could be affected by polluted waters by drinking, having skin contact via bathing, or by preying on aquatic organisms. Human skin contact with water is also considered when defining the limits, meaning that human exposure is also a defining criterion for WQS. Nevertheless, humans have several different socioeconomic backgrounds that can alter their exposure and, consequently, their response to a given chemical due to material conditions [16,17]. The exposure of a farmer working in a soy monoculture differs from that of a child in the poorest neighborhoods of developing countries, and from the exposure of a middle-class person in a developed country. Aiming to solve this problem, some risk assessment strategies have proposed adaptations from standard exposure pathways for different demographic groups [16,17].

3.2. Perspectives

Researchers worldwide have been discussing the criteria for updating WQS values for years. This section will present some of these discussions as well as new propositions that arose from this work and the literature. Each proposition applies to the scenario in which it was developed, and it should be noted that most scenarios apply worldwide with adaptations to the respective local conditions, focusing on the Global South. New approach methodology tools will be presented individually, and subsequently, proposed regulatory frameworks comprising different tools will be listed using different variations.

The AOP concept is based on compartmentalizing each step of the toxic effect [53]. Defining the adverse effects as a chain of mechanistic events at the biological level adapts toxicological data so that professionals at the regulatory bodies can use them without profound biochemical knowledge since AOPs are not species-specific [54,55].

New AOPs can be added to the open online database at which each step could be shared with other existing AOPs, thus creating an AOP network [53,55]. In real cases, most uses of AOP would be by using the AOP network since a single compound can activate multiple molecular initiating events [55]. One key event can be shared by multiple AOPs, thus leading to a scenario in which it is possible to assume that toxicological interactions would only be conceivable through extensive metabolism assays [55,56]. This method simplifies biological processes and has limitations, but it is a valuable foundation to predictive regulatory approaches.

This tool provides essential input data on the influence of climate change, chemical mixtures, and their potential impacts on organisms. Since there is already a significant amount of data generated on the toxicity of several single compounds in the literature, model inputs can be derived from published papers without the need to perform new assays for each analysis [57,58]. New toxicological tests could be used only in specific cases prioritized beforehand, thus significantly reducing the need for testing. AOPs could also be useful for countries that lack extensive laboratory infrastructure for bioassays. Mixture toxicity testing is still far from covering all the possible interactions between all existing compounds due to the exponential number of assays needed; therefore, this approach is time- and resource-intensive [58]. Using modeling tools, time and cost would be reduced, and information on mixtures would be generated.

‘Omics’ methods employ biomolecular analyses to understand complex biological phenomena [59,60]. Understanding biological responses requires characterizing and quantifying the biomolecules, leading to greater knowledge of the molecular interactions integrated into a chain of events [59,60]. Once the main molecular interactions are described, it is possible to highlight changes in the process due to a chemical stressor [59,60]. Regulatory bodies could use ‘omics’ technologies integrated with the AOP tool to help prioritize the chemicals that could have a synergistic effect on populations and prioritize certain mixtures/compounds [59,60]. As mentioned previously, the prioritization of chemicals is a key step in the mixture toxicity regulation [59,60].

Regulatory bodies can define guidelines and help elaborate mixture and temperature-related analysis frameworks, but no rapid action will be taken without a legal definition requiring that industries or governments act [19]. To convince governments to invest in these activities, either chemical mixtures or climate change, legal authority must be established in these domains [19,51].

Relying on the goodwill (and resource investment) of a few countries and organizations will not solve the global problem. Chemical pollution, in the same way as the climate crisis, needs to be addressed globally. Therefore, momentum is building toward establishing an International Panel on Chemical Pollution (IPCP), an organization with a similar structure to the Intergovernmental Panel on Climate Change (IPCC) but focused on addressing chemical pollution [61,62]. Fundamentally, an agency such as IPCP is created with the aim of achieving greater global harmonization. The impacts of the IPCC reports are indisputable and highlight to the public the actions needed by their governments.

Under the IPCP umbrella, discussions could be held to provide a report on the best methodologies for WQS updating or generating incentives for developing countries to advance their environmental protection. Another interesting objective for IPCP could be the harmonization between regulatory silos, pointing out ways to integrate thresholds between different regulatory bodies from the same country.

Worldwide databases with toxicity and concentration data are needed to integrate WQS and serve as input to the regulatory agencies’ models. USEPA’s Ecotox works similarly by gathering toxicity data from the literature, with automatic updates requiring minimal human intervention [63]. Data on the concentration of pollutants in water bodies will also be used to assess mixture toxicity risks, and UNEP has gathered global data from its Global Freshwater Quality Database [64]. Upon integration of these tools, data confidence is crucial; thus, validating the effective integration of the models is a step that must be carried out by different organizations [19].

Different arrangements of tools can constitute different methodologies, but the overall objective in this section is to use modeling to try and predict the possible behaviors of chemicals in different scenarios and compile them in a piece of legislation that is periodically updated.

The model for updating WQS in response to climate change and chemical mixtures should start with the integration of QSAR and Omics technologies to predict possible interactions between a given set of compounds and the biological systems [57]. The first step should demonstrate the behavior of the compounds in the mixture with an increased temperature. The second step should provide a report on the chemical mixtures with the most potential to cause harm to biota and humans and, subsequently, the main biological structures that were affected by the evaluated mixture.

With the biological systems that are most likely to be affected, the model has a response that is independent of evaluated species and shows the most sensible structures, with these being the molecular initiating events. With this step alone, the chemical priority list should already be updated to demonstrate the chemicals that are the most relevant to the analysis. This could include compounds meeting established criteria: the most toxic, most persistent, or most impactful.

After identifying the most affected biological structures by the mixture, these structures could represent molecular initiating events and serve as the input for the AOP model [54,55,56]. AOP analysis of multiple compounds reveals the possible connections between them, for example, when two molecular initiating events share key pathways and thus cause the same adverse outcome. These connections could then show policymakers what the most vulnerable organisms are to the mixture of compounds.

Knowing what organisms to use could drastically reduce the need for bioassays; however, some validation will still be necessary from actual data from bioassays. If any given model shows predicted effects on algae, toxicity testing for other trophic levels could be eliminated, relying on model predictions to establish their thresholds, while algae parameters could be defined by bioassays performed through targeted experimental design.

Therefore, WQS could be updated by this methodology, providing a parameter that would be defined by several calculation steps and different professionals involved. Using modeling for this update process instead of relying exclusively on bioassays significantly reduces the number of tested organisms, thus reducing the ethical questions surrounding using living organisms to define WQS.

This methodology also stimulates better integration between researchers and lawmakers, which is a needed step for both sectors [19,65]. After each cycle of updating WQS, the process must have periodical (yearly or biannual) feedback loops during which policymakers conduct regular reviews and keep regularly updating processes and thresholds.

4. Conclusions

Regulatory bodies should be updating their criteria to the real scenarios, and for that, there is a need to accelerate the updating process of WQS. Therefore, current WQS lack validity since environmental conditions have changed, and the values considered safe in the past may not be currently safe if they are not updated for environmental scenarios.

These topics are often viewed as future concerns; however, current conditions demonstrate that changes are needed rapidly. Existing methodologies, such as TEF and HI, could be used worldwide to avoid further environmental impacts. Structural changes in the functioning of the regulations are necessary to accommodate the use of modeling on the possible impacts of chemical mixtures and climate change.

The creation of an international database containing data on environmental compound emissions could be extracted in one of many responses to this situation. Such infrastructure may become available for all interested stakeholders in a few more decades, but intermediate changes are necessary until a better scenario is applied. Upon database completion, modeling could be used worldwide and with a high level of confidence to establish a priority list and update WQS values. Differences in WQS values could also be considered to accommodate for human variability in terms of socioeconomic disparities. Exposure pathways and the health of individuals exposed to the contaminants are significant aspects that merit consideration when defining thresholds, aiming for the protection of most of the population.

Notably, multiple WQS are needed for human exposure to the same compound. It was mainly highlighted by Van Winckel et al. [3] that some countries are stricter, allowing a lower concentration, while some countries are more permissive and allow the same compound at concentrations orders of magnitude higher. Since the literature available for the policymakers is the same, these concentration differences cannot be justified on purely scientific grounds. When planning a harmonized method worldwide for WQS, these disparities should be minimized to effectively protect humans and biota by adapting only to regional environmental conditions.

Finally, the differences between organizational approaches and the current significant impacts of climate change and multiple stressors on existing criteria validity demonstrate that current standards are not updated to the extent necessary for contemporary environmental scenarios.