Lurking in the Water: Threats from Emerging Contaminants to Coral Reef Ecosystems

Abstract

Coral reef ecosystems represent one of the most biodiverse and productive marine habitats, yet they are increasingly threatened by a range of anthropogenic stressors. Among these, emerging contaminants including pharmaceutical and personal care products (PPCPs) have started to feature as contaminants of concern due to their persistence, bioaccumulation potential, and complex interactions within reef environments. This review synthesizes current research on the occurrence, transport pathways, and ecological impacts of emerging contaminants, specifically focusing on PPCPs on coral reef systems. Evidence indicates that compounds such as UV filters, antibiotics, and endocrine-disrupting chemicals can impair coral physiology, disrupt symbiotic relationships with zooxanthellae, and contribute to bleaching events. The review further highlights the variability in coral species’ sensitivity to these contaminants, with documented effects ranging from oxidative stress to reduced growth and reproductive capacity. Despite advances in detection and risk assessment, significant knowledge gaps remain regarding long-term exposure, mixture effects, and the influence of local environmental conditions on contaminant toxicity. By consolidating recent findings, this review underscores the urgent need for targeted research and policy action to mitigate the threat of emerging contaminants to coral reef ecosystems.

1. Introduction

Marine habitats span about 71% of Earth’s surface, encompassing oceans, estuaries, coral reefs, and coastal ecosystems [1]. However, the integrity of these ecosystems is increasingly undermined by pollution, a worldwide challenge intensified by urbanization, tourism, and unsustainable resource use [2,3].

Discharge and runoff from urban [4], industrial [5], and agricultural sources [6] contaminate aquatic ecosystems, threatening potable water supplies and degrading both freshwater and marine ecosystems [1]. According to recent studies [7,8], the ecological trajectory and long-term fate of pollutants differ due to several factors, but limited to their nature, environmental conditions, and residence time. Some of these factors themselves, for example, environmental conditions may evolve with time, thus causing variations to the environmental fate of the contaminants.

Emerging contaminants (ECs) are recently discovered chemicals of both synthetic and natural origin or biological substances that have been found in the environment and have either been identified as potentially harmful or have recently been found to be harmful to ecosystems and humans [9]. The risks posed by these contaminants are still not entirely recognized. The term “emerging contaminants” pertains mostly to pollutants that lack legal mandates for public disclosure or monitoring in wastewater or water supplies [10]. Often their degradation products in water remain less understood.

The majority of ECs are artificially produced substances, with pharmaceuticals and personal care products (PPCPs), a diverse group of compounds widely used in daily life for personal hygiene, cosmetic enhancement, and therapeutic purposes, representing a major and particularly concerning category alongside persistent organic compounds, disinfecting agents, and their degradation products [11,12]. These substances may enter and contaminate environmental matrices (air, water, soil, and food) via multiple vectors, including industrial effluent release, nutrient leaching and runoff, and improper waste disposal practices. They may combine to form intricate combinations of biological threats and chemical contaminants [13]. Long-distance transit and further alteration of these ECs could result in the formation of unidentified and uncharacterized compounds and chemical contamination at considerable distance from the origin [14].

Questions also remain around the toxic impacts of ECs on the physiological metabolism of organisms and/or persistence [15]. This is because the potential of ECs to penetrate and often concentrate in the food chains is already well-established [16]. Naturally, this means that these contaminants will almost inevitably reach humans through food chain dynamics, affecting human health. This risk necessitates sustained and continued research effort in determining ways to reduce their risks.

Progressive analytical developments for the detection of specific compounds in aquatic environments over recent decades [2] as well as the rapid awareness of their existence and concerns around their impacts have led to the identification of several emerging contaminants, and the list grows [9]. For instance, the identification of microplastics in the environment was made possible by improvements in analytical techniques like Fourier Transform Infrared (FTIR) spectroscopy and micro-Raman spectroscopy [17]. In some cases, the emergence of previously unrecognized contaminants can often be attributed to the development of new synthetic compounds or to evolving patterns in the utilization and disposal of existing substances [18].

1.1. Coral Reefs: Ecological Importance and Current Threats

Coral reefs constitute the most biologically diverse ecosystems within marine environments, functioning as habitats for an estimated one-third of all known marine organisms alongside 32 of the 34 identified phyla [19,20]. Spanning over 100 countries and territories [21], they provide essential ecosystem services ranging from food and income generation, carbon regulation, coastal protection and tourism revenue estimated at trillions annually [21,22]. The Great Barrier Reef (GBR) contributes approximately $9 billion in value added annually to the Australian economy and supports around 77,000 full-time equivalent jobs [23]. Furthermore, it is widely recognized that coral reefs can save up to $4 billion in flood protection costs [24].

Coral’s symbiosis with algae, macroalgae, and other species are crucial to the functioning of ocean ecosystems [25]. It preserves the biogeochemistry of oceans and open coastal regions [26]. For example, the GBR contains ~1600–1625 species of fish, hosts ~450–600 species of hard and soft corals [27], along with vast seagrass meadows [28] (that sustain nutrient cycling and food web [29,30]). These diverse symbiotic relationships sustain the reef’s high productivity and ecological resilience [31], even as the system faces increasing climate driven bleaching [32]. The Red Sea represents a distinctive marine system, bordered by a continuous coral reef framework and hosting some of the world’s most extensive and productive reef ecosystems [33]. Though limited to 0.1% of the Earth’s surface, coral reefs maintain extraordinary biodiversity and contribute essential services that sustain millions in adjacent coastal regions [34].

At present, 75% of coral reef systems confront serious challenges arising from the overlap of global climate drivers and local anthropogenic impacts [35]. Over the past four decades, approximately 20–50% of the world’s coral reefs have experienced loss or degradation. Regionally, coral decline has been recorded at approximately 53% in the Western Atlantic, 40% in the Indo-Pacific, and 50% in the Great Barrier Reef (GBR). Projections indicate that this downward trajectory is likely to persist throughout the century [36,37].

As much as 50% of reef system decline has been attributed to reduced water quality alongside climate related impacts, including bleaching events [38]. Within the Red Sea, Egyptian reef systems experience major impacts from land derived sediment loads and human induced disturbances [39]. Given that some of the most biologically vibrant and economically significant reefs are situated in underdeveloped regions [40], the difficulties in implementing integrated management solutions towards their stewardship is sometimes difficult to achieve, as has been said in the case of the Belize Reef [41]. Malaysia’s coral reefs, encompassing approximately 4006 km² and hosting 550 species, are experiencing accelerated degradation due to the combined effects of environmental and anthropogenic contaminants [42].

Some anthropogenic causes of reef stressors via degraded water include overfishing, deforestation, and fossil fuel burning, and the influx of nutrients and harmful chemicals can impair coral health by reshaping their ecological dynamics with competitors, predators, pathogens, and mutualistic species [25]. The decline in biodiversity in coral reefs may be attributed to human activity, which started decades ago, but has achieved a dangerously high trajectory since resulting in unprecedented damage of ecosystem services [43].

When coupled with the impact of climate change, degraded water quality may cause more aggravated stress to coral reef ecosystems compared to the impact of individual stressors (for example elevated temperature or nutrient loading) alone [44], a phenomenon referred to as the ‘multiple stressor effect’ [45]. Neglecting local stresses might also raise the possibility of harmful synergistic or additive interactions with climate change, which could eventually reduce the efficacy of conservation measures [46].

This review aims to elucidate the threats posed by emerging contaminants within ecologically sensitive reef environments. It provides an overview of contaminant metabolites and their biological significance, emphasizing the susceptibility of key coral-associated flora and fauna. Furthermore, case studies from major reef ecosystems worldwide, including the Great Barrier Reef in Queensland, Australia, are presented to illustrate the extent and variability of these impacts.

1.2. The Great Barrier Reef: Confronting a Complex Threat Environment

Stretching more than 2900 km along the Queensland coast, the Great Barrier Reef (GBR) is the biggest and most well-known reefal system on the planet [47]. The esteemed reef, possessing substantial ecological, cultural, social, and economic significance, is concurrently facing heightened pressure from sediments, particulate nutrients, dissolved nutrients, pesticides, pollutants, and anthropogenic activities [48]. The GBR underpins extraordinary biodiversity, serving as a critical refuge for fish, corals, turtles, dugongs, whales, and countless additional species [49]. Being among the world’s most important reservoirs of biodiversity, it encompasses thousands of species, including numerous threatened taxa, distributed across 70 bioregions (30 reefal and 40 non-reefal). In addition to its ecological functions, it underpins the livelihoods of communities within and outside its region [50].

Even under comprehensive governance structures spanning commonwealth and state authorities, the condition of GBR ecosystems has steadily degraded in recent decades [51]. Optimal water quality is imperative for coral reefs, both to sustain ecological health and to support recovery following stressors such as large-scale bleaching or intense weather events. Inshore reefs of the GBR, however, are persistently undermined by degraded water quality [52]. Adverse weather interacts with land-based pollution to further degrade water quality, sustaining its role as a critical stress factor [53]. ECs including PPCPs, are increasingly recognized as additional risks in GBR waters, particularly from urban, tourism, and shipping sources [54]. While pesticides [55], dissolved inorganic nitrogen (DIN) [56], suspended sediment, and organic runoff [57] remain the dominant threats, emerging PPCPs such as UV filters from sunscreens and pharmaceuticals from wastewater represent an understudied dimension in GBR water quality, warranting integration into future monitoring and risk assessments [54].

2. Mechanisms of Pollutant Transport: From Catchment to Coast

ECs arise from a spectrum of sources and, depending on their chemical characteristics, follow varied transport processes that culminate in their presence within soils, the atmosphere, or water bodies [2]. Figure 1 depicts the major sources of emerging contaminants.

The primary pathway for chemical entry into marine environments is through terrestrial discharges, particularly rivers and streams contaminated by industrial, agricultural, or other land-based activities within the catchment [58]. Pollutants may be transported through surface or groundwater in particulate or dissolved forms [59].

Coral reefs in inshore areas are more susceptible to underwater groundwater flow and land-based runoff due to their closer proximity to the catchments. They also deteriorate more quickly than reefs in outer coastal waters [60]. It is estimated that 25% of coral reef degradation in coastal regions is caused by adjacent anthropogenic impacts, such as the influx of pollutants and sediments from riverine sources into coastal waters. It is anticipated that this influence will grow over the next 50 years [61].

Due to the water-based solubility (and thus mobility through dissolution) of most chemicals [9], estuaries, wetlands, or adjacent urban centers with high density of runoff channels will unsurprisingly have the highest quantities of chemical stressors in the water loads. Added to this, the persistence of contaminants widens the risk into sites farther offshore through high volume movements of water, such as via monsoonal flood-plumes [62] and floodwaters in tropical cyclones such as those frequenting North Queensland, where the Great Northern Great Barrier Reef is found [63].

3. Pharmaceutical and Personal Care Products (PPCPs) as Emerging Contaminants in Coral

Pharmaceuticals and personal care products (PPCPs) represent a diverse group of chemical substances used in everyday human activities. The pharmaceutical category covers a broad spectrum of medications, including antibiotics, antihypertensives, anticonvulsants, anti-inflammatory agents, and pain relievers. Personal care products, conversely, encompass an array of consumer goods such as fragrances and perfumery items, emollients and moisturizing preparations, lip cosmetics, hair cleansing shampoos, dentifrices, and surfactant-based detergents [64].

The global use of PPCPs has increased [65]. This creates an increasing challenge of their disposal, which gives them a pseudo-persistent presence in the environment. PPCPs come from various sources (Figure 2) and their inherent mechanism of action on living things makes them harmful to non-target creatures [66]. These substances are present across freshwater and marine surface waters around the world, often at low concentrations that nonetheless have physiological significance [67]. Between 0.01 and 6800 ng/L of 113 pharmaceutical compounds and their byproducts have been detected in coastal waterways [68]. Among these, the top 10 PPCPs are shown in

Table 1. The top 10 pharmaceutical and personal care products found in coastal marine environments.

PPCP	Found in	Reference
Sulfamethoxazole	Red sea stony corals Seawater of Eastern Cape coastline, South Africa	[69] [70]
Oxybenzone (Benzophenone-3)	Coastal waters of Oahu, Hawaii, Iberian coastal marine regions	[71] [72]
Caffeine	Southern North Sea coastal waters	[73]
Diclofenac	Mombasa Creeks & Ghazi Bay, Kenya False Bay, Cape Town, South Africa	[74] [75]
Ibuprofen	East London coastline, South Africa	[70]
Acetylsalicylic acid (aspirin)/Salicylic acid	Cape Town, South Africa	[76]
Trimethoprim	Laizhou Bay, Bohai Sea, China	[77]
Tetracyclines (e.g., tetracycline, oxytetracycline, chlortetracycline, doxycycline)	Coastal waters and surface sediments of the Yangtze River Estuary, Beibu Gulf, China Mahdia coastline, Mediterranean Tunisia	[78] [79] [80]
Octocrylene	South Carolina Oahu, Hawaii Balearic Islands, Mediterranean Sea	[81] [71] [82]
Zinc Oxide (ZnO)	Surface microlayer nearshore water, Majorca Island (Spain)	[83]

.

Despite well documented presence in the environment and the broad agreement on their harmful impacts arising from their own inherent bioactive nature [66], the full long-term impact and environmental ramifications of ECs remains unknown. Second, the concurrent use of numerous pharmaceuticals, now numbering in the hundreds, creates the potential for unrecognized interactions and synergistic outcomes. In addition, the scarcity of data on the ecological implications of prolonged, low-level drug exposure further challenges risk evaluation in aquatic habitats [84]. Finally, the environmental fate of ECs varies and can include interaction with each other, forming complex chemical contaminants and presenting novel biological risks [9].

Similarly, personal care products (PCPs) that are not intended for internal use in humans (meaning that they are discharged unmetabolized) are released into waterways in large amounts globally [66]. For instance, around 1500 tons of PCP-derived microplastics leak out of Wastewater Treatment Plants (WWTPs) and into global aquatic environments annually. Based on PCP use and microplastic levels, up to 12 kilotons of PCP-derived microplastics are emitted globally each year [85]. Numerous studies have confirmed that many such high use compounds exhibit bioactivity, persistence in the environment, and potential for bioaccumulation [66,86,87].

3.1. PPCPs Interaction with Micro- and Nanoplastics

Over the past decades, persistent plastic waste in aquatic ecosystems has undergone progressive fragmentation, generating secondary microplastics (MPs, <5 mm) [88] and nanoplastics (NPs, 1–1000 nm) [89]. Due to their small size and colloidal properties, MPs and NPs exhibit high mobility and stability in aquatic systems, where interactions with microorganisms, dissolved ions, and organic matter reduce aggregation and hinder gravitational sedimentation. These particles possess high surface area-to-volume ratios and predominantly hydrophobic surfaces, enabling them to act as effective sorbents for organic contaminants including PPCPs [90,91].

Microplastics can adsorb PPCPs and serve as carriers, which can affect bioaccumulation and have toxicological and transgenerational consequences on aquatic life [92]. A laboratory study showed that NPs and MPs (made of polystyrene and polyethylene) significantly decreased freely dissolved concentrations of PPCPs like carbamazepine and triclocarban, indicating strong adsorption (of 1–2× orders of magnitude stronger than for MPs) by NPs [93]. The adsorption dynamics are influenced by pH, salinity, polymer type, and environmental conditions. These factors are critical for understanding vector transport behavior [94].

Despite studies examining the risks from MPs and relating these to coral reef ecosystems, deriving methodologically sound comparisons across environments and taxa remains a challenge due to methodological inconsistencies, non-uniform reporting standards, and spatial–temporal variability [95]. What is agreed upon, however, is that with their chemical inertness and low likelihood of complete removal, the concentrations will continue to gradually rise [96].

3.2. Endocrine Disrupting Properties of PPCPs

Industrial chemicals, insecticides, plasticizing agents, polymeric materials, illicit drugs, endogenous hormones (such as estrogens and androgens), and a wide spectrum of pharmaceuticals and personal care products utilized in both human and veterinary medicine are all among the substances that demonstrate endocrine disruptor behavior [97]. In particular, numerous PPCPs including UV filters (e.g., oxybenzone) [98], preservatives (e.g., parabens) [99,100], antiseptics (e.g., triclosan) [101], and synthetic hormones (e.g., ethinylestradiol) [102], exhibit endocrine disrupting properties through mechanisms such as receptor binding or interference with hormone synthesis and metabolism. Once discharged into the aquatic environment, EDCs impair endocrine functions essential for reproductive maturation [97]. They exhibit an affinity for estrogen receptors, disrupting reproductive processes in affected fauna [103].

In corals, these chemicals exert comparable effects by interfering with normal reproductive physiology and behavior [103]. Earlier, xenobiotics that bind to estrogen receptors and exert anti-estrogenic activity by inhibiting natural estrogen signaling, were the focus of EDCs. Recent investigations have revealed that multiple chemical classes exhibit complex and diverse modes of action, for instance, detection of phthalates and oxybenzone in coral tissues and their potential to bioaccumulate and affect reproductive physiology [104]. Further research encompasses diverse aspects of EDCs, including their effects on humans, fish, and other wildlife, the development of bioassay methodologies, and regulatory strategies aimed at mitigating associated risk [105].

4. Toxicity of PPCPs

Rising ocean temperature and ocean acidification, coupled with local stressors such as pollution and overfishing are known to be major threats to coral health and their proliferation [106]. In terms of pollution impact, toxicity from pollutants can be manifested either individually or in combination with other chemicals.

4.1. Individual Toxicity Effects

The improper disposal of pharmaceutical substances, along with insufficient wastewater treatment techniques, may lead to the environmental buildup of these chemicals. This accumulation can negatively impact non-target species and exert stress on the ecosystem [107].

Chronic toxicity (sublethal effects) of PPCPs results from their tendency to disrupt endocrine systems and disturb the homeostasis of aquatic life, along with various other anomalies [64]. For instance, exposure of Stylophora pistillata (a Scletarian coral) to oxybenzone (benzophenone-3) has been demonstrated to cause endocrine-mediated developmental anomalies in planulae, such as loss of motility, morphological deformities, premature ossification, and sessility at environmentally relevant concentrations, with a reported deformity EC₂₀ of around 6.5 µg·L⁻¹ [108]. Similarly, the endangered coral Mussismilia harttii, when subjected to the synthetic estrogen 17α-ethinylestradiol (EE2) at a concentration of 100 µg L⁻¹, demonstrated statistically significant alterations in microbial community composition [109].

Acute toxicity (lethal effects) of PPCPs arises when exposure results in mortality among aquatic organisms [64]. A mortality of 33.3% was recorded in Seriatopora caliendrum subjected to 1000 µg L⁻¹ of EHMC (ethylhexyl methoxycinnamate) [110]. Similarly, exposure of S. pistillata to octocrylene resulted in the accumulation of octocrylene-derived metabolites (otocrylene–fatty acid conjugates and octocrylene heterosides) and triggered mitochondrial dysfunction and cellular senescence [111]. In 2022, around 874 million women aged 15–49 years across the world utilized contraceptives that discharge chemicals like ethinylestradiol into aquatic habitats via human excrement [112]. The environmental significance of this prevalent usage is emphasized by findings that EE2 exposure, even at trace concentrations of 5–6 ng/L, has been associated with feminization in male fish, underscoring the ecological hazards linked to the persistent release of pharmaceutical residues into aquatic ecosystems [107].

4.2. Mixture and Combined Effects

While individual PPCPs pose significant risks to coral reef ecosystems [113], environmental exposures typically involve complex mixtures of multiple compounds, leading to combined toxic effects that can exceed those predicted from single-substance assessments [64]. For example, exposure to 5% sunscreen water containing 422 µg/L ethylhexylmethoxy-cinnamate and 33.5 µg/L octocrylene resulted in considerably elevated mortality in Seriatopora caliendrum (66.7–83.3%) and Pocillopora damicornis (33.3–50%) compared to the individual UV filters, with formulations often showing greater toxicity due to synergistic interactions among ingredients [71,110]. Moreover, organic UV filter mixtures at environmental concentrations can promote bleaching by inducing oxidative stress, with effects amplified under thermal stress [114].

PPCPs such as antibiotics, UV filters, analgesics, and antidepressants frequently co-occur at environmentally relevant concentrations (ng/L to μg/L range) in coastal waters adjacent to coral reefs [69,71,115]. The toxicity of such mixtures is commonly predicted using two classical conceptual frameworks, Concentration Addition (CA) and Independent Action (IA), which estimate mixture effects based on the toxicities of individual compounds and concentrations. Under CA, the combined effect is assumed to be additive, where each compound contributes proportionally to the total toxicity based on its potency, often observed in mixtures of similarly acting chemicals. In contrast, IA posits that dissimilarly acting compounds produce effects independently, with the overall response calculated from the probabilities of individual impacts [116]. While CA often adequately predicts additive effects in similarly acting PPCPs (e.g., estrogenic compounds), deviations toward synergy are observed in dissimilar mixtures or under environmental co-stressors, underscoring the conservative utility of both models for risk assessment [113,116].

At the same time, the impact of the sample matrix on speciation and the environmental fate of chemicals has been well-established [117,118]. From a toxin/chemicals perspective, that would logically extend to PPCPs and mean that chemical risk assessments based on freshwater would not be directly applicable to saline or even brackish matrices for even the same molecule or ion unless the risk modeling captures factors (such as salinity) that distinguish between the matrices. From a species risk perspective (e.g., for corals), the models would additionally need to include stressors such as species sensitivity [119] in order to be accurate.

Furthermore, the vulnerability and response of individual reefs to PPCP mixtures varies considerably based on the reef type and the specific compounds involved. Additionally, factors like the life stage of the exposed organisms and their vulnerabilities and possible interactions with PPCPs may differ markedly [34]. For instance, coral larvae are particularly sensitive due to their undeveloped defense mechanisms [120], whereas adults may exhibit increased resilience; they may nonetheless have prolonged sublethal consequences [121]. Likewise, reef fish and invertebrates exhibit distinct interactions and bioaccumulation of these compounds, resulting in diverse ecological consequences [122,123].

Table 2. Impacts of selected PPCPs, their endocrine disrupting subsets, and interactions with microplastics on coral species and associated organisms.

Contaminant Group	Contaminant	Coral Species	Impact on Coral Health	Reference
Pharmaceutical and Personal care Products (PPCPs)	Climbazole	Galaxea fascicularis	Decline in photosynthetic efficiency, triggered oxidative stress	[124]
	Sunscreen formulations (ZnO)	Stylophora pistillata	Coral bleaching, loss of photosynthetic capacities	[125]
	Oxybenzone (Benzophenone-3)	Galaxea fascicularis	Acute mortality, no bleaching but rapid tissue damage	[126]
	Triclosan	Porites lutea	Lowers the density and Chlorophyll A content of the symbiotic zooxanthellae, impaired antioxidant enzyme activity	[127]
	Ofloxacin (Fluoroquinolone)	Galaxea fascicularis	Reduce antioxidant levels in the algal symbionts	[128]
	Doxycycline (DOX)	Sarcophyton trocheliophorum	Altered bleaching indicators, oxidative stress markers, enzyme and detox responses	[129]
Microplastics		Pocillopora damicornis	Activates its apoptosis, disturb its symbiosis	[130]
		Acropora cervicornis	Significant reduction in skeletal growth rates, reduces calcination	[131]
		Heliopora coerulea	Negative impacts on growth parameters, reduced calcification rates	[132]
		Pseudodiploria clivosa	Reduced calcification and tissue surface area	[133]
Endocrine disrupting chemicals	Estradiol	Montipora spp.	Reduction of egg–sperm bundles	[134]
	Estrone	Montipora spp.	Increase in tissue thickness
	Ethinylestradiol (EE2)	Mussismilia harttii	Shifts in microbiome abundances	[109]

summarizes the documented effects of key PPCPs on various coral species and life stages, illustrating their negative impacts on health, functioning, and recovery potential.

Despite the recognition of the potential harm caused by PPCPs, a large knowledge gap remains around understanding their full impact, especially in vulnerable ecosystems such as coral reefs. Most of the research has hitherto focused on the well-known, or legacy pollutants, e.g., pesticides, sediments and nutrients in the case of the GBR integrated management [55]. Addressing these gaps including long-term exposures, co-stressors, and synergistic potentials is crucial, as PPCP mixtures may amplify ecological threats in warming oceans [113].

5. Risk Minimization and Policies

Marine pollution poses significant threats to oceanic ecosystems, influencing food availability, economic livelihoods, wildlife populations, and human welfare [135]. Despite increasing evidence of the ecological damage of PPCPs, regulatory solutions have always been disjointed and ineffective [136]. In the EU, pharmaceutical marketing authorizations have historically mandated the filing of an Environmental Risk Assessment (ERA). Nonetheless, the results of ERAs have had minimal impact on the approval decisions for human medications [137]. Recent studies [137,138,139] reveal that numerous ERA submissions are either incomplete or of substandard quality, hence diminishing their practical utility in decision making. This regulatory disparity is pronounced: Veterinary medications may be rejected on environmental grounds (such as when they provide AMR hazards), whereas human medicines have, until very recently, been largely insulated from rejection based on environmental effects. Effective risk mitigation necessitates more than regulations and technologies, and includes improved monitoring, reporting, and transparent assessment. Standardized reporting and evaluation instruments, such as the RIMES checklist and its implementation science extension (RIMES-SE), provide systematic advice for documenting the design, execution, and efficacy of risk minimization strategies in the pharmaceutical sector. The implementation of these reporting standards can enhance the quality of evidence utilized by regulators and facilitate cross jurisdictional learning regarding the efficacy of various policies and mitigation initiatives [140]. Policy design must address inevitable trade-offs [141]. According to ethical-legal assessments, making environmental risk a determining factor in human medicine clearance decisions poses tough considerations concerning patient access, justice, and the prioritization of individual vs. collective health benefits [142]. Stronger approval-stage constraints on the environment can encourage positive industry change (greener design, lower emissions), but they may also raise costs, slow innovation, or limit access to critical medicines if not accompanied by mitigation techniques that protect clinical benefits [141,143]. Therefore, current research advocates for a multifaceted policy package that includes: (1) improving ERA quality and transparency; (2) requiring and verifying workable mitigation measures at approval or as post-market conditions; (3) investing in targeted wastewater treatment in hotspots; and (4) harmonizing monitoring and reporting standards (so policy effects are measurable). This combined approach strikes a balance between environmental protection and the moral obligation to preserve access to necessary medications [142,143,144,145].

The European Union Directive (EU) 2024/3019 mandates quaternary treatment processes for micropollutants, including PPCPs, necessitating a minimum degradation rate of 80% in urban WWTPs catering to populations of at least 150,000 population equivalents (p.e.) or ≥10,000 p.e. in areas vulnerable to micropollutant contamination. The directive requires achieving an average removal efficiency of 80% relative to the influent load, evaluated under dry weather flow conditions, for a minimum of six indicator substances. The selection of these substances follows a 2:1 ratio, with two compounds from Category 1 (pharmaceuticals such as amisulpride, carbamazepine, diclofenac, metoprolol, and venlafaxine) for every one compound from Category 2 (e.g., benzotriazole, candesartan, irbesartan, and methylbenzotriazole) [146].

Reusing wastewater provides a sustainable way to restrict the introduction of ECs by lowering the direct release of treated effluent into rivers and coastal waterways. For instance, large scale reuse schemes in agriculture have been shown to lower the flux of PPCPs into receiving water bodies compared with conventional disposal [147]. Advanced treatment techniques including membrane bioreactors (MBRs), ozonation, and reverse osmosis improve the effectiveness of pollutant removal, removing >90–95% of metals and pharmaceuticals, making reuse a dependable choice for lowering marine pollution loads [148]. Beyond pollution control, reuse helps alleviate freshwater scarcity, which is a major driver of over extraction near coastal zones while simultaneously acting as a risk management tool by diverting contaminant rich effluent away from sensitive ecosystems [149].

A protective framework towards sustainable marine resources stewardship ensures resource longevity and its dependent activities such as fishing, recreation and tourism. The GBR, for instance, is worth AUD $56 billion [150] to the Australian economy, supporting 64,000 livelihoods (Great Barrier Reef Foundation). Timely interventions and actions lead to several advantages including preventing a contaminant from reaching the marine environment (if at all released). Sustainable management practices, for example., smarter synthetic fertilizer applications to minimize excess runoff from agriculture prevents eutrophication further downstream. Even altering the packaging for potential contaminant materials can result in decreased risks of leaching or loss per item [135].

Even with dedicated traditional physical and chemical treatment processes, similar challenges including ineffective purification, reduced efficacy, high operational costs, and the generation of hazardous residues like trihalomethanes (THMs), haloacetic acids (HAAs), and halogenated acetonitriles (HANs) as a result of chlorination [151], are among their drawbacks [152], or overwhelming levels of influent water. Despite advances in waste management technologies, much of the global waste infrastructure remains outdated or underutilized. In rapidly growing populations, the deployment of waste reduction and mitigation methods often falls short of infrastructure demands [135].

6. Containment Strategies

Containment aims to arrest the nexus between source and recipients [153]. Containment strategies include physical, chemical, and biological technology. One strategy is the installation of ozonation or activated carbon barriers as a fourth treatment stage in wastewater plants, which physically block the discharge of micropollutants into receiving waters. Swiss full-scale plants reported up to an 80% reduction in EC release after such upgrades [154]. An alternative method involves the implementation of built wetlands and stormwater retention basins at discharge locations, which effectively filter and hold pharmaceuticals and personal care items prior to the effluent entering coastal areas [155]. Another option involves the implementation of permeable reactive barriers (PRBs) along groundwater flow pathways to the coastline, where layers of activated carbon or zero-valent iron intercept contaminated plumes and inhibit their ingress into marine waters [156]. Graphene-based films and membranes offer a sophisticated passive approach for the containment of EC, surpassing traditional permeable barriers. Their high surface area, tunable composition, and antimicrobial function allow for the effective adsorption of pharmaceuticals, pesticides, and heavy metals while also providing selective permeability and disinfection functions [157].

In regions affected by legacy pollution, thin-layer capping of coastal sediments with activated carbon or mineral composites has been employed to physically sequester contaminants and prevent their discharge into surrounding waters [158]. Such efforts target the investigation of new materials and mechanisms for potential application in water pollution prevention and control [153,159].

7. Degradation and Biodegradation

Potential alternative technologies including advanced oxidation processes (AOPs), which are intended to safeguard aquatic ecosystems against harmful contaminants, may present feasibility [160]. AOPs can destroy a variety of organic molecules due to their highly reactive oxygen species. These reactive species are scarce in conventional wastewater treatment systems, which makes them inappropriate for refractory wastewater [161]. Recently, diverse AOPs have been used for the degradation of pharmaceutical compounds [162]. Methods such as heterogeneous Fenton (rGO–nZVI/H₂O₂), classical Fenton, and catalytic ozonation are particularly efficient in degrading PPCPs. For instance, rGO–nZVI with H₂O₂ removed ~95–99% of a complex PPCP mixture in just 10 min [163].

TiO₂ has emerged as a suitable catalyst for the photodegradation of some pharmaceutical chemicals [164]. It has been used extensively in bench-scale photocatalytic investigations in ultrapure and tap water [165], hospital wastewater [166], and promisingly, suggested for wastewater treatment as well with modifications [167]. Whether TiO₂ can successfully degrade PPCPs in wastewater treatment before being discharged to the oceans, however, remains a challenge to be overcome.

8. Recommendations and Future Directions

Hospitals, care facilities, and veterinary clinics must implement pollution control prior to wastewater release. Continued action is needed to restrict toxic flame retardants and update existing flammability regulations [168]. Activated sludge treatment is effective for organic load reduction but inadequate for trace-level emerging contaminants. Its use further leads to the generation of large volumes of waste sludge requiring disposal [2].

In the case of microplastics and nanoplastics, more specific research gaps exist in the understanding of the mechanisms by which they affect corals. Investigations should extend to the molecular scale, with the effects of ocean warming under rapid climate change warranting closer analysis [169]. Further insight into trace element cycling, speciation, toxicity, and coral bioavailability under multiple stressors would enhance our comprehension of these complex systems [170].

Insufficient knowledge of the prolonged impacts of these compounds on marine systems, particularly coral reefs, hampers effective management planning. Protecting these fragile habitats requires more detailed research to assess their toxicity, potential for bioaccumulation, and interactions with additional environmental pressures. Key uncertainties remain regarding (a) the ecological risks posed by PPCPs found in both nearshore and offshore reef environments, along with the plant and animal species most at risk; (b) the hazards associated with PPCP metabolites within affected organisms; and (c) the direct impacts on coral species and their growth processes arising from such exposure.

We evaluated the constraints of applying freshwater-derived chemical risk assessment models to marine systems, identifying this as a critical research gap. This challenge is exacerbated by the growing disparity between existing scientific frameworks and the extensive inventory of hazardous chemicals. Moreover, risk characterization for taxa such as corals necessitates model refinement to incorporate species-specific sensitivities. Such updates are resource-intensive, both financially and temporally, thereby perpetuating the gap in knowledge.

9. Concluding Remarks

Coral reefs are highly sensitive ecosystems that provide essential ecological, cultural, and economic services, yet they are increasingly undermined by the introduction of emerging contaminants, particularly pharmaceutical and personal care products (PPCPs). The evidence reviewed demonstrates that compounds such as UV filters, antibiotics, and parabens can bioaccumulate in coral tissues and exert a wide range of sub-lethal to lethal effects, including bleaching, oxidative stress, altered symbiont dynamics, and impaired reproduction. While considerable progress has been made in identifying contaminant classes and their acute impacts, knowledge remains limited regarding chronic exposure, interactive effects of contaminant mixtures, and the role of environmental stressors such as rising sea surface temperatures in amplifying toxic responses. These gaps present significant challenges for both ecological risk assessment and management. Addressing them will require multidisciplinary approaches that integrate ecotoxicology, oceanography, and reef ecology, alongside advances in contaminant monitoring technologies. Furthermore, the development of effective containment and wastewater treatment strategies is critical to prevent further contaminant inputs into coastal ecosystems. Strengthening policy frameworks to regulate PPCP discharge and promoting environmentally responsible consumer practices are equally essential. Protecting coral reef resilience in the face of emerging contaminants will depend on coordinated scientific, regulatory, and societal action.