Next Article in Journal
Effect of Blue Finance and Marine Environmental Quality on the Marine Fishery Economy
Previous Article in Journal
Ichthyofaunal Metabarcoding in the Southern Appalachians: Use of eDNA Metabarcoding in Fish Surveys in Lotic Systems of the Great Smoky Mountains National Park with Comparisons to Historic Electrofishing Data
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Fishes
Volume 10
Issue 4
10.3390/fishes10040146
fishes-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Review

Residues of 6PPD-Q in the Aquatic Environment and Toxicity to Aquatic Organisms: A Review

by
Chaoju Li
1,
Yuanqiang Yang
1,
Zikun Tian
1,
Zhiqiu Huang
1,
Yi Huang
1,2,* and
Yuhang Hong
1,2
1
Key Laboratory of Application of Ecology and Environmental Protection in Plateau Wetland of Sichuan, Xichang University, Xichang 415000, China
2
Key Laboratory of Animal Disease Detection and Prevention in Panxi District, Xichang University, Xichang 415000, China
*
Author to whom correspondence should be addressed.
Fishes 2025, 10(4), 146; https://doi.org/10.3390/fishes10040146
Submission received: 16 February 2025 / Revised: 17 March 2025 / Accepted: 21 March 2025 / Published: 25 March 2025
(This article belongs to the Special Issue Aquatic Ecotoxicology: Field and Laboratory Approaches)
Browse Figures
Versions Notes

Abstract

:
N-(1,3-dimethylbutyl)-N’-phenyl-p-benzoquinone (6PPD-Q) is an emerging environmental contaminant that is widely distributed in aquatic environments and presents significant toxicological risks to aquatic organisms. As 6PPD-Q is primarily derived from oxidative transformation of the tire antioxidant N-(1,3-dimethylbutyl)-N’-phenyl-p-phenylenediamine (6PPD), its persistence and potential for bioaccumulation in aquatic organisms have raised widespread concerns. This study reviews the environmental sources, spatial distribution, migration, and transformation behaviors of 6PPD-Q, as well as its degradation mechanisms in different environmental media. Additionally, this review systematically explores the toxicological effects of 6PPD-Q on aquatic organisms, including its physiological, biochemical, and molecular impacts on fish, crustaceans, mollusks, and algae, with a focus on potential toxicological mechanisms. Finally, we discuss the limitations of current research on 6PPD-Q and propose key directions for future studies, including long-term ecological risk assessments, mechanisms of bioaccumulation, metabolic pathway analysis, and optimization of pollution control strategies, aiming to provide a scientific basis for the ecological risk assessment and pollution management of 6PPD-Q.
Keywords:
6PPD-Q; aquatic pollution; residual concentration; toxic effects
Key Contribution: This review highlights the environmental persistence, bioaccumulation, and toxic effects of 6PPD-Q on aquatic organisms, emphasizing its ecological risks. It identifies key knowledge gaps and provides a foundation for future research and pollution management.

Graphical Abstract

1. Introduction

N-(1,3-Dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD) serves as a widely employed antioxidant and anti-ozonant in tire manufacturing. It is commonly incorporated into tire formulations at concentrations ranging from 0.4% to 2% by weight. Its main function is to safeguard the rubber from degradation, cracking, and aging caused by heat, ultraviolet radiation, and oxidation [1]. Under certain environmental conditions, however, 6PPD undergoes a reaction with atmospheric ozone, resulting in the formation of its oxidative product, 6PPD-Q (N-(1,3-dimethylbutyl)-N′-phenyl-p-benzoquinone) (Table 1). As a newly identified environmental contaminant, 6PPD-Q has attracted considerable attention from the scientific community due to its extensive presence across aquatic environments, the atmosphere, and soil [2,3,4]. The main source of 6PPD-Q is the degradation of rubber products, particularly tires, which release the compound during wear and use. As tires age and degrade, 6PPD undergoes oxidative transformations, forming 6PPD-quinone (6PPD-Q). While ozone is a known oxidant in this process, other environmental factors, such as UV radiation and interactions with atmospheric radicals, also contribute to its formation. Once formed, 6PPD-Q is released into the environment through pathways like road runoff and atmospheric deposition [5]. This process makes 6PPD-Q a significant component of traffic-related pollution. In addition to transportation sources, 6PPD and 6PPD-Q may also be released into the environment through other rubber products such as plastic pipes and electrical cables, further increasing their persistence and bioaccumulation in the environment [6].
Regarding the potential threat of 6PPD-Q to aquatic organisms, several studies have examined its effects on aquatic ecosystems in recent years. For instance, research by Tian et al. [7] showed that even at concentrations <1 μg/L, 6PPD-Q can cause acute mortality in coho salmon. Exposure experiments further revealed that its toxicity to aquatic organisms significantly surpasses that of 6PPD itself. Furthermore, the accumulation of 6PPD-Q in aquatic environments may disrupt other levels of the food chain. Recent studies have shown that 6PPD-Q can bioaccumulate in various organisms within the aquatic food chain, including algae, zooplankton, and fishes. This bioaccumulation may indirectly threaten predatory fish and other species in a higher position in the food chain [8,9,10]. This cross-species impact not only disrupts the stability of local aquatic ecosystems but could also have a significant impact on aquaculture, further influencing the global fishing economy.
The high persistence and bioaccumulation potential of 6PPD-Q in the environment have led to growing global scientific and public concern. While studies have already documented the toxic effects of 6PPD-Q on some aquatic organisms, there is still a huge gap in research regarding its toxicological mechanisms. In particular, the impacts of 6PPD-Q exposure on the structure of aquatic communities and ecosystem functions remain poorly understood. Despite increasing awareness in both academic and industrial circles about the potential risks posed by 6PPD-Q, pollution control technologies and regulatory measures are still in their infancy, with a lack of comprehensive preventive strategies. Considering the increasing consequences of 6PPD-Q on aquatic ecosystems, this study aims to investigate the toxicological mechanisms and ecological risks associated with 6PPD-Q. Furthermore, it seeks to evaluate its potential threats to aquaculture and provide a scientific foundation for the development of targeted pollution control approaches. While recent reviews, such as Bohara et al. (2024), have provided valuable insights into the sources, transformations, and toxic effects of 6PPD-Q in animals [11], this current review offers a more comprehensive examination of the ecological implications of 6PPD-Q, especially in relation to its bioaccumulation, long-term environmental persistence, and chronic toxicity in aquatic species. By addressing these underexplored areas, this review provides actionable insights for both environmental management and industrial practice.
To ensure a comprehensive and systematic review of the available literature on 6PPD-Q, we conducted an extensive bibliographic search across multiple scientific databases, including Web of Science, Scopus, PubMed, and Google Scholar. The search focused on peer-reviewed journal articles, reports, and conference proceedings published from 2000 to 2024. Keywords used in the search included “6PPD-Q”, “tire-derived pollutants”, “aquatic toxicology”, “bioaccumulation”, “oxidative stress”, “environmental persistence”, and “ecotoxicology”. Additional relevant references were identified through a snowballing approach, where cited studies in key publications were reviewed for further inclusion. The selection criteria prioritized original research articles and reviews that provided empirical data on 6PPD-Q’s environmental fate, toxicity, and ecological risks. This methodological approach ensures that the review captures the most relevant and up-to-date scientific findings on the impacts of 6PPD-Q in aquatic ecosystems. By conducting such a literature review and data analysis, we aim to support future ecological risk assessments and enhance water resource management strategies.

2. Distribution and Concentration of 6PPD-Q in the Environment

In industry, 6PPD is widely used as an antioxidant in tire rubber to prevent tire oxidation. During tire wear or aging, 6PPD decomposes and transforms into 6PPD-Q, with its formation process accelerated when exposed to environmental factors such as ozone (O3). This transformation will lead to the release of 6PPD-Q into the environment [7]. As tires degrade, 6PPD-Q enters the environment, particularly in water bodies, air, and soil through road particles. Therefore, 6PPD-Q has become a significant component of pollution from transportation and the rubber industry (Figure 1). Research by Cao et al. (2022) indicates that 6PPD-Q is not only widely present in urban waterways but also detectable in the air and soil of some urban areas [4]. The widespread distribution and persistence of 6PPD-Q make it an emergent environmental pollutant, particularly in regions with considerable traffic.
A study by Hiki et al. [12] demonstrated that the concentration of 6PPD-Q in Tokyo, Japan, shows a distinct seasonal variation, especially during the spring and autumn when atmospheric ozone concentrations are higher. This pattern suggests that the formation of 6PPD-Q is closely linked to ozone concentrations in the atmosphere, implying that its levels may fluctuate with seasonal climate changes. In terms of 6PPD-Q distribution in aquatic environments, Yan et al. [13] conducted a comprehensive analysis of its dissipation behavior. The findings indicated that 6PPD-Q primarily undergoes degradation in water via direct photolysis, with a rapid dissipation rate, achieving 100% breakdown within just 4 h. Solar irradiation induces Norrish-type cleavage of 6PPD-Q’s quinoid structure, generating hydroxylated derivatives (e.g., 6PPD-Q-OH) and dimerized byproducts. Secondly, the fate of 6PPD-Q is governed by microbial redox metabolism, in which sediment-associated anaerobes (e.g., Geobacter spp.) mediate reductive deamination of 6PPD-Q, producing N-dealkylated intermediates that subsequently undergo β-oxidation. Moreover, hydrolytic pathways stand out. pH-dependent hydrolysis dominates in oligotrophic waters (pH > 8.5), yielding phenylenediamine fragments via quinone ring opening [10,13].
Additionally, one study showed that under natural decay and indirect photolysis, the dissipation rate of 6PPD-Q slows, but it still reaches complete dissipation within 30 h [13]. The natural decay rate constant was 0.27 h−1, with a half-life of 2.57 h. This suggests that the degradation of 6PPD-Q in aquatic environments is influenced not only by light but also by water quality and microbial activity. It should be noted, however, that while 6PPD-Q demonstrates an overall high degradation efficiency in aquatic environments, its degradation capacity exhibits significant variability across different aquatic conditions, such as temperature fluctuations, pH variations, light exposure levels, and microbial community differences. Di et al. [14] found that the hydrolysis half-life of 6PPD-Q in river water was 12.8–13.2 days, with the difference in half-life under different water composition and microbial activity. Furthermore, a report showed that the half-life of 6PPD-Q in dechlorinated tap water at 23 °C was 33 h, indicating a slower degradation rate [15]. The study also concluded that hydrolysis is less effective in degrading 6PPD-Q compared to direct photolysis. While studies show that 6PPD-Q can degrade through photolysis and natural decay in aquatic environments, hydrolysis proceeds at a slower rate, with its degradation efficiency significantly influenced by environmental factors such as water quality and temperature. In addition, research on the degradation cycle of 6PPD-Q in air and soil is still limited. Further studies are needed to explore its degradation behavior and persistence in these media.

3. Residues of 6PPD-Q in Aquatic Environments

With increasing traffic and tire wear, 6PPD-Q enters water bodies through runoff, becoming a significant pollutant in urban areas. Studies have shown that the concentration of 6PPD-Q in water is influenced by several factors, including geographic location, seasonal variations, and water body type [13]. In highly urbanized areas, particularly those with dense traffic, the concentration of 6PPD-Q is typically higher (Table 2). For example, studies in Seattle and Los Angeles, USA, found that 6PPD-Q concentrations in roadway runoff ranged from 0.8–19 μg/L and 4.1–6.1 μg/L, respectively, with these concentration levels approaching or exceeding the 24 h LC50 (lethal concentration for 50% of the population) for sensitive aquatic species, posing a potential threat to local aquatic ecosystems [7]. Similarly, in Ontario, Canada, in the Greater Toronto Area, 6PPD-Q concentrations were reported at 0.54 ± 0.04 μg/L and 0.72 ± 0.26 μg/L [16], indicating significant pollution from traffic and industrial emissions in this region. In contrast, in areas with lower traffic density and less urbanization, 6PPD-Q concentrations tend to be lower. For example, in the southwest branch of the Brisbane River in Australia, concentrations ranged from 0.4 to 88 ng/L [17], which is remarkably lower than the pollution levels found in major cities. This difference may be because of the relatively low traffic emissions and limited pollution sources in the region.
The residue of 6PPD-Q varies significantly across different water body types. In rivers and lakes, concentrations of 6PPD-Q are generally higher, particularly near major transportation hubs and industrial areas. For example, a study by Di et al. [14] in the Pearl River Delta, China, found that 6PPD-Q concentrations in rivers range from 1.87 to 18.2 ng/g, indicating notable pollution levels. In contrast, concentrations in less polluted reservoirs and groundwater are typically lower, often falling below detectable levels. This is likely due to the closed nature of these water bodies, their reduced flow rates, and limited pollution inputs [18]. Additionally, 6PPD-Q residue differs between freshwater and seawater environments. Generally, concentrations are higher in freshwater systems, especially in urbanized areas and traffic-heavy rivers, where contamination is more serious. In seawater, however, 6PPD-Q concentrations are typically lower. Nonetheless, certain levels of 6PPD-Q remain detectable in coastal sediments, particularly in regions influenced by human activities. For instance, sediment samples from the Pearl River estuary showed a 6PPD-Q concentration of 2.71 ng/g [19].
The concentration of 6PPD-Q in water bodies tends to be lower in more remote areas, such as high-altitude regions and rural areas. These regions generally have fewer pollution sources and cleaner environments, so the concentrations of 6PPD-Q do not reach the pollution levels observed in urban areas. However, with the increase in global traffic and the increasing use of rubber products, these areas may also face the threat of 6PPD-Q pollution in the future, particularly in rapidly developing regions with increasing road construction and industrialization [20]. Therefore, future research should focus on the water pollution in these remote areas and the potential long-term ecological impacts.
Overall, the residue of 6PPD-Q in aquatic environments is influenced by various factors, and the differences in 6PPD-Q concentrations across different regions and water body types indicate that its global distribution is uneven, with the pollution problem being severe in areas with high traffic and industrialization. As our understanding of the 6PPD-Q pollution issue deepens, it is necessary to conduct more comprehensive studies on its global distribution, degradation characteristics, and ecological risks to aquatic organisms, providing scientific support for water pollution management and the protection of aquatic ecosystems.

4. Toxicity of 6PPD-Q to Aquatic Organisms

Over time, 6PPD-Q has emerged as a global environmental contaminant, exerting multilevel disruptive pressures on aquatic ecosystems that may instigate cascade effects across natural equilibria. Research shows that 6PPD-Q can lead to acute mortality, developmental abnormalities, and long-term ecological impacts by affecting metabolic pathways, inducing oxidative stress, disrupting the endocrine system, and altering behavioral patterns in aquatic organisms [21]. Furthermore, due to the pseudo-persistence of 6PPD-Q in the environment—where continuous emissions from tire wear maintain its presence despite degradation—the accumulation of 6PPD-Q in aquatic environments may lead to bioaccumulation through the food chain, further exacerbating ecosystem instability [22].

4.1. Toxicity to Fish

Studies have revealed significant differences in the toxicity of 6PPD-Q among various fish species, with some species being highly sensitive to the compound, while others exhibit greater tolerance (Table 3) [11,14,23,24,25,26]. For example, coho salmon (Oncorhynchus kisutch) is extremely sensitive to 6PPD-Q, with a 24 h LC50 lower than 0.10 μg/L. In addition, 6PPD-Q has a 24 h LC50 of 0.59 μg/L on brook trout (Salvelinus fontinalis) and a 72 h LC50 of 1 μg/L on rainbow trout (Oncorhynchus mykiss). In contrast, arctic char (Salvelinus alpinus), white sturgeon (Acipenser transmontanus), and American sturgeon (Acipenser oxyrinchus) did not show mortality even after 96 h of exposure to concentrations as high as 14.2 μg/L. Furthermore, red drum (Sciaenops ocellatus) showed an LC50 as high as 500 μg/L during 24 to 72 h of exposure, indicating a high level of tolerance to 6PPD-Q.
It is known that 6PPD-Q can induce abnormal behaviors in fishes. For instance, exposure to 6PPD-Q at 10 or 25 μg/L has been shown to affect zebrafish larva swimming behavior and motor abilities, leading to reduced swimming speeds, decreased activity, and motor dysfunction [27]. Additionally, zebrafish exhibit noticeable depressive-like behaviors following 50 μg/L of exposure, such as increased avoidance of darkness, which may be related to 6PPD-Q’s interference with the central nervous system [28].
In terms of developmental toxicity, studies have demonstrated that 6PPD-Q ranging from 0.06 to 2.35 μg/L can cause embryonic malformations, pericardial edema, and growth retardation in rainbow trout (O. mykiss) alevins [29]. Similarly, exposure of zebrafish embryos to 6PPD-Q at 25 μg/L results in reduced embryo movement, decreased heart rate, and intestinal development abnormalities [30]. These observations suggest that 6PPD-Q may severely affect fish growth and survival by interfering with cardiovascular development and neuroregulation pathways.
Moreover, exposure to 6PPD-Q leads to severe oxidative stress in fish. Research has shown that 500 μg/L of 6PPD-Q exposure significantly increases reactive oxygen species (ROS) levels, causing oxidative imbalance within cells, leading to DNA damage, protein oxidation, and mitochondrial dysfunction [31]. Studies also indicate that under 6PPD-Q exposure, fish antioxidant enzyme systems, such as superoxide dismutase (SOD) and catalase (CAT), are inhibited, making it more difficult for the organisms to counteract oxidative damage caused by free radicals [11]. This oxidative stress not only affects individual health but may also impact population survival rates.
Metabolic disruption is another prominent consequence of 6PPD-Q toxicity in aquatic organisms. Research indicates that exposure to 6PPD-Q can cause lipid metabolic disorders in species such as fish [32] and frog [33], impairing the synthesis and breakdown of fatty acids. This disruption affects energy metabolism and can result in weight loss. In addition, 6PPD-Q has been shown to alter the gut microbiota in fish, interfering with immune system regulation and disrupting potassium ion channels as well as voltage-gated ion channels [30,34]. These findings suggest that 6PPD-Q poses a threat to overall fish health by disrupting multiple physiological systems.
Studies on zebrafish embryos have shown that 6-PPD-quinone has significant bioaccumulation in fish. In a 96 h exposure experiment, its bioconcentration factor ranged from 70 to 220, indicating that it is likely to accumulate in fish tissues. In terms of metabolism and excretion, 6-PPD-quinone is mainly detoxified in fish through phase II metabolic reactions (such as glucuronidation). More than 95% of 6-PPD-quinone in zebrafish embryos will be metabolized, and the formed 6-PPDQ + O + glucuronide conjugate accounts for more than 80% of the total metabolites. Due to its enhanced polarity, it is likely to be excreted more easily through urine or bile. The excretion of 6-PPD-quinone metabolites in fish may occur through the kidneys to excrete water-soluble products or through the gills to expel volatile components [35].

4.2. Toxicity to Aquatic Crustaceans

Studies have demonstrated that the toxicity of 6PPD-Q to aquatic crustaceans changes depending on species differences, exposure duration, and environmental factors. Its acute and chronic toxic effects mainly include growth inhibition, reduced reproductive capacity, DNA damage, and mutagenicity [36]. The water flea, Daphnia magna, a widely used model organism in aquatic ecotoxicology, is highly sensitive to 6PPD-Q. In a 48 h acute toxicity test, the median lethal concentration (LC50) of 6PPD-Q was determined to be 55 μg/L [34]. Furthermore, Hyalella azteca, another crustacean species, exhibited an even lower tolerance to 6PPD-Q, with a 96 h LC50 of just 6 μg/L [15]. Long-term exposure to low concentrations of 6PPD-Q significantly reduced the growth rate of both D. magna and H. azteca, suppressing their body size and weight gain, as well as extending their reproductive cycles. Additionally, prolonged exposure led to a decrease in offspring numbers and survival rates, suggesting that 6PPD-Q may have long-term effects on population dynamics and ecosystem stability [15,37]. These effects are likely linked to mechanisms such as oxidative stress, energy metabolism disruption, and interference with endocrine regulation. This highlights the need for further investigation into the specific toxicological mechanisms involved.
A study on Parhyale hawaiensis revealed the high tolerance of aquatic species to 6PPD-Q. In a 96 h static test, the mortality rate in all 6PPD-Q treatment groups was less than 3.1%, and the 96 h LC50 was higher than 500 μg/L, with no significant acute toxicity observed. However, after exposure to higher concentrations (250 μg/L and 500 μg/L) for 96 h, a significant increase in micronuclei frequency was observed, suggesting that 6PPD-Q may have mutagenic properties [38]. Therefore, further research is necessary to evaluate the potential mutagenic properties of 6PPD-quinone in a broader range of crustacean species.

4.3. Toxicity to Aquatic Mollusks

Research on the toxicity of 6PPD and 6PPD-Q to aquatic mollusks remains relatively limited, but existing studies suggest that these pollutants may have significant toxic effects, particularly under long-term exposure conditions. The toxic effects of 6PPD-Q on mollusks may include growth inhibition, reduced reproductive capacity, tissue damage, and oxidative stress, with the extent of these effects varying by species, exposure duration, and environmental conditions.
Studies have shown that 6PPD-Q also has high toxicity to freshwater mollusks. For example, in a study on the embryotoxicity of the ramshorn snail Planorbarius corneus, the no observed effect concentration (NOEC) was found to be 11.7 μg/L. For the adult washboard mussel Megalonaas nervosa, the NOEC was 17.9 μg/L [25]. However, due to the limitations of NOEC as a toxicity threshold, future studies should focus on deriving EC/LC50 to improve the precision of effect assessments. In addition, a high mortality was observed when the freshwater snail Radix balthica was exposed to 95 ng/L of 6PPD-Q, with a significant decrease in reproduction, growth, and motility [39]. For marine mollusks, research indicates that chemicals from tire products may have more pronounced effects on certain species. For instance, in a study of the Pacific oyster Crassostrea gigas, low-dose exposure (0.1–10 μg/L) to tire leachate resulted in reduced reproduction, embryotoxicity, and oxidative stress [40]. These data suggest that at concentrations commonly found in natural water bodies, either freshwater or marine bivalves may be significantly affected by acute toxicity from 6PPD-Q. Moreover, given that 6PPD-Q is persistent, long-term low-dose exposure will adversely affect their physiological functions, such as disrupting their filter-feeding capacity, impacting energy metabolism, and accumulating in tissues, potentially leading to chronic toxicity effects.

4.4. Toxicity to Algae and Cyanobacteria

The toxic effects of 6PPD-Q on aquatic algae primarily occur through its disruption of photosynthetic electron transport, reduction in photosynthetic efficiency, damage to cellular structures, and induction of oxidative stress [41]. As primary producers in aquatic ecosystems, algae play a critical role in maintaining ecological balance. Their health directly affects the energy flow and nutrient cycling within the ecosystem. Therefore, any toxic impact on algal communities may lead to changes in the structure of aquatic ecosystems, subsequently influencing their stability and function [41,42].
In addition, the toxicity of 6PPD-Q to cyanobacteria, such as Synechocystis sp., mainly results from a similar mechanism, changes in gene and protein expression, and decreased carbon fixation efficiency. Using 13C tracer Raman microspectroscopy (WITec alpha 300RA, Ulm, Germany) and isotope mass spectrometry (Thermo Fisher Scientific, Bremen, Germany), researchers quantified the effect of 6PPD-Q on cyanobacteria’s carbon fixation ability. At low concentrations (such as 100 ng/L), cyanobacteria exhibited a 7% increase in carbon fixation efficiency during the excitation phase. However, during the toxicity and recovery phases, carbon fixation efficiency decreased by 28% and 20%, respectively. At higher concentrations (100 μg/L), carbon fixation efficiency dropped by 6%, 30%, and 29% across the three phases. These results suggest that 6PPD-Q exerts a long-term negative effect on carbon fixation in cyanobacteria, especially at high concentrations, which has significant implications for aquatic photosynthesis and the carbon cycle [43].
For Chlorella vulgaris, a commonly used green algae in aquaculture, studies have found that low concentrations of 6PPD-Q (50, 100, and 200 μg/L) promote its growth, while higher concentrations (400 μg/L) inhibit its growth. The toxicity mechanism of 6PPD-Q in algae is mainly linked to the induction of oxidative stress [44]. It has been found that 6PPD-Q induces oxidative stress more readily than its parent compound, 6PPD, leading to damage in cell membrane permeability and mitochondrial membrane potential [14]. After exposure to 6PPD-Q, researchers observed significant changes in antioxidant enzyme activities and levels of active substances in algae. Fatty acid metabolism was one of the most significant metabolic alterations. Metabolomic analysis further confirmed that fatty acids were the most significantly altered metabolites following exposure to both 6PPD-Q and 6PPD, reflecting the profound impact of these pollutants on algal metabolic processes.
Although the toxicity of 6PPD-Q to algae is relatively low, its bioaccumulation and food chain transfer in aquatic ecosystems warrant further attention. Research has shown that the bioaccumulation factor (log BAF) of 6PPD-Q ranges from 1.3 to 1.9, which is lower than that of its parent compound, 6PPD (log BAF = 3.4–4.2) [22]. While 6PPD-Q has a relatively low bioaccumulation potential, its persistence and mobility in the environment, coupled with its toxicological effects, may still pose a significant threat to aquatic ecosystems. Moreover, 6PPD-Q may accumulate through the food chain, from primary producers (algae) to secondary consumers (fish), thereby increasing the ecological risk and concerns of food safety [45].

5. Conclusions

This study provides a systematic analysis of the environmental persistence of 6PPD-Q in aquatic ecosystems and its toxic effects on aquatic organisms. Drawing on existing literature, we examined the sources of 6PPD-Q, its distribution across various environmental media, and its toxicological impacts on a range of aquatic species, including fish, crustaceans, mollusks, and algae. As a newly emerging environmental pollutant, 6PPD-Q has been detected widely in air, water, and soil. Due to its notable persistence, it poses substantial toxicity risks to aquatic organisms. Through multiple toxicological mechanisms—such as oxidative stress, damage to cell membranes, and alterations in gene expression—6PPD-Q can cause both acute and chronic harm to aquatic species. Its toxicity is especially pronounced in fish and crustaceans, where prolonged exposure can lead to growth inhibition, decreased reproductive capacity, and behavioral abnormalities, thereby threatening the stability of aquatic ecosystems. Furthermore, the toxic effects of 6PPD-Q on algae have gained increasing attention. Although its direct toxicity to algae appears to be relatively low, its bioaccumulation and transfer through the food chain could amplify ecological risks.
Considering the widespread presence of 6PPD-Q in aquatic ecosystems and its significant toxicological impacts, further research is urgently needed to fully understand its long-term effects on aquatic species and ecosystems. In particular, more studies should focus on the mechanisms of bioaccumulation, its effects across different trophic levels, and the potential risks to biodiversity and ecosystem services. Additionally, comprehensive risk assessments, including the development of effective pollution control technologies and mitigation strategies, are essential to manage 6PPD-Q’s environmental impact. Addressing these knowledge gaps will be critical for informing environmental policies and safeguarding aquatic health.

Author Contributions

Conceptualization, Y.H. (Yi Huang); methodology, Y.H. (Yi Huang); software, C.L.; validation, Y.Y.; writing—original draft preparation, C.L., Z.T. and Y.H. (Yi Huang); writing—review and editing, Y.H. (Yuhang Hong); visualization, Y.Y.; supervision, Y.H. (Yuhang Hong); project administration, Y.H. (Yuhang Hong) and Z.H. (Zhiqiu Huang); funding acquisition, Y.H. (Yi Huang) and Y.H. (Yuhang Hong). All authors have read and agreed to the published version of the manuscript.

Funding

This study was financially supported by the ‘Pandeng’ Project in Xichang Univeristy (Grant No. 117630042) and Science Research Program in Xichang City (Grant No. 18JSYJ13).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Zhang, Y.-J.; Xu, T.-T.; Ye, D.-M.; Lin, Z.-Z.; Wang, F.; Guo, Y. Widespread N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine quinone in size-fractioned atmospheric particles and dust of different indoor environments. Environ. Sci. Technol. Lett. 2022, 9, 420–425. [Google Scholar]
  2. Johannessen, C.; Helm, P.; Lashuk, B.; Yargeau, V.; Metcalfe, C.D. The tire wear compounds 6PPD-quinone and 1, 3-diphenylguanidine in an urban watershed. Arch. Environ. Contam. Toxicol. 2022, 82, 171–179. [Google Scholar]
  3. Wang, W.; Cao, G.; Zhang, J.; Wu, P.; Chen, Y.; Chen, Z.; Qi, Z.; Li, R.; Dong, C.; Cai, Z. Beyond substituted p-Phenylenediamine antioxidants: Prevalence of their quinone derivatives in PM2. 5. Environ. Sci. Technol. 2022, 56, 10629–10637. [Google Scholar] [PubMed]
  4. Cao, G.; Wang, W.; Zhang, J.; Wu, P.; Zhao, X.; Yang, Z.; Hu, D.; Cai, Z. New evidence of rubber-derived quinones in water, air, and soil. Environ. Sci. Technol. 2022, 56, 4142–4150. [Google Scholar] [CrossRef]
  5. Li, C.; Zhang, Y.; Yin, S.; Wang, Q.; Li, Y.; Liu, Q.; Liu, L.; Luo, X.; Chen, L.; Zheng, H.; et al. First insights into 6PPD-quinone formation from 6PPD photodegradation in water environment. J. Hazard. Mater. 2023, 459, 132127. [Google Scholar] [CrossRef] [PubMed]
  6. Chen, X.; He, T.; Yang, X.; Gan, Y.; Qing, X.; Wang, J.; Huang, Y. Analysis, environmental occurrence, fate and potential toxicity of tire wear compounds 6PPD and 6PPD-quinone. J. Hazard. Mater. 2023, 452, 131245. [Google Scholar] [CrossRef] [PubMed]
  7. Tian, Z.; Zhao, H.; Peter, K.T.; Gonzalez, M.; Wetzel, J.; Wu, C.; Hu, X.; Prat, J.; Mudrock, E.; Hettinger, R. A ubiquitous tire rubber–derived chemical induces acute mortality in coho salmon. Science 2021, 371, 185–189. [Google Scholar]
  8. Liao, X.-L.; Chen, Z.-F.; Liu, Q.-Y.; Zhou, J.-M.; Cai, W.-X.; Wang, Y.; Cai, Z. Tissue Accumulation and Biotransformation of 6PPD-Quinone in Adult Zebrafish and Its Effects on the Intestinal Microbial Community. Environ. Sci. Technol. 2024, 58, 10275–10286. [Google Scholar] [CrossRef]
  9. Zhao, Y.; Liu, W.; Liu, J.; Shi, R.; Zeb, A.; Li, X.; Ge, Y. Phytotoxicity of 6PPD and its uptake by Myriophyllum verticillatum: Oxidative stress and metabolic processes. Sci. Total Environ. 2024, 955, 177248. [Google Scholar] [CrossRef]
  10. Xu, S.; Wang, Q.; Lao, J.-Y.; Cao, Y.; Hong, P.; Chen, C.; Lam, E.Y.; Fang, J.K.-H.; Lee, S.; Leung, K.M.Y. Typical Tire Additives in River Water: Leaching, Transformation, and Environmental Risk Assessment. Environ. Sci. Technol. 2024, 58, 18940–18949. [Google Scholar] [CrossRef]
  11. Bohara, K.; Timilsina, A.; Adhikari, K.; Kafle, A.; Basyal, S.; Joshi, P.; Yadav, A.K. A mini review on 6PPD quinone: A new threat to aquaculture and fisheries. Environ. Pollut. 2024, 340, 122828. [Google Scholar] [CrossRef] [PubMed]
  12. Hiki, K.; Yamamoto, H. Concentration and leachability of N-(1, 3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD) and its quinone transformation product (6PPD-Q) in road dust collected in Tokyo, Japan. Environ. Pollut. 2022, 302, 119082. [Google Scholar] [PubMed]
  13. Yan, X.; Xiao, J.; Kiki, C.; Zhang, Y.; Manzi, H.P.; Zhao, G.; Wang, S.; Sun, Q. Unraveling the fate of 6PPD-Q in aquatic environment: Insights into formation, dissipation, and transformation under natural conditions. Environ. Int. 2024, 191, 109004. [Google Scholar] [CrossRef] [PubMed]
  14. Di, S.; Liu, Z.; Zhao, H.; Li, Y.; Qi, P.; Wang, Z.; Xu, H.; Jin, Y.; Wang, X. Chiral perspective evaluations: Enantioselective hydrolysis of 6PPD and 6PPD-quinone in water and enantioselective toxicity to Gobiocypris rarus and Oncorhynchus mykiss. Environ. Int. 2022, 166, 107374. [Google Scholar] [CrossRef] [PubMed]
  15. Hiki, K.; Asahina, K.; Kato, K.; Yamagishi, T.; Omagari, R.; Iwasaki, Y.; Watanabe, H.; Yamamoto, H. Acute toxicity of a tire rubber-derived chemical, 6PPD quinone, to freshwater fish and crustacean species. Environ. Sci. Technol. Lett. 2021, 8, 779–784. [Google Scholar]
  16. Johannessen, C.; Helm, P.; Metcalfe, C.D. Detection of selected tire wear compounds in urban receiving waters. Environ. Pollut. 2021, 287, 117659. [Google Scholar] [PubMed]
  17. Rauert, C.; Charlton, N.; Okoffo, E.D.; Stanton, R.S.; Agua, A.R.; Pirrung, M.C.; Thomas, K.V. Concentrations of tire additive chemicals and tire road wear particles in an Australian urban tributary. Environ. Sci. Technol. 2022, 56, 2421–2431. [Google Scholar]
  18. Lane, R.F.; Smalling, K.L.; Bradley, P.M.; Greer, J.B.; Gordon, S.E.; Hansen, J.D.; Kolpin, D.W.; Spanjer, A.R.; Masoner, J.R. Tire-derived contaminants 6PPD and 6PPD-Q: Analysis, sample handling, and reconnaissance of United States stream exposures. Chemosphere 2024, 363, 142830. [Google Scholar] [CrossRef]
  19. Zeng, L.; Li, Y.; Sun, Y.; Liu, L.-Y.; Shen, M.; Du, B. Widespread Occurrence and Transport of p-Phenylenediamines and Their Quinones in Sediments across Urban Rivers, Estuaries, Coasts, and Deep-Sea Regions. Environ. Sci. Technol. 2023, 57, 2393–2403. [Google Scholar] [CrossRef]
  20. Babaei, S.; Reguyal, F.; Sarmah, A.K. A bibliometric analysis of global research hotspots and progress on emerging environmental pollutants 6PPD and 6PPD-quinone from 2004 to 2024. Environ. Pollut. 2024, 362, 124969. [Google Scholar] [CrossRef]
  21. Kazmi, S.S.U.H.; Xu, Q.; Tayyab, M.; Pastorino, P.; Barcelò, D.; Yaseen, Z.M.; Khan, Z.H.; Li, G. Navigating the environmental dynamics, toxicity to aquatic organisms and human associated risks of an emerging tire wear contaminant 6PPD quinone. Environ. Pollut. 2024, 356, 124313. [Google Scholar] [PubMed]
  22. Wei, L.-N.; Wu, N.-N.; Xu, R.; Liu, S.; Li, H.-X.; Lin, L.; Hou, R.; Xu, X.-R.; Zhao, J.-L.; Ying, G.-G. First Evidence of the Bioaccumulation and Trophic Transfer of Tire Additives and Their Transformation Products in an Estuarine Food Web. Environ. Sci. Technol. 2024, 58, 6370–6380. [Google Scholar] [CrossRef] [PubMed]
  23. Montgomery, D.; Ji, X.; Cantin, J.; Philibert, D.; Foster, G.; Selinger, S.; Jain, N.; Miller, J.; McIntyre, J.; de Jourdan, B. Interspecies differences in 6PPD-quinone toxicity across seven fish species: Metabolite identification and semiquantification. Environ. Sci. Technol. 2023, 57, 21071–21079. [Google Scholar]
  24. Anderson-Bain, K.; Roberts, C.; Kohlman, E.; Ji, X.; Alcaraz, A.J.; Miller, J.; Gangur-Powell, T.; Weber, L.; Janz, D.; Hecker, M. Apical and mechanistic effects of 6PPD-quinone on different life-stages of the fathead minnow (Pimephales promelas). Comp. Biochem. Physiol. Part C Toxicol. Pharmacol. 2023, 271, 109697. [Google Scholar] [CrossRef] [PubMed]
  25. Prosser, R.; Salole, J.; Hang, S. Toxicity of 6PPD-quinone to four freshwater invertebrate species. Environ. Pollut. 2023, 337, 122512. [Google Scholar]
  26. Roberts, C.; Lin, J.; Kohlman, E.; Jain, N.; Amekor, M.; Alcaraz, A.J.; Hogan, N.; Hecker, M.; Brinkmann, M. Acute and Subchronic Toxicity of 6PPD-Quinone to Early Life Stage Lake Trout (Salvelinus namaycush). Environ. Sci. Technol. 2024, 59, 791–797. [Google Scholar] [CrossRef] [PubMed]
  27. Varshney, S.; Gora, A.H.; Siriyappagouder, P.; Kiron, V.; Olsvik, P.A. Toxicological effects of 6PPD and 6PPD quinone in zebrafish larvae. J. Hazard. Mater. 2022, 424, 127623. [Google Scholar] [CrossRef] [PubMed]
  28. Huang, Z.; Chen, C.; Guan, K.; Xu, S.; Chen, X.; Lin, Y.; Li, X.; Shan, Y. Protective role of ghrelin against 6PPD-quinone-induced neurotoxicity in zebrafish larvae (Danio rerio) via the GHSR pathway. Ecotoxicol. Environ. Saf. 2024, 285, 117031. [Google Scholar] [CrossRef]
  29. Roberts, C.; Kohlman, E.; Jain, N.; Amekor, M.; Alcaraz, A.J.; Brinkmann, M.; Hecker, M. Sub-chronic and acute toxicity of 6PPD-quinone to early-life stage rainbow trout (Oncorhynchus mykiss). bioRxiv 2024. bioRxiv: 2024.2009. 2025.614982. [Google Scholar]
  30. Zhang, S.-Y.; Gan, X.; Shen, B.; Jiang, J.; Shen, H.; Lei, Y.; Liang, Q.; Bai, C.; Huang, C.; Wu, W. 6PPD and its metabolite 6PPDQ induce different developmental toxicities and phenotypes in embryonic zebrafish. J. Hazard. Mater. 2023, 455, 131601. [Google Scholar] [CrossRef]
  31. Lv, M.; Mao, X.; Lu, Z.; Yang, Y.; Huang, J.; Cheng, Y.; Ye, C.; He, Z.; Shu, L.; Mo, D. 6PPD induces cerebrovascular defects by triggering oxidative stress and ferroptosis in zebrafish. Sci. Total Environ. 2025, 958, 178004. [Google Scholar] [CrossRef] [PubMed]
  32. Fang, C.; Di, S.; Wang, C.; Hu, Q.; Jin, Y. Tire rubber-derived contaminant 6PPD had the potential to induce metabolism disorder in early developmental stage of zebrafish. Comp. Biochem. Physiol. Part C Toxicol. Pharmacol. 2025, 287, 110062. [Google Scholar] [CrossRef]
  33. Liu, Z.; Feng, Y.; Sun, W.; Wang, B.; Shi, C.; Ran, R.; Zhang, Y.; Lu, L.; Zhang, H. Environmental concentrations of 6PPD and 6PPD-quinone induce hepatic lipid metabolism disorders in male black-spotted frogs. J. Hazard. Mater. 2024, 480, 136400. [Google Scholar] [CrossRef] [PubMed]
  34. Fang, C.; Fang, L.; Di, S.; Yu, D.; Wang, X.; Wang, C.; Jin, Y. Bioaccumulation of N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD) and its potential cardiotoxicity in larval zebrafish (Danio rerio). SSRN 2023. [Google Scholar] [CrossRef]
  35. Grasse, N.; Seiwert, B.; Massei, R.; Scholz, S.; Fu, Q.; Reemtsma, T. Uptake and Biotransformation of the Tire Rubber-derived Contaminants 6-PPD and 6-PPD Quinone in the Zebrafish Embryo (Danio rerio). Environ. Sci. Technol. 2023, 57, 15598–15607. [Google Scholar] [CrossRef]
  36. Shi, C.; Wu, F.; Zhao, Z.; Ye, T.; Luo, X.; Wu, Y.; Liu, Z.; Zhang, H. Effects of environmental concentrations of 6PPD and its quinone metabolite on the growth and reproduction of freshwater cladoceran. Sci. Total Environ. 2024, 948, 175018. [Google Scholar] [CrossRef] [PubMed]
  37. Comenges, J.Z.; Fentanes, J.B.; Worth, A. Biology-based dynamic approach for the reconciliation of acute and chronic toxicity tests: Application to Daphnia magna. Toxicol. Lett. 2010, 196, S125. [Google Scholar]
  38. Botelho, M.T.; Militão, G.G.; Brinkmann, M.; Umbuzeiro, G.d.A. Toxicity and mutagenicity studies of 6PPD-quinone in a marine invertebrate species and bacteria. Environ. Mol. Mutagen. 2023, 64, 335–341. [Google Scholar] [PubMed]
  39. De Castro-Català, N.; Lizama, C.; Serra, J.; Cadena-Aizaga, M.I.; Petrovic, M.; Muñoz, I. Crawling Towards Complex Interactions: The Impact of 6ppd-Quinone and Increased Temperatures on the Freshwater Snail Radix balthica. SSRN 2024. [Google Scholar] [CrossRef]
  40. Tallec, K.; Huvet, A.; Yeuc’h, V.; Le Goïc, N.; Paul-Pont, I. Chemical effects of different types of rubber-based products on early life stages of Pacific oyster, Crassostrea gigas. J. Hazard. Mater. 2022, 427, 127883. [Google Scholar] [CrossRef]
  41. Yan, X.; Kiki, C.; Xu, Z.; Manzi, H.P.; Rashid, A.; Chen, T.; Sun, Q. Comparative growth inhibition of 6PPD and 6PPD-Q on microalgae Selenastrum capricornutum, with insights into 6PPD-induced phototoxicity and oxidative stress. Sci. Total Environ. 2024, 957, 177627. [Google Scholar] [PubMed]
  42. Bourgougnon, N.; Burlot, A.-S.; Jacquin, A.-G. Chapter Five—Algae for global sustainability? In Advances in Botanical Research; Jacquot, J.-P., Ed.; Academic Press: Cambridge, MA, USA, 2021; Volume 100, pp. 145–212. [Google Scholar]
  43. You, X.; Chen, X.; Jiang, Y.; Chen, H.; Liu, J.; Wu, Z.; Sun, W.; Ni, J. 6PPD-quinone affects the photosynthetic carbon fixation in cyanobacteria by extracting photosynthetic electrons. Innovation 2024, 5, 100630. [Google Scholar] [PubMed]
  44. Liu, J.; Yu, M.; Shi, R.; Ge, Y.; Li, J.; Zeb, A.; Cheng, Z.; Liu, W. Comparative toxic effect of tire wear particle-derived compounds 6PPD and 6PPD-quinone to Chlorella vulgaris. Sci. Total Environ. 2024, 951, 175592. [Google Scholar] [CrossRef]
  45. Ihenetu, S.C.; Xu, Q.; Khan, Z.H.; Kazmi, S.S.U.H.; Ding, J.; Sun, Q.; Li, G. Environmental fate of tire-rubber related pollutants 6PPD and 6PPD-Q: A review. Environ. Res. 2024, 258, 119492. [Google Scholar] [PubMed]
Fishes 10 00146 g001
Figure 1. The generation process of 6PPD-Q and its distribution map in the environment.
Figure 1. The generation process of 6PPD-Q and its distribution map in the environment.
Fishes 10 00146 g001
Table 1. Chemical characteristics of 6PPD and 6PPDQ.
Table 1. Chemical characteristics of 6PPD and 6PPDQ.
NameAbbreviateStructureStructural FormulaMolecular Weight
N-(1,3-dimethylbutyl)-N′-phenylenediamine6PPDFishes 10 00146 i001C18H24N2268.40
N-(1,3-dimethylbutyl)-N′-phenylenediamine-quinone 6PPD-QFishes 10 00146 i002C18H22N2O2298.39
Table 2. Distribution and concentration of 6PPD-Q in different environmental media and locations.
Table 2. Distribution and concentration of 6PPD-Q in different environmental media and locations.
Environment TypeLocationConcentration RangeMedian Concentration
Road runoff (water)Seattle, USA0.8–19 μg/L——
Road runoff (water)Los Angeles, USA4.1–6.1 μg/L——
urban runoff (water)San Francisco, USA1.0–3.5 μg/L——
Urban streams (water)Don River, Highland Creek, Toronto, Canada0.54 ± 0.04,
0.72 ± 0.26 μg/L		——
River(urban affected) (water)Southwest branch, Brisbane River, Australia0.4–88 ng/L——
River estuary (Sediment)Major rivers in the Pearl River Delta, China1.87–18.2 ng/g9.03 ng/g
River estuary (Sediment)Pearl River estuary, South China Sea<MDL a–4.88 ng/g2.00 ng/g
Coastal rivers (Sediment)Coastal areas, South China Sea0.431–2.98 ng/g1.27 ng/g
Coastal deep-sea (Sediment)South China Sea deep-sea areas<MDL–3.02 ng/g2.71 ng/g
a MDL: method detection limit.
Table 3. Lethal concentrations of 6PPD-Q for different species of fish.
Table 3. Lethal concentrations of 6PPD-Q for different species of fish.
Species of FishLife CycleExposure Duration (h)LC50 (μg/L)
Danio rerioembryo-54
0ncorhynchus kisutchjuvenile fish24<0.10
Oncorhynchus mykissjuvenile fish721.00
Salvelinus fontinalisjuvenile fish240.59
Salvelinus namaycushjuvenile fish960.50
Salvelinus alpinusjuvenile fish9614.2
Acipenser oxyrinchusjuvenile fish9614.2
Gobiocypris rarusjuvenile fish96162.201
Acipenser transmontanusjuvenile fish9614.2
Sciaenops ocellatusjuvenile fish24–72500
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Li, C.; Yang, Y.; Tian, Z.; Huang, Z.; Huang, Y.; Hong, Y. Residues of 6PPD-Q in the Aquatic Environment and Toxicity to Aquatic Organisms: A Review. Fishes 2025, 10, 146. https://doi.org/10.3390/fishes10040146

AMA Style

Li C, Yang Y, Tian Z, Huang Z, Huang Y, Hong Y. Residues of 6PPD-Q in the Aquatic Environment and Toxicity to Aquatic Organisms: A Review. Fishes. 2025; 10(4):146. https://doi.org/10.3390/fishes10040146

Chicago/Turabian Style

Li, Chaoju, Yuanqiang Yang, Zikun Tian, Zhiqiu Huang, Yi Huang, and Yuhang Hong. 2025. "Residues of 6PPD-Q in the Aquatic Environment and Toxicity to Aquatic Organisms: A Review" Fishes 10, no. 4: 146. https://doi.org/10.3390/fishes10040146

APA Style

Li, C., Yang, Y., Tian, Z., Huang, Z., Huang, Y., & Hong, Y. (2025). Residues of 6PPD-Q in the Aquatic Environment and Toxicity to Aquatic Organisms: A Review. Fishes, 10(4), 146. https://doi.org/10.3390/fishes10040146

Article Metrics

Back to TopTop