Ecotoxicity of triphenyltin on the marine copepod Tigriopus japonicus at various biological organisations: from molecular to population-level effects

The contraceptive active ingredient levonorgestrel disrupts the physiology of Macrocyclops albidus

Active pharmaceutical ingredients, such as levonorgestrel (LNG), continue to increase in aquatic ecosystems and are detected in environmental matrices; however, their ability to bioaccumulate and cause reproductive, developmental, and biochemical defects in benthic organisms, such as Macrocyclops albidus, is unknown. This study investigated the effects of LNG on the oxidative stress response, reproduction, and development of M. albidus. Levonorgestrel induced a significant (p < 0.05) increase in total protein with increasing concentrations from 10 ng L-1. Intracellular hydrogen peroxide levels were elevated after exposure to LNG (p < 0.05). Malondialdehyde level declined as LNG concentration increased at day 7 and increased at higher LNG at day 14. Peroxidase activity was significantly (p < 0.05) elevated by lower (1-100 ng L-1) than higher (1000-10000 ng L-1) concentrations of LNG. Glutathione S-transferase activity declined with increasing concentrations of LNG. Increased metamorphosis from the nauplii to the copepodite stage was significantly induced by 1000 and 10000 ng L-1 LNG within four days of exposure. In addition, higher concentrations of LNG induced early production of egg sacs in female M. albidus within four days. Levonorgestrel bioaccumulated in M. albidus, with higher tissue concentrations occurring at high exposures. This study revealed that LNG is readily absorbed and causes stress by interfering with reproduction and metamorphosis in M. albidus, thereby highlighting the role of this zooplankton as a sensitive bioindicator of endocrine disruptors in aquatic ecosystems.

Toxic effects of triphenyltin on the development of zebrafish (Danio rerio) embryos

Triphenyltin (TPT) is known to be an environmental endocrine disruptor and has adverse effects on aquatic animals. In this study, zebrafish embryos were treated with three different concentrations (12.5, 25, 50 nmol/L) based on the LC₅₀ value at 96 h post fertilization (96 hpf), after TPT exposure. The developmental phenotype and hatchability were observed and recorded. Reactive oxygen species (ROS) levels in zebrafish were detected at 72 hpf and 96 hpf using 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA) as a probe. The number of neutrophils after exposure was observed using transgenic zebrafish Tg (lyz: DsRed). RNA-seq analysis was used to compare the gene expression changes in zebrafish embryos at 96 hpf in the control group and 50 nmol/L TPT exposure group. The data revealed that TPT caused a delay in hatching of zebrafish embryos in a time- and dose-dependent manner, as well as causing pericardial edema, spinal curvature and melanin reduction. ROS levels in embryos exposed to TPT increased, and the number of neutrophils increased after TPT exposure to Tg (lyz: DsRed) in transgenic zebrafish. RNA-seq results were also analyzed, and KEGG enrichment analysis showed that significant differential genes were enriched in the PPAR signaling pathway (P < 0.05), and the PPAR signaling pathway mainly affected genes related to lipid metabolism. The RNA-seq results were verified using real-time fluorescence quantitative PCR (RT-qPCR). Oil red O and Nile red staining showed increased lipid accumulation after TPT exposure. These findings suggest that TPT affects the development of zebrafish embryos even at relatively low concentrations.

Reduced Fitness and Elevated Oxidative Stress in the Marine Copepod Tigriopus japonicus Exposed to the Toxic Dinoflagellate Karenia mikimotoi

Blooms of the toxic dinoflagellate Karenia mikimotoi cause devastation to marine life, including declines of fitness and population recruitment. However, little is known about the effects of them on benthic copepods. Here, we assessed the acute and chronic effects of K. mikimotoi on the marine benthic copepod Tigriopus japonicus. Results showed that adult females maintained high survival (>85%) throughout 14-d incubation, but time-dependent reduction of survival was detected in the highest K. mikimotoi concentration, and nauplii and copepodites were more vulnerable compared to adults. Ingestion of K. mikimotoi depressed the grazing of copepods but significantly induced the generation of reactive oxygen species (ROS), total antioxidant capacity, activities of antioxidant enzymes (superoxide dismutase, catalase, and glutathione peroxidase), and acetylcholinesterase. Under sublethal concentrations for two generations, K. mikimotoi reduced the fitness of copepods by prolonging development time and decreasing successful development rate, egg production, and the number of clutches. Our findings suggest that the bloom of K. mikimotoi may threaten copepod population recruitment, and its adverse effects are associated with oxidative stress.

Transcriptomics reveal triphenyltin-induced molecular toxicity in the marine mussel Perna viridis

Triphenyltin (TPT) is widely used as an active ingredient in antifouling paints and fungicides, and continuous release of this highly toxic endocrine disruptor has caused serious pollution to coastal marine ecosystems and organisms worldwide. Using bioassays and transcriptome sequencing, this study comprehensively investigated the molecular toxicity of TPT chloride (TPTCl) to the marine mussel Perna viridis which is a commercially important species and a common biomonitor for marine pollution in Southeast Asia. Our results indicated that TPTCl was highly toxic to adult P. viridis, with a 96-h LC₁₀ and a 96-h EC₁₀ at 18.7 μg/L and 2.7 μg/L, respectively. A 21-day chronic exposure to 2.7 μg/L TPTCl revealed a strong bioaccumulation of TPT in gills (up to 36.48 μg/g dry weight) and hepatopancreas (71.19 μg/g dry weight) of P. viridis. Transcriptome analysis indicated a time course dependent gene expression pattern in both gills and hepatopancreas. Higher numbers of differentially expressed genes were detected at Day 21 (gills: 1686 genes; hepatopancreas: 1450 genes) and at Day 28 (gills: 628 genes; hepatopancreas: 238 genes) when compared with that at Day 7 (gills: 104 genes, hepatopancreas: 112 genes). Exposure to TPT strongly impaired the endocrine system through targeting on nuclear receptors and putative steroid metabolic genes. Moreover, TPT widely disrupted cellular functions, including lipid metabolism, xenobiotic detoxification, immune response and endoplasmic-reticulum-associated degradation expression, which might have caused the bioaccumulation of TPT in the tissues and aggregation of peptides and proteins in cells that further activated the apoptosis process in P. viridis. Overall, this study has advanced our understanding on both ecotoxicity and molecular toxic mechanisms of TPT to marine mussels, and contributed empirical toxicity data for risk assessment and management of TPT contamination.

Glutathione S-Transferases in Marine Copepods

The glutathione S-transferase (GST) is a complex family of phase II detoxification enzymes, known for their ability to catalyze the conjugation of the reduced form of glutathione (GSH) to a wide variety of endogenous and exogenous electrophilic compounds for detoxification purposes. In marine environments, copepods are constantly exposed to multiple exogenous stressors, thus their capability of detoxification is key for survival. Full identification of the GST family in copepods has been limited only to few species. As for insects, the GST family includes a wide range of genes that, based on their cellular localization, can be divided in three classes: cytosolic, microsomal, and mitochondrial. The role of GSTs might have class-specific features, thus understanding the nature of the GST family has become crucial. This paper covers information of the GST activity in marine copepods based on studies investigating gene expression, protein content, and enzymatic activity. Using published literature and mining new publicly available transcriptomes, we characterized the multiplicity of the GST family in copepods from different orders and families, highlighting the possible role of these genes as biomarker for ocean health status monitoring.

The effects of TPT and dietary quercetin on growth, hepatic oxidative damage and apoptosis in zebrafish

The objective of this study was to determine the effects of triphenyltin (TPT) and dietary quercetin on the growth, oxidative stress and apoptosis in zebrafish. A total of 240 fish were divided into 4 groups with three replicates as follows: fish were fed with the basal diet as the control group (D1), only 10 ng/L TPT (D2), 10 ng/L TPT + 100 mg/kg quercetin (D3), and only 100 mg/Kg quercetin as the D4 group. At the end of the study period (56 d), the results showed that the growth performance of the fish that were fed 100 mg/kg quercetin was significantly higher than that of fish that were exposed to 10 ng/L TPT. Quercetin ameliorated oxidative stress, which decreased malondialdehyde (MDA) and nitric oxide (NO) levels and improved antioxidant enzyme activities. The mRNA expressions of the key apoptotic gene and pro-inflammatory cytokines were significantly induced by TPT exposure. However, dietary quercetin prevented a marked increase in the Bax, caspase3 and caspase9 transcript abundances that were induced by TPT. In addition, the quercetin treatments decreased inflammation by regulating the NF-kB signalling pathway. In conclusion, our findings suggested that TPT induced oxidative stress and apoptosis in zebrafish and that the pretreatment with quercetin showed an ameliorative role. Dietary 100 mg/ kg quercetin helps to prevent oxidative damage, apoptosis and inflammation in TPT treated zebrafish.

Review on endocrine disrupting toxicity of triphenyltin from the perspective of species evolution: Aquatic, amphibious and mammalian

Triphenyltin (TPT) is widely used as a plastic stabilizer, insecticide and the most common fungicide in antifouling coatings. This paper reviewed the main literature evidences on the morphological and physiological changes of animal endocrine system induced by TPT, with emphasis on the research progress of TPT metabolism, neurological and reproductive regulation in animal endocrine system. Similar to tributyltin (TBT), the main effects of TPT on the potential health risks of 25 species of animals, from aquatic animals to mammals, are not only related to exposure dose and time, but also to age, sex and exposed tissue/cells. Moreover, current studies have shown that TPT can directly damage the endocrine glands, interfere with the regulation of neurohormones on endocrine function, and change hormone synthesis and/or the bioavailability (i.e., in the retinoid X receptor and peroxisome proliferator-activated receptor gamma RXR-PPARγ) in target cells. Importantly, TPT can cause biochemical and morphological changes of gonads and abnormal production of steroids, both of which are related to reproductive dysfunction, for example, the imposex of aquatic animals and the irregular estrous cycle of female mammals or spermatogenic disorders of male animals. Therefore, TPT should indeed be regarded as a major endocrine disruptor, which is essential for understanding the main toxic effects on different tissues and their pathogenic effects on endocrine, metabolism, neurological and reproductive dysfunction.

Human-engineered hydrodynamic regimes as a driver of cryptic microinvertebrate assemblages on urban artificial shorelines

Urban shorelines undergo substantial hydrodynamic changes as a result of coastal engineering and shoreline armouring that can alter sedimentation, turbidity, and other factors. These changes often coincide with major shifts in the composition and distribution of marine biota, however, rarely are hydrodynamic-mediated factors confirmed experimentally as the mechanism underpinning these shifts. This study first characterized hydrodynamic-related distribution patterns among epilithic and epiphytic microinvertebrates on urban seawalls in Singapore. We found reduced microinvertebrate abundances and distinct microinvertebrate community structure within benthic turf algae in areas where coastal defences had reduced wave energy and increased sediment deposition, among other hydrodynamic-related abiotic changes. Low-exposure areas also had reduced densities of macroinvertebrate grazers and less dense turf algae (lower mass per cm²) than adjacent high-exposure areas. Using harpacticoid copepods as a model taxon, we performed a reciprocal transplant experiment to discern between the effects of exposure-related conditions and grazing. Results from the experiment indicate that conditions associated with restricted wave energy from shoreline engineering limit harpacticoid population densities, as transplantation to low-exposure areas led to rapid reductions in abundance. At the same time, we found no effect from grazer exclusion cages, suggesting harpacticoids are minimally impacted by exposure-related gradients in gastropod macrograzer densities over short time scales. Given the key role of intertidal microinvertebrates, particularly harpacticoids, in nearshore food webs, we postulate that human-engineered hydrodynamic regimes are an important factor shaping marine ecosystem functioning in urban areas.

Assessing the Efficacy of a Sediment Remediation Program Using Benthic and Pelagic Copepod Bioassays

Tributyltin is an organotin chemical that has been commonly used in ship antifouling paints. Despite the global total prohibition of tributyltin-based paint in 2008, tributyltin continues to be found at toxic levels in areas of high maritime traffic such as ports and harbors. A remediation program was conducted at a New Zealand port to reduce tributyltin and copper concentrations to acceptable values. The present study assessed the efficacy of the program using a combination of chemical analyses and copepod bioassays. Sediment and water samples were collected at 3 locations along a spatial gradient within the port, and concentrations of various organotin compounds and trace metal levels were measured pre- and postremediation. The toxicity of sediment and elutriate samples was estimated by benthic and pelagic copepod bioassays. Although acute toxicity in sediment samples was reduced following remediation, reproductive success was still affected for the benthic copepod. This approach combining chemical analysis and bioassays is promising for assessing the efficacy of remediation processes at contaminated marine sites. Environ Toxicol Chem 2020;39:492-499. © 2019 SETAC.

Triphenyltin exposure alters the antioxidant system, energy metabolism and the expression of genes related to physiological stress in zebrafish (Danio rerio)

The adverse influences of triphenyltin (TPT) on aquatic system have been of great concern due to their widespread use and ubiquity in water environment. Here, zebrafish larvae (7 days after hatching) were exposed to TPT for 14 days to study its toxicity on the antioxidant system, energy metabolism and the expression of genes related to physiological stress. Results shows that the oxidative stress was generated in fish larvae exposed to TPT with higher concentrations (10 and/or 100 ng/l), and the energy metabolic parameters (RNA/DNA ratio, Na + -K + -ATPase) were significantly inhibited in fish exposed to 100 ng/l TPT. Additional, the expression levels of genes related to physiological stress were up-regulated in a dose-dependent manner, including heat shock protein70 (hsp70) and metallothionein (mt). Moreover, the PERK-eIF2α pathway was found as the main branch activated by TPT exposure in fish larvae. Thus, TPT-induced antioxidant responses, energy metabolism disorder and physiological stress in fish larvae were reflected by the parameters measured, which could provide some useful information for full understanding the exact mechanisms of TPT toxicity.

Effect of nano zinc oxide on the acute and reproductive toxicity of cadmium and lead to the marine copepod Tigriopus japonicus

Given the absorbability of nZnO and its inevitable coexistence with trace metals such as Cd and Pb in coastal environment, nZnO can adsorb these pollutants thereby affecting their distribution in different media of marine ecosystem. The marine copepod Tigriopus japonicus was applied in the present study to investigate the combined effect of nZnO and Cd or Pb on mortality and reproduction in marine organisms. For acute exposure, presence of 1.0 mg/L nZnO increased the toxicity of both Cd and Pb, as their LC₅₀ decreased from 5.9 and 75.4 mg/L to 3.95 and 48.0 mg/L, respectively. For 21 d chronic exposure, the reproduction of the copepod was influenced by Cd and Pb at environmental relevant concentrations, and the interaction between nZnO and Cd or Pb appeared to be antagonistic. The waterborne Cd and Pb concentration was affected by nZnO for neither acute nor chronic exposure, indicating no adsorption of these two metals to nZnO at relative low concentration. The overall findings of this study suggested the binary exposure to nZnO/Cd or nZnO/Pb might have potential different toxic mechanisms between acute and chronic exposure.

Effect of Multi-walled Carbon Nanotubes on the Toxicity of Triphenyltin to the Marine Copepod Tigriopus japonicus

Marine organisms are often exposed to a mixture of various pollutants in marine environment (i.e., nanoparticles, organic pollutants). The present study investigated the potential effects of multi-walled carbon nanotubes (MWCNTs) on the toxicity of triphenyltin chloride (TPTCl). The results revealed an antagonistic interaction between MWCNTs and TPTCl on the copepod through 96 h acute exposure, which was attributed to the adsorption of TPTCl to MWCNTs and aggregation of MWCNTs in the test solutions. Results of 21 days' chronic exposure showed that the effect concentration of MWCNTs could be 100 times lower than that of acute exposure. The exposure to binary mixture of MWCNT (1.0 mg/L) and TPTCl (0.3 µg/L) caused a reduction by 94% for the 3rd time spawning and 83% for the total number of hatched nauplii. The ingestion and exterior attachment of MWCNTs to the copepod might be the main reasons causing the adverse effect in reproduction.

Triphenyltin exposure affects mating behaviors and attractiveness to females during mating in male guppies (Poecilia reticulata)

The impacts of triphenyltin (TPT) on ecological health have been of great concern due to their widespread use and ubiquity in aquatic ecosystems. However, little is known about the effects of TPT on the reproductive behaviors of fishes. Therefore, the present study was conducted to investigate the effects of TPT at environmentally relevant concentrations (0, 1 and 10 ng Sn/L) on the mating behaviors and the attractiveness to females during mating in male guppies (Poecilia reticulata). The results showed that TPT exposure disturbed the mating behaviors; the TPT-exposed male fish performed more sneaking attempts, but no changes in sigmoid courtship were displayed. The increases in sneaking attempts might be related to increases in testosterone levels induced by TPT exposure. In the context of a competing male, the TPT-exposed males were less attractive to females during mating. The decreases in attractiveness might be related to decreases in carotenoid-based coloration, shown as decreases in caudal fin redness values and skin carotenoid contents. In addition, TPT-induced total antioxidant capacities, the activities of superoxide dismutase and catalase, and the contents of malondialdehyde in liver and intestinal tissues indicated increases in oxidative stress. Both oxidative stress and coloration are linked to carotenoids. Thus, we speculated that the TPT-exposed males might use carotenoids to cope with increases in oxidative stress at the expense of carotenoid-based coloration. The disruption of mating behaviors and the decrease in attractiveness to females in male fish could result in reproductive failure. The present study underscores the importance of using behavioral tests as a sensitive tool in assessing the impact of pollutants present in aquatic environments.

Toxic effect of triphenyltin in the presence of nano zinc oxide to marine copepod Tigriopus japonicus

Marine organisms are naturally exposed to different environmental pollutants including organic pollutants and nanoparticles. The interactive effects between nanoparticles and other chemicals on aquatic organisms have raised concerns regarding the potential of nanomaterials as the vector for other chemicals. In the present study, the effect of nano zinc oxide (nZnO) on the bioavailability of triphenyltin chloride (TPTCl) was studied, and their combined acute and reproductive toxicity to the marine copepod Tigriopus japonicus were evaluated. At experimental concentration ranges of nZnO in this study, the percentage of dissolution of Zn²⁺ was relative stable (from 62% to 66%), and nZnO did not affect the bioavailability of TPTCl to the copepods. The acute toxicity of binary mixtures of nZnO/TPT was equivalent to that of the mixture of Zn²⁺/TPT. In agreement with the decrease in TPTCl's LC₅₀ values at the presence of nZnO, their interacting effect was synergistic based on response addition response surface model, and the interacting parameter was modelled to be -1.43. In addition to acute toxicity test, reproductive toxicity tests revealed that exposure to nZnO and TPTCl didn't affect the successful mating rate and the number of nauplii in the 1st brood, but they extended the time for the eggs to hatch from 2.53 days to 3.94 and 3.64 days, respectively. The exposure to nZnO/TPTCl mixture delayed the time to hatch to 5.78 days.

Predation Risk Potentiates Toxicity of a Common Metal Contaminant in a Coastal Copepod

To examine whether natural stressors like predation risk affect responses to anthropogenic contaminants, we exposed nauplii of the copepod Tigriopus brevicornis to chemical cues from fish (kairomones) and copper (Cu). We tested effects of these treatments, singly and combined, on copepod age and size at maturity, and development stage sensitivity, while controlling for effects of genetic heterogeneity (clutch identity). Predation risk, Cu and clutch identity interacted in their effect on development time. Predation risk alone had minor effects, but potentiated Cu toxicity in the combined treatment by doubling the delay in age at maturity, as compared to Cu exposure alone. This potentiating effect on developmental delay appeared already at the first copepodite stage. The specific strength of response varied among nauplii from different females' clutches. There were no differences in copepod size at maturity among treatments. We did, however, find an interaction between the effect of Cu and clutch identity on copepod growth. Our results demonstrate the importance of ecological interactions for potentiating the toxicity of environmental contaminants. We also demonstrate the need to consider genetic heterogeneity in ecotoxicology. Natural variation in stressor responses has implications for the interpretation of results from toxicological studies using single-clone or inbred culture populations.

Triphenyltin exposition induces spermatic parameter alters of Calomys laucha species

The present study aims to evaluate the influence of triphenyltin (TPT) exposure on reproductive physiology on Calomys laucha species, since this species inhabits regions susceptible to exposure to this contaminant. Animals exposed to the highest dose (10.0 mg/kg) presented signs of severe intoxication in only 7 days of exposure, demonstrating a higher sensitivity of this species to triphenyltin. The 10.0 mg TPT/kg dose was analyzed separately for short-term exposure and results suggest that exposure to this dose was severely detrimental to sperm activity. Among the main results obtained in the evaluation of sperm kinetics, a reduction in total motility was observed from the 0.5 mg TPT/kg group, accentuated according to the increase in the doses of TPT. In progressive motility, there was a decrease from the dose of 0.5 mg TPT/kg and maintained the plateau until the dose of 5.0 mg TPT/kg. It was also observed an increase in the distances and velocities average path, rectilinear and curvilinear in doses of 2.5 and 5.0 mg/kg. From the flow cytometry, evaluation a decrease in mitochondrial functionality was observed as the dose increased. Increased membrane fluidity was also observed from the 5.0 mg TPT/kg dose and the acrosome reaction presented higher values at doses of 0.5 and 5.0 mg TPT/kg. We can conclude that TPT causes impairment of the sperm activity, reducing it in individuals exposed in the adult phase.

Response of the freshwater diatom Halamphora veneta (Kützing) Levkov to copper and mercury and its potential for bioassessment of heavy metal toxicity in aquatic habitats

This study investigates the effects of copper and mercury on growth rate, chlorophyll a content, superoxide dismutase (SOD) activity, SOD mRNA gene expression, and frustule morphology of the benthic freshwater diatom Halamphora veneta (Kützing) Levkov and the potential utility of each for toxicity assessment in aquatic habitats. Results showed the following: (1) Compared to mercury, exposure to copper resulted in greater growth inhibition of H. veneta even at low concentrations and after short durations of exposure; (2) high accumulation of chlorophyll a in H. veneta is a stress response to the presence of heavy metals; (3) SOD activity and SOD gene expression varied in H. veneta according to the concentration, exposure time, and type of heavy metal; and (4) exposure to mercury resulted in deformity in the shape and an increase in size of the frustule of H. veneta. Growth rate, chlorophyll a content, SOD activity and gene expression, and frustule morphology of H. veneta are all potential candidates for the toxicological assessment of copper and mercury in aquatic habitats.

Effects of triclosan (TCS) on fecundity, the antioxidant system, and oxidative stress-mediated gene expression in the copepod Tigriopus japonicus

Triclosan (TCS) is an antimicrobial agent that has been widely dispersed and detected in the marine environment. However, the effects of TCS in marine invertebrates are poorly understood. In this study, the effects of TCS on life cycle history (e.g. mortality and fecundity) along with cellular reactive oxygen species (ROS) levels, GSH content, antioxidant enzymatic activities, and mRNA expression levels of oxidative stress-mediated genes were measured in the copepod Tigriopus japonicus. The no observed effect concentration (NOEC) and median lethal concentration (LC50) of TCS in the adult stage were determined to be 300μg/L and 437.476μg/L, respectively, while in the nauplius stages the corresponding values were 20μg/L, and 51.76μg/L, respectively. Fecundity was significantly reduced (P<0.05) in response to TCS at 100μg/L. Concentration- and time-dependent analysis of ROS, GSH content (%), and antioxidant enzymatic activities (e.g. GST, GPx, and SOD) were significantly increased (P<0.05) in response to TCS exposure. Additionally, mRNA expression of detoxification (e.g., CYPs) and antioxidant (e.g., glutathione S-transferase-sigma isoforms, Cu/Zn superoxide dismutase, catalase) genes was modulated in response to TCS exposure at different concentrations over a 24h period. Our results revealed that TCS can induce reduced fecundity and oxidative stress with transcriptional regulation of oxidative stress-mediated genes with activation of the antioxidant system in the copepod T. japonicus.

Spliced leader-based analyses reveal the effects of polycyclic aromatic hydrocarbons on gene expression in the copepod Pseudodiaptomus poplesia

Polycyclic aromatic hydrocarbons (PAHs) are a group of toxic and carcinogenic pollutants that can adversely affect the development, growth and reproduction of marine organisms including copepods. However, knowledge on the molecular mechanisms regulating the response to PAH exposure in marine planktonic copepods is limited. In this study, we investigated the survival and gene expression of the calanoid copepod Pseudodiaptomus poplesia upon exposure to two PAHs, 1, 2-dimethylnaphthalene (1, 2-NAPH) and pyrene. Acute toxicity responses resulted in 96-h LC₅₀ of 788.98μgL^-1 and 54.68μgL^-1 for 1, 2-NAPH and pyrene, respectively. Using the recently discovered copepod spliced leader as a primer, we constructed full-length cDNA libraries from copepods exposed to sublethal concentrations and revealed 289 unique genes of diverse functions, including stress response genes and novel genes previously undocumented for this species. Eighty-three gene families were specifically expressed in PAH exposure libraries. We further analyzed the expression of seven target genes by reverse transcription-quantitative PCR in a time-course test with three sublethal concentrations. These target genes have primary roles in detoxification, oxidative defense, and signal transduction, and include different forms of glutathione S-transferase (GST), glutathione peroxidases (GPX), peroxiredoxin (PRDX), methylmalonate-semialdehyde dehydrogenase (MSDH) and ras-related C3 botulinum toxin substrate (RAC1). Expression stability of seven candidate reference genes were evaluated and the two most stable ones (RPL15 and RPS20 for 1, 2-NAPH exposure, RPL15 and EF1D for pyrene exposure) were used to normalize the expression levels of the target genes. Significant upregulation was detected in GST-T, GST-DE, GPX4, PRDX6 and RAC1 upon 1, 2-NAPH exposure, and GST-DE and MSDH upon pyrene exposure. These results indicated that the oxidative stress was induced and that signal transduction might be affected by PAH exposure in P. poplesia. However, gene upregulation was followed by a reduction in expression level towards 96h, indicating a threshold value of exposure time that leads to depressed gene expression. Prolonged exposure may cause dysfunction of detoxification and antioxidant machinery in P. poplesia. The transcriptional responses of GST-T, GPX2 and GPX4 upon pyrene exposure were minimal. Our results reveal the different sensitivity of P. poplesia to two PAHs at both the individual and transcriptional levels. As the first attempt, this study proved that copepod spliced leader is useful for obtaining full-length cDNA in P. poplesia exposed to PAHs and provided a valuable gene resource for this non-model species. This approach can be applied to other calanoid copepods exposed to various stressors, particularly under field conditions.

A brominated flame retardant 2,2',4,4' tetrabrominated diphenyl ether (BDE-47) leads to lipogenesis in the copepod Tigriopus japonicus

De novo lipogenesis (DNL) is a fatty acid synthesis process that requires several genes, including sterol regulatory element binding protein (SREBP), ATP-citrate lyase (ACLY), and acetyl-CoA carboxylase (ACC). DNL up-regulation is able to induce fat accumulation through an increase in fatty acids. To investigate the relationship between DNL up-regulation and the accumulation of fatty acids and lipid droplets in response to 2,2',4,4' tetrabrominated diphenyl ether (BDE-47), we examined DNL in the copepod Tigriopus japonicus. Transcription levels of DNL-related genes were increased after exposure to 2.5μg/L BDE-47 for 24h. After exposure to 2.5μg/L BDE-47, palmitic acid was significantly increased (P<0.05) at days 1 and 4, along with upregulation of fatty acid synthesis-related genes (e.g., desaturases and elongases). However, docosahexaenoic acid and arachidonic acid were down-regulated at days 1 and 4, showing an antagonistic effect. Lipid droplet area significantly increased in Nile red staining analysis after 24h of exposure to 2.5μg/L BDE-47 in T. japonicus, while DNL was down-regulated in response to 500μM salicylate (a lipogenesis inhibitor), indicating that BDE-47 exposure is closely associated with an increase in fatty acids in this copepod. This study provides a better understanding of the effects of BDE-47 on DNL in copepods.

Lethal and Sublethal Toxicity Comparison of BFRs to Three Marine Planktonic Copepods: Effects on Survival, Metabolism and Ingestion

The estuarine planktonic copepods have a wide geographical distribution and commendable tolerance to various kinds of contaminants. The primary aim of the present study was to contrast the impacts of model POPs (TBBPA and HBCD) on three common estuarine planktonic copepods (Oithona similis, Acartia pacifica and Pseudodiaptomus inopinus) and establish a protocol for the assessment of acute toxicity of marine organic pollutants. We first quantified the 96h-LC50 (0.566, 0.04 and 0.257 mg/L of TBBPA to the three subjects above respectively and 0.314 mg/L of HBCD to P. inopinus; all reported concentrations are nominal values). In the sub-lethal toxicity tests, it was turned out that the effects of copepods exposed to TBBPA could product different influences on the energy ingestion and metabolism. Different type of pollutions, meanwhile, could also bring varying degree effect on the target copepods. In general, the indicators (the rate of oxygen consumption, ammonia excretion, food ingestion and filtration) in higher concentration groups showed marked significant difference compared with controls as well a dose-effect relationship. The study also extended the research on the joint toxicity of TBBPA and HBCD based on the survival rate of P.inopinus. Whether 1:1 concentration or 1:1 toxic level, the research showed synergy effect relative to single exposure conditions. The result indicated that current single ecological testing used for environmental protection activities may underestimate the risk for copepods. It was also demonstrated that short-term sub-lethal experiment could be a standard to evaluate the sensitivity of copepods to POPs.

Body size-dependent toxicokinetics and toxicodynamics could explain intra- and interspecies variability in sensitivity

Ecological risk assessment of chemicals aims at quantifying the likelihood of adverse effects posed to non-target populations and the communities they constitute, often based on lethal concentration estimates for standard test species. There may, however, be intra- and interspecific differences in responses to chemical exposure. Here with the help of a toxicokinetic-toxicodynamic model, we explored whether differential body sizes might explain the observed variability in sensitivity between species and between life-stages of each individual species, for three model organisms, Daphnia magna, Chaoborus crystallinus and Mesocyclops leuckarti. While body size-dependent toxicokinetics could be used to predict intraspecies variation in sensitivity, our results also suggest that changes in both toxicokinetic and toxicodynamic parameters might be needed to describe differential species sensitivity. Accounting for biological traits, like body size, in mechanistic effect models will allow more accurate predictions of chemical effects in size structured populations, ultimately providing mechanistic explanations for species sensitivity distributions.