Feeding reduces waterborne Cu bioaccumulation in a marine rabbitfish Siganus oramin

De Novo Assembly, Characterization, and Comparative Transcriptome Analysis of Mature Male and Female Gonads of Rabbitfish (Siganus oramin) (Bloch & Schneider, 1801)

The rabbitfish, Siganus oramin, is a commercially important table fish in southeastern China. However, there have been few studies on its gonad development and reproduction regulation. Comparative transcriptome analysis was first performed on adult male and female gonads of S. oramin. In total, 47,070 unigenes were successfully assembled and 22,737 unigenes were successfully annotated. Through comparative transcriptome analysis of male and female gonads, a total of 6722 differentially expressed genes were successfully identified, with 3528 upregulated genes and 3154 downregulated genes in the testes. In addition, 39 differentially expressed reproduction-related genes were identified. Finally, quantitative real-time PCR was used to validate the expression levels of several differentially expressed genes. These results provide important data for further studying the function of reproduction-related genes and the molecular mechanism regulating gonad development and reproduction in S. oramin.

Statement of the PPR Panel on a framework for conducting the environmental exposure and risk assessment for transition metals when used as active substances in plant protection products (PPP)

The European Commission asked the European Food Safety Authority (EFSA) to prepare a statement on a framework for the environmental risk assessment (ERA) of transition metals (e.g. iron and copper) used as active substances in plant protection products (PPPs). Non-degradability, essentiality and specific conditions affecting fate and behaviour as well as their toxicity are distinctive characteristics possibly not covered in current guidance for PPPs. The proposed risk assessment framework starts with a preliminary phase, in which monitoring data on transition metals in relevant environmental compartments are provided. They deliver the metal natural background and anthropogenic residue levels to be considered in the exposure calculations. A first assessment step is then performed assuming fully bioavailable residues. Should the first step fail, refined ERA can, in principle, consider bioavailability issues; however, non-equilibrium conditions need to be taken into account. Simple models that are fit for purpose should be employed in order to avoid unnecessary complexity. Exposure models and scenarios would need to be adapted to address environmental processes and parameters relevant to the fate and behaviour of transition metals in water, sediment and soils (e.g. speciation). All developments should follow current EFSA guidance documents. If refined approaches have been used in the risk assessment of PPPs containing metals, post-registration monitoring and controlled long-term studies should be conducted and assessed. Utilisation of the same transition metal in other PPPs or for other uses will lead to accumulation in environmental compartments acting as sinks. In general, it has to be considered that the prospective risk assessment of metal-containing PPPs can only cover a defined period as there are limitations in the long-term hazard assessment due to issues of non-degradability. It is therefore recommended to consider these aspects in any risk management decisions and to align the ERA with the goals of other overarching legislative frameworks.

Simultaneous uptake of Cd from sediment, water and diet in a demersal marine goby Mugilogobius chulae

The embryonic state of our knowledge regarding the simultaneous uptake of trace metals via multiple routes in aquatic organisms makes it difficult to accurately assess the bioaccumulation and risk of metals. This study used cadmium (Cd) and a demersal marine fish (the yellowstripe goby) as a model system to determine tissue-specific uptake of Cd under conditions of simultaneous exposure to Cd from water, sediment and diet. A triple stable isotope tracing method was used in which each exposure route was spiked by a different stable isotope (¹¹⁰Cd, ¹¹¹Cd and ¹¹³Cd). The results revealed that the fish took up waterborne and sedimentary Cd via gills and gastrointestinal tract (GT), and that of dietary Cd was via the GT. The gills absorbed Cd predominantly from water (77.2-89.4%) whilst the GT absorbed Cd mainly from diet (81.3-98.7%). In the muscle and carcass, the Cd uptake was mainly from the diet (47.1-80.4%) and water (22.8-51.6%). Our study demonstrated that when aquatic animals were subject to simultaneous exposure through multiple uptake routes, the uptake and relative importance of each route for metal accumulation was highly tissue-specific and more complex than a single route of metal exposure.

Biokinetic Modeling of Cd Bioaccumulation from Water, Diet and Sediment in a Marine Benthic Goby: A Triple Stable Isotope Tracing Technique

Aquatic animals are often simultaneously exposed to metals through multiple routes in the natural environment. This study explored a triple stable isotope tracing method to quantify simultaneous cadmium (Cd) uptake biokinetics by yellow stripe goby from water (traced by ¹¹⁰Cd), sediment (traced by ¹¹¹Cd), and diet (traced by ¹¹³Cd) when the fish were exposed to Cd for 24 h. The simultaneous uptake of Cd from multiple routes during 4 weeks was then predicted by the modified biokinetic model. The results demonstrated that the uptake rate constant of waterborne ¹¹⁰Cd, sediment-associated ¹¹¹Cd, and dietary ¹¹³Cd was 3.1 L kg^-1 d^-1, 2.2 × 10^-4 g g^-1 d^-1, and 3.3 × 10^-3 g g^-1 d^-1 in the fish. Sedimentary Cd was less bioavailable than the waterborne and dietary Cd; however, sediment could become the predominant Cd source of the total Cd bioaccumulation when the partition coefficient of Cd between sediment and seawater ( K_d) is larger than 6 × 10⁴ L kg^-1. The simultaneous uptake of Cd from the three routes could be successfully predicted by the modified model. The model revealed that the Cd bioaccumulation generally increased with the increase of ambient Cd concentration in all the three routes. Overall, our findings demonstrated that the multiple stable isotopes tracing method and the modified biokinetic model have a wide generality and applicability for predicting Cd bioaccumulation under multiple routes of metal exposure scenario and may have application to other metals.

Copper bioaccumulation and biokinetic modeling in marine herbivorous fish Siganus oramin

Marine herbivorous fish directly consume macroalgae, which commonly accumulate high levels of trace metals in polluted areas. We proposed that herbivorous fish could be better candidates for biomonitoring marine metal pollution than carnivorous fish. To date, the trophic transfer of Cu from macroalgae to marine herbivorous fish is unclear. In this study, the kinetics of Cu bioaccumulation in a widespread marine herbivorous fish, Siganus oramin, were investigated, and biokinetic modeling was applied to estimate the Cu levels in the fish sampled from different sites and seasons. The results showed that Cu accumulation in the fish was linearly correlated to the dietary Cu levels in the different prey species, which were proportional to the waterborne Cu concentrations. The Cu found in the subcellular trophically available metal fraction (TAM) in the prey contributed the largest proportion of accumulated Cu in S. oramin. The dietary assimilation efficiencies (AEs) of Cu were 15.56 ± 1.76%, 13.42 ± 2.86%, and 21.36 ± 1.47% for Ulva lactuca, Gracilaria lemaneiformis and Gracilaria gigas, respectively. The calculated waterborne uptake rate constant (k_u) of Cu was 0.023 ± 0.011 L g^-1 d^-1, and the efflux rate constant (k_e) was 0.055 ± 0.021 d^-1. Dietary Cu accounted for 60%-75% of the body Cu in S. oramin, suggesting that dietary uptake could be the primary route for Cu bioaccumulation in herbivorous fish. The biokinetic model demonstrated that the Cu concentrations in the water and fish presented a positive linear relationship, which was in line with our field investigation along the coastal areas of South China. Therefore, we suggested that S. oramin could be used as a biomonitoring organism for Cu pollution in the marine environment. However, the heterogeneities between the predicted levels and the measured levels of Cu implied that seasonal changes should be taken into account to improve the accuracy of the model.

The effects of dissolved organic matter and feeding on bioconcentration and oxidative stress of ethylhexyl dimethyl p-aminobenzoate (OD-PABA) to crucian carp (Carassius auratus)

Bioconcentration of UV filters in organisms is an important indicator for the assessment of environmental hazards. However, bioconcentration testing rarely accounts for the influence of natural aquatic environmental factors. In order to better assess the ecological risk of organic UV filters (OUV-Fs) in an actual water environment, this study determined the influences of dissolved organic matter (DOM) (0, 1, 10, and 20 mg/L) and feeding (0, 0.5, 1, and 2% body weight/d) on bioconcentration of ethylhexyl dimethyl p-aminobenzoate (OD-PABA) in various tissues of crucian carp (Carassius auratus). Moreover, oxidative stress in the fish liver caused by the OD-PABA was also investigated by measuring activities of superoxide dismutase (SOD), catalase (CAT) and glutathione S-transferase (GST), and levels of glutathione (GSH) and malondialdehyde (MDA). The bioconcentration of OD-PABA in the fish tissues was significantly decreased with the presence of DOM indicating a reduction of OD-PABA bioavailability caused by DOM. The bioconcentration factors (BCFs) decreased by 28.00~50.93% in the muscle, 72.67~96.74% in the gill, 37.84~87.72% in the liver, and 10.32~79.38% in the kidney at different DOM concentrations compared to those of the non-DOM treatments. Significant changes in SOD, CAT, GST, GSH, and MDA levels were found in the DOM- and OD-PABA-alone treatments. However, there were no significant differences in the SOD, CAT, GST, and MDA levels found when co-exposure to OD-PABA and DOM. Feeding led to lower OD-PABA concentrations in the fish tissues, and the concentrations were decreased with increasing feeding ratios. BCFs in various tissues reduced by 39.75~72.52% in the muscle, 56.86~79.73% in the gill, 66.41~87.50% in the liver, and 75.88~89.10% in the kidney, respectively. In the unfed treatments, the levels of SOD and MDA were significantly higher than those of the fed ones while GST and GSH levels were remarkably inhibited indicating the enhanced effect of starvation to oxidative stress. There was no markedly alternation of the biomarker levels observed between different fed treatments. In conclusion, our study indicated that both DOM and feeding reduced bioconcentration of OD-PABA and alleviated oxidative stress to some extent in the crucian carp.

The simultaneous uptake of dietary and waterborne Cd in gastrointestinal tracts of marine yellowstripe goby Mugilogobius chulae

Aquatic animals under waterborne metal exposure are also very likely exposed to elevated dietary metals. This study quantified the simultaneous uptake of dietary and waterborne Cd in gastrointestinal tracts (GT) of marine yellowstripe goby using a dual stable isotope tracer method. The Cd spiked diet (10-100 μg g^-1, ¹¹¹Cd as tracers) were fed to the fish as a single meal, and then the fish were exposed to waterborne Cd (0-500 μg L^-1, ¹¹³Cd as tracers) for 48 h, during which the time-course uptake of Cd in the stomach and intestine was determined. The findings revealed that the dietary Cd uptake mainly occurred within 12 h after feeding. The fish exposed to 500 μg L^-1 waterborne Cd showed significantly lower Cd assimilation efficiency (2.07%) than the control group (3.48%) at the dietary Cd of 100 μg g^-1. Moreover, during 4-12 h when there was chyme in the GT, the waterborne Cd uptake in the intestine was lowest but the stomach showed the highest waterborne Cd uptake rate. The uptake of dietary and waterborne Cd, and the relative importance of dietary vs waterborne Cd was positively correlated with the Cd concentration in the chyme. Overall, this research demonstrated that there was interaction between dietary and waterborne Cd uptake in the GT of marine fish. The simultaneous uptake of metal from two routes is far more complex than the situation of a single route of metal uptake, which should be evaluated in determining metal bioaccumulation and toxicity in both laboratory and field metal exposure scenario.

Effects of salinity and copper co-exposure on copper bioaccumulation in marine rabbitfish Siganus oramin

Marine fish living in estuaries and coastal areas commonly encounter the stress of both salinity and metal pollution. In this study, euryhaline rabbitfish Siganus oramin were exposed to 50 μg L^-1 waterborne Cu or 300 μg g^-1 dry wt dietary Cu at salinity 33‰, 25‰, 20‰, 10‰, and 5‰ for 30 days. The Cu accumulation in the liver (>20-fold increase) and intestine (>5-fold increase) significantly increased after either waterborne or dietary Cu acclimation. Moreover, Cu accumulation was further enhanced in the liver, intestine, plasma, and whole body of Cu-exposed fish at lower salinities. Similarly, the waterborne Cu uptake rate constants (k_us) were stable in the control at different salinities but increased significantly (2-4 times higher) after waterborne Cu exposure. Conversely, the dietary Cu assimilation efficiencies (AEs) were significantly lower in the dietary Cu-exposed fish (3-5%) than in the control fish (8-16%) at different salinities, suggesting that dietary Cu acclimation partially alleviated the dietary Cu uptake from the high-Cu diet. The Cu efflux rate constants (k_es) were comparable among all treatments as 0.060-0.071 d^-1. The changes of Cu accumulation by different salinities and Cu exposure were well estimated by the biokinetic modeling. In summary, the present study indicates that rabbitfish can regulate Cu uptake and accumulation when acclimated to different salinities, but the Cu-exposed rabbitfish failed to prevent the elevation of Cu accumulation at low salinities. It therefore suggested that the concurrence of low salinity and high Cu exposure enhances the risks of Cu bioaccumulation and toxicity in rabbitfish.

Homeostatic regulation of copper in a marine fish simulated by a physiologically based pharmacokinetic model

Copper (Cu) is an essential yet potentially toxic metal, thus delicate homeostatic controls are developed in the fish. In this study, a physiologically based pharmacokinetic (PBPK) model was developed to simulate the homeostatic regulation of Cu in a marine fish (Terapon jarbua) under dietary and waterborne exposures. In this model, fish were schematized as a six-compartment model, with the intestine being divided into two sub-compartments (chyme and gut wall). The blood was assumed to be the "carrier" distributing Cu into different compartments. The transfer rates between different compartments were determined in fish during Cu exposure (20 d) and depuration (20 d). The differences in Cu transfer from chyme to gut wall between dietary and waterborne treatments suggested that the intestine regulated the dietary uptake and re-absorption of Cu from the chyme. The extremely low uptake rate constant (0.0013 d^-1) for gills under waterborne exposure indicated that gills strongly restricted Cu uptake from the ambient water. For both treatments, the liver had considerable input rate through the enterohepatic circulation and comparably high exchange rate with the blood, suggesting that the liver can efficiently accumulate newly absorbed Cu. The differences in Cu output from the liver between dietary and waterborne treatments suggested that it can effectively regulate the redistribution of Cu. All of these observations demonstrated that the liver played the central role in Cu homeostasis by serving as the main depository and distributing center. Modeling results also indicated that renal and branchial excretion was of minor importance, whereas biliary excretion combined with defecation played the most important role in whole-body Cu elimination in marine fish. The effective regulation by the "Blood-Liver-Intestine" cycle could be the main reason for the relatively low levels of Cu in fish.