Assessment of sediment quality of Yangtze River estuary using zebrafish (Danio rerio) embryos

Sediment toxicity assessment using zebrafish (Danio rerio) as a model system: Historical review, research gaps and trends

Sediment is an important compartment in aquatic environments and acts as a sink for environmental pollutants. Sediment toxicity tests have been suggested as critical components in environmental risk assessment. Since the zebrafish (Danio rerio) has been indicated as an emerging model system in ecotoxicological tests, a scientometric and systematic review was performed to evaluate the use of zebrafish as an experimental model system in sediment toxicity assessment. A total of 97 papers were systematically analyzed and summarized. The historical and geographical distributions were evaluated and the data concerning the experimental design, type of sediment toxicity tests and approach (predictive or retrospective), pollutants and stressors, zebrafish developmental stages and biomarkers responses were summarized and discussed. The use of zebrafish to assess the sediment toxicity started in 1996, using mainly a retrospective approach. After this, research showed an increasing trend, especially after 2014-2015. Zebrafish exposed to pollutant-bound sediments showed bioaccumulation and several toxic effects, such as molecular, biochemical, morphological, physiological and behavioral changes. Zebrafish is a suitable model system to assess the toxicity of freshwater, estuarine and marine sediments, and sediment spiked in the laboratory. The pollutant-bound sediment toxicity in zebrafish seems to be overall dependent on physical and chemical properties of pollutants, experimental design, environmental factor, developmental stages and presence of organic natural matter. Overall, results showed that the zebrafish embryos and larvae are suitable model systems to assess the sediment-associated pollutant toxicity.

Micro-distribution of arsenic and polycyclic aromatic hydrocarbons and their interaction in Pteris vittata L

Interactive effects of inorganic arsenic (As) species and polycyclic aromatic hydrocarbons (PAHs) on their uptake, accumulation and translocation in the hyperaccumulator Pteris vittata L. (P. vittata) were studied hydroponically. The presence of PAHs hindered As uptake and acropetal translocation by P. vittata, decreasing As concentrations by 29.8%-54.5% in pinnae, regardless of the initial As speciation. The inhibitive effect of PAHs was 1.6-8.7 times greater for arsenite [As(III)] than for arsenate [As(V)]. Similarly, inorganic As inhibited the uptake of fluorene (FLU) and benzo[a]pyrene (BaP) by P. vittata roots by 0.4%-21.7% and by 33.1%-69.7%, respectively. Interestingly, coexposure to As and PAHs slightly enhanced the translocation of PAHs by P. vittata with their concentrations increased 0.3 to 0.8 times in shoots, except for the As(III)+BaP treatment. The antagonistic interaction between As and PAHs uptake is likely caused by competitive inhibition or oxidative stress injury. By using synchrotron radiation micro X-ray fluorescence imaging, high concentrations of As were found distributed throughout the microstructures far from main vein of the pinnae when coexposed with PAHs, the opposite of what was observed with exposure to As only. PAHs could also significantly inhibit the accumulation and distribution of As in vascular bundles in rachis treated with As(III). The results of two-photon laser scanning confocal microscopy revealed that PAHs were mainly distributed in the vascular cylinder, epidermal cells, vascular bundles, epidermis and vein tissues, and this was independent of As speciation and treatment. This work offers new positive evidence for the interaction between As and PAHs in P. vittata, presents new information on the underlying mechanisms for interactions of As and PAHs affecting their uptake and translocation within P. vittata L., and provides direction for future research on the mechanisms of PAHs uptake by plants.

Effects of tubificid bioturbation on bioaccumulation of Cu and Zn released from sediment by aquatic organisms

To investigate the effects of bioturbation on absorption and enrichment of pollutants from sediments by aquatic organisms, microcosm systems similar to natural aquatic environment were established, and the release of Cu and Zn from the sediment, and their accumulation in some typical aquatic organisms, including submerged plants, floating plants and fish, with the presence of tubificids of different densities were measured. The results of this pilot study showed that the presence of tubificids promoted the migration of the trace metals from sediment to overlying water, especially when there were more worms and especially for Cu which is not easily released from the sediment. During the experiment, Cu in overlying water was mainly in particulate fraction. While for Zn, it was mainly in dissolved form in the early stage of the experiment, and then the dominant fraction gradually changed to particulate fraction. The bioturbation of tubificids also promoted the accumulation of both Cu and Zn in the aquatic organisms. In one system, different types of aquatic organisms showed different features for the accumulation of Cu and Zn. Meanwhile, with the presence of different intensity of bioturbation, the concentration of Cu or Zn in the same kind of organism was different. After a 30-day experiment, trace metal concentration in the aquatic organisms generally decreased in the order of floating plants (lesser duckweed) > submerged plants (Amazon sword) > small fish (zebrafish), and the concentration of Zn in the organisms was usually significantly higher than that of Cu in the same organism, especially in duckweed and zebrafish. However, the presence of tubificids and the density of them had more considerable effects on the uptake of Cu by the organisms, than on the uptake of Zn.

Using morphological, behavioral, and molecular biomarkers in Zebrafish to assess the toxicity of lead-contaminated sediments from a retired trapshooting range within an urban wetland

The widespread use of lead (Pb) shot in shooting activities, including at former shooting ranges, continues to pose environmental risks. The La Crosse River Marsh (located in Wisconsin, USA) is a biologically diverse urban riparian wetland with a legacy of Pb-contaminated sediment resulting from its use as a trap shooting range from 1929-1963. Within the shot fall zone, shot densities exceed 43,000 pellets/m² and surface sediments exceed 25,000 mg/kg in some areas. This study used the Zebrafish as a model to determine the acute toxicity of these contaminated sediments. Zebrafish were exposed to sediments containing approximately 13 to 13,450 mg/kg Pb for 5 days (8-120 hr post-fertilization). The toxic responses to sediments were non-monotonic. Only exposure to sediments containing "mid-range" concentrations of Pb (4580 mg/kg) induced mild skeletal malformations and a sluggish C-start response indicating that Pb was marginally bioavailable. Expression of δ-aminolevulinic acid dehydratase (ALA-D) also indicated the potential for uptake of Pb from sediments. Our findings suggest that Pb within the La Crosse River Marsh sediments is not readily bioavailable to Zebrafish, and while this metal poses a minimal acute toxicological risk, toxicity due to chronic exposure of low concentrations of Pb is possible. Further, our data demonstrated that induction of ALA-D gene expression in Zebrafish embryos shows promise as an alternative to ALA-D enzyme activity as a biomarker for acute Pb exposure under lab conditions.

Effects of ashes from a Brazilian savanna wildfire on water, soil and biota: An ecotoxicological approach

Wildfire is very common in Brazilian savannas, and its effects on water, soil and aquatic/soil organisms are poorly understood. In this study, we observed the effects of fire, especially of ashes, on surface soil and subsurface water in a typical Brazilian savanna (Cerrado sensu strictu) for one year. Soil analyses (pH, organic matter content, potential acidity, K, Ca, Mg and P) and subsurface water analyses (NO^3-, PO₄^3- Mg²⁺, Ca²⁺ and K⁺) were assessed. We evaluated the ecotoxicological effects of ashes on three different endpoints and species, in fish Danio rerio (embryonic development), aquatic snail Biomphalaria glabrata (reproduction) and a soil species Enchytraeus sp. (reproduction). We found a higher amount of exchangeable cations and organic matter content in short-term fire effects on soil, but the higher availability of nutrients did not affect the soil pH in field plots. The effects of ashes on soil and subsurface water did not persist for one-year post-fire, except for organic matter content in burned areas. No toxic effects were observed on hatching success and incidences of developmental abnormalities in D. rerio embryos. However, ash input had adverse effects on reproduction in snails and enchytraeids. We reported a statistically significant decrease in snail eggs exposed to the 50g.L^-1 and 100g.L^-1 of ashes after four weeks (p<0.05, Dunnett's test and Tukey test). Enchytraeus sp. reproduction was negatively influenced by the natural soil, which presents high acidity, and also when exposed directly to the ashes from burned area, suggesting that pH and other ash compounds may limit the growth of enchytraeids. More studies in burned areas are strongly encouraged, addressing the potential important routes of exposure to ashes in order to understand the impact of intense fires on soil and aquatic biota in tropical savannas.

The impact of chemosensitisation on bioaccumulation and sediment toxicity

Cellular multixenobiotic resistance (MXR) transport proteins enhance the efflux of numerous organic pollutants. However, MXR proteins may be blocked or saturated by xenobiotic compounds, acting as inhibitors - also called chemosensitisers. Although effective on a cellular level, the environmental relevance of chemosensitisers has not been conclusively demonstrated. Since sediments are an important source of bioaccumulating compounds in aquatic ecosystems, sediments and sediment-associated hydrophobic pollutants were investigated for their potential to increase exposure and toxicity in the presence of chemosensitisation. In this study, we address this issue by (1) comparing the net uptake of 17 hydrophobic environmental pollutants by zebrafish (Danio rerio) embryos in the presence and absence of the model chemosensitiser verapamil and (2) investigating the impact of verapamil on the dose-dependent effect on zebrafish embryos exposed to polluted sediment extracts. None of the 17 pollutants showed a reproducible increase in bioaccumulation upon chemosensitisation with verapamil. Instead, internal concentrations were subject to intra-species variation by a factor of approximately two. However, a significant increase in toxicity was observed upon embryo co-exposure to verapamil for one of three sediment extracts. In contrast, another sediment extract exhibited less toxicity when combined with verapamil. In general, the results indicate only a minor impact of verapamil on the uptake of moderately hydrophobic chemicals in zebrafish embryos.

Linking Ah receptor mediated effects of sediments and impacts on fish to key pollutants in the Yangtze Three Gorges Reservoir, China - A comprehensive perspective

The Three Gorges Reservoir (TGR), created in consequence of the Yangtze River's impoundment by the Three Gorges Dam, faces numerous anthropogenic impacts that challenge its unique ecosystem. Organic pollutants, particularly aryl hydrocarbon receptor (AhR) agonists, have been widely detected in the Yangtze River, but only little research was yet done on AhR-mediated activities. Hence, in order to assess effects of organic pollution, with particular focus on AhR-mediated activities, several sites in the TGR area were examined applying the "triad approach". It combines chemical analysis, in vitro, in vivo and in situ investigations to a holistic assessment. Sediments and the benthic fish species Pelteobagrus vachellii were sampled in 2011/2012, respectively, to identify relevant endpoints. Sediment was tested in vitro with the ethoxyresorufin-O-deethylase (EROD) induction assay, and in vivo with the Fish Embryo Toxicity Test and Sediment Contact Assay with Danio rerio. Activities of phase I (EROD) and phase II (glutathione-S-transferase) biotransformation enzymes, pollutant metabolites and histopathological alterations were studied in situ in P. vachellii. EROD induction was tested in vitro and in situ to evaluate possible relationships. Two sites, near Chongqing and Kaixian city, were identified as regional hot-spots and further investigated in 2013. The sediments induced in the in vitro/in vivo bioassays AhR-mediated activities and embryotoxic/teratogenic effects - particularly on the cardiovascular system. These endpoints could be significantly correlated to each other and respective chemical data. However, particle-bound pollutants showed only low bioavailability. The in situ investigations suggested a rather poor condition of P. vachellii, with histopathological alterations in liver and excretory kidney. Fish from Chongqing city exhibited significant hepatic EROD induction and obvious parasitic infestations. The polycyclic aromatic hydrocarbon (PAH) metabolite 1-hydroxypyrene was detected in bile of fish from all sites. All endpoints in combination with the chemical data suggest a pivotal role of PAHs in the observed ecotoxicological impacts.

Assessment of the Mutagenicity of Sediments from Yangtze River Estuary Using Salmonella Typhimurium/Microsome Assay

Sediments in estuaries are of important environmental concern because they may act as pollution sinks and sources to the overlying water body. These sediments can be accumulated by benthic organisms. This study assessed the mutagenic potential of sediment extracts from the Yangtze River estuary by using the Ames fluctuation assay with the Salmonella typhimurium his (-) strain TA98 (frameshift mutagen indicator) and TA100 (baseshift mutagen indicator). Most of the sediment samples were mutagenic to the strain TA98, regardless of the presence or absence of exogenous metabolic activation (S9 induction by β-naphthoflavone/phenobarbital). However, none of the samples were mutagenic to the strain TA100. Thus, the mutagenicity pattern was mainly frameshift mutation, and the responsible toxicants were both direct (without S9 mix) and indirect (with S9 mix) mutagens. The mutagenicity of the sediment extracts increased when S9 was added. Chemical analysis showed a poor correlation between the content of priority polycyclic aromatic hydrocarbons and the detected mutagenicity in each sample. The concept of effect-directed analysis was used to analyze possible compounds responsible for the detected mutagenic effects. With regard to the mutagenicity of sediment fractions, non-polar compounds as well as weakly and moderately polar compounds played a main role. Further investigations should be conducted to identify the responsible components.

Evaluation of the hazard potentials of river suspended particulate matter and floodplain soils in the Rhine basin using chemical analysis and in vitro bioassays

The purpose of the present study was to assess the hazard potentials of contaminated suspended particulate matter (SPM) sampled during a flood event for floodplain soils using in vitro bioassays and chemical analysis. Sediment-contact tests were performed to evaluate the direct exposure of organisms to native soils and SPM at two different trophic levels. For comparison, acetonic extracts were tested using both contact tests and additionally two cell-based biotests for cytotoxicity and Ah receptor-mediated activity (EROD-Assay). The sediment-contact tests were carried out with the dehydrogenase assay with Arthrobacter globiformis and the fish embryo assay with Danio rerio. The results of this study clearly document that native samples may well be significantly more effective than corresponding extracts in the bacteria contact assay or the fish embryo test. These results question the commonly accepted concept that acetonic extracts are likely to overestimate the toxicity of soil and SPM samples. Likewise, the priority organic compounds analyzed failed to fully explain the toxic potential of the samples. The outcomes of this study revealed the insufficient knowledge regarding the relationship between the different exposure pathways. Finally, there is concern about adverse effects by settling suspended particulate matter and remobilized sediments in frequently inundated floodplain soils due to an increase of the hazard potential, if compared with infrequently inundated floodplain soils. We showed that the settling of SPM and sediments revealed a significant impact on the dioxin-like potencies of riparian soils.

Toxicity of surface water from Huangpu River to luminous bacteria (Vibrio qinghaiensis SP. Q67) and zebrafish (Danio rerio) embryos

Degradation of water quality is an emerging problem in many developing countries. Bioassay is an effective approach to monitor quality of water in aquatic environments. Studies have used luminescent bacteria and zebrafish embryos as bioassay tools in monitoring river water quality. In this study, luminous bacteria (Vibrio qinghaiensis sp. Q67) assay and zebrafish (Danio rerio) embryo toxicity test were performed to assess the ecotoxicity of surface water from the Huangpu River, China, collected during 2012-2013. River water samples inhibited the luminescence [inhibition rates 0-34.6% (±4.82%)] of Q67 and increased the lethal rates and induced morphological abnormalities in zebrafish embryos. The toxicity to luminous bacteria and zebrafish embryos were higher in winter than in summer months. In addition, samples collected in industrial area, urban sampling sites near drainage outlets, and at the intersection of the tributary that flows into the Huangpu River showed higher toxicity.

Evaluation of the ecotoxicity of sediments from Yangtze river estuary and contribution of priority PAHs to ah receptor--mediated activities

In this study, in vitro bioassays were performed to assess the ecotoxicological potential of sediments from Yangtze River estuary. The cytotoxicity and aryl hydrocarbon receptor (AhR)-mediated toxicity of sediment extracts with rainbow trout (Oncorhynchus mykiss) liver cells were determined by neutral red retention and 7-ethoxyresorufin-O-deethylase assays. The cytotoxicity and AhR-mediated activity of sediments from the Yangtze River estuary ranged from low level to moderate level compared with the ecotoxicity of sediments from other river systems. However, Yangtze River releases approximately 14 times greater water discharge compared with Rhine, a major river in Europe. Thus, the absolute pollution mass transfer of Yangtze River may be detrimental to the environmental quality of estuary and East China Sea. Effect-directed analysis was applied to identify substances causing high dioxin-like activities. To identify unknown substances contributing to dioxin-like potencies of whole extracts, we fractionated crude extracts by open column chromatography. Non-polar paraffinic components (F1), weakly and moderately polar components (F2), and highly polar substances (F3) were separated from each crude extract of sediments. F2 showed the highest dioxin-like activities. Based on the results of mass balance calculation of chemical toxic equivalent concentrations (TEQs), our conclusion is that priority polycyclic aromatic hydrocarbons indicated a low portion of bio-TEQs ranging from 1% to 10% of crude extracts. Further studies should be conducted to identify unknown pollutants.

The toxicity potential of pharmaceuticals found in the Douro River estuary (Portugal)--experimental assessment using a zebrafish embryo test

Fish embryos are a particularly vulnerable stage of development, so they represent optimal targets for screening toxicological effects of waterborne xenobiotics. Herein, the toxicity potential of two mixtures of pharmaceuticals was evaluated using a zebrafish embryo test. One of the mixtures corresponds to an environmentally realistic scenario and both have carbamazepine, fenofibric acid, propranolol, trimethoprim and sulfamethoxazole. The results evidenced morphological alterations, such as spinal deformities and yolk-sac oedemas. Moreover, heart rates decreased after both mixture exposures, e.g., at 48hpf, highest mixture versus blank control (47.8±4.9 and 55.8±3.7 beats/30s, respectively). The tail lengths also diminished significantly from 3208±145μm in blank control to 3130±126μm in highest mixture. The toxicological effects were concentration dependent. Mortality, hatching rate and the number of spontaneous movements were not affected. However, the low levels of pharmaceuticals did interfere with the normal development of zebrafish, which indicates risks for wild organisms.

Metal sensitivity of the embryonic development of the ramshorn snail Marisa cornuarietis (Prosobranchia)

We investigated the effects of metal ions on the embryonic development of the ramshorn snail, Marisa cornuarietis, by exposing embryos to varying concentrations of copper (0, 50, 100, and 250 μg Cu(2+)/L), lead (0, 5, 10, and 15 mg Pb(2+)/L), lithium (0, 1, 2.5, and 3 mg Li(+)/L), or palladium (0, 50, 100, and 500 μg Pd(2+)/L). Effects of these metals were examined by recording mortality, the rate of tentacles and eyes formation, heart rate, hatching success, and weight after hatching. Compared to the control, we found a significant delay in the formation of tentacles and eyes after treatment with 100 μg Cu(2+)/L, 15 mg Pb(2+)/L, 2.5 mg Li(+)/L or 500 μg Pd(2+)/L. The heart rate decreased significantly at 500 μg Pd(2+)/L. At 10 mg Pb(2+)/L, 2.5 mg Li(+)/L, or 500 μg Pd(2+)/L, hatching was delayed significantly; 50 μg Cu(2+)/L induced a significantly earlier hatching, and reduced body weight. The LC(50) values were calculated to be about 50 μg Cu(2+)/L, 500 μg Pd(2+)/L, 2500 μg Li(+)/L, and 10000 μg Pb(2+)/L. These results show that the embryonic development of M. cornuarietis is about as sensitive to copper and lithium, compared to the most sensitive fishes used in embryo toxicity testing. Even though the MariETT is a laboratory-based assay focusing on toxicological endpoints of a selected model species, future application is envisaged to include testing of "natural" samples such as stream water or sediment interstitial water.