Elvis Genbo Xu

Time- and Oil-Dependent Transcriptomic and Physiological Responses to Deepwater Horizon Oil in Mahi-Mahi (Coryphaena hippurus) Embryos and Larvae

The Deepwater Horizon (DWH) oil spill contaminated the spawning habitats for numerous commercially and ecologically important fishes. Exposure to the water accommodated fraction (WAF) of oil from the spill has been shown to cause cardiac toxicity during early developmental stages across fishes. To better understand the molecular events and explore new pathways responsible for toxicity, RNA sequencing was performed in conjunction with physiological and morphological assessments to analyze the time-course (24, 48, and 96 h post fertilization (hpf)) of transcriptional and developmental responses in embryos/larvae of mahi-mahi exposed to WAF of weathered (slick) and source DWH oils. Slick oil exposure induced more pronounced changes in gene expression over time than source oil exposure. Predominant transcriptomic responses included alteration of EIF2 signaling, steroid biosynthesis, ribosome biogenesis and activation of the cytochrome P450 pathway. At 96 hpf, slick oil exposure resulted in significant perturbations in eye development and peripheral nervous system, suggesting novel targets in addition to the heart may be involved in the developmental toxicity of DHW oil. Comparisons of changes of cardiac genes with phenotypic responses were consistent with reduced heart rate and increased pericardial edema in larvae exposed to slick oil but not source oil.

Biochar as a novel niche for culturing microbial communities in composting

Biochar has been applied as a bulk agent or an additive to compost. The mixture of biochar and compost has been considered to exert synergistic effect as a soil amendment. In a composting system, the macro-porous sites of biochar may act as a novel niche that selects and cultures the microorganisms from the bulk compost. A variety of volatile organic carbons (VOCs) such as aromatic hydrocarbons and aliphatics were detected in biochar pellets (BC) pyrolyzed at 100°C. In the mesosphilic phase, the water-soluble carbon (WSC) and water-soluble phenols (WSP) in biochar increased from 2.1 to 26mgkg(-1) and 5.9 to 101μgkg(-1), respectively. These labile carbons however, were subjected to a rapid metabolism over the composting course. We further compared the responses of microbial community in BC to those in the bulk organic matter. Both Shannon-Wiener and Richness indexes of bacterial communities were higher in BC than in the adjacent compost (ADJ) and the bulk organic matter (control). As for fungal communities, the two indexes were higher in BC than ADJ and control only in the mature phase. During the composting course, the bacterial activity was higher than the fungal counterpart in terms of the changes of corresponding biomarkers, glucosamine and muramic acids. The results suggested that the diversified labile carbons sources including VOCs and WSC in BC could influence the structure of microbial community and resulted in an enhanced carbon catabolic capacity.

Spatial and temporal assessment of environmental contaminants in water, sediments and fish of the Salton Sea and its two primary tributaries, California, USA, from 2002 to 2012

The Salton Sea, the largest inland surface water body in California, has been designated as a sensitive ecological area by federal and state governments. Its two main tributaries, the New River and Alamo River are impacted by urban and agriculture land use wastes. The purpose of this study was to temporally and spatially evaluate the ecological risks of contaminants of concern in water, sediments and fish tissues. A total of 229 semivolatile organic compounds and 12 trace metals were examined. Among them Selenium, DDTs, PAHs, PCBs, chlorpyrifos and some current-use pesticides such as pyrethroids exceeded risk thresholds. From 2002 to 2012, measurements of chlorpyrifos in sediments generally declined and were not observed after 2009 at the river outlets. In contrast, pyrethroid concentrations in sediments rose consistently after 2009. In water samples, the outlets of the two rivers showed relatively higher levels of contamination than the main water body of the Salton Sea. However, sediments of the main water body of the Salton Sea showed relatively higher sediment concentrations of contaminants than the two rivers. This was particularly true for selenium which showed reductions in concentrations from 2002 to 2007, but then gradual increases to 2012. Consistent with water evaluations, contaminant concentrations in fish tissues tended to be higher at the New River boundary and at the drainage sites for the Alamo River compared to sites along each river. The persistent contaminants DDTs, PAHs, chlorpyrifos and several pyrethroid insecticides were associated with the toxicity of sediments and water collected from the rivers. Overall, assessment results suggested potential ecological risk in sediments of the Salton Sea as well as in water and fish from the two rivers.

Long-Term Spatio-Temporal Trends of Organotin Contaminations in the Marine Environment of Hong Kong

Hong Kong imposed a partial restriction on application of organotin-based antifouling paints in 1992. Since September 2008, the International Maritime Organization prohibited the use of such antifouling systems on all sea-going vessels globally. Therefore, it is anticipated a gradual reduction of organotin contamination in Hong Kong’s marine waters. Using the rock shell Reishia clavigera as a biomonitor, we evaluated the organotin contamination along Hong Kong’s coastal waters over the past two decades (1990–2015). In 2010 and 2015, adult R. clavigera were examined for imposex status and analysed for tissue concentrations of six organotins. We consistently found 100% imposex incidence in female R. clavigera across all sites. Tissue triphenyltin (TPT) concentrations were high in most samples. A probabilistic risk assessment showed that there were over 69% of chance that local R. clavigera would be at risk due to exposure to phenyltins. Comparing with those of previous surveys (2004–2010), both imposex levels and tissue concentrations of organotins did not decline, while the ecological risks due to exposure to organotins were increasing. We also observed high concentrations of monobutyltin and TPT in seawater and sediment from locations with intense shipping activities and from stormwater or sewage discharge. Overall, organotins are still prevalent in Hong Kong’s marine waters showing that the global convention alone may be inadequate in reducing organotin contamination in a busy international port like Hong Kong. Appropriate management actions should be taken to control the use and release of organotins in Hong Kong and South China.

Novel transcriptome assembly and comparative toxicity pathway analysis in mahi-mahi ( Coryphaena hippurus ) embryos and larvae exposed to Deepwater Horizon oil

The impacts of Deepwater Horizon (DWH) oil on morphology and function during embryonic development have been documented for a number of fish species, including the economically and ecologically important pelagic species, mahi-mahi (Coryphaena hippurus). However, further investigations on molecular events and pathways responsible for developmental toxicity have been largely restricted due to the limited molecular data available for this species. We sought to establish the de novo transcriptomic database from the embryos and larvae of mahi-mahi exposed to water accommodated fractions (HEWAFs) of two DWH oil types (weathered and source oil), in an effort to advance our understanding of the molecular aspects involved during specific toxicity responses. By high throughput sequencing (HTS), we obtained the first de novo transcriptome of mahi-mahi, with 60,842 assembled transcripts and 30,518 BLAST hits. Among them, 2,345 genes were significantly regulated in 96hpf larvae after exposure to weathered oil. With comparative analysis to a reference-transcriptome-guided approach on gene ontology and tox-pathways, we confirmed the novel approach effective for exploring tox-pathways in non-model species, and also identified a list of co-expressed genes as potential biomarkers which will provide information for the construction of an Adverse Outcome Pathway which could be useful in Ecological Risk Assessments.

Larval Red Drum (Sciaenops ocellatus) Sublethal Exposure to Weathered Deepwater Horizon Crude Oil: Developmental and Transcriptomic Consequences

The Deepwater Horizon (DWH) incident resulted in extensive oiling of the pelagic zone and shoreline habitats of many commercially important fish species. Exposure to the water-accommodated fraction (WAF) of oil from the spill causes developmental toxicity through cardiac defects in pelagic fish species. However, few studies have evaluated the effects of the oil on near-shore estuarine fish species such as red drum (Sciaenops ocellatus). Following exposure to a certified weathered slick oil (4.74 μg/L ∑PAH50) from the DWH event, significant sublethal impacts were observed ranging from impaired nervous system development [average 17 and 22% reductions in brain and eye area at 48 h postfertilization (hpf), respectively] to abnormal cardiac morphology (100% incidence at 24, 48, and 72 hpf) in red drum larvae. Consistent with the phenotypic responses, significantly differentially expressed transcripts, enriched gene ontology, and altered functions and canonical pathways predicted adverse outcomes in nervous and cardiovascular systems, with more pronounced changes at later larval stages. Our study demonstrated that the WAF of weathered slick oil of DWH caused morphological abnormalities predicted by a suite of advanced bioinformatic tools in early developing red drum and also provided the basis for a better understanding of molecular mechanisms of crude oil toxicity in fish.

Developmental transcriptomic analyses for mechanistic insights into critical pathways involved in embryogenesis of pelagic mahi-mahi (Coryphaena hippurus)

Mahi-mahi (Coryphaena hippurus) is a commercially and ecologically important species of fish occurring in tropical and temperate waters worldwide. Understanding early life events is crucial for predicting effects of environmental stress, which is largely restricted by a lack of genetic resources regarding expression of early developmental genes and regulation of pathways. The need for anchoring developmental stages to transcriptional activities is highlighted by increasing evidence on the impacts of recurrent worldwide oil spills in this sensitive species during early development. By means of high throughput sequencing, we characterized the developmental transcriptome of mahi-mahi at three critical developmental stages, from pharyngula embryonic stage (24 hpf) to 48 hpf yolk-sac larva (transition 1), and to 96 hpf free-swimming larva (transition 2). With comparative analysis by multiple bioinformatic tools, a larger number of significantly altered genes and more diverse gene ontology terms were observed during transition 2 than transition 1. Cellular and tissue development terms were more significantly enriched in transition 1, while metabolism related terms were more enriched in transition 2, indicating a switch progressing from general embryonic development to metabolism during the two transitions. Special focus was given on the most significant common canonical pathways (e.g. calcium signaling, glutamate receptor signaling, cAMP response element-binding protein signaling, cardiac β-adrenergic signaling, etc.) and expression of developmental genes (e.g. collagens, myosin, notch, glutamate metabotropic receptor etc.), which were associated with morphological changes of nervous, muscular, and cardiovascular system. These data will provide an important basis for understanding embryonic development and identifying molecular mechanisms of abnormal development in fish species.

Spatial and temporal ecological risk assessment of unionized ammonia nitrogen in Tai Lake, China (2004–2015)

Ammonia toxicity varies largely due to its pH- and temperature-dependent speciation (unionized ammonia nitrogen, NH3-N). The seasonal and long-term trend of ammonia risk in ecologically significant sections of Tai Lake, China was unknown. In this study, a two-level (deterministic and quantitative) method was developed to assess the special ecological risks posed by NH3-N at 37 sites during two seasons (February and September) of 2014 in Tai Lake. The long-term temporal (2004-2015) risk posed by NH3-N was also assessed by comparing annual quantitative risk values (probability of exceeding acute or chronic threshold values) in three key sections of Tai Lake. The results indicated the species living in the Tai Lake were at a 0.04% and 32.45% chance of risk due to acute exposure, and a 1.97% and 92.05% chance of risk due to chronic exposure in February and September of 2014, respectively. Alarmingly, the chronic ecological risks of NH3-N in the Lanshanzui section of the Tai Lake remained >30% from 2004 to 2011. The chronic risk of NH3-N in all three key sections of Tai Lake started to decrease in 2011. This was likely the consequence of the control practice of eutrophication implemented in the Tai Lake. A significant decline in diversity of the benthic invertebrate community of the Tai Lake could be associated with continuous exposure to ammonia over decades given different sensitivity of taxa to ammonia. The results laid a scientific foundation for risk assessment and management of ammonia in Tai Lake, China, and the developed two-level risk assessment approach can also be applied to other similar aquatic regions.

Developmental Toxicity Of Hydroxylated Chrysene Metabolites in Zebrafish Embryos

One of the primary sources of polycyclic aromatic hydrocarbons (PAHs) in marine environments is oil. Photochemical oxidation and microbial transformation of PAH-containing oils can result in the formation of oxygenated products. Among the PAHs in crude oil, chrysene is one of the most persistent within the water column and may be transformed to 2- and 6-hydroxychrysene (OHCHR). Both of these compounds have been shown to activate (2-OHCHR) and antagonize (6-OHCHR) the estrogen receptor (ER). Previous studies in our lab have shown that estrogen can significantly alter zebrafish development. However, little is known about the developmental toxicity of hydroxylated PAHs. Zebrafish embryos were exposed to 0.5-10μM of 2- or 6-OHCHR from 2h post-fertilization (hpf) until 76hpf. A significant decrease in survival was observed following exposure to 6-OHCHR - but not 2-OHCHR. Both OHCHRs significantly increased the percentage of overall deformities after treatment. In addition to cardiac malformations, ocular and circulatory defects were also observed in embryos exposed to both compounds, while 2-OHCHR generally resulted in a higher prevalence of effect. Moreover, treatment with 2-OHCHR resulted in a significant decrease in hemoglobin levels. ER nor G-Protein coupled estrogen receptor (GPER) antagonists and agonists did not rescue the observed defects. We also analyzed the expression of cardiac-, eye- and circulation-related genes previously shown to be affected by oil. Rhodopsin mRNA expresssion was significantly decreased by both compounds equally. However, exposure to 2-OHCHR significantly increased the expression of the hematopoietic regulator, runx1 (runt related transcription factor 1). These results indicate the toxicity of oxygenated photoproducts of PAHs and suggest that other targets and signaling pathways may contribute to developmental toxicity of weathered oil. Our findings also demonstrate the regio-selective toxicity of hydroxy-PAHs in the effects on eye and circulatory development and raise the need to identify mechanisms and ecological risks of oxy-PAHs to fish populations.

Cyto- and geno-toxicity of 1,4-dioxane and its transformation products during ultraviolet-driven advanced oxidation processes

Ultraviolet-driven advanced oxidation processes (UV/AOPs) are integral steps in water reuse treatment trains. The toxicity of trace organic transformation products during a UV/AOP is critical to its implementation. This study examined the cyto- and geno-toxicity of transformation products of 1,4-dioxane (1,4-D), a trace organic contaminant commonly found in secondary wastewater, in extracts using the CellSensor p53RE-bla HCt-116 cell assay, following UV photolysis at 254 nm with three oxidants, hydrogen peroxide (H2O2), persulfate (S2O82−) and monochloramine (NH2Cl). 1,4-D was transformed into six major oxidation by-products, including ethylene glycol diformate, formaldehyde, glycolaldehyde, glycolic acid, formic acid, and methoxyacetic acid. Formaldehyde and glycolaldehyde were the most geno- and cyto-toxic, while 1,4-D had weak genotoxicity and no cytotoxicity. The order for cytotoxicity on the basis of EC50 values is as follows: glycolaldehyde > formaldehyde > formic acid > glycolic acid > 1,4-D > ethylene glycol diformate ≈ methoxyacetic acid, with glycolaldehyde and formaldehyde showing high genotoxicity. With the three UV/AOPs, genotoxicity expressed as mitomycin equivalency quotient (MEQ) increased significantly by 10 to 100 fold with a UV dosage of 720 mJ cm−2, mainly due to the formation of glycolaldehyde. UV/S2O82− reduced the MEQ with an increased UV dosage of 1440 mJ cm−2, due to the transformation of toxic aldehydes to less toxic organic acids. In contrast, UV/H2O2 increased the MEQ with UV dosage, resulting from the accumulation of aldehyde products. UV/NH2Cl showed the lowest MEQ due to its slow removal of 1,4-D. This study suggests that oxidants and UV dosage can affect the toxicological responses of treatments for recycled water.