Catherine A. Sloan

Aryl Hydrocarbon Receptor-Independent Toxicity of Weathered Crude Oil during Fish Development

Polycyclic aromatic hydrocarbons (PAHs), derived largely from fossil fuels and their combustion, are pervasive contaminants in rivers, lakes, and nearshore marine habitats. Studies after the Exxon Valdez oil spill demonstrated that fish embryos exposed to low levels of PAHs in weathered crude oil develop a syndrome of edema and craniofacial and body axis defects. Although mechanisms leading to these defects are poorly understood, it is widely held that PAH toxicity is linked to aryl hydrocarbon receptor (AhR) binding and cytochrome P450 1A (CYP1A) induction. Using zebrafish embryos, we show that the weathered crude oil syndrome is distinct from the well-characterized AhR-dependent effects of dioxin toxicity. Blockade of AhR pathway components with antisense morpholino oligonucleotides demonstrated that the key developmental defects induced by weathered crude oil exposure are mediated by low-molecular-weight tricyclic PAHs through AhR-independent disruption of cardiovascular function and morphogenesis. These findings have multiple implications for the assessment of PAH impacts on coastal habitats.

Deepwater Horizon crude oil impacts the developing hearts of large predatory pelagic fish

Significance The 2010 Deepwater Horizon (MC252) disaster in the northern Gulf of Mexico released more than 4 million barrels of crude oil. Oil rose from the ocean floor to the surface where many large pelagic fish spawn. Here we describe the impacts of field-collected oil samples on the rapidly developing embryos of warm-water predators, including bluefin and yellowfin tunas and an amberjack. For each species, environmentally relevant MC252 oil exposures caused serious defects in heart development. Moreover, abnormalities in cardiac function were highly consistent, indicating a broadly conserved developmental crude oil cardiotoxicity. Losses of early life stages were therefore likely for Gulf populations of tunas, amberjack, swordfish, billfish, and other large predators that spawned in oiled surface habitats. The Deepwater Horizon disaster released more than 636 million L of crude oil into the northern Gulf of Mexico. The spill oiled upper surface water spawning habitats for many commercially and ecologically important pelagic fish species. Consequently, the developing spawn (embryos and larvae) of tunas, swordfish, and other large predators were potentially exposed to crude oil-derived polycyclic aromatic hydrocarbons (PAHs). Fish embryos are generally very sensitive to PAH-induced cardiotoxicity, and adverse changes in heart physiology and morphology can cause both acute and delayed mortality. Cardiac function is particularly important for fast-swimming pelagic predators with high aerobic demand. Offspring for these species develop rapidly at relatively high temperatures, and their vulnerability to crude oil toxicity is unknown. We assessed the impacts of field-collected Deepwater Horizon (MC252) oil samples on embryos of three pelagic fish: bluefin tuna, yellowfin tuna, and an amberjack. We show that environmentally realistic exposures (1–15 µg/L total PAH) cause specific dose-dependent defects in cardiac function in all three species, with circulatory disruption culminating in pericardial edema and other secondary malformations. Each species displayed an irregular atrial arrhythmia following oil exposure, indicating a highly conserved response to oil toxicity. A considerable portion of Gulf water samples collected during the spill had PAH concentrations exceeding toxicity thresholds observed here, indicating the potential for losses of pelagic fish larvae. Vulnerability assessments in other ocean habitats, including the Arctic, should focus on the developing heart of resident fish species as an exceptionally sensitive and consistent indicator of crude oil impacts.

Exxon Valdez to Deepwater Horizon: comparable toxicity of both crude oils to fish early life stages

The 2010 Deepwater Horizon disaster in the Gulf of Mexico was the largest oil spill in United States history. Crude oils are highly toxic to developing fish embryos, and many pelagic fish species were spawning in the northern Gulf in the months before containment of the damaged Mississippi Canyon 252 (MC252) wellhead (April-July). The largest prior U.S. spill was the 1989 grounding of the Exxon Valdez that released 11 million gallons of Alaska North Slope crude oil (ANSCO) into Prince William Sound. Numerous studies in the aftermath of the Exxon Valdez spill defined a conventional crude oil injury phenotype in fish early life stages, mediated primarily by toxicity to the developing heart. To determine whether this type of injury extends to fishes exposed to crude oil from the Deepwater Horizon - MC252 incident, we used zebrafish to compare the embryotoxicity of ANSCO alongside unweathered and weathered MC252 oil. We also developed a standardized protocol for generating dispersed oil water-accommodated fractions containing microdroplets of crude oil in the size range of those detected in subsurface plumes in the Gulf. We show here that MC252 oil and ANSCO cause similar cardiotoxicity and photo-induced toxicity in zebrafish embryos. Morphological defects and patterns of cytochrome P450 induction were largely indistinguishable and generally correlated with polycyclic aromatic compound (PAC) composition of each oil type. Analyses of embryos exposed during different developmental windows provided additional insight into mechanisms of crude oil cardiotoxicity. These findings indicate that the impacts of MC252 crude oil on fish embryos and larvae are consistent with the canonical ANSCO cardiac injury phenotype. For those marine fish species that spawned in the northern Gulf of Mexico during and after the Deepwater Horizon incident, the established literature can therefore inform the assessment of natural resource injury in the form of potential year-class losses.

Unexpectedly high mortality in Pacific herring embryos exposed to the 2007 Cosco Busan oil spill in San Francisco Bay

In November 2007, the container ship Cosco Busan released 54,000 gallons of bunker fuel oil into San Francisco Bay. The accident oiled shoreline near spawning habitats for the largest population of Pacific herring on the west coast of the continental United States. We assessed the health and viability of herring embryos from oiled and unoiled locations that were either deposited by natural spawning or incubated in subtidal cages. Three months after the spill, caged embryos at oiled sites showed sublethal cardiac toxicity, as expected from exposure to oil-derived polycyclic aromatic compounds (PACs). By contrast, embryos from the adjacent and shallower intertidal zone showed unexpectedly high rates of tissue necrosis and lethality unrelated to cardiotoxicity. No toxicity was observed in embryos from unoiled sites. Patterns of PACs at oiled sites were consistent with oil exposure against a background of urban sources, although tissue concentrations were lower than expected to cause lethality. Embryos sampled 2 y later from oiled sites showed modest sublethal cardiotoxicity but no elevated necrosis or mortality. Bunker oil contains the chemically uncharacterized remains of crude oil refinement, and one or more of these unidentified chemicals likely interacted with natural sunlight in the intertidal zone to kill herring embryos. This reveals an important discrepancy between the resolving power of current forensic analytical chemistry and biological responses of keystone ecological species in oiled habitats. Nevertheless, we successfully delineated the biological impacts of an oil spill in an urbanized coastal estuary with an overlapping backdrop of atmospheric, vessel, and land-based sources of PAC pollution.

Screening for planar chlorobiphenyl congeners in tissues of marine biota by high-performance liquid chromatography with photodiode array detection

A rapid method has been developed to screen for planar chlorobiphenyl (CB) congeners, as well as certain other CBs and DDTs, in tissue samples from marine biota. The analytes were extracted from tissue matrices with 1:1 hexane/pentane (v/v) and interfering compounds were separated from the CBs on a gravity-flow column packed with acidic, basic and neutral silica gel eluted with 1:1 hexane/methylene chloride (v/v). Subsequently, the planar CB congeners were resolved from the DDTs and other CBs by HPLC on Cosmosil PYE analytical columns cooled to 9 degrees C and were measured by an ultraviolet (UV) photodiode array (PDA) detector. Two important advantages of PDA over conventional UV detection were the ability to identify individual analytes by comparing their UV spectra to those of reference standards and the ability to establish the spectral homogeneity (purity) of the analytes by comparing spectra within a peak to the apex spectrum. The HPLC/PDA method was tested with tissue samples from fish, shellfish and marine mammals; concentrations of certain CBs and DDTs in samples determined by screening compared favorably with those in the same samples analyzed by a comprehensive method (e.g., gas chromatography/high resolution mass spectrometry). However, the HPLC/PDA method was about an order of magnitude less sensitive than determinations by comprehensive methods.

Status, correlations and temporal trends of chemical contaminants in fish and sediment from selected sites on the Pacific Coast of the USA

Abstract The National Benthic Surveillance Project (NBSP), a component of NOAAs National Status and Trends Program, monitored sediment and bottomfish for chlorinated hydrocarbon pesticides (CHs), PCBs and polycyclic aromatic hydrocarbons (PAHs) at selected urban and nonurban sites along the west coast of the USA from 1984 to 1993. This project successfully generated an extensive data set to evaluate the recent status and trends of environmental quality in coastal waters. This article summarizes and interprets the status of selected PAHs, PCBs and CHs in surficial sediments and selected species of bottom-feeding fish for 50 sites in Alaska, Washington, Oregon and California for the first 7 years (1984–1990) of the NBSE. The highest concentrations of most sediment-associated organic contaminants were present in the most highly urbanized areas, and many of the organic contaminants were bioaccumulated by indigenous marine fish species. The concentrations of PAHs and CHs in sediments generally correlated with levels of these compounds or their derivatives in bottom-dwelling fish. Assessment of trends in the concentrations of chlordanes, dieldrin, DDTs, PAHs and PCBs for the 7 year period from 1984–1990 suggest that, since the mid-1980s, concentrations of the persistent CHs, such as PCBs and DDTs in sediment and fish, show no consistent temporal trends, whereas levels of PAHs, which are nonpoint source contaminants, showed consistent increases at both nonurban and urban near-coastal sites.

Chemical contaminants in gray whales (Eschrichtius robustus) stranded along the west coast of North America.

The concentrations of selected chlorinated hydrocarbons (e.g. PCBs, DDTs, DDEs, chlordanes) and essential (e.g. zinc, selenium, copper) and toxic (e.g. mercury, lead, arsenic) elements were measured in tissues and stomach contents from 22 gray whales (Eschrichtius robustus) stranded between 1988 and 1991 at sites from the relatively pristine areas of Kodiak Island, AK, to more urbanized areas in Puget Sound, WA, and San Francisco Bay, CA. The majority of animals were stranded at sites on the Washington outer coast and in Puget Sound. The gray whale has the unique feeding strategy among Mysticeti of filtering sediments to feed on benthic (bottom dwelling) invertebrates. Thus, the wide geographical distribution of the stranded whales allowed (1) an initial assessment of whether concentrations of chemical contaminants in these whales exhibited region specific differences and (2) whether toxic chemicals that accumulate in sediments may have contributed to the mortality and stranding of gray whales near the more polluted urban areas. Analyses for chlorinated hydrocarbons in blubber from 22 animals showed no apparent significant differences among stranding sites. The concentrations of sigma PCBs and sigma DDEs in blubber, for example, ranged from 120 to 10,000 and 9 to 2100 p.p.b. (ng/g) wet weight, respectively. Additionally, analyses of chlorinated hydrocarbons and selected elements in liver (n = 10) also showed no apparent significant differences between whales stranded in Puget Sound and whales stranded at more pristine sites (Alaska, Washington outer coast and Strait of Juan de Fuca and Strait of Georgia). For example, the concentrations of sigma PCBs and sigma DDEs in liver ranged from 79 to 1600 and 7 to 280 p.p.b., respectively, and the concentrations of the toxic elements, mercury and lead ranged from 9 to 120 and 20 to 270 p.p.b., respectively. Analyses of stomach contents revealed low concentrations of chlorinated hydrocarbons, but high concentrations (wet weight) of aluminum (1,700,000 +/- 450,000 p.p.b.), iron (320,000 +/- 250,000 p.p.b.), manganese (23,000 +/- 15,000 p.p.b.), and chromium (3400 +/- 1300 p.p.b.), but no significant differences were observed between whales stranded in Puget Sound compared to whales stranded at the more pristine sites. The relative proportions of these elements in stomach contents of stranded whales were similar to the relative proportions in sediments, which is consistent with a geological source of these elements from the ingestion of sediment during feeding. Thus, overall, the concentrations of anthropogenic chemicals in stranded gray whales showed little relation to the levels of chemical contaminants at the stranding sites.(ABSTRACT TRUNCATED AT 400 WORDS)

Potent Phototoxicity of Marine Bunker Oil to Translucent Herring Embryos after Prolonged Weathering

Pacific herring embryos (Clupea pallasi) spawned three months following the Cosco Busan bunker oil spill in San Francisco Bay showed high rates of late embryonic mortality in the intertidal zone at oiled sites. Dead embryos developed to the hatching stage (e.g. fully pigmented eyes) before suffering extensive tissue deterioration. In contrast, embryos incubated subtidally at oiled sites showed evidence of sublethal oil exposure (petroleum-induced cardiac toxicity) with very low rates of mortality. These field findings suggested an enhancement of oil toxicity through an interaction between oil and another environmental stressor in the intertidal zone, such as higher levels of sunlight-derived ultraviolet (UV) radiation. We tested this hypothesis by exposing herring embryos to both trace levels of weathered Cosco Busan bunker oil and sunlight, with and without protection from UV radiation. Cosco Busan oil and UV co-exposure were both necessary and sufficient to induce an acutely lethal necrotic syndrome in hatching stage embryos that closely mimicked the condition of dead embryos sampled from oiled sites. Tissue levels of known phototoxic polycyclic aromatic compounds were too low to explain the observed degree of phototoxicity, indicating the presence of other unidentified or unmeasured phototoxic compounds derived from bunker oil. These findings provide a parsimonious explanation for the unexpectedly high losses of intertidal herring spawn following the Cosco Busan spill. The chemical composition and associated toxicity of bunker oils should be more thoroughly evaluated to better understand and anticipate the ecological impacts of vessel-derived spills associated with an expanding global transportation network.

Natural sunlight and residual fuel oils are an acutely lethal combination for fish embryos.

The majority of studies characterizing the mechanisms of oil toxicity in fish embryos and larvae have focused largely on unrefined crude oil. Few studies have addressed the toxicity of modern bunker fuels, which contain residual oils that are the highly processed and chemically distinct remains of the crude oil refinement process. Here we use zebrafish embryos to investigate potential toxicological differences between unrefined crude and residual fuel oils, and test the effects of sunlight as an additional stressor. Using mechanically dispersed oil preparations, the embryotoxicity of two bunker oils was compared to a standard crude oil from the Alaska North Slope. In the absence of sunlight, all three oils produced the stereotypical cardiac toxicity that has been linked to the fraction of tricyclic aromatic compounds in an oil mixture. However, the cardiotoxicity of bunker oils did not correlate strictly with the concentrations of tricyclic compounds. Moreover, when embryos were sequentially exposed to oil and natural sunlight, the bunker oils produced a rapid onset cell-lethal toxicity not observed with crude oil. To investigate the chemical basis of this differential toxicity, a GC/MS full scan analysis was used to identify a range of compounds that were enriched in the bunker oils. The much higher phototoxic potential of chemically distinct bunker oils observed here suggests that this mode of action should be considered in the assessment of bunker oil spill impacts, and indicates the need for a broader approach to understanding the aquatic toxicity of different oils.

Persistent Organic Pollutants in Juvenile Chinook Salmon in the Columbia River Basin: Implications for Stock Recovery

Abstract Among the populations of Pacific salmon and steelhead Oncorhynchus mykiss (anadromous Rainbow Trout) that inhabit the Columbia River basin there are currently 13 Evolutionarily Significant Units listed as threatened or endangered under the U.S. Endangered Species Act. While habitat loss, dams, overharvest, and climate change have been implicated in declining abundance of Chinook Salmon O. tshawytscha in the Columbia River, chemical contaminants represent an additional, yet poorly understood, conservation threat. In this study we measured concentrations of persistent organic pollutants in juvenile Chinook Salmon from various Columbia River stocks and life history types to evaluate the potential for adverse effects in these threatened and endangered fish. Polychlorinated biphenyls (PCBs) and dichlorodiphenyltrichloroethane (DDTs), recognized contaminants of concern in the Columbia basin, are the primary focus of this paper; other contaminants found in these fish, such as polybrominated diphenyl eth...