Low-level embryonic crude oil exposure disrupts ventricular ballooning and subsequent trabeculation in Pacific herring.

There is a growing awareness that transient, sublethal embryonic exposure to crude oils cause subtle but important forms of delayed toxicity in fish. While the precise mechanisms for this loss of individual fitness are not well understood, they involve the disruption of early cardiogenesis and a subsequent pathological remodeling of the heart much later in juveniles. This developmental cardiotoxicity is attributable, in turn, to the inhibitory actions of crude oil-derived mixtures of polycyclic aromatic compounds (PACs) on specific ion channels and other proteins that collectively drive the rhythmic contractions of heart muscle cells via excitation-contraction coupling. Here we exposed Pacific herring (Clupea pallasi) embryos to oiled gravel effluent yielding ΣPAC concentrations as low as ~ 1 µg/L (64 ng/g in tissues). Upon hatching in clean seawater, and following the depuration of tissue PACs (as evidenced by basal levels of cyp1a gene expression), the ventricles of larval herring hearts showed a concentration-dependent reduction in posterior growth (ballooning). This was followed weeks later in feeding larvae by abnormal trabeculation, or formation of the finger-like projections of interior spongy myocardium, and months later with hypertrophy (overgrowth) of the spongy myocardium in early juveniles. Given that heart muscle cell differentiation and migration are driven by Ca2+-dependent intracellular signaling, the observed disruption of ventricular morphogenesis was likely a secondary (downstream) consequence of reduced calcium cycling and contractility in embryonic cardiomyocytes. We propose defective trabeculation as a promising phenotypic anchor for novel morphometric indicators of latent cardiac injury in oil-exposed herring, including an abnormal persistence of cardiac jelly in the ventricle wall and cardiomyocyte hyperproliferation. At a corresponding molecular level, quantitative expression assays in the present study also support biomarker roles for genes known to be involved in muscle contractility (atp2a2, myl7, myh7), cardiomyocyte precursor fate (nkx2.5) and ventricular trabeculation (nrg2, and hbegfa). Overall, our findings reinforce both proximal and indirect roles for dysregulated intracellular calcium cycling in the canonical fish early life stage crude oil toxicity syndrome. More work on Ca2+-mediated cellular dynamics and transcription in developing cardiomyocytes is needed. Nevertheless, the highly specific actions of ΣPAC mixtures on the heart at low, parts-per-billion tissue concentrations directly contravene classical assumptions of baseline (i.e., non-specific) crude oil toxicity.

Sublethal neurotoxicity of organophosphate insecticides to juvenile coho salmon.

For decades, organophosphate (OP) insecticides have been used as chemical control agents in watersheds that support at-risk populations of Pacific salmon throughout western North America. Spray drift, runoff, and other processes transport OPs to critical surface water habitats for migratory salmonids. While most OPs share a common mechanism of action (i.e., inhibition of neuronal acetylcholinesterase, or AChE), they typically vary in toxic potency. Moreover, dose-response relationships for exposure and sublethal neurotoxicity (e.g., brain AChE inhibition) in salmonids have not been defined for many OPs. Here we exposed juvenile coho salmon (Oncorhynchus kisutch) to five common anticholinesterase insecticides (dimethoate, ethoprop, naled, phorate and phosmet) that are widely used on agricultural, commercial, residential, and public lands. Each of the five pesticides produced a concentration-dependent inhibition of AChE enzyme activity. The effective concentration for 50 % AChE inhibition (96-hr EC50) indicated the highest toxicity for phorate (EC50 = 0.57 µg/L) followed by phosmet (3.3 µg/L), naled (7.8 µg/L), ethoprop (90.6 µg/L) and dimethoate (273 µg/L). These findings can inform 1) relative hazard analyses for OP use near sensitive aquatic habitats, 2) predictions of sublethal OP mixture toxicity, and 3) ecological risk assessments for threatened or endangered species of Pacific salmon.

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

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.

Elevated temperatures increase the toxicity of pesticide mixtures to juvenile coho salmon.

Pesticide mixtures and elevated temperatures are parallel freshwater habitat stressors for Pacific salmon in the western United States. Certain combinations of organophosphate (OP) insecticides are known to synergistically increase neurotoxicity in juvenile salmon. The chemicals interact to potentiate the inhibition of brain acetylcholinesterase (AChE) and disrupt swimming behavior. The metabolic activation and detoxification of OPs involve temperature-sensitive enzymatic processes. Salmon are ectothermic, and thus the degree of synergism may vary with ambient temperature in streams, rivers, and lakes. Here we assess the influence of water temperature (12-21°C) on the toxicity of ethoprop and malathion, alone and in combination, to juvenile coho salmon (Oncorhynchus kisutch). A mixture of ethoprop (0.9 µg/L) and malathion (0.75 µg/L) produced synergistic AChE inhibition at 12°C, and the degree of neurotoxicity approximately doubled with a modest temperature increase to 18°C. Slightly lower concentrations of ethoprop (0.5 µg/L) combined with malathion (0.4 µg/L) did not inhibit brain AChE activity but did produce a temperature-dependent reduction in liver carboxylesterase (CaE). The activity of CaE was very sensitive to the inhibitory effects of ethoprop alone and both ethoprop-malathion combinations across all temperatures. Our findings are an example of how non-chemical habitat attributes can increase the relative toxicity of OP mixtures. Surface temperatures currently exceed water quality criteria in many western river segments, and summer thermal extremes are expected to become more frequent in a changing climate. These trends reinforce the importance of pollution reduction strategies to enhance ongoing salmon conservation and recovery efforts.

Interactive neurobehavioral toxicity of diazinon, malathion, and ethoprop to juvenile coho salmon.

In western North America, mixtures of current use pesticides have been widely detected in streams and other aquatic habitats for threatened and endangered Pacific salmon and steelhead (Oncorhynchus sp.). These include organophosphate insecticides that inhibit acetylcholinesterase (AChE) enzyme activity in the salmon nervous system, thereby disrupting swimming and feeding behaviors. Several organophosphates have been shown to interact as mixtures to produce synergistic AChE inhibition at concentrations near or above the upper range of surface water detections in freshwater systems. To evaluate potential synergism at lower concentrations (near or below 1 part per billion), juvenile coho (Oncorhynchus kisutch) were exposed to a range of mixtures of diazinon-malathion and ethoprop-malathion below a cumulative 0.05 of the predicted EC50 for AChE inhibition, as determined from single chemical concentration-response curves. Brain enzyme inhibition was concentration-dependent, with a 90% reduction and a significant decrease in spontaneous swimming speed at the highest binary mixture concentrations evaluated (diazinon-malathion at 2.6 and 1.1 µg/L, respectively; ethoprop-malathion at 2.8 and 1.2 µg/L, respectively). Brain enzyme activity gradually recovered over six weeks. Our findings extend earlier observations of organophosphate synergism in salmon and reveal an unusually steep concentration-response relationship across a mere 2-fold increase in mixture concentration.

Recurrent die-offs of adult coho salmon returning to spawn in Puget Sound lowland urban streams.

Several Seattle-area streams in Puget Sound were the focus of habitat restoration projects in the 1990s. Post-project effectiveness monitoring surveys revealed anomalous behaviors among adult coho salmon returning to spawn in restored reaches. These included erratic surface swimming, gaping, fin splaying, and loss of orientation and equilibrium. Affected fish died within hours, and female carcasses generally showed high rates (>90%) of egg retention. Beginning in the fall of 2002, systematic spawner surveys were conducted to 1) assess the severity of the adult die-offs, 2) compare spawner mortality in urban vs. non-urban streams, and 3) identify water quality and spawner condition factors that might be associated with the recurrent fish kills. The forensic investigation focused on conventional water quality parameters (e.g., dissolved oxygen, temperature, ammonia), fish condition, pathogen exposure and disease status, and exposures to metals, polycyclic aromatic hydrocarbons, and current use pesticides. Daily surveys of a representative urban stream (Longfellow Creek) from 2002-2009 revealed premature spawner mortality rates that ranged from 60-100% of each fall run. The comparable rate in a non-urban stream was <1% (Fortson Creek, surveyed in 2002). Conventional water quality, pesticide exposure, disease, and spawner condition showed no relationship to the syndrome. Coho salmon did show evidence of exposure to metals and petroleum hydrocarbons, both of which commonly originate from motor vehicles in urban landscapes. The weight of evidence suggests that freshwater-transitional coho are particularly vulnerable to an as-yet unidentified toxic contaminant (or contaminant mixture) in urban runoff. Stormwater may therefore place important constraints on efforts to conserve and recover coho populations in urban and urbanizing watersheds throughout the western United States.

The synergistic toxicity of pesticide mixtures: implications for risk assessment and the conservation of endangered Pacific salmon.

BACKGROUND: Mixtures of organophosphate and carbamate pesticides are commonly detected in freshwater habitats that support threatened and endangered species of Pacific salmon (Oncorhynchus sp.). These pesticides inhibit the activity of acetylcholinesterase (AChE) and thus have potential to interfere with behaviors that may be essential for salmon survival. Although the effects of individual anticholin-esterase insecticides on aquatic species have been studied for decades, the neurotoxicity of mixtures is still poorly understood. OBJECTIVES: We assessed whether chemicals in a mixture act in isolation (resulting in additive AChE inhibition) or whether components interact to produce either antagonistic or synergistic toxicity. METHODS: We measured brain AChE inhibition in juvenile coho salmon (Oncorhynchus kisutch) exposed to sublethal concentrations of the organophosphates diazinon, malathion, and chlorpyrifos, as well as the carbamates carbaryl and carbofuran. Concentrations of individual chemicals were normalized to their respective median effective concentrations (EC50) and collectively fit to a nonlinear regression. We used this curve to determine whether toxicologic responses to binary mixtures were additive, antagonistic, or synergistic. RESULTS: We observed addition and synergism, with a greater degree of synergism at higher exposure concentrations. Several combinations of organophosphates were lethal at concentrations that were sublethal in single-chemical trials. CONCLUSION: Single-chemical risk assessments are likely to underestimate the impacts of these insecticides on salmon in river systems where mixtures occur. Moreover, mixtures of pesticides that have been commonly reported in salmon habitats may pose a more important challenge for species recovery than previously anticipated.

Improved flatfish health following remediation of a PAH-contaminated site in Eagle Harbor, Washington.

Eagle Harbor in Puget Sound, WA became a Superfund site in 1987 due to polycyclic aromatic hydrocarbons (PAHs) released chronically from a nearby creosoting facility. Early studies here (1983-1986) demonstrated up to an approximately 80% prevalence of toxicopathic liver lesions, including neoplasms, in resident English sole (Parophrys vetulus). These lesions in English sole are consistently associated with PAH exposure in multiple field studies, and one laboratory study. Later studies (1986-1988) incorporated biomarkers of PAH exposure and effect, including hepatic CYP1A expression and xenobiotic-DNA adducts, and biliary fluorescent aromatic compounds (FACs). Before site remediation, lesion prevalences and other biomarker values in this species from Eagle Harbor were among the highest compared to other sites in Puget Sound and the US Pacific Coast. To sequester PAH-contaminated sediments, in 1993-1994, a primary cap of clean sediment was placed over the most-contaminated 54acres, with a 15-acre secondary cap added from 2000-2002. Lesion prevalences and biomarker values before primary capping were reduced compared to 1983-1986, consistent with facility closure in 1988 and shore-based source controls begun in 1990. Liver lesion risk, hepatic CYP1A activities, and levels of biliary FACs from fish collected immediately after and at regular intervals up to 2 years after primary capping were variable relative to pre-capping. Over the entire monitoring period since primary capping (128 months), but particularly after 3 years, there was a significantly decreasing trend in biliary FACs, hepatic DNA adducts and lesion risk in English sole. In particular, lesion risk has been consistently low (<0.20) compared to primary cap initiation (set at 1.0), from approximately 4 years after primary capping through April 2004. These results show that the sediment capping process has been effective in reducing PAH exposure and associated deleterious biological effects in a resident flatfish, and that longer term monitoring of pollutant responses in biological resources, such as resident fish, is needed in order to demonstrate the efficacy of this type of remediation.