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Abstract
The toxicity resulting from exposure to oil droplets in marine fish embryos and larvae is still subject for debate. The most detailed studies have investigated the effects of water-dissolved components of crude oil in water accommodated fractions (WAFs) that lack bulk oil droplets. Although exposure to dissolved petroleum compounds alone is sufficient to cause the characteristic developmental toxicity of crude oil, few studies have addressed whether physical interaction with oil micro-droplets are a relevant exposure pathway for open water marine speices. Here we used controlled delivery of mechanically dispersed crude oil to expose pelagic embryos and larvae of a marine teleost, the Atlantic haddock (Melanogrammus aeglefinus). Haddock embryos were exposed continuously to two different concentrations of dispersed crude oil, high and low, or in pulses. By 24 hours of exposure, micro-droplets of oil were observed adhering and accumulating on the chorion, accompanied by highly elevated levels of cyp1a, a biomarker for exposure to aromatic hydrocarbons. Embryos from all treatment groups showed abnormalities representative of crude oil cardiotoxicity at hatch (5 days of exposure), such as pericardial and yolk sac edema. Compared to other species, the frequency and severity of toxic effects was higher than expected for the waterborne PAH concentrations (e.g., 100% of larvae had edema at the low treatment). These findings suggest an enhanced tissue uptake of PAHs and/or other petroleum compounds from attached oil droplets. These studies highlight a novel property of haddock embryos that leads to greater than expected impact from dispersed crude oil. Given the very limited number of marine species tested in similar exposures, the likelihood of other species with similar properties could be high. This unanticipated result therefore has implications for assessing the ecological impacts of oil spills and the use of methods for dispersing oil in the open sea.
Highlights
Worldwide energy demands have resulted in increased hydrocarbon extraction activity in Polar Regions, as well as at greater ocean depths
The PAH constituted 2% of the total oil by weight (19.6 g/kg), and the PAH profile was dominated by the C0–C3 naphthalenes (71%), followed by the tricyclic PAHs which contributed 28% of the total PAHs (S3 Fig)
The total oil concentrations in the tanks were measured at the start of the experiment to; 170 μg total hydrocarbons (THC)/L and 3 μg TPAH/L in the low dose group and 1500 μg THC/L and 34 μg TPAH/L in the high dose
Summary
Worldwide energy demands have resulted in increased hydrocarbon extraction activity in Polar Regions, as well as at greater ocean depths. In recent years large efforts have been put into development and improvement of risk assessment tools by coupling different models such as, i) oil drift and fate models, ii) distribution models for zooplankton and fish embryo/larvae, iii) ecotoxicology effect models and eventually iv) ecosystem models to simulate effects of oil pollution on fish populations or multi species ecosystems [6,7]. To reach this ambitious goal there is a clear need for more and better empirical data in all steps of the modelling. For example fish embryo and yolk sac larvae are sensitive to low total polyaromatic hydrocarbons (TPAH) concentrations (0.1–50 μg/l), and pericardial or yolk sac edema, bone deformities, delayed development or mortality have been observed [9,10,11,12,13,14,15,16]
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