Impacts of oil spills on Arctic marine species: a risk assessment perspective

Fahd, Faisal (2021) Impacts of oil spills on Arctic marine species: a risk assessment perspective. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

The Arctic region is characterized by an ubiquitous presence of sea ice, harsh weather conditions and inhabitation of some unique marine animals. The changing climatic conditions have resulted in receding of the sea ice in the regions along the Arctic boundaries. The receding sea ice has opened the possibilities of tapping into hitherto unexplored reserves of natural resources in the Arctic. Shipping operations along the Northern Sea Route have received an impetus because of the changed sea ice conditions in the region. However, the growing anthropogenic activities also increase the risk of environmental pollution in the region. The Arctic is a home to many unique marine species, such as the polar bear, beluga whales, seals and polar cod. The Arctic marine food chain is non-complex, with limited prey options forming a large portion of the diet of the marine species. Thus, adverse impact to the populations of a species may also impact the well-being of its predators in the Arctic food chain. The knowledge gap in the exposure and toxicological modeling of Arctic marine species were identified to be the presence of limited availability of the toxicity data and dose response relationship. The research questions addressed in this study are as follows: 1. Is the toxicity and impacts in Arctic fish different from their temperate counterparts? 2. What is the risk of mortality to lower tropic sentinel species in the event of an oil spill? 3. What is the risk to apex marine species in the event of an oil spill? The components of Environmental Risk Assessment (ERA) are hazard identification, exposure modeling, toxicological modeling and risk characterization. The thesis followed the steps laid down for ERA and identified the polar cod as the sentinel species for the Arctic food chain. The study also identified apex marine predators, polar bear and beluga whales, as species of interest along with polar cod. Polycyclic Aromatic Hydrocarbons are major constituent of the crude oil that can cause deleterious effects in the marine species. The spill scenarios considered for risk assessment to polar cod, polar bear and whale are as follows: Spill over thick sea ice; Spill over thin sea ice; Spill under thick ice. A review of current exposure and toxicological models used for marine species was conducted and a novel toxicological model where the effects of the toxicant exposure were quantified based on the probability of cellular damage and metabolites interactions was proposed. This toxicodynamic approach in conjunction with physiology based toxicokinetic approach was proposed as the best suited approach for modeling and estimating toxicity in the Arctic marine species. This research studied physiological causal dependencies leading to toxicity and mortality in polar cod from PAH exposure. Toxicity is also affected by environmental factors, such as sea ice and feeding behaviors. Presence of sea ice, could mitigate or aggravate the exposure to crude oil, thereby affecting the toxicity of the fish. The polar cod could biotransform some of the ingested PAH using a two-step process, namely, phase I and phase II processes. In phase one, the cytochrome P 4501A (CYP1A) enzymes react with the lipophilic xenobiotic, such as PAH, and convert it to water soluble metabolites for elimination. Phase II reactions further enhance the water solubility of the metabolites produced during the phase I step. The phase II conjugation reactions with glutathione are facilitated by glutathione-S-transferase (GST). The biotransformation toxicity is a result of cell death when the toxic metabolites resulting from the phase I process exceeds the conjugating capacity of the organism via the phase II process. The other pathways of toxicity in polar cod are lipid peroxidation and cell damage. Although the pathways of PAH toxicity and the impact of sea ice on PAH ingestion for the fish had been studied previously, an effort to combine these factors as causal dependencies to estimate mortality in polar cod was never made. A novel Bayesian Network (BN) based model was developed as a part of this research, combining the physiological and environmental factors affecting the PAH exposure and toxicity in polar cod. To estimate the risk to apex marine predators, an Arctic food chain was considered with the sentinel species, polar cod, at its bottom and apex species at its top. The risk to the apex species can be from exposure and susceptibility due to oil spill and additional risk from reduced food availability owing to decreased prey populations from the spill. Another BN based model was developed based on the food chain and spill conditions. The average daily food consumption and baseline population density of seals, polar bears and whales was collated from literature. The changes in populations of the polar cod, seals polar bear and whales due to oil spill were input in the BN model and probabilities of apex species survival are estimated. The BN based risk models developed in this study were demonstrated for a hypothetical spill scenario in a geographic region around the Svalbard Island and Fram Strait. The oil spill scenarios considered in this research are spill over and under thick sea ice and spill on thin sea ice. Three spill sizes considered in this study were 15000 tonnes, 18000 tonnes and 40000 tonnes for low, medium and high states. The PAH weight percentage of 3.9% is assumed in the crude oil, along with a uniform dissolution in the water column. The results of the BN model developed for polar cod and sensitivity analysis of the results suggested that physiological factors followed by sea ice played important role in risk mitigation.The presence of thick sea ice in winter decreased the risk of mortality in polar cod by 16%. The ability of polar cod target organs to eliminate the xenobiotics, evident by various biomarkers activity, decreased the risk of mortality by 25% for worst case scenario. The spill scenario causing highest risk for polar cod population (29% mortality in population) was spill over thin ice in Autumn. The results from the apex species BN risk model predicted a polar cod recruitment collapse for the spill scenarios considered in this study, causing a higher risk of mortality of polar bears, beluga whales, and Narwhals in the Arctic region. Whales (adult and calves) were predicted to be at higher risk when the spill was under thick ice, while adult polar bears were at higher risk when the spill occurred on thin ice. A spill over the thick ice caused the least risk to whale and adult polar bears. The spill's timing and location had a significant impact on the marine animals in the Arctic region due to its unique sea ice dynamics, simple food web, and short periods of food abundance. In summary, this study identifies key marine species in the region and conducts an ecological risk assessment for the species based on the Arctic food chain. Four peer reviewed journal papers were published in the Marine Pollution Bulletin journal as the outcome of this research/thesis.

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