Two new papers on the toxicological effects of chemical dispersants on capelin reproduction have shown that capelin are at high risk if oil spills occur near spawning areas — and not just from the oil.
The first paper was released in October, while the more recent was published last month. Both stem from experiments led by Dr. Craig Purchase, an associate professor with the Department of Biology, Faculty of Science, at Memorial, in the summer of 2016.
Capelin at higher risk
“Capelin are one of the most important fish species in the Northwest Atlantic food web, and are of great significance in the Arctic, Pacific and Northeast Atlantic, being a major forage for top predators such as cod, seabirds and marine mammals,” said Dr. Purchase. “However, their reproductive behaviour puts them at higher risk of oil spills than other fish.”
During their short reproductive season, which is just a few weeks, capelin form dense schools in near shore areas and spawn on beaches or nearby on the sea floor. That makes them susceptible to the effects of oils spills that concentrate near shore.
“We believe actions should be taken to minimize risks of oil spills during times and places where capelin spawn.”
Marine oil spills are frequently treated with dispersants that contain solvents and surfactants designed to separate the floating oil into small droplets. Following the 2010 Deepwater Horizon oil spill, more than 1.8 million gallons of dispersants were used during the cleanup.
“When you use a dispersant there is more oil dissolved in water, so it doesn’t wash up on a beach,” Dr. Purchase said. “That’s great for seabirds that might otherwise get coated in it, but it’s not so great for aquatic animals that end up taking more of these toxins into their bodies.”
Dispersants harm fish
The first experiment looked at how oil and dispersant components in water affect capelin sperm behaviour and fertilization capacity.
“We found chemically dispersed oil diminishes the ability of sperm to fertilize eggs, even though sperm were only exposed to the chemicals for a few seconds,” he said. “There’s a brief window from the time they leave a male’s body until they make contact with an egg, but we saw a dramatic effect from that exposure with a large reduction in the number of eggs being fertilized.”
He believes that may be because sperm cell membranes are lipids, which, like oil, are not soluble in water. Dispersants, which are designed to break down oils, may also have similar impact on the cell membranes.
Dispersants a ‘bigger problem’
To test the impact that contaminants have on capelin embryo development, Dr. Purchase, in collaboration with Dr. Valerie Langlois at Quebec City’s Institut national de la recherche scientifique, exposed tens of thousands of embryos to solutions of crude oil in water; dispersant and oil in water; and dispersant in water alone.
“The adults were not exposed, and in this case the sperm were not exposed, but after fertilization we exposed embryos to the various treatments,” Dr. Purchase said. “We found certain concentrations of chemically dispersed oil is lethal to embryos within 10 hours of exposure, and it completely impairs their survival if exposed longer. There were other long-term, non-lethal affects, as well.
“But what was most interesting is that dispersant alone caused similar levels of embryotoxicity,” he continued. “So, while we found chemically dispersed oil is more toxic than mechanically dispersed oil, the dispersant itself is as much, or an even bigger problem.”
Action should be taken during spawning season
Oil and dispersant samples were acquired from Fisheries and Oceans Canada for the evaluations. The department also provided funding through the National Contaminants Advisory Group.
Dr. Purchase had also hoped to conduct tests on the toxicity of shoreline washing agents that are used on oil spills that reach coastal areas. However, the company that produces both the offshore dispersant and the shoreline washing agent refused to provide samples, causing public controversy.
Dr. Purchase says the findings are particularly relevant to the province of Newfoundland and Labrador, where oil drilling and transportation create risk of spills that could be particularly problematic if they occur in the same place and time as capelin spawning.
“In the event of an oil spill close to spawning grounds, incubating embryos can be continuously exposed to the components in the water,” said Dr. Purchase. “This could be compounded by accumulating effects on exposed adults that are passed to the embryo.
“Our studies indicate capelin embryo survival and development are likely to be compromised by an oil spill, but how a spill is treated will also affect the impact,” he continued. “Because of the importance of this species to the food-web, we believe actions should be taken to minimize risks of oil spills during times and places where capelin spawn.”