By: Megan Hall
Hi, my name is Megan, and I’m entering my fourth year as a PhD student in the Marine Environmental Biology program at the University of Southern California (USC). I’ve been on Catalina Island at the Wrigley Marine Science Center for a large part of the summer as a 2014 WIES Summer Fellow, doing experiments with baby mussels and metals.
Copper—did you know…?
When I tell people that I study copper pollution, a common reaction is, “I didn’t even know copper was a pollutant!” But believe it or not, copper is a major contaminant in coastal waters. Numerous bays and harbors exhibit copper concentrations that exceed the safe limits for at least some portion of the year.
Where does this copper come from, you may ask? Copper is washed into the sea with urban runoff, which occurs in Southern California during our infrequent rainfall events. Copper is also the predominant chemical used in antifouling paint: a special paint that covers the hulls of almost all boats to prevent “pests” like barnacles, tunicates, and mussels from growing there. These animals can be pesky for boat owners, who incur high costs in scraping and cleaning their hulls to get rid of them. But they are also important members of coastal ecosystems, and when copper dissolves from the antifouling paint into surrounding waters, it can be very harmful for the local marine populations.
Monitoring with mussels
The Environmental Protection Agency (EPA) requires that coastal waters and effluent be tested for copper toxicity to ensure that ecosystems are not being damaged by human inputs.
Copper is toxic to many marine organisms, but to varying degrees. So to protect all organisms in coastal waters, regulators set the copper limits low enough to protect the most sensitive organism in the system. In most U.S. marine waters, that organism is the bay mussel Mytilus.
Safe concentrations of copper are determined by exposing mussel embryos to copper-contaminated water samples for 48 hours, and then counting the number of animals that survive and normally develop to the early larval stage.
In theory, this information should tell us how many animals make it through a copper exposure at a given concentration, and will thus make it into adulthood and possibly reproduce. However, toxicologists are increasingly questioning this approach for understanding the effects of pollutants on an animal’s chances of surviving, reproducing, and contributing to the next generation of the species.
Problems, and solutions?
Although toxicity tests that are currently used provide good baseline data, they don’t provide some important information that could be very useful in determining safe pollutant levels. For example, if an animal is still alive and well after 48 hours of copper exposure, does that mean it got out scot free and will be okay for the rest of its life?
Prior evidence suggests that this might not be the case. Recent findings from my own summer research also indicate that after 48 hours of copper exposure, some animals that survive will still go on to display reduced growth rate, delayed development, and increased mortality.
Additionally, I am curious about what is happening below the surface in these toxicity tests. The physical analysis that is currently used does not consider anything about the animals’ molecular physiology inside. Imagine if a doctor were to just look at you without any blood tests or scans, and say, “You’re fine!” Doesn’t seem thorough, right?
For that reason, I’m analyzing the animals’ gene expression: a good basic way to determine what is happening inside the animal, and an indicator of physiological stress that may not be evident at the whole organism level. So far, I’ve found that gene expression in mussel larvae changes significantly with increasing copper concentrations, and that expression also changes in animals that appear abnormal when compared to those that appear normal.
Gene expression measurements are already telling us a ton about the effects of copper on the development of mussels, and it will be very exciting to see what we uncover next! Together, longer-term monitoring of these physical and molecular measurements can provide more detailed information on safe copper limits in coastal waters, and hopefully allow us to better protect mussels and other sensitive marine organisms.
Megan is a Wrigley Institute 2014 Summer Fellow, and a PhD student in the lab of Dr. Andrew Gracey in the Department of Biological Sciences at USC.