About This Project

While mercury is naturally available in the environment, human activities have increased the amount of available mercury, and this has been reflected in the high levels of mercury in shark and ray tissues. However, little is known about how mercury distribution within animals’ tissues changes with age. Using round stingrays, this project will examine how mercury accumulates in different tissues and investigate how their physiology changes with exposure and age.

Ask the Scientists

What is the context of this research?

Mercury concentrations in the earth’s atmosphere have significantly increased with human activities such as mining and fossil fuel burning. Mercury can be transformed into its more dangerous form (methylmercury) and this form is what becomes concentrated in animals’ tissues. For animals that occupy higher positions in the food web such as elasmobranchs (sharks and rays), mercury can bioaccumulate to high levels due to their long life and carnivorous behavior. Mercury is well known to accumulate in the muscle of sharks. However, the distribution of this contaminant within different tissues and how mercury fluxes from one part of the body to another with age is poorly understood in elasmobranchs, especially for rays and skates as most attention has been directed towards sharks.

What is the significance of this project?

Previous studies on sharks have started to examine the interplay between mercury that is accumulated in muscle and liver. However, the dynamic that exists between these two tissue types is still not well understood. The liver plays a detoxification role in the body while the muscle potentially represents a mercury reservoir. Therefore, mercury accumulation will be dependent on the dynamics of mercury distribution in the body between these two major tissues. Investigating how mercury concentrations change in each of these compartments (i.e. liver and muscle) with age is important for understanding what negative physiological impacts mercury exposure may be having in elasmobranchs. Mercury accumulation and distribution has implications for human health when elasmobranchs are consumed.

What are the goals of the project?

Using analytical chemistry, we plan to measure mercury concentrations in the liver and muscle of round stingrays from juveniles to adults. In addition, we will also quantify the trace metal selenium, which is thought to have a protective effect against mercury exposure. Since the liver is the main detoxifying organ of the body, we will also be using a specific assay to determine the liver’s ability to detoxify mercury, and measure its ability to protect itself from mercury exposure. We will take these measurements for stingrays over a range of sizes to examine how mercury distributions change with age. In addition, we will use several markers (i.e. selenium concentrations and an important liver enzyme) to determine the ability of stingrays to cope with mercury exposure.