A lot of college students are eating large amounts of tuna in dining halls and exposing themselves to high levels of the toxic heavy metal mercury, according to a new paper published in Environmental Toxicology and Chemistry, reports UC Santa Cruz (UCSC).

Although fish is highly nutritious and supports heart health and lowers blood pressure, among other benefits, consumers are advised not to eat more than two to three servings each week of low-mercury fish, such as chunk light tuna, or one serving each week of fish with higher mercury levels, such as yellowfin tuna.

These recommendations help people avoid consuming excessive quantities of mercury, which is found in the form of methylmercury in seafood in varying levels and can cause neurological damage. (Tuna contains relatively high levels of mercury.)

Researchers surveyed UCSC students on their tuna consumption habits and knowledge of mercury exposure risks. In addition, scientists also measured mercury levels in hair samples from some individuals. Results showed a correlation between the quantity of mercury found and how much tuna students ate; some amounts were high enough for concern.

About a third of students reported consuming tuna weekly, with 80% of their tuna meals eaten at campus dining halls. Half of those who ate tuna said they consumed three or more meals with tuna each week, which is beyond the Environmental Protection Agency’s (EPA) recommended dose of 0.1 micrograms of methylmercury per kilogram of body weight per day. (Some surveyed reported chowing down on more than 20 servings of tuna in one week.)

During a period of several months, researchers checked tuna in the dining halls for mercury and found that some samples contained five times more mercury than others.

A second survey tested students’ knowledge about mercury in tuna and recommended consumption rates. Results showed that a majority of students—whether or not they ate tuna—knew very little about mercury in tuna. Many thought it was OK to consume two to three times as much tuna in a week than what is recommended.

In response to these findings, UCSC posted signs in their campus dining halls to inform students about the mercury content in tuna as well as guidelines for fish consumption. (Further changes may follow a more thorough assessment.)

Researchers said overconsumption of tuna could be a concern for all institutions with dining halls, where tuna is often a salad bar staple.

Because mercury can cause neurological development and harm reproductive health, the Food and Drug Administration has established guidelines regarding fish consumption among pregnant women and children.

Click here to read about the FDA warning to consumers about skin products tainted with mercury.