How are seafood consumption advisories created?

Lena Beck

If you've fished at any of the popular spots along San Diego Bay, as with other public fishing areas throughout the state, you've likely seen signs warning of potential health concerns related to eating the fish you're angling to catch. Fish consumption advisories serve as recommendations for how frequently you can safely eat fish from California waters. But have you ever wondered just how these consumption advisories are determined?

To develop these advisories, commonly consumed fish are routinely sampled throughout the state. This sampling may reveal common contaminants, such as mercury, as well as newer chemicals, alerting scientists to potential consumption risks.

In a recent study examining the Pacific oyster, California Sea Grant researchers partnering with the California State Water Resources Control Board and others found good news and bad news. Older, more established chemicals like DDT are present in lower amounts than they have been historically, but evidence of newer contaminants like microplastics and phthalates are a growing concern. 

“It almost feels like, as a regulator, we're playing Whac-A-Mole,” said Chad Loflen, senior environmental scientist at the California State Water Resources Control Board. “There's always a new chemical.” 

But the researchers revealed other concerns, including long-standing environmental contaminants in the Pacific oysters.

“We found relatively high concentrations of contaminants that have been around for a long time, like copper and zinc,” said Theresa Talley, California Sea ​​Grant Extension Specialist and project co-lead. “We may have been seeing these compounds because their use in car brake pads and tires has increased, as have the sheer number of cars on the road. This study is a reminder that we need to stay on our toes when it comes to monitoring contaminants.”

Unfortunately, simply detecting the presence of a chemical isn’t enough to determine whether a locally caught fish is safe to eat. Monitoring agencies also need to determine if the chemical is present in quantities that pose risks for human consumption. 

Entities like the California State Water Resources Control Board collect samples using a published protocol to ensure that all samples are standardized and can be used in formal assessments. After collection, monitoring agencies send those samples out for chemical analysis at state-certified labs and upload that information to the California Environmental Data Exchange Network (CEDEN), which is then evaluated by another state agency called the California Office of Environmental Health Hazard Assessment (OEHHA). 

“We calculate the average concentration of contaminants, usually mercury or polychlorinated biphenyls (PCBs), in each fish species,” said Wesley Smith, staff toxicologist at OEHHA. “Then, we compare these concentrations to the levels that someone can safely eat to inform the number of recommended servings.”

It’s not possible to sample every species, so monitoring agencies prioritize fish and shellfish that have recreational, subsistence or tribal significance. They also prioritize the sampling of species that are known to have high concentrations of contaminants, including freshwater, bottom-feeding catfish and carp that take up organic contaminants like PCBs and can also accumulate mercury over time. Monitoring agencies may also focus on species like rainbow trout that generally have lower concentrations of contaminants and are high in healthy fats like omega-3 fatty acids, as those may ultimately provide a healthier alternative for consumers.

Fish consumption guidelines poster for San Diego Bay. Courtesy of OEHHA.
Fish consumption advisory for San Diego Bay. Courtesy of OEHHA.

Before issuing consumption guidance, OEHHA weighs the known health benefits of consuming seafood, such as reducing the risk of heart disease, against concerns of consuming seafood that may contain various levels of contaminants.

OEHHA is responsible for the Good Catch California fish consumption advisory program that provides guidance on how to choose and prepare fish to maximize health benefits and minimize exposure to contaminants. The vast majority of safe consumption guidelines in California are based on mercury and PCBs, though OEHHA is also evaluating the potential risks associated with newer contaminants like microplastics.

OEHHA’s fish consumption advisories include coastal marine waters like San Diego Bay, brackish or freshwater rivers, lakes and site-specific bodies of water that contain known high levels of contaminants or are popular fishing spots. Currently, OEHHA has site-specific guidelines for over 130 bodies of water in California. This allows people to educate themselves about the fish they want to eat, which is the best way to stay safe.

“The benefits of seafood can and mostly do far outweigh the risks from contaminants,” Talley said, adding that following your public health and seafood recommendations is especially important if you eat a lot of seafood, catch your own seafood or are in a vulnerable group such as children or pregnant women.

To minimize exposure to chemical contaminants that may be in fish, OEHHA recommends that people eat smaller, lower trophic level species of fish. Anchovies, sardines and herring are all great choices. Larger and longer-lived species like tuna may be more likely to have accumulated contaminants like mercury. 

Certain kitchen practices can also reduce risks, and OEHHA advisories are written under the assumption that these practices are being followed. For example, removing skin and viscera from fish and shellfish will reduce the risk of exposure to compounds that accumulate in these fatty tissues (like biotoxins in viscera or PCBs in fish skin). Cutting off any visible fat before cooking also reduces that risk. And cooking the fish in a way that drains