Beneath the beauty of the San Francisco Bay, a silent toxin has infiltrated the complex ecosystem: mercury. 

Mercury’s effects are everywhere in the food chain. The toxin has detrimental impacts across the entire ecosystem, from marine life to land animals.

A study by the San Francisco Estuary’s Regional Monitoring Program found high mercury concentrations in the South Bay caused lowered hatchability in the eggs of double-crested cormorants and Forster’s terns. 

Richard Looker, a senior resource control engineer for the San Francisco Bay Regional Water Quality Control Board, said mercury is most detrimental to fish-eating birds.

“They tend to have a problem with their shells being thinned by the presence of the mercury,” Looker said. “A higher amount has (caused) failed-to-hatch problems in certain species of birds.”

While mercury poisoning is prominent throughout the Bay, Cormorant eggs from the South Bay — specifically in the Don Edwards area — can contain high mercury concentrations , and Tern eggs have been documented to have readings even higher. Embryo mortality can occur below the readings documented, and according to the same study, high levels of mercury are concerning for birds who call the Bay their home.

However, more than just the eggs are affected. Researchers noticed a 40% decrease in reproduction for the Common Loon when their mercury levels increased past a certain threshold. In a study on Mercury bioaccumulation and risk to three waterbird species, 48% of breeding terns’ blood mercury levels exceeded this threshold.

AP Environmental Science teacher Nicole Loomis said mercury can also affect animals’ cognitive and neuromuscular abilities.

“It could impair their movements,” Loomis said. “It could impair their reaction time. (It) might prevent them from being able to survive, as well.”

 As one of the strongest toxins found in the Bay, Loomis said mercury can also be detrimental to human health. 

“If we’re eating fish that has mercury, then that’s going to lead to things like cognitive decline (in humans),” Loomis said.

Mercury — and specifically its organic form methylmercury —,  is a fat soluble substance. The brain and nerves in a human body are about 60% fat, making it easy for mercury to penetrate them. Combined with its high absorption rate, methylmercury poisoning damages neurons and leads to rapid cognitive decline. Loomis said humans are especially vulnerable to the toxin due to the body’s inability to remove mercury.

“It will just build up over your life,” Loomis said. “So it’s really important that kids do not eat mercury. That amount of mercury will have a much bigger impact on them. In terms of adults, there’s recommendations … don’t eat carnivorous fish more than once a week.”

And Looker said some demographics should be especially cautious when it comes to mercury contamination..

“If the mother who’s providing breastmilk has too much mercury in her system, it is going to be delivered to the baby in the proteins,” Looker said. “The breastmilk and the developing children who are breastfeeding are going to be vulnerable to neurological effects.” 

Looker also said mercury is prevalent in the Bay Area water system due to abandoned mercury mines once used to process gold.

“A bunch of mercury came down the Sacramento and San Joaquin river systems, historically, and filled San Francisco Bay with mercury,” Looker said. “We’re still dealing with that.” 

According to the United States Environmental Protection Agency, California currently has between 550 and 2000 abandoned mercury mines. 

Although much of the mercury found in the Bay is there as a result of mining and other historical practices, Looker said atmospheric deposition also leads to increased levels. Mercury can be released by fossil fuel combustion in Asia, sending it into the atmosphere, where it is carried by wind across the ocean to California.

“When it reaches California, there’s a chemical transformation that happens,” Looker said. “The mercury changes chemical form, making it more likely to come down in precipitation.” 

Senior and fisher Alessio Dorigo said he takes precautions when fishing in the Bay, including avoiding consuming the fish, because of his concerns about mercury contamination..

“The fish that you do catch there, which are sharks and big rays, accumulate a lot of mercury because they feed on the bottom of the floor and they live a really long time,” Dorigo said. “Over time, the mercury builds up in their bodies and is just not safe to eat. As far as fishing and catch and release goes, it’s pretty safe, but … I wouldn’t eat it very often.”

Dorigo said awareness is a key factor in reducing harm from mercury poisoning.

“I think there are good resources that can tell you how much mercury you (can) ingest,” Dorigo said. “Every time I go fishing there, I see a sign and it says, ‘Eat this, and do not eat this.’”

Although mercury pollution has plagued the Bay for decades, it is not an issue that is easily solved, Loomis said, especially once it enters the water system.

“Mercury just likes to stick to sediments,” Loomis said. “It’s heavy. It sinks. It’s dense, so it’s very hard to get rid of (and) very expensive.”

Loomis did say, though, that mercury levels will eventually lower with time. 

“The big tides come in and go out, so some will be taken away every year,” Loomis said. “But it takes a lot of time, and there are some sources that are still going in. Over time, it will clean itself, but it will take hundreds of years.” 

 In the meantime, Loomis said there are ways to safely consume fish from the Bay.

“Eating vegetarian fish is better. Eating short lived fish is better,” Loomis said. “Eating long-lived predatory fish is a problem, not just in the Bay, but pretty much everywhere.”

In some cases, completely eliminating the risk is the best option. Senior and Environmental Service Club co-founder Nathan Lee said.

“The predators at the very top are the ones that can have (high mercury levels),” Lee said. “So, share the information. Maybe avoid fish if you’re a pregnant woman, and especially (don’t give it to) young kids.”

Looker said there is no magic or new innovations coming to cure the Bay anytime soon.

“The trick is really just working through time to try to reduce the inputs to San Francisco Bay,” Looker said. “The hope is that eventually, with reduced amounts in the sediments, there would be less available for incorporation into the food web, and fish (mercury) levels will come down.”