Actor Jeremy Piven, best known as loudmouth talent agent Ari Gold on HBO's Entourage, has made an early exit from the Broadway play Speed the Plow, blaming a mercury-rich sushi diet and possibly use of herbal medicine. His doctor says tests revealed Piven has mercury levels five to six times higher than normal, and has ordered a fish-free diet and rest.

“I talked to Jeremy on the phone, and he told me that he discovered that he had a very high level of mercury,” playwright David Mamet told Variety. “So my understanding is that he is leaving show business to pursue a career as a thermometer.”

Piven's doctor, Carlon Colker, told the showbiz publication that “insensitive comments like that are not only unkind and unfair, they reflect a profound lack of understanding of a problem that can actually kill.”

“The etiology is unclear, but his level of mercury was uncharacteristically high, one of the highest we’ve seen,” Colker, an internist at Greenwich Hospital in Connecticut, told Variety. “We’re not sure if this is from his diet, which is high in fish, or Chinese herbs, which he’s been a fan of in the past, or a combination of both. He needs convalescence and rest and treatment, and this will clear his body and he will be back in action very soon."

Colker told the Wall Street Journal Health Blog that Piven's treatment would include dietary restrictions, nutritional supplements and antioxidants. 

We asked Jay Schauben, director of the Florida/U.S. Virgin Islands Poison Information Center-Jacksonville, to explain mercury poisoning. Below is an edited transcript of our conversation.

So, what's mercury?

There are three kinds of mercury. Depending on what the exposure is, you could have different symptoms and disease states.

Elemental, or metal mercury, is found in thermometers. The problem with that is the inhalation of fumes that come off that mercury. Playing with it and ingesting it is not as toxic. That kind of mercury causes significant amounts of neurological damage. As the exposure gets longer, there may be additional changes in the bone marrow that affect the ability to produce blood cells, infertility and problems with heart rhythm.

Mercury salts, which are basically industrial, if you breathe in or ingest them, gravitate more toward the kidney and not so much the nervous system.

The organic mercury is what gets into the food chain. It's put into the water by chemical plants that are manufacturing things and they get into shellfish and fish, or elemental mercury that gets into the water is changed into organic mercury by sea life; we eat fish or shellfish and we get mercury exposure. That organic mercury acts very similarly to the elemental form. It affects a lot of nervous system damage. If a woman is pregnant, this can also cause birth defects and loss of the fetus if the levels get high enough.

Is mercury something we need in our diets, or is no amount nutritionally safe or necessary?

No level is normal. Zero is normal. It doesn’t have a specific reason to be in our body. As long as we live on this Earth, because it's in Earth's crust and in the atmosphere, we're going to be exposed. But there is no specific function for that metal in our body.

The issue is one of looking at the total body burden: How much mercury is in the body and what's known to be a normal background? Theoretically, there's going to be a baseline level, a general population average, but depending on where you live, that level may be higher or lower. If you live near a coast, you're more up to eating seafood. Or you may be in an industrial area where mercury is put into the water or the air. 

What's the difference between having mercury exposure and mercury poisoning?

A lot of this has to do with numbers versus symptoms. Just because you're exposed to a toxin doesn’t mean you get poisoned. You can build up a blood or tissue level but not yet manifest symptoms related to poisoning. Call it a threshold.

A person with no symptoms, no changes physically or chemically, we just say they've been exposed and have a high mercury level. It doesn’t become poisoning under the true definition unless someone has had physical or chemical changes in his or her  body. It's a very fine distinction, but one person is symptomatic and the other asymptomatic. The person who is symptomatic is poisoned. The one who is asymptomatic has a high blood level consistent with exposure.

That doesn’t mean it's safe to have levels without symptoms. Over time, even if you're exposed at low levels, the symptoms may not manifest until weeks or months later.

A person can find out if they had a higher-than-normal exposure — the urinary level is the most specific way. Blood levels can also be used, and we plot those against your geographic area.

What are the symptoms of mercury poisoning?

Symptoms can occur in many ways. Unfortunately in mercury, symptoms can look like many disease states. When levels are building up,  there could be a variety of symptoms that a physician may interpret as another illness. Only when the physician can't find a real cause or gets a toxicologist involved will they do blood tests and say, "Yes, this is probably due to mercury exposure."

It's a difficult diagnosis. You have to know by history that a person has been exposed to this and put two and two together. No specific set of symptoms will say, "Ah, this is mercury poisoning."

If it's mercuric salts the person has been poisoned by, it may just be a problem with the kidneys, issues with the ability to urinate, or they're feeling out of whack because of renal dysfunction.

If someone is inhaling fumes from elemental mercury, that can show up as an upper respiratory illness, like a flu, at first. They might find they can't concentrate well, have trouble with fine motor control or their perception of smell, eyes or touch. If it was affecting their heart, it could be palpitations or just in general not feeling well. If something is not going well with their blood cells forming, they may have issues similar to anemia, feeling very tired, easy bleeding or bruising.

With organic mercury exposure, the symptoms are pretty much the same, but probably not respiratory. The nervous system effects are what someone would see first.

How would mercury toxicity or poisoning be treated, and how long would it take for someone to get well?

What is used, when, and how is decided by a doctor on case-by-case basis in consultation with a toxicologist. If you do have high levels, the first thing to do is stop the exposure.

Chelating agents make metals more water-soluble so they can be excreted by the kidneys. That works fairly well for inorganic salt forms of mercury poisoning but not so much for neurologic forms from the elemental.

There are old World War II antidotes, actually: Injectables are used when we have high levels and only when we don’t have the organic form of mercury poisoning; it's the elemental and inorganic poisonings that we use them in. British anti-Lewisite (BAL), or dimercaprol, is one of these agents: it's an antidote the British developed against lewisite gas, and it's a potent chelator used against mercury, arsenic and lead.

If it's eating too much fish, we stop them from eating the fish and get the levels to come down naturally. Otherwise, there's nothing we can do.

How long treatment takes has to do how high the level is and how chronic the exposure is. If it's somewhat low levels, chelating might happen relatively quickly. If it's exposure for many years, it may take longer for those levels to come out.

Can you recover from mercury poisoning?

Yes and no. If the symptoms just started and you haven’t been exposed for years and years, it's very possible that those symptoms will dissipate. If it's occupational — you've been exposed to this for many, many years and you've physically damaged the nervous system — that may or may not reverse. It may if the nervous system can repair itself. If not, you may end up with a residual or permanent problem.

Is it plausible to get mercury poisoning from eating sushi or other fish?

There are certain types of fish that can accumulate higher levels of mercury than others. If you exist on a diet of that fish, you can mount some very high levels.

Tuna, depending on the type, may be higher in mercury content. It doesn’t matter how you cook it; whether raw or by cooking, it's [the levels] going to be similar.

[Shark, swordfish, king mackerel and tilefish may have high levels of mercury, according to a 2004 advisory from the FDA and Environmental Protection Agency (EPA). The FDA is considering relaxing its recommendations about how much fish is safe for pregnant women to eat.]

Are there herbs that could cause elevated mercury levels?

Yes. Herbal medicines made outside the country can potentially contain toxic quantities; it depends where they're coming from and how they're being made. These products aren’t controlled by the FDA and don’t need to adhere to any general standard of purity or potency so you end up with voluntary adherence to what the company says is in the bottle. You're always at risk when taking significant amounts of herbal products or remedies that have decent levels of this and other agents.