Dose makes the poison: Too much of anything can make you sick

When former “Friends” actor Matthew Perry died last year from an overdose of the drug ketamine, star-watchers assumed he got hooked at closed-door Hollywood raves. Not true: A licensed medical clinic had been giving him intravenous “infusion therapy,” administering vanishingly small doses in 40-minute sessions to treat his depression.

At higher concentrations, ketamine is an effective surgical anesthetic for people and animals. Pump up the dose enough, though, and you’ll end up like Matthew Perry. The 16th-century Swiss physician Paracelsus explained this succinctly: “The dose makes the poison.”

This rule plays out everywhere when you look for it. There’s arsenic in tap water and every bottle of apple juice, but at levels that are too low to harm children. Acetaminophen (Tylenol) is a wonderful pain reliever, but too much can cause liver damage. One glass of wine with dinner might make you chatty. Drink too much, though, and you might land in a hospital with alcohol poisoning.

Scientists call this the “dose-response” relationship. The U.S. government has toxicity assessments for chemicals in the form of what they call “LD50” numbers. That’s the dose that kills half the people who take it. There’s an LD50 for cyanide and one for sarin gas. There’s also one for caffeine, but it takes 122 cups of coffee for the average woman in the U.S. to reach it. Eating 15 pounds of dark chocolate in one sitting will give a typical human being a coin-flip chance of dying from a natural toxin called theobromine.

I was reminded of this sliding scale a few days ago when I read about scientists from the University of New Mexico who claim that one-half of 1% of human brains are now made up of nanoparticles of plastic. If that were true, it would be horrifying. That I can still remember my children’s names and where I parked my car suggests that someone botched the math. (The research hasn’t been peer-reviewed or published.)

Half of 1% of the typical 3-pound human brain is nearly a quarter of an ounce. That’s roughly the weight of three dimes. Is there really that much plastic messing with our gray matter?

Don’t bet on it. A 2021 study determined that the average adult ingests about 600 nanograms of plastic daily. A Royal Society of Chemistry fellow wrote this year that it would take 30,000 years at that rate to reach the one-half of 1% level. And that assumes every nanoplastic particle we unwittingly eat or inhale goes straight to our brains and stays there.

The vast majority of it passes through us, making our plastic “doses” anything but poisonous. Our bodies naturally eliminate all sorts of foreign materials we inhale and ingest, which shouldn’t be surprising. We sweat out arsenic, we excrete mercury and lead, we exhale carbon dioxide. We also cough out or unconsciously swallow mucus, which traps many of the nanoparticles we inhale. And a large majority of them aren’t plastic at all.

The truck exhaust you smell when your car windows are open? What looks like smoke is actually a sooty cloud of nanoparticles, mostly carbon and toxic metals. Forest fires and dust storms are even worse. By comparison, secondhand tobacco smoke seems overhyped, and so does plastic.

Ditching plastic bottles in favor of aluminum cans has become fashionable. And that is despite nano plastic particles being nontoxic vs. those bits of aluminum that will make you sick. Aluminum nanoparticles reach the brain and put down roots there. Coroners can see aluminum deposits in the brains of deceased Alzheimer’s disease patients. There’s usually a lot of it, and it might play a part in causing dementia. Yet science reporters with English degrees have yet to discover this potential threat hiding in plain sight.

Another fear-factor nothingburger is the naturally occurring mercury in tuna. Environmental nongovernmental organizations have systematically terrified us of this, forgetting that the working poor can‘t afford other food that are high in omega-3 fats — the oils that make fish “brain food” for children. For pregnant women, their unborn pay the price in lost IQ points. Mercury toxicity typically takes decades to develop, and the risk is practically zero if you’re not from a culture where people eat a lot of mercury-accumulated whale meat.

Again, the dose makes the poison. Click-driven scare stories, though, work immediately, and we’re all worse off for it.

Rick Berman is president of RBB Strategies.