By Parker Donham

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After a career writing about politics and the environment, followed by a stint on a massive and controversial environmental cleanup, I have one nugget to offer journalists and citizen environmentalists. I commend to their attention the man pictured here, the improbably named Philippus Aureolus Theophrastus Bombastus von Hohenheim (1493-1591). Paracelsus, as he called himself, had a remarkable career as an itinerant physician, botanist, alchemist, astrologer and occultist. Among many other things, he gave zinc its name and is credited with being the first systematic botanist (viz. here, here, here, here, and here.)

Paracelsus is best remembered for this declaration: Dosis sola facit venenum. "The poison is in the dose."

More than 500 years later, it's a principle reporters and environmentalists constantly ignore. They treat toxicity -- poison -- as a binary concept. In too many environmental news stories and press releases, potential hazards are either toxic or they're not, end of story. In reality it's only half the story. Important as it is to know what people are exposed to, it's also critical to know how much they are exposed to. Water can kill you, if you drink enough. Rat poison can save you, in appropriate doses.

In general, potential for harm is roughly proportional to dose received, and it's important to distinguish the trivial from the worrisome. When sloppy reporting causes us to fret about the trivial, we waste energy that could better be spent on the serious.

My friend Walter Van Veen, an environmental engineer with Conestoga-Rovers, the Canadian company that cleaned up Love Canal, used to give tours of the Sydney Tar Ponds and Coke Ovens, which we were trying to clean up. Standing on the old coke-oven grounds, which had yet to be cleaned up, he would describe the blood curdling process by which coal was turned into coke, one of the most common industrial processes of the 19th and 20th centuries, and the basis for many Superfund cleanups.

Wide-eyed eco-tourists would inevitably ask, "Is it safe for us to be standing here?"

"Well," Walter replied, "Most of the volatiles have long since evaporated, but if we had a VOC [volatile organic compound] meter with us, we could probably detect trace amounts of benzene, toluene, ethylbenzene, and xylene. But if you were filling up at a self-serve gas station, you'd be getting 1,000 to 10,000 times more of those chemicals than we are now."

The visitors would nod at this standard-issue reality check. Then Walter would add the kicker.

"In fact, I don't let my daughters out of the car at a gas station, because I don't think that level of exposure is good for them."

Walter is an affable fellow whom people naturally tend to like and trust. His declaration always made jaws drop. This guy was sensitive enough to environmental issues that he would avoid an everyday risk none of them had ever even considered. But he would have no problem showing his daughters around a project widely -- and falsely -- described in news reports and environmental websites as "Canada's worst toxic waste site."

On the Columbia Journalism Review website, David Ropeik makes a similar point in much greater detail. Journalists and citizen environmentalists, please read. And just so the rest of you don't forget, I offer this mnemonic, courtesy of a Spaniard known to me only as Gabrielziya:

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Parker Donham, a writer and consultant who lives on Cape Breton Island, Nova Scotia, blogs at Contrarian.ca.