I seem to recall the Obama Administration did the same when the Fukushima reactor meltdown happened. The EPA or similar agency dramatically increased the exposure to Cesium-137, Iodide-131, Strontium-90, and other radioactive isotopes as a result of the Fukushima disaster. The Petkau Effect states long term exposure of extremely low radiation (i.e., one-ten millionth of a rad) was found to be 100 BILLION times MORE lethal than a short term exposure to exceedingly high level radiation (i.e., 10,000 rads per minute). 

Could a Petkau Effect be applied to exposure of hazardous chemicals. It's very plausible in my mind. Today, the most prevalent cause of disease is from environmental chemical toxins that attack the neurological system and cause cancer and auto-immune diseases, et. al. In 2002, Dr. Tom Mack of USC stated --

“My credentials include probably spending more time working up [analyses of] population-based outbreaks of smallpox than virtually anybody ever has.”

Mack then stated --

“If people are worried about endemic smallpox [long lingering or permanent presence of the disease in the population], it disappeared from this country not because of our mass herd immunity [derived from a vaccine]. It disappeared because of our economic development. And that’s why it disappeared from Europe and many other countries…[its disappearance is] not from universal vaccination.”

In my mind's eye I see the Petkau Effect applies not only to radiation exposure, but may apply to chemical exposure too.