Regulation and Risk Assessment of 1,4-Dioxane - Environmental Investigation and Remediation - page 261

6 Regulation and Risk

Assessment of 1,4-Dioxane

Thomas K.G. Mohr

A fundamental maxim of toxicology is “The dose makes the poison.” * Regulations must protect
against exposure to toxic chemicals at doses large enough to result in toxic effects. Exposure pre-
vention extends to multiple routes of exposure. For example, effective regulation will prevent the
combination of ingesting contaminated drinking water and inhaling chemical vapors while shower-
ing with the same contaminated water. Unfortunately, the regulations promulgated by different
agencies pursuing a wide range of protective oversight (such as food quality, air quality, water qual-
ity, and drinking water treatment) may not be holistically integrated to produce a framework that
accounts for the additive effects of multiple routes of exposure to the same contaminant. For
example, perchlorate, the oxidizing salt used in the production of solid rocket motors, i rst emerged
as a drinking water concern. We have subsequently learned that the relative source contribution
(RSC) from ingestion of perchlorate in food is much larger than was originally understood; how-
ever, perchlorate in food is not regulated and remains the subject of ongoing investigation. Similarly,
the concentration in water and air was the primary focus of regulations for trichloroethylene (TCE),
whereas haloacetic acids—the breakdown products in the liver—were not. When accounting for
total exposure to haloacetic acids from inhaling TCE vapors and ingesting haloacetic acids present
in drinking water as disinfection by-products, it may be warranted to adjust the regulatory threshold
for TCE downward to minimize the RSC to haloacetic acid exposure. These examples underscore
the difi cult challenge faced by government scientists who work to establish protective regulations.
Their challenge is exacerbated by the large uncertainty associated with correlating laboratory ani-
mal data to estimation of toxic effects in humans.
Regulating chemical use, handling, and disposal protects us against risk from exposure to
harmful doses of toxic chemicals used widely in industry, consumer products, crop protection, and
other applications. Regulations establishing exposure thresholds protect human health by providing
regulatory agencies with a framework for evaluating and enforcing the safety of chemical use and
associated exposure. The many ways by which chemical exposure may occur is mirrored in the
complex web of regulations that have evolved to govern

• Worker health and safety

• Drinking water quality

• Chemical residues in food

• Pharmaceuticals and sundries

• Ecological effects of wastewater discharges

• Ambient air quality

• Transportation safety

* This adage is attributed to the Swiss scientist “Paracelsus,” aka Phillip von Hohenheim, 1493-1541, who said, “Alle
Ding' sind Gift und nichts ohn' Gift; allein die Dosis macht, dass ein Ding kein Gift ist.” (“All things are poison and
nothing is without poison, only the dose permits something not to be poisonous.”) The axiom is sometimes wrongly
attributed to Pericles, a Greek statesman.

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