Insight
Go to the Head of the Class
Carcinogen Classification: Oldies but Goodies
BY FRANK MIRER
Some risk assessment issues never die—
and unlike old soldiers, they don’t fade
away, either. Such is the case with the
classification of chemicals and exposures
as “carcinogens,” which has reemerged
now that NIOSH is revising its cancer
policy. Other recent developments in carcinogen classification include a bruising
political effort by industry to delay or
derail publication of the National Toxicology Program’s (NTP) 12th Report on
Carcinogens (ROC), which lists formaldehyde as a known human carcinogen
(causing leukemia) and styrene as reasonably anticipated to be a carcinogen.1
Also, IARC Monograph 101 reclassified
diethylhexyl phthalate (DEHP) and di-ethanolamine (DEA) from “not classifiable” to “possibly carcinogenic,” and, for
the first time, classified methyl isobutyl
ketone as possibly carcinogenic.2
My aim in this article is to explain the
terms and frame the disputes for practicing industrial hygienists who will likely
be required to explain MSDSs and update hazard communication training
programs. Back in the day, the scientific
paradigm for chemical carcinogenesis
predicted that there was no zero-risk
dose for a carcinogen. The OSH Act’s
statutory prescription requires a standard
that assures “that no employee will suffer material impairment of health or
functional capacity even if such employee has regular exposure to the hazard dealt with by such standard for the
period of his working life.” To achieve
that goal, the PEL for a carcinogen must
be the lowest feasible level. After the
first OSHA benzene standard was overturned, some quantification of risk was
considered necessary for rulemaking,
but methods for risk extrapolation and
lower dose quantification for carcinogens were generally accepted. These accepted risk quantification methods—
which showed risks to life from specific
occupational chemical exposures to be
much higher than those from injury hazards—explain why 13 of the 16 chemical
agents for which OSHA set PELs were
carcinogens. However, to apply these extrapolation methods, it was considered
necessary to first establish that an agent
was a carcinogen.
An immediate impact of carcinogenicity classification is the requirement that
the cancer hazard of a chemical mixture
be disclosed on the MSDS and label if
the mixture contains 0.1 percent of a
carcinogen.
How Many Carcinogens?
At least eight carcinogen classification
schemes are in play: IARC, the ROC,
OSHA, NIOSH, ACGIH®, EPA, the state of
California, and the Globally Harmonized
System (GHS). As of 2011, IARC has classified 107 agents, exposures and mixtures
as “carcinogenic to humans,” 59 as
“probably carcinogenic,” 267 as “possibly
carcinogenic,” and 508 as “not classifiable,” with one agent (caprolactam)
termed “probably not” carcinogenic to humans. In 1982, IARC listed 30 agents as
carcinogenic, 13 as probably carcinogenic,
48 as possibly and 46 as not classifiable.
Clearly, identification of carcinogenic potential has greatly expanded since the
1970s, when regulatory activity was active and frameworks for understanding
and action (and misunderstanding and
reaction) were being developed.
The 12th Report on Carcinogens lists
54 agents and classes of agents as
known to be carcinogenic and 186 as
reasonably anticipated. NIOSH lists 132
agents and classes of agents as “
potential occupational carcinogens.” The ROC
generally lags the most recent IARC
monographs in time, and NIOSH, unlike
the IARC, does not include styrene, di-ethanolamine and MIBK. The discrep-
