projects to support. The agents are mostly Group 2A and 2B
(probable and possible carcinogens) with a few Group 3 (
unclassifiable); formaldehyde is the lone Group 1 agent. The full text is
available at http://monographs.iarc.fr/ENG/Publications/
techrep42/ index.php.
Readers should go to these sites to see what’s known and
what’s unknown. For Volume 100, the agents are known
knowns; estimating exposure in the human studies would lead
straight to acceptable exposure limits.
For Report 42, what’s known largely corresponds to hazard
identification: sufficient evidence in laboratory studies and limited evidence of carcinogenicity in people. In many cases, Report 42 includes substantial information on exposure response
(i.e., potency) for estimating risks at occupational exposure levels. These risks, therefore, are either known knowns or unknown knowns. In my opinion, the data needs addressed in
Report 42 are largely those necessary to overcome management
objections or Houdini risk assessments.
The review of welding fumes in IARC Publication 42 exemplifies the frozen state of worker protection. IARC has categorized welding fumes as Group 2B (possibly carcinogenic to
humans) since 1990. The 2010 summary states:
As reviewed by Ambroise et al. (2006), there have been around
60 studies published that are informative about lung cancer
risks in welders. While there remained some uncertainty about
possible confounding by smoking and by asbestos, and some
possible publication bias, the overwhelming evidence is that
there has been an excess risk of lung cancer among welders
as a whole in the order of 20%-40%.
Personally, I’d pull the trigger on “sufficient” evidence in
people, although a working group would have to read those 60
studies to draw a conclusion. The review found only spotty laboratory data. The document is about research needs, so it called
for more epidemiology, but another study added to 60 extant
studies is not likely to change the picture. A 20 percent excess
of lung cancer is about a 1 percent risk, 10 times the border of
significance. The recommendations for laboratory research are
also weak. I believe the highest priority must be given to a full-scale inhalation bioassay of nano-sized iron oxide—not because
it’s needed for the “sufficient” classification or exposure response assessment for welding, but because widespread exposures to iron oxide particles are likely in other settings.
OSHA doesn’t have a PEL for welding fume but allows 10
mg/m3 for iron oxide. NIOSH recommends lowest feasible exposure for welding fume because it’s carcinogenic, but the
absence of a recommended exposure limit (REL) provides zero
guidance. The ACGIH® TLV® is 5 mg/m3.
The Precautionary Principle and Intentional Indecision
The precautionary principle is hardly a fringe concept. It’s embodied in the UN World Charter for Nature (1982), the UN Rio
Declaration on Environment and Development (1992), the
Wingspread Conference Report (1998) and a report from the
European Commission (2000) (http://ec.europa.eu/dgs/health_
consumer/library/pub/pub07_en.pdf). From the Rio Declaration:
In order to protect the environment, the precautionary approach shall be widely applied by States according to their
capabilities. Where there are threats of serious or irreversible
damage, lack of full scientific certainty shall not be used as a
reason for postponing cost-effective measures to prevent
environmental degradation.
The precautionary principle is intended to guide decision
making in the face of uncertainty. Conservative scholars attack
the precautionary principle, insisting on detailed quantitative
risk assessments and cost-benefit analyses as the basis of any
government intervention in economic activity, such as exposing
workers to chemicals. The current climate for chemical hazard
control in the occupational environment forces workers to suf-
fer from our refusal to decide in the face of certainty. The pre-
cautionary principle is needed for issues that correspond to
Rumsfeld’s “unknown unknowns.”
There is some precautionary tilt in the OSHA law and in U.S.
environmental legislation. The Clean Air Act amendments of
1990 require users of air toxics to apply the “maximum available
control technology” (MACT) in new source review, regardless of
whether risky exposures are predicted. That tilt is limited. For ex-
ample, the Toxic Substances Control Act requires EPA to present
existing evidence of danger from a chemical before it can order
testing to find evidence of danger. This flaw explains, in part,
EPA’s failure to order test rules for existing chemicals such as
metalworking fluids. Some interpretations of the OSH Act require
the agency to show “significant risk” from uncontrolled exposure
levels before ordering routine engineering controls.
Shifting the framing of chemical exposure limits toward a
precautionary approach is important for the hundreds of chemicals and chemical mixtures in workplaces. Applying an MACT
approach to industrial processes that generate worker exposures is important. Reduction of toxic chemical use is important. “Green” chemistry is attractive, although I question
whether the hazards of “safer” substitutes are known. All of
these priorities have ramifications for the known unknowns
and unknown unknowns.
However, focusing on the known knowns and unknown
knowns is much more immediate and productive. In my experience, IH is effective when there’s an OEL to target and vague
and ineffective without it.
FranklinMirer,PhD,CIH,isaprofessorintheEnvironmentalandOccupational
HealthSciencesUrbanPublicHealthProgramatHunterCollegeSchoolofHealth
Sciences in New York. He can be reached at (212) 481-7651 or
fmirer@hunter.cuny.edu.
