Full Text:
I certainly agree with Gwen Ottinger and Rachel Zurer
("Drowning in Data", Issues, Spring 2011) and the followup
letter by Sarah A.Vogel (Issues, Summer 2011, p. 16) that it is a
fundamental challenge to translate chemical concentration data into
information that is meaningful to the public. However, both of these
pieces include some incorrect information and miss key aspects of the
issues.
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First, Ottinger refers to various ambient air standards and the
fact that there is "no consensus on what constitute [s] a safe or
permissible level." A casual reader could get the impression that
all of the health-effects research that has been done to date has
basically been useless in terms of relating con-centrations to health
effects, which would be misleading. Although there is some variability
in the underlying technical information, much of the variability in
standards is because standards have different purposes and/or are
applied to different situations. For example, contrary to what Ottinger
and Zurer say, the federal Clean Air Act does not set ambient air
standards for volatile organic compounds (VOCs); however, Clean Air Act
regulations do set stack concentration limits for VOCs, for some
industrial sources. Not surprisingly, if you are comparing stack
concentration limits to ambient concentration limits, you are going to
expect orders of magnitude differences, but these differences are not
due to a lack of scientific consensus. They are due in part to the fact
that they are applied to different locations (inside an exhaust stack
versus in the ambient air) and in part because they are not both based
on what is "safe." For example, some industrial equipment
standards are based on what is achievable with available control
technologies, which may be more or less than what someone deems to be
safe. In addition, some air standards are not standards for what are
safe levels in the ambient air, but are conservative standards used for
issuing air pollution permits. In other words, the standards are for
purposes of comparing the worst-case effects of a facility to a person
standing at the facility's fence line for an extended period of
time.
Second, it needs to be recognized that while identifying safe
levels can and should be based on scientific information, there is also
some political judgment involved. Although there are some health effects
with thresholds, others do not have clear thresholds. For example, the
default assumption for cancer risk is that the only concentration that
corresponds to zero risk is zero. In addition, there are questions about
how to address scientific uncertainty, how to extrapolate animal data to
humans and account for the most susceptible humans, and how to
extrapolate data that were taken at very high doses in order to produce
a measurable effect down at the low doses. Vogel states that "what
is safe for a 180-pound healthy man is not safe for a newborn, but our
safety standards for industrial chemicals, except for pesticides, treat
all humans alike." But this is incorrect, because many of the
health-based air standards are in fact designed to be protective of the
most sensitive individuals and do take children explicitly into account
(OSHA standards are one obvious exception, because they are applicable
to workplace conditions experienced by adults). For cancer risk, some
areas of the country like using a 1-in-a-million lifetime cancer risk
benchmark, but there is absolutely no technical basis for this standard.
If people are made aware of the fact that calculations based on
conservatively derived risk factors of lifetime cancer risk associated
with urban ambient air quality are typically a couple of orders of
magnitude higher than 1-in-a-million (but in many cases have been
decreasing over the last several decades), that people's exposures
indoors and in their cars are in most cases significantly higher than if
they were simply exposed to ambient air quality, and that the American
Cancer Society's calculations of Americans' actual lifetime
risk of contracting cancer is closer to 300,000 to 500,000 in a million,
they tend to feel that the 1-in-a-million standard is very or overly
protective; however, if you simply put a 1-in-a-million standard in
front of somebody, say it is health-based, and show concentrations that
are above or even only slightly below it, they are likely to be much
more alarmed. Vo-gel's recommendation to obtain better information
about real-life exposure scenarios is a good one because this
information could be used to both establish the extent to which
exposures are resulting from ambient air versus more localized exposures
(not just industrial facilities, which appear to be the targets of the
authors, but also situations such as poorly ventilated cooking, travel
on busy streets, etc.) and help provide context to people as to what
their current exposure levels are.
Third, there needs to be an understanding that epidemiology (the
solution identified by Ottinger and Zurer and Vogel) can have
significant limitations. Although it can show correlations, it does not
show causality, and there is often a multitude of confounding
correlating factors. In addition, it can effectively detect only
correlations that are epidemics; for example, a 10% or more effect on
the population, or at best maybe 1%. Although epidemiology may be useful
for evaluating some of the highest exposures, many people would argue
that regulatory standards should be set more stringently than what
epidemiology is capable of de-tecting, as many of them currently are.
But perhaps most important, the fourth thing that needs to be
recognized is that there are and always have been countless chemicals in
the air at some concentration or another. We have always been and always
will be, in Vogel's words, "silently exposed to
chemicals," some of which are man-made and some of which are not,
all of which are potentially dangerous at some level, and the number of
variables that could be studied are endless. Therefore, there is a need
for both prioritization (at a multimedia, comprehensive level) and
science, by which I mean the organization of scientific information
regarding health effects, and not just the existence and continued
execution of scientific studies on individual chemicals or situations.
Todd Tamura Tamura Environmental, Inc. Petaluma, California
todd@tamuraenv.com