Page 8 - Mecklenburg_Medicine_October-2019

Feature
Air Pollution and Cancer
By Lawrence W. Raymond, MD, ScM, Director, Occupational & Environmental Medicine,
Atrium Health Employer Solutions and Past President, Medical Advocates for Healthy Air
W e each draw thousands of breaths every day, having
little control over the quality of the air in those breaths, and air pollution.6 Mortality from lung cancer due to air pollution was
short of a major relocation. So the issue of air quality
can be divided in two familiar domains: good news
and bad news. The good news: A series of federal and state legislative
and regulatory steps aimed at improving air quality were enacted between
Physicians and other 1970 and 2005, well chronicled
by Kravchenko et al.1 Earlier
health professionals can regulations, such as the Clean Air
Act, targeted tail-pipe emissions
join in advocating for
and those from coal-fired
motorists to embrace power plants for remediation.
In addition, air pollutants from
“trip chaining” (combining chemical plants came under
regulation by the Environmental
multiple errands into one Protection Administration,
trip), car pooling, limiting including 188 toxic agents,
such as benzene, arsenic and
engine idling as much mercury. In North Carolina, our
possible, and using mass Environmental Management
Commission published rules
transit when feasible. in 2001 limiting the release of
ozone-forming oxides of nitrogen
from coal-fired power plants and large industrial sources. The next year,
our legislature passed the Clean Smokestacks Act, having a similar focus.
As Kravchenko et al. have shown, the ambient levels of nitrogen dioxide,
carbon monoxide and particulates PM2.5 or PM10, defined as having mass
median diameters of 2.5 and 10 microns, respectively, fell sharply between
1995 and 2012 in association with these regulatory steps. Sulfur dioxide
levels also decreased, while ozone concentrations were unchanged.
What were the health consequences of these improvements in
ambient air quality? As the investigators demonstrated, death rates from
emphysema, asthma and pneumonia declined in concert with the more
salubrious air quality. The cost/benefit function of this sequence of
events was beyond the scope of their study. But, as they point out, control
of PM2.5 emissions could yield $100 billion in annual benefits.1 Less
dramatic, but equally important, was the decrease in incident asthma
episodes among 4,140 children linked to improved air quality between
1993 and 2014 in nine Los Angeles Basin communities, as identified by
Garcia et al.2 As Thurston and Rice put it, “a new chronic disease entails
many years of treatment and missed productivity.3 ”
The bad news: Air pollution causes cancer. As might be expected,
most such malignancies are lung cancers. The British research physician
Passey4 laid the groundwork for our understanding of this association
when he induced skin cancer in mice by painting them with extracts of
“town soot,” later shown to be rich in the carcinogen benzpyrene (BP).
Three decades later, Waller traced BP in smoke to internal combustion
engines and domestic fires, peaking in winter.5 Others advanced the
8 | October 2019 • Mecklenburg Medicine
supposition that lung cancer was caused by BP from both cigarette smoke
described by Pope et al.7 They reported a relative risk (RR) of death
from smoking equal to 9.73 compared to non-smpokers, but also found
a significantly increased RR due to sulfate levels in ambient air (1.36), as
well as fine particulates (RR = 1.31). Raaschou-Nielsen O et al. analyzed
results from 17 European cohort studies and found an increase in the
risk of lung cancer related to increases in either PM2.5 or PM10, while
higher neighborhood road traffic also was indicated.8 At a more general
level, the International Agency for Research on Cancer (IARC) 9 found
sufficient evidence to classify outdoor air pollution in general, and PM2.5
in particular, as human carcinogens. IARC blamed sources such as
transportation, power generation, industry, biomass burning and domestic
heating and cooking, and added bladder cancers to the adverse effects
of unhealthy air.10,11 The most recent analysis12 presented evidence of
air pollution’s links to colorectal, liver and stomach cancers, as well as
childhood leukemia.
What might be the mechanisms underlying these neoplastic changes?
Some are the shortening of telomeres, those protective caps at the ends
of our chromosomes. Other candidates include harmful effects on genes
involved in DNA repair, as well as oxidative stress and inflammation. The
latter may work by releasing chemokines and cytokines which trigger
abnormal angiogenesis.
Other bad news is local. The American Lung Association gave
Charlotte an “F” for 2018, due to 17 days of “orange” ozone days. As
AIRNow states, orange days translate to an Air Quality Index of 101-
150, where higher is worse. And this means patients with lung diseases,
as well as all older adults and children, are at increased risk of airway
inflammation and other adverse effects. Most recently, Liu et al13 described
mortality related to short-term increases in PM2.5 or PM10, even within
levels considered acceptable by the U.S. National Ambient Air Quality
Standards. Clearly, those who perish from these spikes in unhealthy air
will never appear as cancer victims.
What does the future hold? Over the next 10 years, the Charlotte
Metro population is projected to increase at 2.4 percent per year, from
2.6 million to 3.3 million. Road traffic will rise on parallel from 42 to 53
million vehicle miles per day, unless motorist behaviors and use of mass
transit improve. CATS ridership rose steadily by 41 percent in the decade
ending in 2014, only to drop by 15 per cent over the next three years.14
What do these trends portend for air quality and associated cancers? Given
the current administration’s plan to relax fuel economy and greenhouse gas
emission standards,15 it seems like more bad news.
Physicians and other health professionals can join in advocating for
motorists to embrace “trip chaining” (combining multiple errands into one
trip), car pooling, limiting engine idling as much possible, and using mass
transit when feasible. Learn more about Medical Advocates for Healthy
Air (easy Google). Please answer the call, doctor! Visit Clean Air Carolina
at cleanaircarolina.org.