From: Robina Suwol
Date: 10 Apr 2003
Time: 03:01:24
Remote Name: 172.200.113.162
BAD AIR LINKED TO CHILDHOOD LEUKEMIA
Date: 6 Apr 2003
From: "Peter Montague" {Peter@rachel.org}
By Ernie Hood, Environmental Health Perspectives, April 2003
Researchers in the Environmental Health Investigation Branch of the California
Department of Health Services have discovered a possible association between
exposure to hazardous air pollutants (HAPs) and the incidence of childhood
leukemia. Their epidemiologic evaluation suggests that children living in areas
of high ambient air pollution are at increased risk of developing leukemia.
Peggy Reynolds and her coauthors set out to evaluate whether
childhood cancer rates were elevated in areas estimated to have high exposure to
potentially carcinogenic HAPs. They used the population- based California Cancer
Registry to gather information on all cancer cases diagnosed in children under
age 15 from 1988 to 1994. They used a geographic information system to map
nearly 7,000 childhood cases within individual California census tracts. Their
analysis also examined the incidence of the most common childhood cancers -
acute
lymphocytic leukemia, acute nonlymphocytic leukemia, and gliomas
(brain tumors).
On the pollution side of the equation, the investigators focused on 25 of the
189 HAPs identified in 1990 as potential human carcinogens by the U.S.
Environmental Protection Agency (EPA). These 25 compounds - which included
benzene, dioxins, lindane, and vinyl chloride - were selected because they had
the best information on their potential to cause cancer via inhalation. The
investigators also utilized an EPA dispersion model that combined 1990 emissions
inventories with meteorologic data to estimate the annual HAP concentration for
each census tract in the country.
Following the EPA model, they estimated which California census
tracts had the greatest HAP exposures. They calculated census tract emission
scores for all sources combined, as well as for three distinct source
categories: mobile sources (such as motor vehicles, planes, trains, and ships),
area sources (such as dry cleaners, gas stations, residences, farm pesticide
use, and forest fires), and point sources (large industrial manufacturing
facilities). For each of these emission source groups, they further calculated
exposure scores for
each census tract by multiplying the modeled air concentration by the
corresponding inhalation unit risk factor for each HAP. The inhalation unit risk
factor combines the cancer potency for each compound with standard assumptions
for body weight and breathing rate.
When they ran the exposure score data and the cancer case incidence data through
statistical analysis, they found little evidence of an increased risk of gliomas.
However, they did find the risk of both types of leukemia to be elevated by 21%
in census tracts with the greatest overall HAP exposure. More disturbingly, they
found the most dramatically elevated childhood leukemia incidence rates - a 32%
increase - within census tracts with the highest HAP exposure from
industrial facilities. The association was even greater in children aged 0-4
years, which the investigators speculate may be due to the fact that younger
children tend to spend more time at home than older ones.
Of course, many other factors could contribute to the development of cancer in
children, including individual susceptibility and exposure to indoor pollutants
such as environmental tobacco smoke. The authors acknowledge the inherent
limitations of their investigation, but conclude that it "suggests that
background air quality, as estimated
by HAPs, may be associated with incidence of childhood leukemia." They have
begun a follow-up study focusing more closely on the relationship between
cumulative exposure to HAPs and childhood leukemia, which will include
questionnaire information on personal activity patterns and indoor pollution
sources.
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