Childhood cancers and atmospheric carcinogens
E G Knox
Correspondence to:
Professor E G Knox
Mill Cottage, Front Street, Great Comberton, Pershore, Worcestershire
WR10 3DU, UK
http://jech.bmjjournals.com/cgi/content/abstract/59/2/101
[full article free online]
Abstract:
Study objectives: To retest previous findings that childhood cancers are
probably initiated by prenatal exposures to combustion process gases and
to volatile organic compounds (VOCs); and to identify specific chemical
hazards.
Design: Birth and death addresses of fatal child cancers in Great
Britain between 1966 and 1980, were linked with high local atmospheric
emissions of different chemical species. Among migrant children,
distances from each address to the nearest emissions "hotspot" were
compared. Excesses of outward over inward migrations show an increased
prenatal or early infancy risk.
Setting and subjects: Maps of emissions of many different substances
were published on the internet by the National Atmospheric Emissions
Inventory and "hotspots" for 2001 were translated to map coordinates.
Child cancer addresses were extracted from an earlier inquiry into the
carcinogenic effects of obstetric radiographs; and their postcodes
translated to map references.
Main results: Significant birth proximity relative risks were found
within 1.0 km of hotspots for carbon monoxide, PM10 particles, VOCs,
nitrogen oxides, benzene, dioxins, 1,3-butadiene, and benz(a)pyrene.
Calculated attributable risks showed that most child cancers and
leukaemias are probably initiated by such exposures.
Conclusions: Reported associations of cancer birth places with sites of
industrial combustion, VOCs uses, and associated engine exhausts, are
confirmed. Newly identified specific hazards include the known
carcinogens 1,3-butadiene, dioxins, and benz(a)pyrene. The mother
probably inhales these or related materials and passes them to the fetus
across the placenta.
Introduction:
Previous studies have shown (1) that childhood cancers and leukaemias in
Great Britain exhibit geographical clustering of birth places: (2) they
occur at increased densities around industrial sites with large scale
combustion processes or using volatile organic compounds (VOCs), or
which incinerate waste: (3) among children who moved house between birth
and death the first addresses were closer to these hazards than were the
later ones and migrations were more often directed away from a nearby
hazard than towards one.1-
<http://jech.bmjjournals.com/cgi/content/full/59/2/101#R1>7
<http://jech.bmjjournals.com/cgi/content/full/59/2/101#R7> The increased
effectiveness of early exposure, combined with the known effects of
obstetric radiation exposures,8
<http://jech.bmjjournals.com/cgi/content/full/59/2/101#R8> suggests that
these diseases are often initiated prenatally.
The use of hazard proximity birth-death comparisons was initially
dictated by the absence of a suitable set of non-cancer controls in the
study from which the case material was extracted. These data were
designed to measure the effects of obstetric radiation by comparing
cases with paired non-cancer controls8
<http://jech.bmjjournals.com/cgi/content/full/59/2/101#R8>; but the
controls had been geographically matched with the cases and could not
then be used to make geographical comparisons. The migration based
method gave coherent results but was open to the possible objection that
the migration patterns in the cancer children may have reflected a
general population movement, perhaps related to area demolitions and
subsequent rehousing. The recent publication of independent and
comprehensive national pollution data now affords an opportunity to
retest the atmospheric birth hazard hypothesis, and to identify specific
chemical hazards. This is the objective of this study.
The UK National Atmospheric Emissions Inventory (NAEI) has recently
published through its web site, detailed geographical displays of
emissions of many different chemical species for 2001. These maps9
<http://jech.bmjjournals.com/cgi/content/full/59/2/101#R9> were
downloaded and individual pixels--resolved at 412.8 metres per
pixel--were translated to grid references (see appendix, available on
line http://www.jech.com/supplemental). Emission levels are expressed
"'per square km per year" on a seven point colour coded scale, using
units that vary from grams (dioxins), through kilograms (chromium,
nickel), to tonnes (sulphur dioxide, PM10 particles). Some were measured
directly and others by ascertaining activities with known emission
characteristics. Lower scale values are indicated as broad map zones,
but the highest levels are shown as small clusters of red pixels or by
individual pixels, often appearing to represent individual sources. The
maps are readily available for inspection.
Except for the red pixel hotspots, the main scale divisions were too
broad for effective comparisons of birth and death addresses. NAEI also
points out that because of atmospheric diffusion the emission estimates
do not directly represent the air we breathe. However, as in earlier
studies, it is possible to compare birth and death addresses by
measuring hotspot distances. The "case centred" method, used again here,
examines the surroundings of each address in turn to identify the
nearest of the hotspots. The selection is entirely objective and the
resulting comparative distance measurements are available in very large
numbers.
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