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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

[full article free online]


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 

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.


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- 
<> The increased 
effectiveness of early exposure, combined with the known effects of 
obstetric radiation exposures,8 
<> 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 
<>; 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 
<> were 
downloaded and individual pixels--resolved at 412.8 metres per 
pixel--were translated to grid references (see appendix, available on 
line 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 

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