2nd CHILDREN with LEUKAEMIA Conference
29th & 30th April 2008
Childhood Leukaemia Causes and Prevention
What environmental factors are linked to childhood
leukaemia and are they detectable epidemiologically?
Denis L Henshaw
H H Wills Physics Laboratory
University of Bristol
I will consider….

Natural Background Radiation
Childhood leukaemia is believed to have
shown a real increase last century
low-LET stable over time; highLET (radon) small increase

Light-at-night
large increase last century

Power frequency magnetic fields
low average exposures but a
general increase

Air pollution
significant increase in
ultrafine/nano particles
(Shah & Coleman BJC 2007; 1 - 4)
Natural background ionising radiation
HPA/NRPB
Natural background radiation
exposure rate in the UK is
~2.7 mSv y-1.
 Childhood leukaemia risk has been extensively studied at medium and high
level exposures in the Japanese Atomic Bomb survivors and fallout from
nuclear weapons testing (Wakeford Oncogene 23: 6404-, 2004)
 Increased risk in relation to in utero exposure from obstetric X-rays has been
demonstrated with acute doses of 10 mSv or lower
1997)
(Doll & Wakeford BJR 70: 130-,
Risk estimates derived from these exposures suggest that natural
background radiation contributes to childhood leukaemia incidence
UK COMARE 4th Report (1996) page 62:
Natural background radiation…………..
For high-LET (a-particles) the 14% link divides:
~9% 210Po → RR = 1.09 at “normal” 210Po levels compared with zero 210Po
~5% Radon → RR = 1.05 at 20 Bq m-3 compared with zero radon
Both high and low-LET estimates are essentially undetectable in a case-control
study because:
(i) of ubiquitous exposure to low-LET radiation with little place-to-place variation
and
(ii) for radon, too few statistics in the high vs low exposure category to provide
statistical power
Radon–leukaemia correlations
There have been a number of reports of geographical
associations between radon and leukaemia:
Lucie 1989, Henshaw et al 1990, Alexander et al 1990,
Butland et al 1990, Lucie 1990, Muirhead et al 1991 & 1992,
Cohen 1993, Richardson et al 1995, Lyman et al 1986,
Collman et al 1991, Viel 1993, Forastiere et al 1992, Hoffman
et al 1993, Thorne et al 1996, Kohli et al 2000, Anne-Sophie
Evrard et al 2004
But few case-control studies have reported an association
Light-at-night (LAN)
Europe in the Present
Europe in the past
The Melatonin Hypothesis and breast cancer
– Richard Stevens University of Connecticut 1987
 Exposure to light-at-night or magnetic fields suppresses the nocturnal
production of the natural anti-cancer agent melatonin in the pineal
gland leading to increased risk of breast cancer
 Has much support for visible light: evidence that female night shift
workers have elevated breast cancer risk (Meta-analysis of 13 studies:
Megdal et al. Eur J Cancer 41: 2023-2032, 2005)
 Women’s blood containing normal physiological concentrations of
nocturnal melatonin prevents growth of MCF-7 breast tumours
transplanted into rats (Blask et al. Cancer Res, 65: 1-11, 2005)
 2007: IARC has classed night shift work as a Class 2A, “probable”
carcinogen
Melatonin
(N-acetyl-5-methoxytrptamine)
 Melatonin is a hormone produced in the
pineal gland mainly at night
 Ganglion cells in eye (not visual system)
signal when there is no light – pineal
melatonin produced at night
 Powerful anti-oxidant with multiple actions,
many receptor mediated
 By a scavenging cascade – one melatonin
molecule can scavenge up to 10 ROS/RNS
(Tan et al J Pineal Res. 42; 28-42, 2006)
Light-at-night and childhood leukaemia
Has not been studied but:
 Melatonin protects against oxidative damage to the fetus in
animals
(Wakatsuki et al 1999a, b &c; Okatani et al 2001)
 Melatonin is highly protective of oxidative damage to the human
haemopoietic systems (Vijayalaxmi et al Mutat Res: 371; 221-,1996):
Four human volunteers took 300 mg melatonin, after 2 hours blood samples exposed to 1.5 Gy
g-radiation. 50-70% reduction in DNA damage in lymphocytes
 Melatonin inhibits proliferation of HL60 myeloid leukaemia cells
(Rubio et al J Pineal Res 42: 131-, 2007, 42)
Serum melatonin level and its relationship to feto-placental
unit during pregnancy (Nakamura et al J Pineal Res 30: 29-33; 2001)
Fig. 1. Changes of maternal serum melatonin levels at night-time
(solid line) or daytime (dotted line) in the normal singleton pregnancy.
Power frequency electric & magnetic fields
- especially magnetic fields, MFs
Appliances:
can be tens
of mT close to
(Richard Box’s ‘FIELD’ February 2004 Photo: Stuart Bunce, www.richardbox.com)
Under powerlines MFs can be several mT or evens tens of mT
Doubling of CL risk associated with 0.3/0.4 mT
Average MF home levels 0.05 mT
Childhood leukaemia and magnetic fields (MFs)
Reported MF associations with childhood leukaemia at various stages:
a) Paternal peri-conceptual - Pearce et al (Pediatr Blood Cancer, 49: 280-, 2007)
b) Birth address - Draper et al (BMJ, 330, 1290-, 2005);
c) Diagnosis address - Ahlbom et al. (2000) and Greenland et al. (2000) – doubling of risk above
0.3/0.4 mT average exposure. More recently Kabuto et al (Int J Cancer¸ 119: 643-, 2006);
a) Reduced survival in children treated for ALL - Foliart et al (B J Cancer, 94, 61-, 2006);
International Agency for Research on Cancer (IARC) 2001 declares magnetic fields
a Class 2B “possible carcinogen” Statements about precaution - WHO (2007);
SCENIHR (2006); UK SAGE Report (2007)
A linear no-threshold model would suggest ~11% of CL cases
linked to MFs in the UK
But, stepping back from CL:
Review bodies’ assessments of MF causation of various diseases.
Disease
1.
2.
3.
4.
5.
Childhood Leukaemia
Adult Leukaemia
Adult Brain Cancer
Miscarriage
ALS
IARC 2002
2B*
Yes
NIEHS 1999** Calif 2002
2B
2B
Yes
Yes
Yes
Yes
Yes
Yes
Yes
*Class 2B, possible carcinogen
**US National Institute of Environmental Sciences
See also O’Carroll & Henshaw (Risk Analysis, 28(1), 225-, 2008)
Evidence for MF link with Adult leukaemia, and at least as good as for childhood leukaemia.
Alzheimer's disease also comparable (Garcia et al Meta Analysis 25 studies: Int J Epidemiol 2008)
Illnesses associated with MFs – Is there a
common factor?
Childhood leukaemia, Adult leukaemia, Adult brain cancer,
ALS, Alzheimer's disease, Depression, Suicide,
Miscarriage, Breast cancer
Disruption of
Melatonin
Populations exposed to neighbourhood EMFs shown melatonin
disruption with fields as low as 0.2 mT
(Review by Henshaw & Reiter, Bioelectromagnetics S7: 86-97, 2005)
The Radical Pair Mechanism:
Magnetic fields can increase the lifetime of free radicals
- More available to damage DNA
When two radicals created from one precursor, spin
states are coupled (+½, -½) – singlet state (t~ns)
If the spin of one of the species changes, radical pair
will have parallel spins – triplet state (t~ms)
+½
+½
+½
Spin
change
+½
-½
-½
Molecule
spin = 0
Separation:
Free radicals
+½
+½
Singlet
radical
Pair (ns)
Triplet
radical
Pair (µs)
Magnetic fields can increase the lifetime
of free radicals
by driving singlet spin states to triplet states
 Low magnetic field effects – previously
degenerate energy states resolve (Timmel et al.
Mol Phys 95: 71-89, 1998)
 Increases probability of transitions from
singlet (ns) to triplet state (ms) of radicals
 Results in more triplets – longer lived (ms),
more available to cause biological damage
 Experimental support in chemical systems
(e.g. Liu et al Chem Commun 174-, 2005)
Biological evidence for the RP mechanism
– increased lifetime of free radicals
 Juutilainen et al. (IJRB 82; 1-12, 2006) review of 65 in vitro &
animal studies – MFs enhance the effects of known
harmful agents, p<0.0001
 Lupke et al. (Free Radical Res 38; 985-993, 2003) – monocyte
cells from cord blood exposed to 1 mT fields release
reactive oxygen intermediates
Childhood leukaemia & MFs
apparent MF effects at ~0.4 mT 50/60 Hz
against the Earth’s static magnetic field of 50 mT
Similarly:
Fluctuations in the Earths MF of ~0.3 mT appear to be linked to
acute health effects e.g. depression (Review: Palmer et al: Surv.
Geophys, 27, 557-,2006)
Animal navigation
- Birds detect tiny changes in magnetic fields
 Homing pigeons sensitive to 10-20 nT changes in
the Earth’s 50 mT field (Wiltschko, 2005)
 Some amphibians have receptors in the pineal
gland…
 But of most interest in birds is the compass in the
eye (e.g. robins).
Ritz et al studied the magnetic compass in robins
(Nature 429: 177-, 2004)
The compass is based on the radical pair mechanism
Evidence suggests the avian compass
uses cryptochromes in the eye
Ritz et al (Biophys J 78: 707-, 2000); Ritz et al (Nature 429: 177-, 2004)
Review by Wiltschko & Wiltschko, BioEssays, 28; 157-168, 2006
 In the cryptochrome proteins visible light of
particular wavelength creates free radicals
whose spin states are affected by MFs.
 Thus, cryptochromes, detect and amplify
small MF changes for transmission to the
brain.
 Ritz et al 2000 & 2004 postulated and then
identified RPM in eye
 Ongoing work has identified ms lifetimes of
triplet state cryptochromes in garden
warblers (Leidvogel et al 2007 - Oxford)
University of Illinois
(www.ks.uiuc.edu/Research/cryptochrome)
Cryptochromes contd…
 Cryptochromes CRY1 & CRY2 proteins are expressed by the cryptochrome 1
& 2 genes – part of the family of 8 core circadian genes identified to date
 50 – 70 kDa in molecular size; ~4 nm in physical size
 Cryptochromes are expressed in plants which can respond to magnetic fields
(Review: Galland & Pazur J Plant Res 118: 371-, 2005)
 Cryptochromes do not necessarily need visible light to create radical pairs
 The circadian genes are present in all cells, but it is not known whether they
express cryptochromes in cells in general to facilitate the MF effects reported
by Lupke et al and others
Air pollution
Peggy Reynolds, California Health Dept: Odds ratios and 95%
confidence intervals for childhood leukaemia in proximity to highest vs.
lowest levels of traffic-associated exposures for twelve published studies
Savitz (1989)
Alexander (1996)
Feychting (1998)
Harrison (1999)
Pearson (2000)
Raaschou-Nielsen (2001)
Reynolds (2001)
Langholz (2002)
Reynolds (2002)
Crosignani (2004)
Reynolds (2004)
Steffen (2004)
0.1
0.5
1
5
10
50
100
dM dlogDa (mgm-3)
1.4
Urban
Manchester in winter
1.2
Organics
Sulphate
Nitrate
1.0
0.8
With kind permission of
Drs Rami Alfarra and Hugh Coe.
0.6
0.4
0.2
0.0
2
3
4
5
6 7 8 9
100
2
3
4
5
6 7 8 9
2
3
1000
Aerodynamic Diameter (nm)
Hydrocarbons (PAHs) mainly on the nano-aerosols
– travel considerable distances from production site
Nano-particle component of air pollution
Number particle distribution,
dN/d[ln(diam)]
Bristol roadside measurements
Total conc’n (11-083nm)
roadside = 53 900 cm-3
50000
40000
30000
20000
10000
0
11.1 17.3
27
42.6 68.2 111.9 191.3 348.9 692.1
Particle diam eter, nm
Number particle distribution,
dN/d[ln(diam)]
Passing 'heavy emitter' and 'normal' roadside
400000
Total conc’n (11-1083nm)
'heavy emitter' = 241 000 cm-3
350000
300000
250000
Heavy emitter
200000
Normal roadside
150000
100000
50000
0
11.1 17.3
27
42.6 68.2 111.9 191.3 348.9 692.1
Particle diam eter, nm
Inhaled nano-particles pass into the bloodstream

Nano-particles (NPs) when inhaled penetrate deeply into the
lung and pass into the bloodstream

In the context of cardio-vascular disease, NPs release
reactive oxygen species:
(i) Talk by Delfino (University of California, Irvine):
<http://www.aqmd.gov/tao/Ultrafine_Presentations/Session4_4_Delfino.pdf>
(ii) Simko et al (Toxicology Lett 161: 73-, 2006)
– Mono Mac 6 cells release ROS by 14 nm particles
Heritable mutations from air pollution
Steel Mills, Hamilton Harbour
Lake Ontario
26 PAHs measured
1 km downwind of steel mills:
1 km
 Exposed mice – ambient air
 Controls – air filtered to 0.01 mm (10 nm)
 Further controls – rural location 30 km away
1.5 – 2-fold increased heritable
germ line mutations in exposed group
Somers et al PNAS 99: 15904-, 2002
& Science 304: 108-, 2004
McKinney et al UKCCS: Occup Environ Med 60: 901-, 2003
Papers by George Knox 2005 & 6
(birth and death addresses of fatal child cancers in GB between 1966-80)
 Knox 2005a (J Epidemiol Comm Health, 59, 101-105)
- Childhood cancer associated with hotspots for carbon monoxide, PM10 particles,
VOCs, nitrogen oxides, benzene, dioxins, 1,3-butadiene and benzo[a]pyrene
 Knox 2005b (J Epidemiol Comm Health, 59, 755-760)
- Childhood cancer associated with short distances of bus stations, hospitals,
railways, oil installations and industrial transport centres: 1,3-butadiene especially
implicated
 Knox 2006 (J Epidemiol Comm Health, 60, 136-141)
- Childhood cancer associated with short distances of bus stations, railway stations,
railways, A,B class roads: again 1,3-butadiene especially implicated
Knox: Compared outward/inward migration wrt birth and
diagnosis address
Among migrant children,
distances from each address to
the nearest pollution emission
hot-spot were composed. Excess
of outward over inward migrations
show an increased prenatal or
early infancy risk.
1km
Case 1
D
B
D
Case 2
Hazard site, e.g.
Bus station
D Address
B
diagnosed
B Birth address
Findings – 2 (2005a):Benzene is a major component of motor fuel
1,3-butadiene is largely derived from petrol and diesel exhausts
Close ratios for 1,3-butadiene:
Distance (km)
Ratio out/in
0.3
8.39
0.5
7.65
0.7
4.66
Knox - conclusions
 Excess relative risks within 1.0 km of bus stations, hospitals, heavy transport centres and
oil stations. Most significant result: RR = 12.6 for joint <0.5 km exposure to bus stations
and 1,3-butadiene
 The associations with 1,3-butadiene, dioxins and benzo[a]pyrene are sufficiently specific
to conclude that they are probably the truly active agents
 Size of the effects suggests 30 - 80% of childhood leukaemia and cancer could be linked
to vehicle related air pollution in the UK at the in utero/early infancy stage
Draper et al. British Medical Journal 2005; 330: 1290-3
29,081 children with cancer, 9,700 with leukaemia 1962-1995 (322 leukaemia cases <600 m)
NB: Unlike other studies, this used the birth address and not the diagnosis address
Lowenthal et al. Internal Medicine Journal 2007
854 patients diagnosed with LPD or MPD aged 0-94 years diagnosed in Tasmania 1972-1980
2.06
(0.87-4.91)
<50 m
1.3
(0.88-1.91)
50-300 m
3.23 (1.26-8.29)
1st 15 years of life
4.74 (0.98-22.9)
1st 5 years of life
ORs for ever having lived within 50 and 300 m of a high voltage power-line
compared with never residing within 300 m and for risk associated by age of
exposure within 300 m.
Corona ion hypothesis
 Direct fields cannot explain findings of Draper and Lowenthal distant
from the power lines
 Indirect mechanism could be due to corona ions (Fews et al. 1999)
 High voltage line ionises the air and forms atmospheric small-ions
 Small-ions attach to pollutant aerosols, changing their charge state
 Increased charge on aerosols can lead to increased lung deposition
Attaches to pollutant
aerosol (10-100 s)
High E-field ionises the air
Charge
separation
and ion
emission
Initial
‘bare’ ion
+
+
+
Forms cluster
of molecules
(~100 ns)
When inhaled, electrically
charged aerosols could have a
higher probability of depositing in
the lung
Selected environmental exposures:
possible attributable fractions childhood leukaemia risk
Agent
Infections etc
Natural
Background
ionising radiation
Light-at-night
Magnetic fields
Air pollution
Attributable
fraction
Comment
This conference
This conference
34%:
20% low LET
14% high LET
Overall: essentially undetectable
epidemiologically
?
Not researched
~11%
Overall
(Using linear no-threshold model)
30 - 80%
By birth address (1st hit: in utero?)
Acknowledgements
Team members:
Websites:
Julie Close
Matthew Wright
James Matthews
Alison Buckley
Andrea Lazenby
Supported by
www.electric-fields.bris.ac.uk/presentations.html
www.electric-fields.bris.ac.uk
Dose response for light
Zeitzer et al. J Physiol (2000) 526, 695-702
Childhood leukaemia near nuclear installations
 UK: Sellafield – ‘Black Report’ (NRPB-R171; 1984)
 Germany: Childhood leukaemia and all malignancies near nuclear power plants
(Kaatsch et al Int J Cancer 1220: 721-, 2008; Spix et al Eur J Cancer 44: 275-284; 2008)
The problem is one of dose levels:
Natural a-activity in children’s teeth: 5 – 20 Bq kg-1
Plutonium in children’s teeth: ~mBq kg-1
(O’Donnell et al Sci Tot Environ 201; 235-, 1997)
a-activity in upper right 4 tooth from a 13-year-old boy:
outer enamel 210Pb-supported 210Po; circumpulpal 226Ra.
The incidence of childhood leukaemia is believed to have
shown a real increase last century
(Shah & Coleman BJC 2007; 1 - 4)
Properties of melatonin
 Unlike vitamins C & E,
melatonin enters cells and can
act directly on DNA
 By a scavenging cascade – one
melatonin molecule can
scavenge up to 10 ROS/RNS
(Tan et al J Pineal Res. 42; 28-42, 2006)
Knox - conclusions
 The associations with 1,3-butadiene, dioxins and
benzo[a]pyrene are sufficiently specific to conclude that they are
probably the truly active agents
 Assessment of the size of the effects suggests that up to 80% of
childhood leukaemia and cancer could be linked to vehicle
related air pollution in the UK at the in utero/early infancy stage
Papers by George Knox 2005 & 6
(birth and death addresses of fatal child cancers in GB between 1966-80)
 Knox 2005a (J Epidemiol Comm Health, 59, 101-105)
- Childhood cancer associated with hotspots for carbon monoxide, PM10 particles,
VOCs, nitrogen oxides, benzene, dioxins, 1,3-butadiene and benzo[a]pyrene
 Knox 2005b (J Epidemiol Comm Health, 59, 755-760)
- Childhood cancer associated with short distances of bus stations, hospitals,
railways, oil installations and industrial transport centres: 1,3-butadiene
especially implicated
 Knox 2006 (J Epidemiol Comm Health, 60, 136-141)
- Childhood cancer associated with short distances of bus stations, railway stations,
railways, A,B class roads: again 1,3-butadiene especially implicated