California power lines study

Following the findings of the CCRG epidemiological studies into childhood cancer and proximity to power lines in the UK, various studies were set up to see if the same unexpected effects - elevated leukaemia rates at distances out to 600 m, and, subsequently, the finding that the risk declined from the 1960s to the present - could be replicated in other countries.  One of these was the French Geocap study.  The largest, however, was in California.  That has now (2016) published its results for distance (the results from calculated magnetic field are coming in a separate paper).  A summary of the results is given in the following graph from the paper:

graph of results of california study

There is a raised risk for leukaemia in the 0-50 m band but not statistically significant, and, looking at the whole of the results, it would be hard to claim that much weight should attach to it.  The CCRG finding of consistently increased risks out to 600 m is clearly not replicated.  The paper concludes:

Our findings did not clearly support an increased childhood leukaemia risk associated with close proximity (<50 m) to higher voltage lines, but could be consistent with a small increased risk. Reports of increased risk for distances beyond 50 m were not replicated.

These are the results for power lines >200 kV.  Results for 100 kV and 60 kV show even less suggestion of any risks.

Does this contradict the CCRG findings?

Well, it certainly doesn't support the CCRG findings, and neither did the French Geocap study.  But this study covers 1986-2008, and Geocap covered the even later period 2002-2007.  These are periods when CCRG results (see graph below) also found no, or much reduced, risks in the UK:

graph of CCRG follow on results

So neither Geocap nor this California study lend direct support to the CCRG findings - but neither do they actually contradict the CCRG.

The results for magnetic fields

In September 2017, the authors published their results for calculated magnetic fields.  Not surprisingly, given that they found a modest elevation in risk for the closest distances, they also found a modest elevation in risk for the highest fields: the relative risk for >0.4 μT compared to <0.1 μT is 1.52 (95% confidence interval 0.71, 3.25).  This would probably be viewed as an intemediate result - it is elevated, but it's not statistically significant and not as much elevated at the relative risk of 2 that was broadly found in the various pooled analyses.

The authors' own summary is:

Our large, statewide, record-based case–control study of childhood leukemia in California does not in itself provide clear evidence of risk associated with greater exposure to magnetic fields from power lines, but could be viewed as consistent with previous findings of increased risk.

 

The abstracts of the papers

The distance results paper:

Br J Cancer. 2016 May 24. doi: 10.1038/bjc.2016.142. [Epub ahead of print]

Childhood leukaemia and distance from power lines in California: a population-based case-control study.

Crespi CM, Vergara XP, Hooper C, Oksuzyan S, Wu S, Cockburn M, Kheifets L.

BACKGROUND:

Studies have reported an increased risk of childhood leukaemia associated with living near high-voltage electric power transmission lines that extend to distances at which magnetic fields from lines are negligible. We conducted a large records-based case-control study of childhood leukaemia risk in the population living near power lines in California.

METHODS:

The study included 5788 childhood leukaemia and 3308 central nervous system (CNS) cancer cases (for comparison) born in and diagnosed in California (1986-2008), and matched to population-based controls by age and sex. We geocoded birth address and estimated the distance from residence to transmission lines using geographic information systems, aerial imagery, and, for some residences, site visits.

RESULTS:

For leukaemia, there was a slight excess of cases within 50 m of a transmission line over 200 kV (odds ratio 1.4, 95% confidence interval 0.7-2.7). There was no evidence of increased risk for distances beyond 50 m, for lower-voltage lines, or for CNS cancers.

CONCLUSIONS:

Our findings did not clearly support an increased childhood leukaemia risk associated with close proximity (<50 m) to higher voltage lines, but could be consistent with a small increased risk. Reports of increased risk for distances beyond 50 m were not replicated.

The magnetic fields results paper:

Residential magnetic fields exposure and childhood leukemia: a population-based case–control study in California
Leeka Kheifets, Catherine M. Crespi, Chris Hooper, Myles Cockburn, Aryana T. Amoon, Ximena P. Vergara

 

 
Purpose
Studies have reported an increased risk of childhood leukemia associated with exposure to magnetic fields. We conducted a large records-based case–control study of childhood leukemia risk and exposure to magnetic fields from power lines in California.
Methods
The study included 5,788 childhood leukemia cases (born in and diagnosed in California 1986–2008) matched to population-based controls on age and sex. We calculated magnetic fields at birth addresses using geographic information systems, aerial imagery, historical
information on load and phasing, and site visits.
Results
Based on unconditional logistic regression controlling for age, sex, race/ethnicity, and socioeconomic status using subjects geocoded to a basic standard of accuracy, we report a slight risk deficit in two intermediate exposure groups and a small excess risk in the highest
exposure group (odds ratio of 1.50 (95% confidence interval [0.70, 3.23])). Subgroup and sensitivity analyses as well as matched analyses gave similar results. All estimates
had wide confidence intervals.
Conclusion
Our large, statewide, record-based case–control study of childhood leukemia in California does not in itself provide clear evidence of risk associated with greater exposure to magnetic fields from power lines, but could be viewed as consistent with previous findings of increased risk.

 

The methods papers:

J Expo Sci Environ Epidemiol. 2015 Jan;25(1):45-52. Sep 18.

Epidemiologic study of residential proximity to transmission lines and childhood cancer in California: description of design, epidemiologic methods and study population.

Kheifets L, Crespi CM, Hooper C, Oksuzyan S, Cockburn M, Ly T, Mezei G.
 

We conducted a large epidemiologic case-control study in California to examine the association between childhood cancer risk and distance from the home address at birth to the nearest high-voltage overhead transmission line as a replication of the study of Draper et al. in the United Kingdom. We present a detailed description of the study design, methods of case ascertainment, control selection, exposure assessment and data analysis plan. A total of 5788 childhood leukemia cases and 3308 childhood central nervous system cancer cases (included for comparison) and matched controls were available for analysis. Birth and diagnosis addresses of cases and birth addresses of controls were geocoded. Distance from the home to nearby overhead transmission lines was ascertained on the basis of the electric power companies' geographic information system (GIS) databases, additional Google Earth aerial evaluation and site visits to selected residences. We evaluated distances to power lines up to 2000 m and included consideration of lower voltages (60-69 kV). Distance measures based on GIS and Google Earth evaluation showed close agreement (Pearson correlation >0.99). Our three-tiered approach to exposure assessment allowed us to achieve high specificity, which is crucial for studies of rare diseases with low exposure prevalence.

Environ Res. 2015 Jul;140:514-23.

Estimating magnetic fields of homes near transmission lines in the California Power Line Study.

Vergara XP, Kavet R, Crespi CM, Hooper C, Silva JM, Kheifets L.

The California Power Line Study is a case-control study investigating the relation between residences near transmission lines and risk of childhood leukemia. It includes 5788 childhood leukemia cases and 5788 matched primary controls born between 1986 and 2007. We describe the methodology for estimating magnetic fields at study residences as well as for characterizing sources of uncertainty in these estimates. Birth residences of study subjects were geocoded and their distances to transmission lines were ascertained. 302 residences were deemed sufficiently close to transmission lines to have non-zero magnetic fields attributable to the lines. These residences were visited and detailed data, describing the physical configuration and dimensions of the lines contributing to the magnetic field at the residence, were collected. Phasing, loading, and directional load flow data for years of birth and diagnosis for each subject as well as for the day of site visit were obtained from utilities when available; when yearly average load for a particular year was not available, extrapolated values based on expert knowledge and prediction models were obtained. These data were used to estimate the magnetic fields at the center, closest and farthest point of each residence. We found good correlation between calculated fields and spot measurements of fields taken on site during visits. Our modeling strategies yielded similar calculated field estimates, and they were in high agreement with utility extrapolations. Phasing was known for over 90% of the lines. Important sources of uncertainty included a lack of information on the precise location of residences located within apartment buildings or other complexes. Our findings suggest that we were able to achieve high specificity in exposure assessment, which is essential for examining the association between distance to or magnetic fields from power lines and childhood leukemia risk.

See also:

Other epidemiological studies of childhood cancer and power lines: