Robotic Lawn Mower: A New Source for Domestic Magnetic Field Exposure

A robotic lawn mower can be found today in many village gardens, and the sales of these robots are many times higher than that of traditional mowers. However, the robot requires a set of electric boundary wires defining the lawn area to be mowed, and also providing a pulsed magnetic field to be sensed by the robot electronics. This is a new source for domestic environmental magnetic field exposure. We discuss it in this article.

People moving around on the lawn are more or less constantly exposed to a pulsed magnetic field. We have measured the magnetic field from the boundary wires of two different common brands of lawn mowers. In both cases, we found pulsed magnetic field “packages” in the ELF range that pulse frequencies around some tens of kHz. This “household” source of environmental exposure to the magnetic field has not been discussed from a health perspective point of view.

Example of the pulsed field from one lawn mower (B) is given here.

The maximum magnetic field strength recorded for lawn mower A with the probe on the ground close to the cable, positioned to get a maximum reading, was Hrms = 0.17 A/m.

For lawn mower B, the rms values were lower, and a maximum reading with the probe on the ground next to the boundary wire gave Hrms = 20 mA/m. Here, the general level was around Hrms = 10 mA/m. The maximum peak value in the pulses on the ground was around 0.5 A/m.

The peak value exposure is not so far off the values (equals 0.2–0.4 μT, i.e. about 0.2–0.3 A/m) that led IARC in 2001 to classify low‐frequency magnetic field as a class IIB, i.e. “possibly carcinogenic” to humans.

It would be pertinent to point out that many organisms, such as earthworms, snails, and other animals, are sensitive to EMFs in different frequency regions (both DC and AC). We are not aware of any studies relating lawn mower electronic signals to the reactions of these animals, e.g. snail passages above a sling. This is also the case for plant growth and movements, which are sensitive to low‐intensity magnetic fields .

Some advice is to make sure when buying a new machine that the system turns off the pulsed current when the machine is loading the battery. Do turn off the system when children are playing on the lawn, and especially when there is a baby sleeping in a baby carriage placed on the lawn. Do not run the machine at night since with the boundary wire just outside the house, you may have exposure in your bed of up to some tens of mA/m.


Case-control study on occupational exposure to extremely low-frequency electromagnetic fields and glioma risk

Exposure to extremely low-frequency electromagnetic fields (ELF-EMF) was in 2002 classified as a possible human carcinogen, Group 2B, by the International Agency for Research on Cancer (IARC) at WHO. In the international Interphone study on mobile phone use and glioma risk, glioma was associated with occupational ELF-EMF exposure in recent time windows. The authors concluded that such exposure may play a role in late stage carcinogenesis of glioma.

We assessed life time occupations in case-control studies during 1997-2003 and 2007-2009 on e.g. use of wireless phones and glioma risk. An ELF-EMF Job-Exposure Matrix was used for associating occupations with ELF exposure (μT). Cumulative exposure (μT-years), average exposure (μT), and maximum exposed job (μT) were calculated.

Cumulative exposure gave for astrocytoma grade IV (glioblastoma multiforme) in the time window 1-14 years before diagnosis odds ratio (OR) = 1.9, 95% confidence interval (CI) = 1.4-2.6, p linear trend <0.001, and in the time window 15+ years OR = 0.9, 95% CI = 0.6-1.3, p linear trend = 0.44 in the highest exposure categories 2.75+ and 6.59+ μT-years, respectively.

We concluded that we found an increased risk in late stage (promotion/progression) of astrocytoma grade IV for occupational ELF-EMF exposure. No statistically significant interaction was found between exposure to ELF-EMF and use of wireless phones (exposure to radiofrequency radiation; RF-EMF). They were independent risk factors for astrocytoma grade IV.