For anyone who flies into Shanghai Pudong International Airport, it鈥檚 a rite-of-passage to take the Maglev -- short for magnetic levitation -- train into the city. The railway is as much a tourist attraction as it is a transportation system.
I was on board the train this summer, gleefully watching the speed climb to over 300 km/hour, when I overheard the woman beside me ask if the magnetic field emissions posed a health risk.
This discussion echoes familiar debates about phones, Wi-Fi, and microwaves -- all devices that emit (EMF). Maglev trains mostly emit EMF, while the former devices emit higher-frequency fields. But both are forms of , meaning they lack the energy to directly damage DNA or cells.
What is so compelling about magnetism?
arises when the motion of electrically charged particles produces magnetic fields. Every magnet has two poles -- north and south -- determined by magnetic field direction. When two magnets meet, opposite poles (e.g. north and south) experience a force of attraction, while like poles (e.g. north and north) repel. Maglev trains leverage these magnetic forces.
Maglev stands for magnetic levitation
The two major components of Maglev motion are suspension and propulsion, which refer to how the train levitates and advances forward, respectively.
For suspension, there are : German versus Japanese technology. The German design uses attractive forces to pull up the train by its hanging arms, while the Japanese design uses repulsive forces to push up the body of the train. This is a high-level comparison of intricate technologies, but in both cases, the magnetic force must be greater than the gravitational force weighing down the train.
Propulsion is achieved using a , which extends along the entire track. It鈥檚 similar to a conventional rotary motor that鈥檚 been unrolled into a straight line. Coils embedded in the guideway change polarity in sequence to create a traveling magnetic field; the field simultaneously attracts the train forward and repels it from behind to produce linear motion.
By removing contact friction altogether, Maglev trains can reach incredible speeds -- China claims it has achieved . Materials undergo marginal wear and tear, and without fuel, little pollution is produced. Maglev technology is also inherently safe. Historically, there has been , and it was attributed to human error.
But this technology is pricey. Shanghai鈥檚 Maglev launched operations in 2004, and cost approximately . Few countries can finance projects of this scale, hence there are only commercial Maglev systems worldwide.
Are magnetic fields harmful?
Watching the train glide into the station feels like a futuristic sci-fi scene. It鈥檚 understandable that feelings of awe may coincide with some anxiety: can the magnitude of magnetism involved affect physiological functions?
Many have investigated potential links between low frequency magnetic fields (LF-MF) and childhood leukemia, but the evidence to establish a causal relationship. Animal studies mostly show LF-MF aren鈥檛 dangerous to mammals. A showed that LF-MF increased the odds of developing leukemia in mice, but not in rats. As for humans, this data is lackluster.
Evaluating the safety of Maglev EMF exposure is constrained by a limited evidence base. The most effective method to assess risk is through large-scale randomized studies, but long-term random assignment to different transportation modes is neither ethical nor practically feasible. The next best thing is a retrospective observational study: collecting ridership data as it naturally occurs. But given high costs and scarcity of Maglev systems, existing observational evidence remains incomplete.
A published in BMJ Occupational & Environmental Medicine studied Maglev employees and compared them to a control group without any Maglev EMF exposure. They found Maglev employees had statistically significant differences in lipid metabolism and cognition. There was no difference in blood cell counts, thyroid function, or melatonin levels. These results, though, should be taken with a healthy degree of skepticism. For one, the sample size was 48, which is much too small to draw decisive conclusions. Neural symptoms were assessed using a self-administered questionnaire, which is a weak methodology prone to recall bias. Most critically, this was an abstract, not a full-length publication, meaning the study never underwent rigorous peer review.
Other have measured or modeled Maglev EMF emission levels and compared them to international guidelines established by the International Commission on Non-Ionizing Radiation Protection (ICNIRP). Consistently, emissions remain below the threshold. The recorded magnetic flux density of Maglev trains ranges from effectively , depending on the location of measurement. The ICNIRP sets safety thresholds at for the general public, and for occupational exposure at the frequencies commonly used by Maglev systems. These limits are based on comprehensive reviews of published research. After identifying the lowest level at which harm could occur, they apply additional safety factors to account for scientific uncertainty.
There are additional about magnetic fields interfering with the medical devices of passengers, like pacemakers, but have generally shown programming changes for such devices are unlikely. states passengers with pacemakers can safely ride their Maglev, but they don鈥檛 include any citations. If you鈥檙e in this situation, it鈥檚 always best to speak with a provider beforehand.
Back to earth
A seven-minute airport ride on the Maglev poses no health risk. But the larger implications are socioeconomic. Risk is a function of exposure -- tourists aren鈥檛 the at-risk group. The populations to monitor are those with chronic exposure: engineers, maintenance staff, nearby residents. For these groups, more research is needed on the long-term effects of magnetic fields produced by Maglev systems.
In fact, magnetic levitation is more likely to detect cancer than cause it. Maglev technology is now being applied to : researchers can separate the components of biological samples according to density, allowing cells and proteins implicated in disease to be isolated and studied. This technology is rapid and inexpensive -- magnetism is just magnetic.
Haleh Cohn graduated with a BSc in Anatomy & Cell Biology and Economics minor at 涩里番.
