The fist and most important one is the electric field. This is measured in Volts per Meter. Everything that is connected to the grid, emmits a Voltage. Electric Fields are know to be very bad for the health (source)
The 2nd are the magnetic fields. Everything that uses energy emits a magnetic field. In office environments these fields are not the biggest problem, but it could be... depending on the location of your desk. If you sit next to an elevator shaft for example (or something that uses a lot of power) you could be electro polluted very strongly.
Then there are the microwaves, coming from cell phones and wifi (and more). Many Scientists warn that these fields are bad for the health. It is best to reduce them as much as possible.
What is also important to take into consideration is that most offices have high levels of Dirty Electricity. According to scientist Sam Milham, Dirty Electricity is the most dangerous and carcinogenic form of EMF Pollution, allthough it is hard to say this since it also depends on the levels and compared to the levels of the other fields.
Looking at a screen for a long time is also not good for the eyes, because of the blue light.
Lightning such as LED and CFL are also possible disturbands, since they could create light noise.
If you want to know more, schedule a meeting for an online intake