There is a LOT of garbage in orbit. Apparently over 4 million pounds of trash bigger than one centimeter and an unknown but much larger quantity of smaller stuff. Estimates are over 330 million bits larger than one mm.
Note: Free use image from Wikimedia Commons.
The soviets were the worst offenders. Their nuclear powered radar satellites (RORSAT series) were a major contributor. At least sixteen of these leaked huge numbers of radioactive sodium-potassium droplets up to several centimeters in size from the reactor cooling systems. There are estimated to be over 115,000 of these frozen droplets alone at about the orbit of Hubble.
What really has some people worried is that we may be approaching a critical mass where collisions begin a chain reaction that could make LEO off limits for a long time.