Martian Material on Earth
The estimate “up to 500 kg of Martian material per year” has a scientific origin, but it is a model estimate, not a yearly weighed total of recovered Martian meteorites. A 2001 Lunar and Planetary Science Conference paper gives an estimate of about 500 kg of Martian rocks reaching Earth per year, based on models of meteorite transfer between planets.
It is important to distinguish total material reaching Earth from large meteorites that survive atmospheric entry and can be recovered. The known collection of Martian meteorites has a combined mass of only about 211 kg, accumulated over the entire history of finds, not per year. The precise estimate depends on particle sizes and delivery models.