Let's see: mass of Earth 6e27kg. Assume change in kilogram standard is due to change in mass of Earth (which it isn't). 50ug in 1kg = 50e-9 times. So Earth must have increased by 3e20kg. Surface area of Earth is 5e14 square metres, so each square metre of Earth has gained 600000kg in 118 years, or about 5 tonnes/ square metre/ year, or a bit over a pound per hour for you anti-SI brigade.

I haven't noticed anywhere near an ounce of meteorite falling on me in the last 5 minutes.

A few grams in several years is more like it.