A walk through some measurement systems:
A metric ton (tonne) is about 2200 lbs. It is 1000 kilograms, and therefore 1 million grams. Love the metric system, as it makes things so easy.
If you have aggregate that tests 10 ppm, then there are 10 grams per ton. Not bad.
Cheers
EDIT, GMS posted his just as I did mine...