Milk, water and air radioactivity measurment limits differences question

The BRAWN Team,

I have a question about your measurements of Cs134 and CS 137 in air, milk and water. It seems that the level of radioactivity Bq/L of the Cs134 and CS137 is ~400,000 times larger in the milk (and water) and in the air. The milk and water were more radioactive than the air by that amount according to your graphs. Why is your detection limit in milk and water so different (by the same factor of ~400,000) to the air? Thanks.

Steve Smith