The contamination of soil, food and water is given in Becquerel/sq.metre or Becquerel/Kg or litre.
Becquerel (Bq) means one disintegration per second.
A measure of the biological damage to living tissue as a result of radiation exposure. Also known as the " biological dose," the dose equivalent is calculated as the product of absorbed dose in tissue multiplied by a quality factor and then sometimes multiplied by other necessary modifying factors at the location of interest.
The dose equivalent, measured in sievert, defined as the dose of absorbed radiation that has the same biological effect as a dose of one joule of gamma rays absorbed in one kilogram of tissue. In the United States the roentgen equivalent man (rem), equal to 0.01 sievert, is still in common use, although regulatory and advisory bodies are encouraging transition to sieverts
Conversion Becquerel/Sievert and Sievert/Becquerel
1 Bq = 0,0125 microsievert
1 microsievert = 80 Beq
Eating an amount of food with 80.000 Becquerel Caesium 137 is equivalent to approximately one millisievert.
Eating 200 g mushrooms contaminated with 4.000 Becquerel Caesium 137/Kg s equivalent to 0,01 Millisievert.
The radiation exposure considers how long the exposure took place. It is given in Millisievert/year.
Example; The natural radiation exposure in Germany is 2,1 Millisievert/year (0,24 Microsievert/hour) another 2Millisievert are added as artificial radiation (mainly medical devices)
Radiation limits for food
Food radiation should not exceed 500 Becquerel/Kg.
Baby food radiation should not exceed 400 Becquerel/Kg for Caesium and 100 Becquerel for iodine.
 Nuclear Regulatory Commission. "NRC Regulations: §34.3 Definitions". United States Government.