Student or Learner
He said the iodine will quickly lose its radioactivity but that the cesium can build up over time in fish.
The above sentence was quoted from VOA.
Could you tell me what does " build up over time in fish " mean?
From Tien-sung ( Taiwan )
Some organisms, such as fish, will retain more and more of a substance instead of processing it through. It will build up over time.
This may be too technical, but see this: Bioaccumulation | Define Bioaccumulation at Dictionary.com
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.