Answer: Option A
Explanation:
A cesium's half life is relatively long( 30 years) which is quite a long period. This element can enter the food chain of the marine ecosystem and can lead to biomagnification.
Bio magnification can be defined as the phenomenon in which there is an increases in the toxic concentration as we move up in the food chain.
Cesium can enter into plankton and form there the concentration of cesium will increase as we will move towards the upper side of the food chain.