What term is given to the phenomenon where a harmful chemical enters a food chain and starts accumulating?

The increase in the concentration of harmful chemicals (pesticides) in the body of a living organism at each trophic level of a food chain is called biological magnification. Its level will increase as we move from bottom to top of a food chain. For example, when pesticides are sprayed they enter the food chain through producers while they are absorbing nutrients from the soil. Since herbivores eat many types of plants, therefore their body will accumulate more amounts of pesticides. Similarly, carnivores will feed on more than one herbivore; hence it will have much more amount of pesticide in it.