The increase in concentration of the toxicant at successive trophic levels is referred to as :

The correct answer is (4) biomagnification. Biomagnification is the process by which the concentration of a toxicant or pollutant increases at successive trophic levels in a food chain. As organisms at lower
trophic levels consume contaminated food or water, they accumulate the toxic substances in their tissues. When organisms at higher trophic levels consume these contaminated organisms, they ingest a larger amount of the toxicant, leading to an increase in concentration.
(1) Eutrophication refers to the excessive nutrient enrichment of a body of water, typically due to the runoff of agricultural fertilisers or sewage. 
(2) Bioremediation is the use of living organisms or their products to degrade or remove contaminants from polluted environments.
(3) Biotransformation is the process by which organisms, typically through enzymatic reactions, convert one
chemical compound into another.