Observe the figure and answer the following questions.
$(i.)$ What ecological term is used to describe the $DDT$ accumulation at different trophic levels?
$(ii.)$ List any one effect of $DDT$ accumulation on birds.
$(iii.)$ Will $DDT$ accumulation lead to eutrophication?
$(iv.)$ Does it affect the $BOD$?
$(v.)$ Name a disease caused by the accumulation of any heavy metal.

(N/A) $(i)$ Biomagnification.
$(ii)$ High concentrations of $DDT$ disturb calcium metabolism in birds,which causes thinning of the eggshell and their premature breaking,eventually causing a decline in bird populations.
$(iii)$ No,$DDT$ accumulation does not directly lead to eutrophication. Eutrophication is primarily caused by nutrient enrichment (nitrogen and phosphorus) in water bodies.
$(iv)$ No,$DDT$ accumulation does not directly affect the $BOD$ (Biochemical Oxygen Demand). $BOD$ is a measure of organic matter pollution.
$(v)$ Diseases caused by heavy metal accumulation include:
$(1)$ Minamata disease: Caused by mercury $(Hg)$ poisoning.
$(2)$ Itai-itai disease: Caused by cadmium $(Cd)$ poisoning.
$(3)$ Black foot disease: Caused by arsenic $(As)$ poisoning.