What is the full form of $BOD$?

Brewery and sugar factory waste alters the quality of a water body by increasing

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.

Noise is:

Spraying $DDT$ on crops causes pollution of .......

$BOD$ is a standard measure used for the quantitative expression of which of the following?