Cadmium pollution may cause

Choose the incorrect sentence regarding an electrostatic precipitator.

If the concentration of $DDT$ in water is $0.003\, ppm$,what could be its concentration in small fish due to biomagnification (in $, ppm$)?

Consider the following statements:
$I.$ Algal blooms are formed by free-floating algae.
$II.$ Algal blooms cause fish mortality and deterioration of water quality.
$III.$ Water hyacinth, the world's most problematic aquatic weed, is also called 'Terror of Bengal'.
Which of the statements given above are correct about algal blooms?

$3, 4-$ benzopyrene causes:

Black foot disease is caused by the toxicity of which of the following?