Particulate pollutants from smoke chimneys can be removed by which of the following?

Differentiate between biodegradable pollutants and non-biodegradable pollutants.

Increased concentration of $DDT$ affects birds by:

$A$ - Micro-organisms involved in the biodegradation of organic matter in the receiving water body consume a lot of oxygen,and as a result,there is a sharp decline in dissolved oxygen in the stream from the point of sewage discharge.
$R$ - $BOD$ decreases when the dissolved oxygen amount decreases in water.

The pollutants which are already present in nature,but are released in substantial amounts by man are known as

$DDT$ was first synthesized by