$A$: Ecological sanitation is a sustainable system for handling human excreta.
$R$: It is a practical and hygienic method of using dry composting toilets.

Which of the following statement$(s)$ is/are not correct regarding biomagnification?
$I.$ Heavy metals and persistent pesticides pass into the food chain and increase in amount per unit weight of organisms with the rise in trophic level due to their accumulation in fat.
$II.$ Accumulation of zinc can cause thinning of eggshells in birds.
$III.$ $DDT$ accumulation is a major cause of the killing of fish-eating birds.
$IV.$ Biomagnification occurs only in marine food chains.

More than $70\%$ of the world's freshwater is contained in $............$.

If an agricultural field is liberally irrigated for a prolonged period of time,it is likely to face the problem of:

Which of the following statements is correct?

$A$ pollutant is an agent which causes change in