Which of the following refers to the increase in the concentration of a toxicant at successive trophic levels?

Where are Ecosan toilets used?

Consider the following reasons for the massive fish mortality observed in a lake near a village within a few days:
$(1)$ Excessive use of urea and phosphate fertilizers in nearby crops.
$(2)$ Spraying of $DDT$ using aircraft.
$(3)$ The lake water turned green and foul-smelling.
$(4)$ Initial decrease in phytoplankton in the lake leads to a maximum decrease in photosynthesis.
Which of the above reasons are responsible for the massive fish mortality?

What happens when sewage is discharged into a river?

Which of the following is a degradable pollutant?

Which one of the following is a non-renewable exhaustible natural resource?