Human activities are the basic cause for it.
Causes – 4 major causes (The evil Quartet along with suitable examples of each:
i) Habitat loss and fragmentation-decline in covered forest area from 14% to 6%.
ii) Overexploitation- extinction of steller’s sea cow
iii) Alien species invasion-Nile perch introduction into Lake Victoria resulted in extinction of 200 species cichlid fish.
iv) Co-extinction-coevolved plant pollinator mutualism.
Harms: (a) Decline in plant production
b) Lowered resistance to Env. Perturbations like drought.
c) Increased variability in certain ecosystem processes such as plant productivity, water use etc.

Biomagnification or biological magnification.

Flocs are the masses of bacteria associated with fungal filaments to form mesh-like structure. 

Sewage is treated in sewage treatment plants to remove pollutants and retrieving clean water for its reuse again. This treatment is carried in two stages.
1. Primary treatment: It is a physical process of removal of small and large particles through filtration and sedimentation.
2. Secondary treatment. It is a biological process that employs bacteria. The activated sludge after primary treatment is pumped into a large tank called anaerobic sludge digester where anaerobic bacteria act on the organic matter in anaerobic conditions to produce the mixture of gasses(biogas). The latter can be used as the source of energy as it is inflammable.

An electrostatic precipitator is a device to remove particulate matter present in the foul air. In situations when it stops functioning in a thermal power plant, it may lead to breathing and respiratory problems, irritation in the throat, inflammation, and damage to lungs in people working in it or living around.