2. (n.) [U] - a process of making water, air, soil, etc. dirty. - POLLUTION
3. (n.) [U; C] - when sb or sth becomes impossible to see or find.-DISAPPEARANCE
4. (n) [C] - a person who carefully studies the topic to find new facts or information. - RESEARCHER
5. (n.) [U] - the process of something being made worse. - DEGRADATION
6. (n.) [U] - the state of being safe and protected from danger. - SAFETY
7. (n.) [C; U] - a rise in the number.-INCREASE
8. (n.) [U] - physical harm to something that makes it less attractive or useful. - DAMAGE