accident

bubble

catastrophe

chemical

chemistry

city

concepts

conservation

dam

danger

death

dirty

disaster

discharge

dump

ecology

environment

factory

filters

future

garbage

green

industry

lake

law

life

nature

pipes

poisonous

pollution

poverty

problems

river

scum

sewage

slimy

slum

stream

substance

the

toxins

unhygienic

unpleasant

violation

violet

waste

water

wildlife