How do scientists monitor populations for signs of pollution?

Scientists monitor populations for signs of pollution relating to the individual categories of pollution, the six types of pollution. For thermal pollution, the scientists test to see the temperature of the water. For noise pollution, they may test to see how high the decibel level of the sound is. For land pollution they will test the soil to see if there is any contaminants and they test to see the permeability of the soil. For light pollution they will use special cameras to test the quality of the night sky. For visual pollution, a bill was passed to regulate the visual pollution around a highway. For air pollution, they have air monitoring stations that are maintained.