An advantage or advantages to using hair for toxicology studies is that

Drug abuse in the workplace puts employers at risk for higher insurance costs, increased accidents, more absenteeism and lower productivity. Hair testing is one method that helps mitigate these risks by screening out applicants and employees who use drugs.

air quality

poor drinking water

and heavy polution

can lead to poor health

indicate valleys, hills, steepness and gentleness of slopes.

explanation:

contour lines on a map indicate elevation, or depth. numeric notations on contour lines refer to the level of elevation, or height about sea level.