The Terms polluted and contaminated Have Different Meanings When It

The terms polluted and contaminated have different meanings when it comes to substances put in the environment by human activity. With respect to these substances, what does polluted mean?

A) concentration is high enough to cause harm to living organisms.
B) concentration is above natural levels, but not harmful to living organisms.
C) concentration is above natural levels, but harmful only to humans.
D) concentration is below natural levels and unlikely to harm humans.
E) concentration is simply above the detection limit of modern instruments.