As the curve shows the quantity of the chemical's concentration in the air which people usually can be input to the body.That may cause adverse effects, even if they have been in less quantities.
A curve that shows the concentration of chemicals in the air, regular people can get into the body , which may cause adverse effects, although it has been reduced to a minimum.
A curve that shows the concentration of chemicals in the air, which ordinary people can get into the body, which may cause adverse effects, although will be small quantities.