Can environmental exposures cause ADHD?

There is some evidence that various environmental exposures can cause problems with behavior and attention similar to those seen in children with ADHD. However, there is little evidence that environmental exposures clearly cause ADHD. The relationship between each environmental exposure (lead, environmental tobacco smoke [a.k.a. second-hand smoke], PCBs, and mercury) and ADHD will be discussed separately below.

Lead:
Lead is a heavy metal widely distributed on the earth’s surface. To learn more about lead, click here.

Several individual case studies suggest that lead exposure may be linked with ADHD. [2-3] Keep in mind that this type of information does not clearly show that lead exposure causes ADHD.

Many human studies demonstrate that children with elevated lead levels have problems with behavior, impulsivity, and concentration. [4-9] This may suggest a possible link between lead exposure and ADHD, but does not clearly indicate that lead exposure causes ADHD.

Environmental Tobacco Smoke (ETS):
ETS is also known as second-hand smoke. Any time someone smokes indoors, ETS is produced. To learn more about ETS, click here.

One study suggests that mothers who smoke during pregnancy have an increased risk of having children with ADHD. [10]

Several human studies show that children of smoking parents have increased behavioral problems. [12-15] This may suggest a possible link between ETS exposure and ADHD, but does not show that ETS causes ADHD.

PCBs:
PCBs, or polychlorinated biphenyls, are members of a chemical family that were widely used in the past in industry as lubricants, coatings, and insulation materials for electrical equipment like transformers and capacitors. To learn more about PCBs, click here.

Some human studies suggest that children exposed to high levels of PCBs while in the womb are more likely to have problems with behavior and attention. [16-18] However, this does not show that PCBs cause ADHD.

Several human studies also suggest that lower levels of PCBs may be linked with disorders of behavior and attention. [19-20] However, not all studies support this association. [21]

Also, several animal studies suggest that PCB are linked with problems in behavior and attention. [22-26]

Mercury:,br> Mercury is an element that is naturally found on the surface of the earth. Three basic types of mercury can be found in the environment: elemental mercury, mercury salts, and organic mercury compounds. To learn more about mercury, click here.

Several human studies suggest that children exposed to methylmercury have an increased risk of behavioral problems. [27-29] However, this finding is controversial. Not all studies support this association. [30-32]