Attention deficit hyperactivity disorder ( ADHD ) appears to be on the rise in the United States , and in the search for explanations researchers have begun to scrutinize fetal exposure to a wide range of toxins , including lead , tobacco , pesticides , and chemicals such as PCBs . ADHD symptoms were noted when the children were 5 years old . This research shows associations , not cause - and - effect . Fish consumption is not independently linked to the symptoms . However , salmon and tuna are more likely to contain high levels of mercury .
ADHD symptoms were noted when the children were 5 years old . This research shows associations , not cause - and - effect . Fish consumption is not independently linked to the symptoms . However , salmon and tuna are more likely to contain high levels of mercury .