Mental Illness and Toxicity
700 billions pounds of over 650 different chemicals are released into the air and water each year. The real question to ask is not if you are toxic. We all are. The real question is how toxic are we and to what degree is it interfering in our health. 
This page goes over some of the more common toxins that produce mental symptoms.
Heavy metal toxins
Lead affects the whole body, and especially the central nervous system. Cognitive dysfunction, neurobehavioral disorders and neurological damage are associated with lead.
Symptoms in children with high lead levels have hyperactivity, anorexia, decreased play activity, low intelligence and poor school performance. Even in children with no obvious signs of lead exposure, bone lead content was found related to fatigue, concentration, short-term memory, insomnia, anxiety, irritability, reduced performance on visual intelligence and visual-motor coordination tests. Learning disabilities have been significantly correlated with teacher rated learning disabilities.
Mental affects of mercury include: excessive irritability, excitability or sensitivity to stimulation, depression, short term memory loss, difficulty concentrating, insomnia and fatigue. Additional signs of toxicity include loss of vision, hyperreflexia, sensory disturbances, impairment of speech, hearing, and muscular rigidity.
Parkinson's disease, Alzheimer's and multiple sclerosis have all been associated with aluminum exposure. Studies have also shown that aluminum causes apoptosis (cells kill themselves).
Exposure to arsenic (such as from drinking water) can lead to gastroenteritis, cancer, diabetes, neurological and vascular dysfunction. 
Testing options for heavy metals
The body will not keep metals in the blood for long before storing them away in tissue. Therefore serum tests for metals such as lead and mercury are not useful in determining long term toxic load. Occasionally these tests may reveal a recent exposure, but they should not be used to rule out the possibility that symptoms are caused by metal toxicity.
Hair and urine
Hair analysis is not expensive, and easy to collect a sample. It does require expertise in interpretation. For example, very low levels of mercury in hair, may indicate toxicity due to the body's inability to eliminate the metal.
Urine only shows what the body is excreting. It's possible to be very toxic, yet not dump them out into the urine. Therefore a provoking agent (something which binds to metals and takes them out through the urine) must be used. Traditionally this has been DMSA. DMSA has two drawbacks. First it is toxic to the kidneys. Secondly, it's no longer readily available the FDA took it off the market as an over the counter drug several years ago. 
Porphyrins are chains of proteins found in the red blood cells. They are needed to make heme, which is the molecule that carries oxygen in blood. Lead, mercury and organic toxins have been found to inhibit specific porphyrin pathway enzymes. Testing levels of intermediates in porphyrin production can thus help determine toxic load. 
The above test, shows markers above 95th percentile which indicates a burden on the body and worth treating. Ideally porphyins should be well within the green area (not borderline green/yellow).
Although porphyrin testing is not a direct measurement for any toxin, it does help show what the burden of toxicity is on the body. Thus it is a clinically relevant test. It doesn't require a provoking agent like a urine metal test does.
Besides showing burden of heavy metals, porphyrin tests also help to show what the burden of organic pollutants such as hexachlorobenzene, dioxin, methylchloride, polyvinylechloride and polybrominated biphenyl are on the body. Persistent organic pollutants may contribute to numerous symptoms, including psychiatric. 
Heavy metal detoxification
There are numerous methods of detoxification. Some practitioners use intra-venous chelator such as DMSA. A chelator is something which will binds to and remove a toxin from the body. DMSA is expensive (often given as a series of I.V. treatments over a course of months), and potentially harmful to the kidneys. In addition, it's availability has recently been limited by the FDA.
Fortunately we don't need to use DMSA and other such chemical to detoxify metals. Nature has given us many great nutrients that help the body detoxify.
In my practice I combine nutritional supplements, with biotherapeutic drainage. This is effective at detoxification, without the need for harsher protocols.
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 Lord, Richard S., J. Alexander. Bralley, and J. Alexander. Bralley. Laboratory Evaluations for Integrative and Functional Medicine. Duluth, GA: Metametrix Institute, 2008. 74-77. Print.
 Lord, Richard S., J. Alexander. Bralley, and J. Alexander. Bralley. Laboratory Evaluations for Integrative and Functional Medicine. Duluth, GA: Metametrix Institute, 2008. 49. Print.
 Brown, J. S. (2013) Psychiatric Effects of Organic Chemical Exposure, in Effects of Persistent and Bioactive Organic Pollutants on Human Health (ed D. O. Carpenter), John Wiley & Sons, Inc., Hoboken, NJ, USA. doi: 10.1002/9781118679654.ch19