To find out just how much we are exposed to chemicals, look up the research from National Human Adipose Tissue Survey performed by U.S. Environmental Protection Agency and others (1-3). Unfortunately, according to their research, most of us have organophosphate and carbamate pesticides accumulated in our fat tissue. Included in these are neurotoxins that can affect cognition, mood, and associated with chronic neurological illnesses like Alzheimer's disease (3). The organophosphates, first synthesized for nerve gas research, actually destroys acetylcholinesterase and its effects are irreversible (3). Without it you get an excess of acetylcholine causing problems and the effects worsen if exposure continues (3). More of the enzyme needs to be produced to restore health of the synapses (3). Carbamates bind to acetylcholinesterase and its effects don't last because the bond is reversible via hydrolysis (3).
References
1. Phillips LJ, Birchard GF. Regional variations in human toxics exposure in the USA: an analysis based on the National Human Adipose Tissue Survey. Arch Environ Contam Toxicol 1991;21:159-68.
2. Phillips LJ. A comparison of human toxics exposure and environmental contamination by census division. Arch Environ Contam Toxicol 1992;22:1-5.
3. Crinnion, WJ. Environmental Medicine, Part 1: The Human Burden of Environmental Toxins and Their Common Health Effects. Available at: http://www.headlice.org/lindane/health/toxicology/enviromed_crinnion.htm.