The Great Pumpkin is out to get you...

So, I have a calendar from the Nature Conservatory in the lab, and on it, for the month of October, there is a little blurb about pumpkins being treated with pesticides that are toxic to the human nervous system.  The chemicals in question are: malathion and diazinon, and they are neurotoxins... at least to bugs, which is why they make such good pesticides.  When it comes to humans, their toxicity is debatable.  Malathion, at the low doses used in agriculture, is completely harmless to humans (though I don't suggest drinking or eating it at higher doses).  Diazonin, on the other hand, can be more toxic, though, again, you should be okay unless you are eating or drinking it directly.  That being said, you should always was any pumpkins you plan on carving or cooking with.  AND you should always wash your hands thoroughly anytime after you've been handling any pumpkins.  Also, I agree with the Nature Conservancy in their recommendation to find a local, organic grower to avoid the chemicals altogether (you can find one at http://www.localharvest.com/).  The reason being that, while these chemicals are not harmful to humans, they can certainly be harmful to other, smaller animals that might raid a farm, and not have the benefit of being able to wash with soap or cut through the tough skin of the pumpkin with a knife. Plus, we don't want to have these chemicals build up in the soil and groundwater to the point where they reach concentrations that are toxic.  You can even look at your local grocery store to see if they sell certified organic pumpkins, if they are USDA certified organic, that means no chemical pesticides were used, and you and the environment can breathe a sigh of relief. 
Of course, I can't stop there because there's a great opportunity here to talk a little neuroscience.  I said that malthion and diazonin are neurotoxins, but what are they, and how are they toxic?  Both are chemicals of a class known as organophosphates, and both are cholinesterase inhibitors, which means that they block the action of an enzyme in the nervous system called acetylcholinesterase.  In a previous post, I described how the transmission of nerve impulses occurs, describing how those impulses travel across synapses in the form of chemicals called neurotransmitters (here).  What I neglected to mention was that after the signal has been conducted, the neurotransmitters need to be removed from the synapse, or else the post-synaptic cell will be fooled into thinking that another impulse has been transmitted, and another, and another, indefinitely, until the neurotransmitter molecules are gotten rid of.  Some neurostransmitters, like serotonin, are reabsorbed by the presynaptic cell.  Antidepressants like Zoloft and Prozac work by preventing this reuptake, thus increasing the activation of cells responsive to serotonin. In the case of another neurotransmitter called acetylcholin, the molecules get broken down by the enzyme acetylcholinesterase.  Acetylcholine is primarily used by the neurons that allow your brain to control muscle movements.  Blocking acetylcholinesterase from breaking down acetylcholine in synapses can lead to continued muscle contraction.  Which may not sound so bad until you realize that this is actually the mechanism of action of another organophosphate/cholinesterase inhibitor: Sarin "Nerve" gas.  Sarin is a very potent acetylcholinesterase inhibitor that causes its victims to convulse wildly, often dying from suffocation as the diaphragm and accessory muscles involved in breathing contract uncontrollably preventing the victim from taking in sufficient air.  Now, I know that's scary, but, despite being organophosphates and cholinesterase inhibitors, malathion and diazonin are not nearly as potent as Sarin gas, and like I said, in low doses, malathion is actually quite harmless to humans (unless you eat or drink it at high concentrations).  Diazonin, while still far from lethal, is a little more caustic, and has been banned by the EPA for residential use, (though it can still be used for agricultural use).  Now, if you still want to buy some pumpkins from the store (or already have), the good news is that they were likely mainly treated with malathion, BUT, if you have some really GIANT pumpkins, they were probably treated with diazonin (or both diazonin and malathion).  In order to get giant pumpkins, you have to leave them in the field longer... the longer they're in the field, the more likely bugs are to camp out and have a good meal, thus, in order to grow large pumpkins, insecticides like diazonin must be used.  Of course, by buying these pumpkins you are supporting the widescale use of these chemicals which can cause damage to the nervous systems of lots of smaller animals like birds and rodents who might raid the pumpkin patch for a meal, or fish and amphibians who may be getting higher doses of these chemicals in the water runoff to streams and ponds.  So while the "Great Pumpkin" may not be real, the real pumpkins at your local grocer can be just as scary.  By the way, the cartoon comes from http://shinjiku.deviantart.com/ , I hope the artist doesn't mind my swiping it for this post.