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Thread: Toxicology

  1. #1 Toxicology 
    Forum Radioactive Isotope skeptic's Avatar
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    Just some thoughts and internet research results.

    I have had, over the years, to assess chemicals on the basis of their toxicity, and learned a few basics of toxicology, which I found interesting. So here are some facts and some musings.

    Toxicology, of course, is the science of poisons, and the first rule is that the dose makes the poison. This means that every substance is toxic in high enough dose, and every substance is non toxic in low enough dose. There are a number of ways of measuring toxicity, but the most common is the LD50. Oral lethal dose 50%. That is : the amount of a substance that will kill half the population ingesting it if it is swallowed. This is tested on laboratory animals, and gives a nice, neat little number for comparing toxicities, though error factors can make it misleading at times.

    The number is big for substances that are not very toxic, and small for very toxic materials. Water has got to be about the least toxic material, and we have to drink one hell of a lot for it to have a chance at killing us. The oral LD50 is roughly 70 grams per kilogram of body weight. A very big number.

    Alcohol, by contrast is about 7 grams per kilogram, which is still a big number, and makes alcohol very low in toxicity. This is ironic since alcohol is doubtless the recreational drug that causes the most harm to society. Yet it is the least toxic of all recreational drugs.

    The most toxic substance ever synthesized by humans is 2,3,7,8 TCDD, which is one of the dioxins. It has an LD50 of about 0.01 micrograms per kilogram. The most toxic substance ever discovered is botox - the toxin manufactured by the bacterium, Clostridium botulinum. It is 1000 times as toxic as 2,3,7,8 TCDD. Botox injections are non toxic only because the amount injected is diluted almost to homeopathic levels!

    Chocolate is interesting. It has a substance within that is mildly toxic. Theobromine. Oral LD50 to people is 1 gram per kilogram. However, there is not enough in chocolate for it to cause harm. Not so for dogs. Theobromine is more than 3 times as toxic to dogs at 300 milligrams per kilogram. A bar of chocolate might have enough theobromine to kill a small dog. So do not let your dogs eat chocolate.

    People who are enthusiastic about organic food often talk of how conventional food contains pesticides. However, organic food contains much larger amounts of natural pesticides, due to the higher amount of insect attack on crops that have not been sprayed. Plants make natural insecticides in response to insect attack. The total toxicity of all pesticides, natural and synthatic, in organic food is worse than in conventional food that has been sprayed, on average.

    In fact, natural chemicals are frequently much more toxic that synthetic.


    Last edited by skeptic; September 28th, 2014 at 09:35 PM.
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  3. #2  
    Forum Professor jrmonroe's Avatar
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    I also have had some toxicology experience.

    As for dogs and chocolate, the danger also extends to holiday seasons when people set out candies for themselves and guests, which the dogs might gobble up or unwitting guests might feed to them, and also allowing dogs to run free outside during holiday seasons around the days for trash collection in the neighborhood because people might throw out chocolates, and dogs might rummage through people's trash and eat them. Dogs don't know any better. Chocolate's lethality manifests itself because a dog's body cannot metabolize theobromine as quickly as humans. Cats also don't metabolize theobromine as quickly as humans, but they aren't attracted to chocolates because their sense of taste doesn't detect sweetness, and so, theobromine poisoning is less of a threat to them.

    As for natural pesticides in vegetation, I don't have much depth of knowledge, but I think that some vegetation evolved to produce caffeine and nicotine and similar substances as natural pesticides. Nicotine, if I remember correctly, accelerates growth in insects, which kills them. Caffeine overstimulates and kills a variety of pests insects, slugs etc.

    BTW, why non-smokers choose to smoke e-cigarettes is beyond me (and foolish) as nicotine is the most addictive substance for humans.


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    Forum Masters Degree mat5592's Avatar
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    Chocolate's toxicity to dogs seems a bit overblown. I realize it's more toxic than it is for humans, but I have seen too many people act like a bite of chocolate will kill their dog. My 40 pound dog would probably have to eat over a pound of milk chocolate before it killed him. There are higher levels of theobromine in dark chocolate, but that stuff is gross anyway
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