The Good, Bad, and Ugly

When it comes to chemical agents, there is the good, the bad, and the ugly.  I know I said previously that ‘dose makes the poison’, and that is still true, but there are many chemicals that require only a very small amount of exposure to be fatal.  For example, it takes about 6 liters of water for an average weight individual to drink in an hour to over hydrate and potentially die (depending on individual health), whereas 52 milligrams (mg) of arsenic is fatal.  As you can see, water and arsenic can both be harmful or even fatal, but at very different amounts:

In toxicology, scientists classify what I call the ‘good, bad, and ugly’ chemicals in terms of an LD₅₀.  The LD₅₀ stands for lethal dose at 50%, and this is a measure of how much of a chemical it takes to kill 50% of the population being tested.  So, back to the water and arsenic example, the LD₅₀ for a rat (which is fairly representative of a human in this case):

LD₅₀ water = 41 g/lb (41 grams of water ingested per 1 pound of the animal).  For an average human that weighs ~ 150 lbs, it would take 6150 grams (6.15 liters) of water to be fetal.

LD₅₀ arsenic= 0.35 mg/lb (0.35 milligrams of arsenic ingested per 1 pound of the animal).  For an average human that weighs ~ 150 lbs, it would take 52.5 milligrams of arsenic to be fatal.

What I hope is a little clearer after this example is that there are some chemical agents that people (and organisms) should NEVER come into contact with, because even a very small dose can be dangerous.  Then there are some chemicals that are not ideal to have contact with in large amounts, or over long periods of time, but it will not cause lasting harm at small amounts or shorter times. And, there are a lot of things that will not hurt you, even in larger exposures.

By — Gina Hilton is a third year PhD student in the Toxicology program at NC State. She has 10 years of experience as a research scientist in various fields including organic chemistry, complex human genetics, and toxicology. Gina is also an avid animal lover (to a 20 year-old kitty), swimmer, hiker, biker, local food shopper, loving daughter, sister, and best friend to many.