Issue 1, April 22, 2021

Dermal Toxicity and Absorption Rates

What comes to mind when you think of absorption rates?  When I think of an absorption rate, the first thing that comes to mind is a paper towel and how fast it can absorb mom's first cup of coffee that was just knocked off the counter by two little boys in a sword fight. Of course, some brands of towels are faster than others. It isn't often that I think about my body's skin being like a paper towel, but it too can absorb substances. Imagine this slogan, “Your skin, the quicker picker-upper.“ Our skin is a vital organ to our body and can take in substances, including pesticides. A dermal exposure occurs when a pesticide contacts and enters the body through the skin. Dermal exposure can occur when mixing, applying, or otherwise handling a pesticide. It also happens to be the most frequent route of pesticide entry into the body, often going undetected.

(Dermal absorption rates as compared with the forearm)

The severity of this exposure depends on several factors:

  • Dermal toxicity- the ability of a pesticide to cause injury when absorbed through the skin
  • The absorption rate through the skin
  • Size of the area of the skin that is contaminated
  • Length of time the pesticide is in contact with the skin.

Pesticide manufacturers determine a product’s toxicity by exposing test subjects to various amounts of the pesticide. Because folks tend to shy away from volunteering to participate in these types of studies, researchers must rely on test subjects such as rats, mice, rabbits, etc. For dermal tests, the pesticide is placed on the skin of the test subject and covered with a bandage for 24 hrs. The dose of pesticide that kills 50% of the test animals is known as the LD50 value. For example, if 5 out of 10 animals weighing 1 kilogram die being given 100 milligrams of pesticide, the dermal LD50 is 100 mg/kg. The value can be high or low based on how toxic it is. A product with an LD50 value less than 200 mg/kg is poisonous in that it takes very little of that product to be lethal compared to a product with an LD50 of 2,000-20,000 mg/kg.

You will not find the LD50 number on a pesticide label. Instead, manufacturers provide a signal word based on the pesticide’s acute toxicity. The signal word allows users to gauge a pesticide’s toxicity quickly. In order of degree of toxicity, the signal words are DANGER (highly toxic), WARNING (moderately toxic), and CAUTION (slightly toxic).  Be aware; some pesticides that are considered very low in toxicity are no longer required to have a signal word on the label. Remember, even though a pesticide may not have an indicated signal word, that does not mean it isn't toxic. All pesticides, even those very lowly toxic, must be handled responsibly and with care.

Rates of absorption through the skin vary for different parts of the body. Areas of the body that are warm or moist (for example, head, groin, armpits, and neck) tend to absorb pesticides to a greater degree. Absorption can be quicker if there are cuts or abrasions on the skin but can be slower if there is more hair or thicker skin like calluses.

Pesticide formulations can vary in their ability to penetrate the skin. Additionally, it is not only the active ingredients that may be dangerous; many pesticides are carried in oil-based materials. If the oil carrier gets into the bloodstream, the results can be fatal. An oil-based formula like an emulsifiable concentrate will pass through the skin much faster than a water-soluble formulation. The oil crosses the skin barrier very rapidly and can carry pesticide’s active ingredients with it.

The absorption of some pesticides through the skin in higher absorption areas is rapid enough to approximate the effect of injecting the pesticide directly into the bloodstream. At this rate, this is more dangerous than swallowing the pesticide. Absorption continues to occur through the affected skin areas as long as the pesticide remains in contact with the skin. The exposure is more severe if the contaminated area is large or if the pesticide stays on the skin for a long time. It is recommended to wash work clothes and personal protection equipment (PPE) daily so that pesticides that reach the clothing or PPE do not create a repeated pesticide exposure.

Protecting your skin is vital when protecting yourself from pesticide poisoning. To reduce or avoid the potential for a dermal exposure, be sure to carefully read, understand, and follow the product label's instructions. Be sure to wear adequate PPE. Finally, to reduce your potential for a pesticide-related accident, take proper precautions before and observe good safety practices during the application. Otherwise, your skin could be that paper towel.

Maria Turner

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