Transmission Through the Skin


In my previous two posts, I gave a picture of the testimony of the toxicology expert Dr. Vyvyan Howard, who was testifying as one of my expert witnesses in the Castillo-DuPont case.

 

One of the significant features in the case was the fact that there had been quite a strong wind blowing on the day Donna Castillo was exposed.

 

We had shown this to be true through her testimony, but we also substantiated it with weather charts, records of prevailing meteorological conditions at the time, and expert-witness testimony.

 

When it comes to a substance like Benlate, air is a transport mechanism. Air will carry droplets of liquid and deposit them on the skin. This can happen on uncovered skin as well on the skin of a person who is lightly clothed, provided they are doused with enough of the liquid.

 

The source of the droplets on this day was a tank attached to the sprayer, which contained a mixture of water and Benlate. As this liquid was sprayed from the tank, each droplet maintained the same concentration of Benlate as it had in the tank. When the chemical gets deposited on the skin of a person, such as Donna Castillo, it is called “dermal exposure.” If water evaporates from the droplet at any point, the concentration of Benlate within the droplet will rise, because Benlate is a nonvolatile substance. Unfortunately, Benlate does not evaporate like water.

 

According to Dr. Howard, and based on the information we had from the DuPont ICI studies, once Benlate is deposited on a subject’s skin, it will start to be assimilated through dermal transfer at a measured rate of 3%.

 

This means that while the majority of the Benlate deposited on Donna’s skin remained on the surface during the length of her exposure (from the time the drops landed on her until she showered), 3% of the total portion made its way through the epidermis, was picked up by the capillaries under the skin, and then was transported through the veins and into the heart.

 

From the heart, it was sent to the lungs where the blood was oxygenated, returned down to the left side of the heart, and was ultimately pumped out into the circulation system, which extends to everything in the body. This is called the “systemic side” of the circulation system. The blood, which will now have benomyl in it if the chemical has been absorbed through the skin, will reach the placenta. Once there, molecules of the size of those that make up benomyl, which are really quite small, have no difficulty traveling across the placenta and reaching the developing fetus.

 

To better understand this process, it’s critical to note that it doesn’t take much of the chemical to make an impact. Molecules are measured in terms of molecular weight. Substances with a molecular weight of less than 1,000 grams per mol have little trouble getting through the placenta. Certainly those with a molecular weight of less than 400 ­g/mol can be absorbed even more quickly. Most drugs—and, indeed, benomyl—fall into this category. In rat studies, benomyl was able to get to the embryo or fetus very easily, so the assumption is that it would be able to get through in humans, too.

 

Remember that 80% of the time something happens in rats, it also happens in humans.

 

In my next post, I continue my recounting of the testimony of Dr. Vyvyan Howard.

 

In the meantime, I’d love to hear from you. How aware are you of the effects of certain chemicals used around you in your daily life? Do you take pains to detoxify your environment? In what way? Thank you for sharing.

Leave a Reply

Your email address will not be published. Required fields are marked *