Dermal Absorption

[Guest guest]

A snip from The Dept. of Health and Human Services about chemical

exposure.

 

I hope this promotes and brings some useful information to the

discussion of EO's and dermal absorption of them

 

*Smile*

Chris (list mom)

http://www.alittleolfactory.com

 

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 

http://www.atsdr.cdc.gov/training/toxmanual/modules/2/lecturenotes.html

 

Routes of Exposure

 

It has been estimated that about 70,000 chemicals are used worldwide,

and the chemical industry introduces about 200 to 1,000 new chemicals

each year (8). Because of this, we are exposed to a number of chemicals

in our home, at work, and in the general environment. Trace amounts of

toxic chemicals are present in the food, the air, and the drinking

water. Exposure to toxic substances occurs through the three major

routes listed below. Trainer instructions icon.

<http://www.atsdr.cdc.gov/training/toxmanual/images/pointer.gif> Refer

to Handout 2.1. Routes of Exposure

 

* The skin (dermal absorption)

 

 

 

 

* The respiratory tract (inhalation)

 

 

 

 

* The digestive tract (ingestion)

 

 

 

 

A. Dermal Absorption

Contact with the skin is the most common path of toxic substance

exposure (1). The skin is composed of three layers:

 

 

 

* Epidermis (outer layer). The outermost layer is the stratum

corneum (carnified layer). This is the structure that determines the

rate of absorption of substances through the epidermis. For example, a

pesticide such as Malathion, which easily penetrates the stratum

corneum, moves quickly through the other layers of the skin and is

rapidly absorbed into the bloodstream. DDT, another type of pesticide,

does not easily penetrate the stratum corneum, so the rate of absorption

is much slower.

 

 

 

 

* Dermis (inner layer). The inner layer of the skin is sometimes

referred to as the true skin. In animal hides, this is the layer that

turns to leather when chemically processed. The dermis is the source of

oxygen and of nutrients for the epidermis. The hair follicles, sweat

glands, and sebaceous (oil) glands are found in this layer. These

structures play a limited role in the absorption of substances across

the skin.

 

 

 

 

* Subcutaneous fatty tissue. This layer provides a cushion for the

underlying structures and allows the skin to move to some extent.

 

 

 

 

Factors affecting dermal absorption of toxic substances include

 

* The condition of the skin. An intact stratum corneum (epidermis)

is an effective barrier to absorption of some toxic chemicals. However,

physical damage to the protective barrier, such as a cut or abrasion,

allows toxic substances to penetrate the epidermis and enter the dermis

where they more readily enter the bloodstream and are carried to other

parts of the body.

 

 

 

 

* The chemical make up of the substance. Inorganic chemicals and

substances are not easily absorbed through intact, healthy skin (such as

cadmium, lead, mercury, and chromium. Organic chemicals dissolved in

water do not easily penetrate the skin because the skin is impermeable

to water. However, organic solvents, such as paint thinner or gasoline,

are easily absorbed through the epidermis.

 

 

 

 

* Increasing the concentration of the toxic substance or the

exposure time can increase the rate or amount of material absorbed.

 

 

 

 

B. Inhalation

 

 

Inhalation is the easiest and fastest means of exposure to toxic

substances because toxic substances are readily absorbed in the

respiratory tract. The lining of the respiratory tract is NOT effective

in preventing absorption of toxic substances into the body. The

respiratory tract consists of the nasal passages, trachea (windpipe),

larynx (voice box) and the lungs. The following factors affect

inhalation of toxic substances:

 

* Concentration of toxic substance in the air,

 

 

 

 

* Solubility of substance in the blood and tissue,

 

 

 

 

* Respiration rate,

 

 

 

 

* Length of exposure,

 

 

 

 

* Condition of respiratory tract, and

 

 

 

 

* Size of toxic particle.

 

 

 

 

C. Ingestion

 

 

Ingestion of toxic substances usually occurs accidentally or

unknowingly. The digestive tract consists of the mouth, the esophagus

(food canal), stomach, and intestine (large and small). The major

function of the digestive tract is to digest and absorb the foods we

eat. Physical and chemical factors affect the absorption of toxic

substances. Absorption is affected because of the structure of the body

and the length of time food containing the substance remains in the

body. Once a chemical is absorbed, its effects depend on its

concentration in the target organs, its chemical and physical form, what

happens to it after it is absorbed, and how long it remains in the

tissue or organ of choice. After being taken up in the blood, a chemical

is be quickly distributed throughout the body; it may be moved from one

organ or tissue to another (translocation), or changed into a new

compound (biotransformation).