Toxicology

Deals with long-term effects of foreign chemicals on the body.

Chemicals affect the body with doses producing a response.

Controls can be engineered, administration, or personal protection.

Effects of Poisons

Effects may be permanent or reversible. Threshold limit values are based on

nonreversible functional changes in an organ. Response may lag the dose by many years. Workers tend to ignore hazards with long

delayed response times. Financial benefits accrue to organizations,

heath costs to individuals. Teratogens cause defects in fetal

development. TLV approach considers humans to be the

most sensitive species.

Dose/Response

The Leaky Bucket

Chemicals can be detected in extremely low concentrations.

The problem is to define “excess.”

Poisoning depends on the rate of input, kind of poison, body size, target organ susceptibility, and poison removal capability.

Poison Routes

To enter the body, a poison must enter the blood.

Poisons may be characterized by their ability to penetrate the body’s perimeter.

The most important entrance points are the skin, mouth, and lungs.

Skin The skin is a superb barrier. Most compounds run off the skin rather than

penetrate. Problems arise from wet clothing and cuts and

abrasions. In general poisons that enter through the skin

are not serious problems.

Dermatitis

Accounts for 35–40% of reported industrial disease.

Causes include: Mechanical and physical Chemical Plant poisons Biological agents

Dermatitis Prevention

Protective clothing Good housekeeping around workstations Barrier creams Personal cleanliness Cleanliness of clothing

Mouth

For adults the problem is toxic compounds in food or drink.

Forbid eating, drinking, and smoking in work areas.

Provide clean, convenient areas for eating and drinking.

Consider enclosing these areas.

Lungs

The lungs are the major route in poison absorption.

Particle size is the most important characteristic in inhalation.

Particles below 10 μm in diameter tend to be retained in the lungs.

Straight and short fibers penetrate deeper than long or curved ones.

Interior Poison Targets

Respiratory system Blood Other organs Fetuses

Poison Elimination

The liver biotransforms compounds. Transformed materials leave the liver in bile for

excretion. Blood from liver goes to kidneys and general

circulation. Kidney puts transformed compound into urine. Not all blood goes to liver and not all of

compound is transformed.

Threshold Limit Values Issued by American Conference of Governmental

Industrial Hygienists. Three different types:

Time-weighted average (TLV-TWA): recognizes chronic effects

Short-term exposure limit (TLV-STEL): concerned with acute effects

Ceiling (TLV-C): an absolute limit of concentration Applying TLVs

Excursions are permitted above the TWA and STEL but not the ceiling.

TLVs assume concentration × time = a constant, which is unlikely. STEL limits duration of high exposures. TLVs are based on 8-h exposure

Example of TLV Calculation

Assume worker exposed to acetone for 4 h at 500 ppm, 2 h at 750 ppm, 2 h at 1500 ppm.

TWA = [500 × 4 + 750 × 2 + 1500 × 2] ÷ 8 = 812

Is this acceptable?

Controlling Exposure Engineering Controls:

Substitute a less harmful material. Change the material or process. Enclose (isolate) the process. Use wet methods. Provide local or general ventilation. Use good housekeeping. Control waste disposal.

Controlling Exposure, cont. Personal Protective Equipment

This is the last line of defense. Use equipment that fits properly. Maintain the equipment and know how to use it.

Know its limits.

Have clothing cleaned professionally. Have workers shower before leaving work.

Administrative controls: Screen potential employees. Periodically examine employees. Train engineers, supervisors, and workers. Reduce exposure time.