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 × × × 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.