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 • 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. The Leaky Bucket
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.