Chapter 11 Risk, Toxicology, and Human Health

Transcription

1 Chapter 11 Risk, Toxicology, and Human Health

2 Risk Expressed in terms of probability: how likely it is that some event will occur. Risk = (Exposure)(harm) Risk assessment (identifying, occurrence, assessing) and risk management (make decisions)

3 Hazards 4 main types: Biological: from pathogens that can infect humans Chemical: in air, water, soil, and food Physical: fire, earthquake, volcanic eruption, flood, etc. Cultural: smoking, unsafe work conditions, diet, etc.

4 Toxicology Toxicity: measures how harmful a substance is Depends on: Size of dose (amount ingested) How often exposure occurred Who is exposed (adult or child) How well the body s detox system works Genetic makeup/sensitivity to a toxin

5 Trace amounts Basic concept: any synthetic or natural chemical can be harmful if ingested in a large enough quantity. Most chemicals have a safe, threshold level of exposure in which their harmful effects are insignificant.

6 Poisons Poison: classified by LD 50 LD 50 (median lethal dose):: the amount of a chemical received in one dose that kills exactly 50% or the animals within a 14 day period.

7 Chemical Hazards Toxic chemicals: substances that are fatal to more than 50% of test animals Hazardous chemicals: cause harm by being flammable, explosive, irritating, asphyxiants, or inducing allergic reactions

8 3 major type of toxic agents 1) Mutagens: Chemicals or ionizing radiation that cause or increase the frequency of random mutations in DNA molecules. Ex: UV light, Nitrous acid, Bromine, Benzene 2) Teratogens: chemicals, viruses or radiation that cause harm or birth defects to a fetus or embryo Ex: Alcohol and thalidomide 3) Carcinogens: chemicals or ionizing radiation that cause or promote cancer. Ex: tobacco

9 But the FDA said it was safe.. Under existing laws most chemicals are considered innocent until proven guilty Estimating toxicity is difficult, uncertain, and expensive Only 10% of the 75,000 chemical in commercial use have been screened for toxicity Most have never been checked to determine what type of toxic agent Federal and state governments DO NOT regulate 99.5% of the commercially used chemicals

10 What to do??? Use precautionary principle: when we are uncertain about potentially serious harm from chemicals, decision makers should act to prevent harm to humans and the environment. Better safe, than sorry

11 11.4 Biological Hazards Nontransmissible diseases: not caused by a living organism and does not spread from one person to another. Ex: cardiovascular disorders, cancers, diabetes Typically have multiple causes and develop slowly and progressively.

12 Transmissible disease: caused by living organism and can spread from person to person The infectious agent is called a pathogen and is spread by a vector (air, water, food, insects, etc) The types of diseases threatening developing countries are primarily infectious diseases in childhood, while in developed countries it is usually chronic diseases of adults.

13 Deadly diseases World health organization (WHO) estimates each year 13.6 million people (most in developing, poor countries) die from one of the 7 deadly infectious diseases. These diseases include 1) Acute respiratory infections 2) AIDS 5) Malaria 3) Diarrheal diseases 6) Hepatitis B 4) Tuberculosis 7) measles

14 Mostly because of human activities, infectious diseases are moving fast from one species to another and from one animal species to humans. Avian flu, West Nile, Lyme disease, and Hantavirus (pulmonary syndrome) are all transmitted to humans from wild or domesticated animals

15 Viral Disease Influenza Ebola West Nile Virus Rabies AIDS Viral diseases Transmitted Body fluids or airborne emissions Blood or other bodily fluids Bite of mosquito carrying virus Dogs, coyotes, raccoons, skunks, bats Unsafe sex, needles, blood Treatment of Viral Disease: Hard to fight because treatments harm the cells of the host Antibiotics useless leads to resistant bacteria Best treatment are vaccines stimulate immune system to create antibodies

16 Case Study: Malaria ~40% of the worlds people live in tropical and subtropical regions where malaria is present. Malaria is caused by four protozoa species of the genus Plasmodium. The parasite circulates from mosquito to human and back to mosquito. Malaria cycle repeats itself until immunity develops, treatment is given, or death occurs

17 Prevention of Malaria 1) increasing water flow irrigation systems 2) using mosquito nets dipped in insecticide for windows and doors 3) cultivating fish that feed on mosquito larvae 4) clearing vegetation around houses 5) planting trees to soak up water in marsh areas 6) using zinc and vitamin A to boost children s resistance 7) increased public education

18 11-5 Risk Analysis Involves (1) risk assessment (identifying hazards) (2) comparative risk analysis (ranking risks) (3) risk management (determining options) (4) risk communication (informing decision makers and public)

19 Risk Management Strategies Market-based method: relies on market forces to control response Hierarchical method: relies on response from lawmakers Sectarian method: relies on emotions (citizens) Rational method: relies on logic and facts

20 Greatest Risks In terms of number of premature deaths per year and reduced life span, the greatest risk by far is poverty. Followed by voluntary choices people make such as smoking, sun exposure, drinking, eating high fat meals, not exercising, and obesity. People are bad at estimating risks because of misleading media, denial and irrational fears.