Chapter 19 – The Environment and Human Health Hong Kong residents concerned about SARS

© 2013 Pearson Education, Inc. DDT vs. Malaria Malaria is one of the most important diseases Major issues in Africa 20% of children under 5 years old died from malaria DDT was developed and was effective in controlling mosquitoes that vectored malaria Helped eradicate malaria from many regions of world DDT affects wildlife Reduced use, banned in some regions © 2013 Pearson Education, Inc.

"DDT - Powerful Insecticide, Harmless to Humans"

Introduction to Public Health Measuring public health Population level statistics Life expectancy at birth Worldwide 67 years (1950: 46 years) Mortality rate Infant mortality Percentage of infants that die before age 1 Worldwide 4.9% (1950: 15.3%) © 2013 Pearson Education, Inc. 4

Introduction to Public Health Hazards and risks May be immediate or delayed Grouped into four categories Physical Chemical Biological Cultural Latent consequences Delayed effects Exposure to radiation © 2013 Pearson Education, Inc. 5

Introduction to Public Health Risk perception and reality Human perception differs from reality Key factors influence risk perception Myth of zero risk Public awareness Risk–risk tradeoffs Control Risk and time © 2013 Pearson Education, Inc. 6

Environmental Health In some parts of Eastern Europe and the former USSR, up to 90 % of all children suffer from environmentally linked diseases.

At any given time, about 2 billion people suffer from worms, protozoans, and other internal parasites.

Physical Hazards in the Environment Geological hazards Earthquakes, tsunamis, volcanoes Weather hazards Hurricanes/typhoons Floods Fire in the environment Wildfires © 2013 Pearson Education, Inc. 11

Chemical Hazards in the Environment Toxicology: The study of toxins (poisons) and their effects on living systems. Scientific discipline that studies chemical poisons and effect on human health Dose-response curves Toxicity threshold Median lethal dose (LD50) The dose makes the poison Acute exposure Chronic exposure © 2013 Pearson Education, Inc. 12

Chemical Hazards in the Environment Human vulnerability to toxins Effects of toxins depend on various factors Genetics Environmental cause Age Health Socioeconomic status © 2013 Pearson Education, Inc. 13

Chemical Hazards in the Environment Toxin transport and fate Impact of certain toxins depends on movement through environment Persistence Volatility Solubility in water Uptake and fate in other organisms Bioaccumulation Body burden Persistent organic pollutants (POPs) © 2013 Pearson Education, Inc. 14

Movement, Distribution, and Fate of Toxins

Bioaccumulation and Biomagnification Bioaccumulation - dilute toxins in the environment can reach dangerous levels inside cells and tissue Biomagnification - the effects of toxins are magnified through food webs

Persistence Some chemical compounds are very unstable and degrade rapidly under most conditions, thus their concentrations decline quickly after release. Others are more persistent. Stability can cause problems because these materials persist in the environment and have unexpected effects far from their original use. PBDE (flame-retardants in textiles)

Minimizing Toxic Effects Every material can be poisonous under some conditions. Taken in small doses, most toxins can be broken down or excreted before they do much harm. Liver - primary site of detoxification Tissues and organs - high cellular reproduction rates replace injured cells - down side: tumors, cancers possible

Every material can be poisonous under certain conditions. Most chemicals have a safe threshold under which their effects are insignificant. Metabolic Degradation In mammals, the liver is the primary site of detoxification of both natural and introduced poisons.

Excretion Effects of waste products and environmental toxins reduced by eliminating via excretion. Breathing Kidneys Urine Feces

Measuring Toxicity Animal Testing Most commonly used and widely accepted Expensive - hundreds of thousands of dollars to test one toxin at low doses Time consuming Often very inhumane Difficult to compare toxicity of unlike chemicals or different species of organisms

A Typical Dose/Response Curve

LD50 - the dose of a toxin that is lethal to half the test population

Acute Versus Chronic Doses and Effects Acute effect - immediate health effect caused by a single exposure to a toxin (can be reversible) Chronic effect - long lasting or permanent health effect caused by (1) a single exposure to a very toxic substance or (2) continuous or repeated sub lethal exposure to a toxin

Chemical Hazards in the Environment Kinds of toxins Corrosive toxins Asphyxiants Carcinogens Teratogens Allergens Neurotoxins © 2013 Pearson Education, Inc. 25

Endocrine Disruptors Chemicals that disrupt normal endocrine hormone functions. Hormones are chemicals released in blood by glands to regulate development and function of tissues and organs elsewhere in the body. Environmental Estrogens and Androgens

Chemical Hazards in the Environment Toxin testing and regulation Contains both ethical and practical challenges EPA charged to monitor over 75,000 industrial chemicals Most chemicals assumed to be nontoxic until proved otherwise Model organisms Used to test effects of chemicals for humans © 2013 Pearson Education, Inc. 27

Biological Hazards in the Environment Infectious disease and the environment Environmental factors influence populations of disease agents and vectors Population size, movement, climate, water quality Pathogens Virulence Anthroponosis Disease only in humans Zoonosis Disease shared by animals and humans © 2013 Pearson Education, Inc. 28

Brown Recluse

Biological Hazards in the Environment Respiratory disease Influenza Avian flu H1N1 Diarrheal disease Most from poor sanitation and polluted water Most die from dehydration Cholera, cryptosporidium © 2013 Pearson Education, Inc. 30

Biological Hazards in the Environment Blood-borne diseases HIV Malaria Transmitted by mosquitoes Caused by parasite Plasmodium Evolutionary change Coevolution between pathogen and hosts Tends to diminish disease severity Sickle-cell and malaria © 2013 Pearson Education, Inc. 31

Biological Hazards in the Environment Landscape change Altered landscapes and waterways provide habitats for disease agents Climate change Global warming altering habitats Allows disease organisms and agents to expand range © 2013 Pearson Education, Inc. 32

Factors Contributing to the Spread of Contagious Diseases High population densities Settlers pushing into remote areas Human-caused environmental change Speed and frequency of modern travel Contact with water or food contaminated with human waste

Antibiotic and Pesticide Resistance Indiscriminate use of antibiotics and pesticides - perfect recipe for natural selection Protozoan that causes malaria now resistant to most antibiotics, and mosquitoes have developed resistance to many insecticides Drug resistance: TB, Staph A, flesh-eating bacteria