Chapter 17: Human Health and Ecotoxicology

Infectious Disease

Caused by pathogens - ex. viruses, bacteria, fungi, protists, and helminths

Acute Diseases

Rapidly impairs the functioning of the organisms

Chronic Diseases

Slowly impairs the functioning of the organism (lasts a long time)

Chronic-Disease Risk Factors in Low-Income Countries

Poverty, unsafe drinking water, poor sanitation, and malnutrition

Chronic-Disease Risk Factors in High-Income Countries

Availability of tobacco, less-active lifestyles, poor nutrition, and overeating

Plague

Caused by an infection from a bacterium that is carried by fleas - these fleas attach to mice and rodents which allows them a lot of mobility - ex. bubonic plague, black death

Malaria

Caused by an infection from several species of protists in the genus Plasmodium - has killed millions over many centuries - causes recurrent flu-like symptoms - use of pesticides to control mosquitos who carry the disease (biomagnification)

Tuberculosis

A highly contagious disease caused by a bacterium that mainly infects the lungs - spreads when someone coughs and bacteria can live in the air for several hours - can be infected but have no symptoms - can be treated with antibiotics

Emergent Infectious Disease

An infectious disease that has not been previously described or has not been common for at least 20 years - many come from pathogens that infect animal hosts - these diseases can mutate rapidly

HIV/AIDS

Acquired Immune Deficiency Syndrome (AIDS) - caused by the Human Immunodeficiency Virus (HIV) - origin is traced back to a wild chimpanzee population - antiviral drugs are helpful in maintaining low levels of the virus

Ebola Hemorrhagic Diseases

Caused by several species of Ebola viruses - high death rate - first discovered in the Democratic Republic of the Congo

Mad Cow Disease

Prions mutate into deadly pathogens and slowly damage the cow’s nervous system - can be transmitted to humans who ingest infected cattle - humans then develop Creutzfeldt-Jakob Disease (CJD) - would get into cattle only if the ground up remains of an infected cow was ingested

Prions

A small, beneficial protein that occasionally mutates into a pathogen

Swine Flu

A type of flu caused by the H1N1 virus - similar to the flu but normally only affects pigs - occasionally can jump from pig to human

Bird Flu

Caused by the H5N1 virus - not easily transmitted between people, but can jump to humans from an infected bird

SARS

Severe Acute Respiratory Syndrome - caused by a coronavirus

MERS

Middle Eastern Respiratory Syndrome - originated from an animal source - also caused by coronavirus

West Nile Virus

Lives in hundreds of species of birds - can be transmitted through mosquitos - first human case in the West Nile region of Uganda in 1937

Lyme Disease

Caused by a bacterium that is transmitted by ticks - primarily the black-legged tick, AKA the deer tick - mainly in the Northeastern United States

Zika Virus

Caused by a pathogen that causes babies to be born with unusually small heads and damaged brains - carried by mosquitoes - no known treatment

Neurotoxins

Chemicals that disrupt the nervous system - ex. insecticides, lead, mercury, chromium

Carcinogens

Chemicals that cause cancer - mutagens are carcinogens that cause damage to the genetic material of the cell - ex. asbestos, radon, and formaldehyde

Teratogens

Chemicals that interfere with the normal development of embryos or fetuses - ex. alcohol, tobacco

Allergens

Chemicals that cause allergic reactions - cause an abnormal response in the immune system - ex. peanuts, penicillin

Endocrine Disruptors

Chemicals that interfere with the normal functioning of hormones - binds to receptive cells and cause the cells to behave in ways not beneficial to the organism - ex. hormones found in wastewater

Dose-Response Studies

Expose animals/plants to different amounts of a chemical and then look for a variety of possible responses, including mortality, changes in behavior, or changes in reproduction - experiments can either be acute or chronic studies - finds LD50, ED50, and NOEL - scientists try to test on birds, mammals, fish and invertebrates (typically mice or rats) and try to use LD50 and ED50 to determine concentrations that won’t cause harm to humans

LD50

The lethal dose that kills 50% of the individuals in a dose-response study - typically take the LD50 from rats/mice and divide by 1000 to determine the levels safe for humans

ED50

Used to determine the effective dose that causes 50% of the individuals in a dose-response study to display a harmful effect - some chemicals have sub-lethal effects which don’t kill the organism but impair its behavior, reproduction, or physiology

Testing Standards for Dose-Response Studies (legislation)

Regulated by the EPA

• Toxic Substance Control Act of 1976 - doesn’t include food, cosmetics, and pesticides

• Federal Insecticide, Fungicide, and Rodenticide Act of 1996

No-Observed Effect Level (NOEL)

The highest concentration of a chemical that causes no lethal or sub-lethal effects

Retrospective Studies

Monitor people who have been exposed to an environmental hazard - study groups who have been exposed with unexposed groups (control) - monitor both groups to see if the exposed group has more health problems through the years

Prospective Studies

Monitor people who might become exposed to an environmental hazard at some point in the near future - ask people in the group to keep track of food, tobacco, and alcohol they consume (synergistic interactions)

Synergistic Interactions

Multiple risks can cause synergistic interactions where they cause more harm than expected based on the risks of each separate risk - ex. smog and smoking

Routes of Exposure

The way in which an individual might come into contact with an environmental hazard - includes exposure to air, water, and environments where they work, play, live, or visit - exposed by contact, breathing, or ingesting

Solubility of Chemicals

Solubility determines the movement of chemical in the environment - chemicals soluble in water can wash off surfaces and runoff into surface water and groundwater (herbicides, salts, acids, heavy metals) - chemicals soluble in fats and oils are found attached to soils (insecticides)

Bioaccumulation

From chemicals that can be stored in fats and oils - an increased concentration of a chemical within an organism over time (ex. DDT)

Biomagnification

An increase in chemical concentrations in animal tissues as the chemical moves up the food chain

Persistence

The length of time a chemical remains in the environment - depends on Ph, whether in soil or water, degraded by sunlight or microbes - measured by observing the time needed for the chemical to degrade to half its original concentration (half-life)

Steps of Environmental Risk Assessment (ERA)

1. Risk Assessment

2. Risk Acceptance

3. Risk Management

Risk Assessment (Step One of Risk Analysis)

Tries to identify a potential hazard and determine the magnitude of potential harm - qualitative (judgments, perception) vs. quantitative (data-based) data

Environmental Hazards

Include pollutants, chemical contaminants, combustion of fossil fuels, and natural catastrophes

Risk

Probability of being exposed to a hazard times the probability of being harmed if exposed - the risk of rare event that has a high likelihood of causing harm can be equal to the risk of a common event that has a low likelihood of causing harm

Risk Acceptance (Step Two of Risk Analysis)

Determine the level of risk that can be tolerated - much disagreement about what can be tolerated based on personal preferences of individuals - need to look at costs and benefits of activities affecting humans and the environment

Risk Management (Step Three of Risk Analysis)

Uses the data on risk assessment and analysis on acceptable levels of risk with other factors - factors include economic, social, ethical, and political issues - regulated by governments (ex. arsenic regulation)

Worldwide Standards of Chemicals

About 80,000 regulated chemicals, but they’re not all regulated the same way around the world

• Innocent until Proven Guilty Principle

• Precautionary Principle

• Stockholm Convention

• REACH

Innocent Until Proven Guilty Principle

A potential hazard should not be considered an actual hazard until the scientific data definitely demonstrates that it actually causes harm

Precautionary Principle

Action should be taken against a plausible environmental hazard - must have scientific basis - ex. asbestos

Stockholm Convention

In 2001, 127 nations agreed to ban, phase out, or reduce 12 chemicals - the “Dirty Dozen” (Persistent Organic Pollutants - POPs)

REACH

In 2007, 27 nations of the European Union agreed how chemicals should be regulated in the EU - places responsibility on industry - the Registration, Evaluation, and Authorization of CHemicals (REACH)