Toxins

__**Summary of Chapter 7 in the Textbook**__

//3 Main Causes of Death in the US are//
 * 1) cardiovascular disease
 * 2) cancer
 * 3) chronic obstructive pulmonary disease (of the lungs)
 * These problems are associated with aging and are noninfectious
 * Premature deaths in the United States are caused by individual lifestyle habits like __poor diet__, __lack of exercise__, and __smoking__.

__**Health Issues in Developing Countries**__
 * **HIV/AIDS**- first appeared in the 1980's and has reduced life expectancy by 20 years in sub-Saharan African countries. Affects adults as well as children.
 * AIDS first appeared 60-70 years ago as a viral jump from non-human to human Primates, probably when humans were exposed to Primate blood during butchering or consumption of Chimpanzees.
 * **malnutrition**- lack of access to MACRONUTRIENTS like proteins, carbohydrates, and good fats and lack of access to MICRONUTRIENTS like vitamins, iron, and calcium
 * **unsafe water**- bacterial and viral diseases spread through contaminated water that is not regulated by health organizations
 * **poor sanitation**- general cleanliness and proximity to trash, waste, and toxic materials
 * **air pollution**- may be locally or internationally caused

__**Emerging vs. Reemerging Diseases**__ //Emerging Diseases// are diseases that have recently appeared on the global scence. AIDS, Lyme Disease, West Nile virus are examples. //Reemerging Diseases// are those that have appeared before but are currently increasing in incidence. Tuberculosis is an example. //We have seen an increase in threats to human health from diseases because of//
 * evolution in infectious organisms- they are now capable of moving from human to host
 * evolution of antibiotic resistance in the infectious organisms (ie Streptococcus bacteria has evolved resistance to penicillin treatments)
 * urbanization- associated with overcrowding, poor sanitation, and easy disease transmittance
 * growing numbers of elderly people who are more susceptible to infectious diseases
 * pollution, environmental degradation, and climate change
 * growth in international trade and commerce (brings diseases to new areas and exposes those without immunity to new diseases)
 * diseases may be ENDEMIC (characteristic and isolated) to an area but spread to PANDEMICS (widespread, affecting multiple areas/countries) when many others are exposed to the diseas
 * poverty and social inequity

__**Specific Issues Associated With Chemical Use**__ //Specific Examples of harmful chemicals are DDT, radioactive isotopes, heavy metals (like lead and mercury), flame retardants (like PBDE- polybrominated diphenyl ether), industrial chemcials (like dioxins and PCB- polychlorinated biphenyls), and plastic compounds (like phthalates)//

1. **Persistence**
 * Materials that do not easily decompose when introduced to natural systems
 * characteristic of chemicals/synthetic materials
 * EXAMPLE- DDT
 * "dichlorodiphenyl-trichloroethane"
 * used as a pesticide in northwester US forests
 * resulted in weakened bird eggs (causing a drastic drop in eagle population) and blinding of fish, particularly salmon
 * Rachel Carson explained its effects in her book for the General Public, //Silent Spring//
 * DDT is now illegal unless needed to control a life-threatening pest

2. **Bioaccumulation**
 * Organisms that consume toxic materials that do not break down will eventually excrete or store these chemicals in their fatty tissues
 * over time, organisms can have a build up of toxins/chemicals

3. **Biological Magnification/ Biomagnification**- see diagram in textbook page 155
 * the increased concentration of toxins in the tissues of organisms that are in higher levels of the food web/chain
 * Example showing the DDT found in tissues of different organisms within an aquatic ecosystem
 * DDT in a water system- 0.00005 ppm
 * Water is consumed by algae, and the toxin is concentrated to 0.04 ppm
 * Algae are consumed by primary consumers, shrimp, and the toxin is concentrated to 0.16 ppm
 * Shrimp are consumed by Secondary Consumers, eels, and the toxin is concentrated to 0.28 ppm
 * Eels are consumed by the Tertiary Consumers, the ring-billed gull, and the toxin is concentrated to 75.5 ppm

4. **Endocrine Disruption**
 * List of US Fish & Wildlife Service Endocrine Disrupters & their effects can be found here
 * many chemicals (listed above) are now outlawed in the United States
 * these chemicals either MIMIC or INTERFERE with normal human and animal hormonal systems.
 * There are 3 main types of hormones that are effected by endocrine disruption
 * ESTROGEN- estrogen is naturally present in males and females but is more prevalent in females
 * Endocrine disruptors can mimic estrogen in males can cause them to have female-like characteristics or not be able to reproduce
 * Endocrine disruptors can interfere with females' natural hormones and affect reproduction
 * ANDROGEN- male hormones such as testosterone, present in both males and females
 * may mimic androgen in females and cause females to have male-like characteristics
 * may interfere with males' natural development and affect reproductive ability and body maturity
 * THYROID HORMONES- hormones in both males and females that regulate growth, metabolism, and energy availability
 * Thyroid disruptors may slow metabolism and reduce energy availability
 * Specific examples of Endocrine Disruption in nature are seen in alligators, frogs, amphibians, fish, birds, turtles, polar bears, and otters (many of these organisms require aquatic habitat, and endocrine disruptors may run off from other areas and be present in the aquatic habitat these organisms need
 * Phthalates, commonly used in plastic products, toys, packaging, cosmetics, fragracnes, nail polish, and medicines, cause extreme damage to fetuses and reproductive abilities in lab studies of rats.
 * Per the Safe Drinking Water Act of 1996, endocrine disruptors should be removed from drinking water systems. However, public drinking water treatment systems are not able to remove trace pharmaceuticals (medicines) that may act as endocrine disruptors when consumed.

__**Toxicology- The Study Of Toxins (chemicals with negative effects to humans)**__ //Acute Toxicology//- symptoms of exposure to toxin occur immediately or within a few days of exposure to the toxin //Chronic Toxicology//- damage (ie to the kidney or liver) occurs over long periods of exposure to chemicals

Toxic amounts are measured by DOSE (the amount that enters the body) and RESPONSE (the effect that dose has on the body)

//Lethal Dose- 50% or LD50// is an important term to understand.
 * the amount of toxin that kills 50% of a population of test organisms
 * usually reported in mg/unit of body weight (ie 200mg/kg)
 * the SMALLER the LD50 the MORE TOXIC the chemical. The LARGER the LD50 the LESS TOXIC the chemical
 * Examples of LD50's (this is the amount of the toxin, per body unit, that would KILL 50% of a population) based on a test of rats
 * Aspirin- 1750 mg/kg
 * Ethanol (simple alcohol)- 1000 mg/kg
 * Morphine- 500 mg/kg
 * Caffeine- 200mg/kg
 * Heroin- 150 mg/kg
 * lead- 20mg/kg
 * Cocaine- 17.5 mg/kg
 * Nicotine- 2 mg/kg
 * This explains why drugs, medicines, and toxins have a stronger effect on people of smaller body size (ie children). Children are less weight, therefore they can handle less amounts of toxins like caffeine before seeing a negative effect.

//Effective Dose- 50% or ED50//
 * The amount of the toxin that gives 50% of the test population the desired response
 * Not all organisms will have the same response to a drug, medicine, toxin, etc. The dose that gives 50% the desired response is usually the starting point, and doctors and pharmacists can adjust the dosage from there based on body weight, size, age, and lifestyle.

//Threshold Level//
 * The maximum dose that causes a minimum effect on test populations
 * can also be described as the minimum dose needed to see an effect on test organisms
 * Scientists measure responses based on a dose-response curve. They test high doses on test populations and then work backwards to find the level of dose that does not affect the population- this is the THRESHOLD. Amounts of toxins below this level are typically deemed as "safe".

//The Hormesis Effect (graph on pg. 159)//
 * Some materials can be helpful in small doses but toxic in higher doses
 * Example- Vitamin D (necessary in small doses but causes digestive complications if dose is too high)

__**Effects of Toxins On Children**__
 * children tend to play on floors and lawns where they are more exposed to toxic materials like cleaners and pesticides
 * household pesticides (like bait poxes, bug bombs, flea collars, pesticide pet shampoos) cause 130,000 reports of childhood exposure to toxins each year
 * Research-based study- children from areas where agricultural pesticides are widely used were unable to draw pictures with any kind of organization, while those of the same age but of an area without extensive pesticide use were able to draw comprehensive pictures.

__**Illnesses Related To Natural Systems**__
 * Drinking or exposure to contaminated water with bacteria or viruses
 * Examples- cholera, E. coli
 * Consuming contaminated or undercooked meat and fish products
 * algal blooms- intense growths of algae due to increased nutrients (see the "red tide" picture on pg 165) can cover the surface of water, clouding other organisms from getting sunlight, and disrupts local food systems
 * algal blooms occur when algae are exposed to excess nutrients (nitrogen and phosphorus) and warm temperatures and available sunlight

__**Risk Assessments**__
 * Scientists assess hazards and gauge risks of exposure to chemicals
 * Some risk assessment includes characterization, focusing on populations more likely to encounter that risk.
 * Example- Mexican-Americans typically have over 3x the amount of DDT in their blood as compared to non-hispanic white Americans. DDT is a common chemical in pesticides.
 * Risks must be weighed against costs and gains- this is called a COST-BENEFIT ANALYSIS
 * Risk Assessments may be more economic or they may be more environmental. The EPA conducts environmental risk assessments whenever a project occurs that will alter the environment.