Chapter 7 Human Health and Environmental Toxicology. Overview of Chapter 7. Human Health Health issues in developed countries Health issues in developing countries Environmental Pollution and Disease Environmental Contaminants Endocrine Disrupters
Overview of Chapter 7 • Human Health • Health issues in developed countries • Health issues in developing countries • Environmental Pollution and Disease • Environmental Contaminants • Endocrine Disrupters • Determining Health Effects of Pollutants • Ecotoxicology • Risk Assessment
Human Health • Two indicators of human health in a given country are: • Life expectancy- how long people are expected to live • Infant mortality- how many children die before age of 1 year • Vary greatly between countries • Developed countries • Developing countries
Health Issues in Highly Developed Countries • By many measures- health is good in these countries • Great sanitation • Few childhood diseases • Average life expectancy • Men = 75 years • Women = 80 years • Leading causes of death in US: • Cardiovascular disease • Cancer • Chronic Obstructive Pulmonary Disease (of the lungs)
Health Issue inHighly Developed Countries • Premature deaths caused by individual lifestyle decisions • Poor diet • Lack of exercise • Smoking • Obesity is big problem • Body Mass Index (BMI) • (Weight X 740)/ (height (in))2 • If your BMI is less than 18.5, you are underweight • If your BMI is 18.5-24.9, you are at a healthy weight • If your BMI is 25-29, you are overweight • A BMI of greater than 30 is obese
Health Issues in Developing Countries • Biggest problems • Malnutrition, unsafe water, poor sanitation • Life Expectancy • Overall is 65 years • Very poorest developing countries = 45 years • Most of these countries have high AIDS epidemics • Childhood mortality is high (18% of deaths) • Diarrheal diseases • Malnutrition • Malaria • AIDS/HIV
Emerging and Reemerging Diseases • Emerging Disease - not previously observed in humans • Usually jumps from animal host • Ex: AIDS, lyme disease, West Nile Virus, SWINE FLU!!!!! • Reemerging Disease- existed in the past and are recently increasing in incidence • Ex: tuberculosis, yellow fever, malaria
Reasons for Emergence/Reemergence • Evolution of disease so it can move to human host • Evolution of antibiotic resistance in disease • Urbanization and overcrowding • Increased pop. of elderly- susceptible to disease • Pollution and environmental degradation • Growth in international travel and commerce • Poverty and social inequality
Environmental Pollution and Disease • Often difficult to link pollutants to their effects on people • Three ways to analyze toxic effects of pollutants: • Persistence • Bioaccumulation • Biomagnification
1. Persistence • A characteristic of certain chemicals that are extremely stable and may take many years to be broken down into simpler forms by natural processes • Synthetic chemicals (those not found in nature) • Ex: DDT • Natural decomposers (bacteria) have not evolved a way to break it down
Bioaccumulation • The buildup of a persistent toxic substance in an organism’s body, often in fatty tissues • Synthetic chemical do not metabolize well • They remain in the body for extended periods of time
Biomagnification • The increased concentration of toxic chemicals in the tissues of organisms that are at higher levels in food webs • Diagram is example of biomagnification of DDT
Endocrine Disrupters • A chemical that mimics or interferes with the actions of the endocrine system in humans and wildlife • i.e. It effects the ability of the hormones in the organisms to function properly • Examples include: • PCBs, Dioxins • Heavy metals – lead and mercury • DDT • Animals exposed to these chemicals have altered reproductive development and are often sterile
Endocrine Disrupters • Case Study: 1980 chemical spill into Lake Apopka, FL • Male alligators began to exhibit low testosterone levels and high estrogen levels
Endocrine Disrupters and Humans • Infertility and hormonally related cancers are increasing • Breast cancer and testicular cancer • Phthalates have been implicated as potential endocrine disrupters • Common ingredient in: cosmetics, fragrances, nail polish, medication, toys, food packaging • Cannot make a link between endocrine disrupters and human illness • Too few studies have been performed
Determining Health Effects of Pollutants • Toxicology is the study of the effect of toxicants on the human body • Toxicant- chemical with adverse human health effects • Acute toxicity • Adverse effects occur within a short period after exposure to toxin • Chronic toxicity • Adverse effects occur some time after exposure, or after prolonged exposure to toxin • Symptoms often mimic other diseases- hard to assess source
Toxicity • Toxicity measured by dose and response • Dose: amount that enters the body of an exposed organism • Response: the amount of damage caused by a specific dose • Dose – Response Curve • Typically the dose is plotted against the percentage of the population of test organisms showing the response…on logarithmic graph paper
Toxicity • Dose-Response Curve • Illustrates the effect of different doses on a population • Threshold Level • Maximum dose with no measurable effects Threshold Level
Toxicity: Dose-Response Curves • ED50 = Effective Dose • The dose that causes 50% of the population to exhibit whatever effect is under study (effective dose) • LD50 = Lethal Dose • The dose that is lethal to 50% of the test organisms • Smaller the LD50, the more lethal the chemical • Determined for all new synthetic chemicals
ED50 • This dose-response curve demonstrates two assumptions of classical toxicology. • The biological response increases as the dose is increased • There is a “safe” dose below which there is no response (the threshold level)
Results of Toxicology Testing • Dose response curves for 2 hypothetical toxicants, A and B • Toxicant A has a lower Effective Dose than toxicant B • Toxicant B, however, is MORE toxic at lower doses!
Results of Toxicology Testing • Hormesis = occurs when a toxin is healthy at low doses (necessary) but harmful at high doses (cadmium, vitamin D, etc) • Aka the “hormetic effect”!
Children and Chemical Exposure • Children more susceptible to chemicals • Weigh less than adults • Bodies are still developing • Play on floors and lawns • Exposed to cleaning products and pesticides • Put things into their mouths • Diagram • Children in foothills not exposed to pesticides • Children in valley were exposed
Identifying Cancer Causing Substances (Carcinogens) • Toxicologists • Dose rats with varying levels of chemicals to see if they develop cancer • Difficult to extrapolate results to humans • Both mammals, but very different body size, metabolic rates, diet, etc. Humans may respond the same as rats, or very differently for a given toxin! • Doses given to animals are usually much larger than the typical doses humans are exposed to! • Lab animals only live about 2 years…humans 75-80! • Human exposure is much more sporadic…and involves multiple chemicals and exposure pathways
Toxicology vs. Epidemiology… • Epidemiologists • Look at historical exposure of groups of humans • See if exposed group have increased cancer rate • Make generalizations about risk based upon likelihood of exposure and effects. • A very uncertain science!
Chemical Mixtures • Most studies look at one chemical, but humans tend to be exposed to chemical mixtures • Ex: automobile exhaust • Chemical Mixtures interact by • Additivity = exactly what one would expect, the combined effect of two toxins is the sum of the two toxins • Synergy = when the effect of two toxins has a greater combined effect than the sum of the two individual toxins • Antagonism = when the combined effect of two toxins is less than the sum of the two individual toxins • Toxicity studies are expensive and take a while to complete
Ecotoxicology • Dilution Paradigm is not valid • “Dilution is the solution to pollution” • Boomerang Paradigm is accepted • “What you throw away can come back and hurt you” • Ecotoxicology • The study of contaminants in the biosphere and their harmful effects on ecosystems • Helps policy makers determine costs and benefits of industrial and technological “advances” • And how they often adversely effect ecosystems
Case Study: The Ocean • Land based nutrient and pollution runoff into ocean is affecting microorganisms • Ex: Red Tide • Red pigmented poisonous algal blooms • Toxins kill off fish and make humans sick
Red Tides…. (Diatoms) • Algal bloom = a sudden increase in the diatom population in shallow coastal waters • “Brown tides” on Long Island were a sudden diatom bloom that occurred in the 1980’s…and devastated the scallop industry….no known cause for this! • Harmful Algal Blooms (HAB’s) are now monitored by NOAA
Harmful Algal Blooms Bulletin… • See a HAB bulletin from January 2008 for NE Florida
Gulf of Mexico “The Dead Zone”…
The Dead Zone • The dead zone is a large area of the Gulf of Mexico, where the Mississippi River drains and deposits sediment into the delta • Hypoxia = an oxygen-free condition; this is why the area is “dead” • this occurs in the Gulf of Mexico due to excess nutrient loading from the Mississippi River watershed
Hypoxia: • Every summer, this environmental phenomenon occurs off the coast of Louisiana, covering over 7,000 square miles of the Gulf of Mexico at times. • The Gulf of Mexico "Dead Zone", or hypoxic zone, is an expanse of oxygen-depleted waters that cannot sustain most marine life. • This hypoxic zone is caused by excessive amounts of nitrogen pollution delivered to the Gulf by the Mississippi River, and the subsequent eutrophication process (dead algae eaten by bacteria)
The Dead Zone…. • The Dead Zone has become a serious threat to commercial fishing, shrimping and recreation industries. • The livelihoods of many thousands of people and their communities are at risk, as is the large marine ecosystem on which they depend. • The vast size of the Dead Zone and the severity of its impact are largely a consequence of human activity — such as river course and landscape alterations, industry, municipal waste treatment and agriculture — throughout the Mississippi River Basin.
The Dead Zone…. • Human activity has resulted in enormous increases in the amount of dissolved inorganic nitrogen delivered to the Gulf by the Mississippi River. • Current estimates suggest that three times as much nitrogen is being carried into the Gulf today compared with levels 30 years ago or at any previous time on record.
Life in the Dead Zone • During the summer months of low oxygen, while fish and other mobile animals can escape the developing Dead Zone, bottom dwellers that are attached to the ocean floor are doomed as the normal bottom ecosystem collapses. • Significantly, when the autumn mixing brings oxygen levels back to normal, the bottom communities do not have the chance to revive. Instead, the area tends to be re-colonized by only a few short-lived species (such as polychaete worms) that can establish themselves in the aftermath of the Dead Zone.
Life in the Dead Zone • Larger, longer-lived species (such as gastropods, bivalves, starfish, brittle stars and sea anemones) vanished from this part of the Gulf 30-40 years ago. • These new bottom communities fall far short of the normal ecosystems in diversity, abundance or biomass. • Ken Teague of the U.S. Environmental Protection Agency says “In the Dead Zone, the original bottom communities were lost a long time ago.”
Risk Assessment • Risk- probability that a particular adverse effect will result from some exposure or condition • Risk Assessment = the use of statistical methods to quantify the risks of a particular action so they can be compared or contrasted with other risks • We assess risk daily with four steps • Hazard identification • Dose response assessment • Exposure assessment • Risk characterization