Note
Studied by 10 people
APES Unit 8
Introduction to Toxicology
Key Concepts of Toxicology
Toxicology examines the relationship between the dose of a substance and the toxic response it elicits, emphasizing that higher doses typically lead to greater effects.
A critical assumption is the existence of a threshold dose below which no measurable response occurs, although exceptions exist where low doses can have significant effects.
LD50 (lethal dose for 50% of the population) is a standard measure of acute toxicity, indicating the dose required to kill half of a test population.
LD50 is measured in the units of mg of toxin / kg of body weight. So it tells us how much we must uptake per kg to be considered a 50% chance for lethal toxicity.
This number assumes that the amount of substance is uptaken all at once
LD50 and Its Implications
LD50 values vary significantly; a low LD50 (e.g., 5 mg/kg) indicates high toxicity, while a high LD50 (e.g., 1,000-5,000 mg/kg) suggests low toxicity.
Examples of LD50 values:
LD50 does not account for non-lethal toxic effects, meaning substances with high LD50 can still cause harm at lower exposure levels.
Understanding LD50 is crucial for assessing the risks associated with chemical exposure in both environmental and health contexts.
Dose-Response Curves
Dose-response curves graphically represent the relationship between the dose of a substance and the magnitude of its effect, helping to identify threshold doses and LD50 values.
To analyze these graphs, we first mark a horizontal line across the graph at the 50% dead line.
Wherever this line intersects the graph, we then draw a vertical line down to the x axis to get our results!
Types of Toxins
Biomagnification vs Bioaccumulation
Bioaccumulation:
Process where the toxin collects within an organism over its own lifetime
The older you are, the more the toxin you have
Key Examples: Mercury and Fish, Lead and Humans
Biomagnification:
The process where the contaminant collects in the tissues of an organism and through the eating of organisms it moves up the food chain
A key part about biomagnification is that the effects magnify (get worse) as you move up in trophic levels
Key Example: DDT and Bald Eagles
Specific Toxins
Pathogens and Infectious Diseases
Many pathogens and diseases that impact humans, tend to be very connected to the environment as they use vectors like animals, water, air, etc. to adapt and spread around.
For APES, there are 8 diseases that are important for us to understand because of how they work with the environment to take advantage of new opportunities for spreading/infection:
Bubonic Plague
Tuberculosis
Malaria
West Nile Virus
Severe Acute Respiratory Syndrome (SARS)
Middle East Respiratory Syndrome (MERS)
Zika
Cholera
Vectors of Transmission
When it comes to the spread of the diseases and APES, there a few vectors we care about:
Air
Water
Mosquito/Insect Bites
The problem we are noticing is that with the increasing temperatures seen by some regions, diseases that were once considered more tropical (like Zika, Malaria, and West Nile) are beginning to move further north and south from the Equator as the environment supports the vector of spread more.
Specifics about Diseases
Human Impact and Water Quality
Point Source vs. Nonpoint Source Pollution
Point Source
Nonpoint Source
Pollution that comes from a single, identifiable source, such as a sewage treatment plant or an oil spill.
Examples: Industrial discharges, wastewater treatment facilities, and specific oil spills (Exxon Valdez, Deepwater Horizon, etc.)
Diffuse pollution that comes from multiple sources, such as agricultural runoff or urban stormwater, making it harder to control.
Examples: Runoff from agricultural fields, urban areas, and construction sites.
Management Strategies: Effective water quality management requires addressing both point and nonpoint sources through regulations and best practices.
Case Study: The impact of agricultural runoff on the Mississippi River and the Gulf of Mexico, leading to hypoxic zones.
Human Impacts on Aquatic Ecosystems
Impact
Description
Effects
Plastic Pollution
A significant environmental issue that alters habitats, kills marine and terrestrial life, and inhibits natural processes.
Microplastics have been found in water sources and even in human blood, indicating widespread contamination.
Alters habitats and ecosystems, leading to the death of marine life. Garbage patches, such as the Great Pacific Garbage Patch, illustrate the scale of this issue.
Thermal Pollution
Occurs when excess heat is released into water bodies, negatively affecting aquatic ecosystems.
It can lead to decreased dissolved oxygen levels and increased metabolic rates in ectothermic organisms, disrupting food webs.
Eutrophication***
A process where excess nutrients, primarily from agricultural runoff, lead to algal blooms. The subsequent decomposition of algae depletes oxygen, creating hypoxic zones that can kill aquatic life.
Results in hypoxic environments, increased turbidity, and toxicity in water, affecting both aquatic life and human health.
Coral Reef Damage
Coral reefs are sensitive to changes in water quality and temperature, leading to bleaching and loss of biodiversity.
Coral reefs provide essential ecosystem services, and their degradation leads to loss of biodiversity and increased vulnerability to storms. (They help break the waves coming into shore!)
Oil Spills
Catastrophic events that severely impact marine ecosystems due to the release (either intentional or unintentional), causing long-term damage to water quality and marine life.
The Exxon Valdez and Deepwater Horizon spills are examples of how oil spills can devastate marine environments and economies as the clean up is long term and the impacts can be permanent!
Wetland/Mangrove Destruction
The loss of these critical ecosystems affects water filtration, biodiversity, and coastal protection.
Wetlands act as natural water filters and their destruction leads to increased flooding and loss of biodiversity.
Eutrophication and Biochemical Oxygen Demand (BOD)
Eutrophication occurs naturally, however, it takes thousands of years for bodies of water to go from oligotrophic (where the water is low in plant nutrients and high in oxygen) to eutrophic (where the water is high in plant nutrients and low in oxygen due to the decomposition that occurred)
Humans have had the unfortunate effect of causing this process to take decades (if not less time) to go from oligotrophic to eutrophic.
This is due to the excess of nutrients that are being introduced from:
Urban Runoff
Industrial Discharge
Fertilizers
Erosions
Sewage
The Biochemical Oxygen Demand (BOD) is the measurement of how much oxygen is needed for decomposition to occur.
Events like eutrophication typically cause the demand for oxygen to increase dramatically as the excess nutrients cause algal blooms that die off creating huge amounts of organic matter that decomposers devour like crazy.
The image below shows what happens to the amount of DO and the BOD when sewage is dumped into a body of water like a river or creek.
Key Water Quality Indicators
Water Quality Test
What is it checking for?
What does the result mean?
Temperature
Temperature can determine the amount of oxygen in the water, the rate of photosynthesis, and the sensitivity of organisms to various stressors
DO and Temperature have an inverse relationship with one another.
Meaning that warm water does not hold onto oxygen as much as cold water.
Dissolved Oxygen (DO)
Measures the amount of oxygen in the water
Water with consistently high DO is more likely to be healthy, stable, and can support a larger diversity of aquatic organisms
Nitrate
Nitrate is needed by aquatic plants and animals to build protein
However, Too much nitrate can lead to overgrowth of plants, their eventual death, and their decomposition
This leads to a decrease in oxygen levels in the water, as the decomposition process consumes oxygen
Excess nitrogen in the water is the result of sewage and agricultural runoff
Phosphate
Phosphate is another nutrient needed for plant and animal growth
Too much phosphate also leads to eutrophication
Sources include human/animal waste, excess soap runoff (wastewater), and agricultural runoff
pH
pH is a measure of how acidic or basic the water is
Natural water typically has a pH between 6.5 and 8.2
A slight change in pH can have catastrophic effects on living organisms
pH is affected by waste, agricultural runoff, or draining from mining operations
Turbidity
Turbidity is the measure of how clear the water is
Turbid water is caused by matter such as clay, silt, organic matter, and microorganisms
Turbid water can be the result of soil erosion, urban runoff, algal blooms, and sediment disturbances
Macroinvertebrates
Measuring the macroinvertebrates in the area can give a measure of the biodiversity in the area
Some organisms are much more tolerant of pollution than others
More of these pollution tolerant organisms in an environment compared to pollution intolerant
organisms can indicate polluted water
A diverse macroinvertebrate community is indicative of a healthy aquatic ecosystem, supporting various food webs.
Waste Study Guide
Overview of Waste Types
Waste is categorized into several types:
Municipal Solid Waste: Non Liquid waste from homes, institutions, and small businesses, commonly referred to as trash or garbage.
Industrial Solid Waste: Generated from the production of consumer goods, mining, agriculture, and petroleum extraction.
Hazardous Waste: Toxic, chemically reactive, flammable, or corrosive waste that poses a risk to health and the environment.
Wastewater: Water that has been used and is drained or flushed away, often requiring treatment before disposal.
Sanitary Landfills and Their Management
Sanitary landfills are engineered sites designed to bury waste safely, preventing environmental contamination.
Governed by the Resource Conservation and Recovery Act (RCRA) of 1976, which sets national standards for solid waste management.
Landfills must be located away from wetlands and earthquake-prone areas, and at least 6 meters above the water table to prevent leachate contamination.
Closed landfills can be repurposed for public use, such as parks, exemplified by FreshKills Park in New York City.
Waste Decomposition and Management Techniques
Waste decomposition in landfills is facilitated by bacteria and soil layering, which helps reduce odor and pest issues.
Incineration is a method of waste management that reduces waste volume by up to 95% and weight by up to 85%, but releases toxic dioxins, lead, mercury, etc. into the atmosphere.
The waste stream refers to the flow of waste from its source to disposal, highlighting the importance of managing waste effectively.
Recycling and Economic Considerations
Recycling rates vary significantly by material, and developed countries have seen improvements in waste collection and recycling efforts.
Low commodity prices can hinder recycling programs, as new materials may be cheaper than recycled ones, despite the environmental costs.
Financial incentives, such as 'pay-as-you-throw' programs and bottle bills, have proven effective in increasing recycling rates.
Waste Generation and Consumption Trends
Historical Context of Waste Generation
Waste generation in the U.S. has nearly tripled since 1960, largely due to increased packaging and the prevalence of nondurable goods.
The increase in affluence in developing nations correlates with rising waste production and consumption patterns.
Source Reduction and Waste Minimization
Source reduction is the most effective strategy for managing waste, focusing on minimizing waste generation at its origin.
Strategies for source reduction include designing products with less packaging and promoting reusable materials.
Composting as a Waste Management Strategy
Composting converts organic waste into mulch or humus, enriching soil and mimicking natural cycles.
It involves the use of 'green' (nitrogen-rich) and 'brown' (carbon-rich) materials to facilitate decomposition.
Waste Reduction Strategies
The 5 Rs of Waste Management
Recycle: Involves breaking down items for reuse in producing the same or another kind of item. It is considered the least efficient method of reducing waste.
Reuse: Refers to using an item repeatedly to prevent it from ending up in a landfill. This can include using glass jars for storage or repurposing old furniture.
Reduce: The most effective way to minimize waste is to consume less. This can be achieved by purchasing items with minimal packaging or opting for bulk purchases.
Repurpose: Involves using an item for a new or different purpose, such as turning an old ladder into a bookshelf.
Refuse: The most impactful method of waste reduction, which involves declining unnecessary items, such as plastic bags or straws.
Hazardous Waste Management
Definition and Characteristics of Hazardous Waste
EPA Definition: Hazardous waste is defined by its potential to be harmful to human health or the environment. It must exhibit at least one of the following characteristics:
Ignitable: Can easily catch fire.
Corrosive: Capable of corroding metals.
Reactive: Chemically unstable and can react violently with other substances.
Toxic: Harmful when inhaled, ingested, or touched.
E-Waste: Electronic waste is increasingly treated as hazardous due to its heavy metals and flame retardants.
Disposal Methods for Hazardous Waste
Surface Impoundments: Shallow depressions lined with materials to store liquid hazardous waste, allowing water to evaporate and leaving solid residues for disposal.
Deep-Well Injection: Involves drilling into porous rock to inject waste, posing risks of soil contamination and potential earthquakes.
Historical Context and Legislation - YOU MUST KNOW THE ACTS!!
Love Canal Disaster: A pivotal event in the 1970s that highlighted the dangers of improper hazardous waste disposal, leading to significant health issues in the community.
Resource Conservation and Recovery Act (RCRA): Established standards for hazardous waste management, requiring tracking from 'cradle to grave'.
Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA): Created the Superfund program for cleaning up hazardous waste sites, initiated after the Love Canal incident.
Sewage Treatment Processes
Stages of Sewage Treatment
Primary Treatment: Removes solid materials from wastewater, including trash and sediment.
Bar Screens: Remove the larger solids (💩)
Grit Chamber: Removes the smaller solids the size of sand/dirt
Primary Clarifiers: Allow the particles to settle and help remove them from water
The goal is to remove particles larger 10 μm (micrometer)
Secondary Treatment: A biological process where bacteria break down organic matter into carbon dioxide and inorganic sludge, often enhanced by aeration.
Aeration Chambers: Use O2 and returned sludge (sludge that has bacteria from secondary clarifiers) to breakdown organic matter
Secondary Clarifiers: Similar to primary, but these help remove sludge created from aeration and return some as it contains bacteria to break down organic matter
By the end of this treatment, around 85% of organic matter has been removed
Tertiary Treatment: Involves additional ecological or chemical processes to eliminate remaining pollutants, followed by disinfection using chlorine, ozone, or UV light.
Common Waterborne Illnesses
All of these are made worse in areas that lack water sanitation facilities or processes. Around 3.6 billion people do not have access to sanitation facilities and toilets. With over 1 billion people use their environment as a facility.
Diarrhea: Often caused by pathogens in contaminated water.
Giardiasis: A parasitic infection leading to gastrointestinal distress.
Dysentery: Involves severe diarrhea with blood, often due to bacterial infection.
Typhoid Fever: A serious illness caused by Salmonella typhi, often linked to contaminated water.
E. Coli Infection: Can result from consuming contaminated water or food.
Salmonellosis: A bacterial infection that can be contracted through contaminated water.