Lecture 9: Environmental Toxicology Flashcards
Environmental Toxicology
“The study of the fate and effects of chemicals in the environment”
Study on adverse effects of environmental chemicals on human health
Ecotoxicology: effects of environmental contaminants on ecosystems (maybe another time…)
Overall objectives of the field: Environmental Toxicology
- Identify the chemicals we’re exposed to in the environment
- Often of anthropogenic (human-derived) sources
- Measurement of levels and exposure
- Characterize chemicals with respect to:
- Movement in environment
- Availability and toxicity
- Toxicity (target, mechanism, sensitive populations)
- Determine:
- Exposure scenarios
- Chemical Hazard
- Risk of health effects
- Mitigate risk and avoid health effects
Exposure, Hazard & Risk
- Exposure: how you come in contact with an agent or chemical
- Includes contact through time and space
- e.g. breathing a chemical 8 hours/day at the workplace
- Hazard: potential for harm due following exposure
- Modified by the severity of the consequences
- e.g. dioxin is a very hazardous toxic chemical, while butter is not (at the same dose)
- Risk: magnitude of hazard and probability of occurrence
- e.g. chronic exposure to acetaminophen is more risky than never being exposed to cyanide
Environmental Chemistry Definition
“…the sources, identity, levels, reactions, transport, and fate of chemical species in water, soil, and air environments.”
How a chemical:
gets into,
moves around in,
changes in the environment…
…and how that affects exposure and toxicity.
Environmental Chemistry
- Physicochemical properties determine fate and transport
- Influence chemical movement between environmental media (air, water, soil, biota)
- Affect persistence (how long it’s in the environment after it’s released)
- Determine exposure potential and toxicity
Fate & Transport
- Chemicals partition into different media based on physicochemical properties (Px, Kow/logP, molecular composition, etc.)
- High vapor pressure chemicals will volatilize from soil or water into air (even through buildings)
- Very hydrophobic chemicals will stick to soil or sediment and not move
- Less hydrophobic chemicals will partition from soil into water
- Saltwater reduces water solubility of hydrophobic compounds
“Persistent Organic Pollutants” (POPs)
“Persistent Organic Pollutants” (POPs) are a major concern in environmental toxicology
- Identified in the Stockholm Convention
- long environmental half-lives (degradation resistant)
- transport long distances
- Bioaccumulate in organisms and magnify in food webs
- Chlorinated pesticides, polychlorinated biphenyls (PCBs), brominated flame retardants (BFRs), etc. are all POPs
Bioaccumulation:
- Hydrophobic chemicals can bioaccumulate in fatty tissues
- DDT in water at 0.1 ppb can bioaccumulate in fish to 1000 ppb!
- Chemicals accumulate their way up the food web causing health effects in upper trophic levels (including us!)
- DDT interfered with Calcium metabolism in birds, causing thin eggshells
Transformation
1) Abiotic degradation
2) Biotic degradation
Abiotic degradation
- Photolysis (UV degradation), photooxidation
- Hydrolysis (increases with high temp and pH extremes)
- Radical reactions (NO2 + UV -> NO + O• ; O• + O2 -> O3)
Biotic degradation
- Microbes in soil & water degrade chemicals for energy
- Often reduction reactions in soil (O2 poor environment)
- Can sometimes produce toxins (methylmercury)
Understanding _____will inform evaluation of toxicity, risk, and ways to mitigate risk.
- Source of chemical
- Physicochemical properties
- Half-life and degradation reactions
Chemicals of Concern
Metals
Chlorinated Hydrocarbons & Volatile Organic Compounds
Polycyclic Aromatic Hydrocarbons (PAHs) & Polychlorinated biphenyls (PCBs)
Endocrine Disrupting Compounds
Disinfection Byproducts (new!)
Metals
- Often found in soil AND in groundwater
- Lead, Arsenic, Mercury, Chromium (expecially CrVI), Selenium are some of the most important (especially in Western US)
- Come from natural rock formations and industrial activity
- Exposure through drinking in groundwater
- Exposure through dust inhalation and crop contamination in soil
- Lead & Mercury are neurotoxins (upcoming lecture)
- Arsenic & CrVI are carcinogens
- CrVI is genotoxic and an oxidative stressor -> kidney & liver damage
Chlorinated HCs & VOCs
- Persistent chemicals -> prolonged exposure opportunity
- Halogenated compounds are resistant to biotic degradation
- Come from industrial (aerospace, technology) and commercial (dry cleaners, mechanics) activity
- Found in groundwater and buildings via vapor intrusion from soil or groundwater
- CHCs & VOCs make a “plume” in groundwater – you can smell it
- Carcinogenic
