Lecture 9: Environmental Toxicology Flashcards Preview

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Flashcards in Lecture 9: Environmental Toxicology Deck (20):

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)
*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



-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



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


Chlorinated Hydrocarbons & Volatile Organic Compounds

Polycyclic Aromatic Hydrocarbons (PAHs) & Polychlorinated biphenyls (PCBs)

Endocrine Disrupting Compounds

Disinfection Byproducts (new!)



-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


PAH’s & PCBs

-Benzo[a]pyrene, TCDD, and related compounds
-Products of incomplete combustion from industry, incinerators; byproducts of chemical synthesis
-VERY stable, very persistent, resistant to degradation

-Mostly found in soil (too hydrophobic for much water)

-PCBs can also act as endocrine disruptors


Endocrine Disruptors

-Chemical that perturbs normal endocrine signaling, often sex hormones
-Can agonize or antagonize hormone receptor (Estrogen or Androgen Receptor)
-DES & Genistein = ER Agonist
-Phthalates = AR antagonists
-DDT & BPA = ER agonists AND AR antagonists
-Feminized fish & amphibians are well established


Disinfection Byproducts

-Emerging class of toxicants
-Municipal water is disinfected (chloramines, etc.), but reacts with other chemicals in water and with UV to form breakdown products
-N-nitrosodimethylamine (NDMA) is very concerning
*Does not biodegrade, adsorb to solids, or volatilize
*High intensity UV can degrade, and RO filters ~50% out
*Very toxic to liver at low doses and a suspected human carcinogen

-High exposure AND hazardous… RISK!


TCE Toxicity

-1,1,2-Trichloroethene (trichloroethylene)
-One of the most widely used chemicals
-Degreaser, cleaner, anaesthetic, dry-cleaning solvent
-Most common groundwater contaminant in Superfund sites

-US EPA classified as “Human Carcinogen”
-Linked to increased risk of kidney cancer, liver cancer
-Mutagenic by Ames assay, increased oxidative stress
-Allergic dermatitis from high dermal exposure (factories)
-Proposed to cause Parkinson’s Disease


Mitigate Risk & Improve Safety

-Established pathway(s) for:
*Release into environment
*Understanding of the fate and transport in environment
*Potential for- and sources of exposure
*Study exposed populations for health effects
*Understand toxicity/hazards and risks associated with exposure

-Make decisions on how to prevent public exposure