Lecture 9: Environmental Toxicology Flashcards Preview

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Flashcards in Lecture 9: Environmental Toxicology Deck (20):
1

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…)

2

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

3

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

4

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.

5

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

6

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

7

“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

8

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

9

Transformation

1) Abiotic degradation
2) Biotic degradation

10

Abiotic degradation

-Photolysis (UV degradation), photooxidation
-Hydrolysis (increases with high temp and pH extremes)
-Radical reactions (NO2 + UV -> NO + O• ; O• + O2 -> O3)

11

Biotic degradation

-Microbes in soil & water degrade chemicals for energy
-Often reduction reactions in soil (O2 poor environment)
-Can sometimes produce toxins (methylmercury)

12

Understanding _____will inform evaluation of toxicity, risk, and ways to mitigate risk.

-Source of chemical
-Physicochemical properties
-Half-life and degradation reactions

13

Chemicals of Concern

Metals

Chlorinated Hydrocarbons & Volatile Organic Compounds

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

Endocrine Disrupting Compounds

Disinfection Byproducts (new!)

14

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

15

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

16

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)

-Carcinogenic
-PCBs can also act as endocrine disruptors

17

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

18

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!

19

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

20

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
*Regulatory
*Advisory
*Education