principles of toxicology: the study of...

Arizona Water Issues

Principles of Toxicology:The Study of Poisons

1The University of Arizona – HWR 203 Adopted from: Casarez/ Donnelly


The study of the adverse effects of a toxicant on living organisms• Adverse effects

– any change from an organism’s normal state– dependent upon the concentration of active

compound at the target site for a sufficient time.

• Toxicant (Poison)– any agent capable of producing a deleterious

response in a biological system



Axioms of Toxicology

• There is a dosage or exposure level that has no observable effect on the health of animals – as measured by methods which have a finite sensitivity to measure dysfunction or injury. (NOAEL)

Does this mean it is safe?

• Any substance can provoke a dysfunction or injury at some degree of exposure – the dose makes the poison. Attenuation of injury can often be achieved by dilution. Complications can occur when there is exposure to more than one agent – even at “non-toxic” doses. In general, laboratory studies do not look at these complicated cases.

What does this say about the state of our knowledge?



Axioms of Toxicology

• There is essential uniformity in the biochemistry in similar species – among biological mechanisms in mammals. This means animal data is extrapolatedfor predictions in humans.

What are advantages/disadvantages of animal testing?

• Toxicological data from animal experiments can be used to assess the degree of exposure or dosage that will NOT adversely affect human health. However, potential or real differences between animals and humans require that judgmental factors be applied when extrapolating animal threshold doses in order to insure an adequate margin of safety for humans.

Animal testing must be extrapolated carefullyWe should error on the side of caution



DoseDose: The amount of chemical entering the body

This is usually given as mg of chemical/kg of body weight = mg/kg

The dose is dependent upon:* The environmental concentration* The properties of the toxicant* The frequency of exposure* The length of exposure* The exposure pathway (route)



What is a Response?

• Change from normal state– could be on the molecular, cellular, organ, or organism

level--the symptoms

• Local vs. Systemic • Reversible vs. Irreversible• Immediate vs. Delayed• Graded or Quantal

– continually varying vs. all-or-none

The degree and spectra of responses depend upon the dose and the organism



Dose-Response Relationship:

2

3

4

0 1 DOSE

RE

SPO

NSE

Ranges:4 Maximum Response2-3 Linear Range0-1 NOAEL

Dose determines the biological response

As the dose of a toxicant increases, so does the response

Limitations• Often derived fromacute exposure data.• Species variation



LD50

• If Mortality is the response, the dose that is lethal to 50% of the population LD50 can be generated from this curve

Not everybody reacts in the same way to a toxic exposure

(or ED) DoseLD50

100%

50%

10-30 fold variation w/in a population!



LD50 ComparisonChemical LD50 (mg/kg) Ethyl Alcohol 10,000 Sodium Chloride 4,000 Ferrous Sulfate 1,500 Morphine Sulfate 900 Strychnine Sulfate 150 Nicotine 1 (1 mg) Black Widow 0.55 Curare 0.50 Rattle Snake 0.24 Dioxin (TCDD) 0.001 Botulinum toxin 0.0001

Different toxicants can be compared--lowest dose is most potent9The University of Arizona – HWR 203

Adopted from: Casarez/ Donnelly


Sources of CaffeineSource Amount

mg / 12 ozDose if 150lbs

ie. 68 kg

Coffee - brew 137-260 250/16oz or 3.6 mg/kg

Coffee - decaf 5

Iced tea 70

Nestea 25

Coke 34 102/36oz or 1.5 mg/kg

Mt. Dew 55Monster, RedBull 80-160 240/24oz or 3.5 mg/kg


Source: www.energyfiend.com/the-caffeine-database

Read Carefully!“The actual caffeine content for many energy drinks is not easily identified on product packaging or via the Internet. The total amount of caffeine contained in some cans or bottles of energy drinks can exceed 500 mg (equivalent to 14 cans of common caffeinated soft drinks) and is clearly high enough to result in caffeine toxicity.23 A lethal dose of caffeine is considered to be 200 to 400 mg/kg.24”Clinical Report–Sports Drinks and Energy Drinks for Children and Adolescents: Are They Appropriate?Guidance for the Clinician in Rendering Pediatric Care:www.pediatrics.org/cgi/doi/10.1542/peds.2011-0965

WARNING: distinguish amount from dose

Arizona Water Issues The University of Arizona – HWR 203 Adopted from: Casarez/ Donnelly

11

Toxicity vs. Health Impacts

“MY COUSIN IS 16 YEARS OLD AND HE WOULD DRINK UP TO FIVE MONSTERS A DAY. FOR THE PAST MONTH HES BEEN ACTING REALLY WEIRD. HE TALKS TO HIMSELF, HES REALLY SHAKY, HE CANT SIT NOT EVEN FOR A MINUTE. HE HAS TO BE MOVING AND HE SLEEPS ALOT THE FAMILY IS SO WORRIED. ITS SCARY TO SEE WHAT A ENERGY DRINK IS DOING TO MY TEENAGE COUSIN.”Anonymouswww.aboutlawsuits.com/energy-drink-health-risk-warnings-1161/


12


Exposure Routes & DosesChemical Animal Route LD50 Dose

Caffeine MouseRatRat

Mouse

OralOralIVIV

620 mg/kg192 mg/kg105 mg/kg68 mg/kg

HgCl (II) RatMouse

OralOral

37 mg/kg10 mg/kg

Dimethylarsenic(cotton defoilant)

Rat Oral 700 mg/kg

Amt: 200 g rat 38 mg; 70 kg person 13,440 mg = 54 cups



Factors Influencing Toxicity

• Related to the:– chemical– person– exposure– environment



The Human Factors

• Gender• Age• Duration• Route of exposure• Genetics• Species variation



Individual SusceptibilityThere can be 10-30 fold difference in response to a

toxicant in a population

• Genetics-species, strain variation, interindividualvariations (yet still can extrapolate between mammals--similar biological mechanisms)

• Gender (gasoline nephrotox in male mice only)• Age--young (old too)

– underdeveloped excretory mechanisms– underdeveloped biotransformation enzymes– underdeveloped blood-brain barrier



Individual Susceptibility

• Age--old– changes in excretion and metabolism rates, body fat

• Nutritional status• Health conditions• Previous or Concurrent Exposures

– additive --antagonistic– Synergistic

The disadvantaged are often more susceptible



Exposure: DurationAcute < 24hr usually 1 exposureSubacute 1 month repeated dosesSubchronic 1-3mo repeated dosesChronic > 3mo repeated doses

Over time, the amount of chemical in the body can build up, it can redistribute, or it can overwhelm repair and removal mechanisms



Exposure: Pathways• Routes and Sites of Exposure

– Injection • intravenous

– Inhalation (Lungs)– Injection

• Intraperitoneal, intramuscular– Ingestion (Gastrointestinal Tract)– Dermal/Topical (Skin)

• Typical Effectiveness of Route of Exposureiv > inhale > ip > im > ingest > topical



Response to Toxic Substances

• Skin/eyes• Central Nervous system• Respiratory tract• Circulation system• Liver / Kidneys• Digestive system• Reproductive system• Bones and joints• Cancer and others



Target Organs: adverse effect is dependent upon the concentration of active compound at the

target site for enough time• Not all organs are affected equally

– greater susceptibility of the target organ– higher concentration of active compound

• Liver--high blood flow, oxidative reactions• Kidney--high blood flow, concentrates chemicals• Lung--high blood flow, site of exposure• Neurons--oxygen dependent, irreversible damage• Myocardium--oxygen dependent• Bone marrow, intestinal mucosa--rapid divide



ADME: Absorption, Distribution, Metabolism, and Excretion

• Once a living organism has been exposed to a toxicant, the compound must get into the body and to its target site in an active form in order to cause an adverse effect.

• The body has defenses:– Membrane barriers

• passive and facilitated diffusion, active transport

– Biotransformation enzymes, antioxidants– Elimination mechanisms



Absorption:ability of a chemical to enter the blood

• Inhalation--readily absorb gases into the blood stream via the alveoli. (Large alveolar surface, high blood flow, and proximity of blood to alveolar air)

• Ingestion--absorption through GI tract stomach (acids), small intestine (long contact time, large surface area--villi; bases and transporters for others)

• Dermal--absorption through epidermis (stratum corneum), then dermis; site and condition of skin



Distribution: the process in which a chemical agent translocates

throughout the body

• Blood carries the agent to and from its site of action, storage depots, organs of transformation, and organs of elimination

• Rate of distribution (rapid) dependent upon– blood flow– characteristics of toxicant (affinity for the

tissue, and the partition coefficient)• Distribution may change over time



Distribution:Storage and Binding

• Storage in Adipose tissue--Very lipophylic compounds (DDT) will store in fat. Rapid mobilization of the fat (starvation) can rapidly increase blood concentration

• Storage in Bone--Chemicals analogous to Calcium--Fluoride, Lead, Strontium

• Binding to Plasma proteins--can displace endogenous compounds. Only free is available for adverse effects or excretion



Complex Mixtures

• Cigarette smoke • Breakdown products of PCE• Gasoline

• Potential Health Effects:– May be similar to “dominant” chemical– potential interactions VERY uncertain

Exposure guidelines are just now being written


Oral Reference Dose (RfD)

• An estimate, with uncertainty spanning perhaps an order of magnitude, of a daily oral exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime.

RfD = NOAEL/(uncertainty factors>100)Units: mg/kg/day


27


Complex ExampleConcentration (mg/L) / Oral Ref Dose (mg/kg*d) = Non carcinogenic Risk factor (Rn)

Concentration (mg/L) * Slope Factor (kg*d/mg) = Carcinogenic Risk factor (Rc)

Rn + Rc = Rtotal (compound specific)

Volume Weighted Average Concentrations from Both Wells

Che

mic

al

Wat

er C

once

ntra

tion

(mg/

L)

Wat

er Q

ualit

y St

anda

rd

(mg/

L)

Ora

l RfD

(mg/

kg*d

)

Ora

l SF

(kg*

d/m

g)

R o

ral,

nonc

arci

noge

nic

(che

mic

al s

core

)

R o

ral,

carc

inog

enic

(c

hem

ical

sco

re)

Rto

tal

Perc

ent R

tota

l

Ran

k

Cum

ulat

ive

Perc

ent

Ris

k

Arsenic 0.055 0.010 3.0E-04 1.5 183 0.083 183 56.7 1 56.7Fluoride 7.7 4/2 0.06 128 128 39.7 2 96.4Nitrate 17 10 1.6 10.6 11 3.3 3 99.7Barium 0.060 2 0.07 0.86 1 0.3 4 100

32328The University of Arizona – HWR 203



Target Sites: Mechanisms of Action

• Adverse effects can occur at the level of the molecule, cell, organ, or organism

• Molecularly, chemical can interact with Proteins Lipids DNA

• Cellularly, chemical can– interfere with receptor-ligand binding– interfere with membrane function– interfere with cellular energy production– bind to biomolecules– perturb homeostasis (Ca)



Excretion: Toxicants are eliminated from the body by several routes

• Urinary excretion– water soluble products are filtered out of the blood by

the kidney and excreted into the urine• Exhalation

– Volatile compounds are exhaled by breathing• Biliary Excretion via Fecal Excretion

– Compounds can be extracted by the liver and excreted into the bile. The bile drains into the small intestine and is eliminated in the feces.

• Milk Sweat Saliva



Metabolism: adverse effect depends on the concentration of active

compound at the target site over time• The process by which the administered chemical

(parent compounds) are modified by the organism by enzymatic reactions.

• 1o objective--make chemical agents more water soluble and easier to excrete– decr. lipid solubility --> decr. amount at target– increase excretion rate --> decrease toxicity

• Bioactivation--Biotransformation can result in the formation of reactive metabolites



Biotransformation (Metabolism)

• Can drastically effect the rate of clearance of compounds

• Can occur at any point during the compound’s journey from absorption to excretion

Compound WithoutMetabolism

WithMetabolism

Ethanol 4 weeks 10mL/hr

Phenobarbital 5 months 8hrs

DDT infinity Days to weeks

32

The University of Arizona – HWR 203 Adopted from: Casarez/ Donnelly


Biotransformation

• Key organs in biotransformation– LIVER (high)– Lung, Kidney, Intestine (medium)– Others (low)

• Biotransformation Pathways* Phase I--make the toxicant more water soluble* Phase II--Links with a soluble endogenous

agent (conjugation)



Toxicology• Exposure + Hazard = Risk• All substances can be a poison• Dose determines the response• Pathway, Duration of Frequency of Exposure and

Chemical determine Dose• Absorption, Distribution, Metabolism & Excretion• The extent of the effect is dependent upon the

concentration of the active compound at its site of action over time

• Bioactivation: compounds to reactive metabolites• Individual variation of the organism will affect

ADME



EPA Risk Paradigm

Chemical

Emission Transport Receptor

Health Effect



ConclusionsDue to the variability of humans, it is extremely

difficult to establish causation with any degree of certainty

Prevention is the most effective method to minimize the impact of exposure to environmental chemicals

Human exposures are most often associated with complex mixtures.

All populations include sensitive and resistant individuals, thus it is difficult to predict effects based on an “average”.

Uncertainty is a fact of life36The University of Arizona – HWR 203



What is a Poison?

All substances are poisons;there is none that is not a poison.

The right dosedifferentiates a poison and a remedy.

Paracelsus (1493-1541)


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