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1. Lecture 20Lecture 20
ToxicologyToxicology
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2. ToxicologyToxicology
Environmental HazardsEnvironmental Hazards are the pollutants that are potentiallyare the pollutants that are potentially
harmful and may pose long-term health risks to people who liveharmful and may pose long-term health risks to people who live
and work around the area or facilities that produce or use themand work around the area or facilities that produce or use them
Hazardous materialsHazardous materials includeinclude::
Infectious AgentsInfectious Agents
► Environmentally transmitted infectious diseasesEnvironmentally transmitted infectious diseases spread fromspread from
interactionsinteractions of individuals with food, water, air, or soilof individuals with food, water, air, or soil
► Environmentally transmitted diseases includeEnvironmentally transmitted diseases include Salmonella,Salmonella,
malaria, etc.malaria, etc.

3. ToxicologyToxicology
Toxic Heavy MetalsToxic Heavy Metals
► Among the heavy metals,Among the heavy metals,
mercury, lead, arsenic,mercury, lead, arsenic,
cadmium, copper, zinc,cadmium, copper, zinc,
seleniumselenium are of most concernare of most concern
► Have directHave direct physiologicalphysiological
toxictoxic effectseffects
► Some are stored orSome are stored or
incorporated inincorporated in living tissueliving tissue,,
sometimes permanentlysometimes permanently
Organic CompoundsOrganic Compounds
► Difficult to generalize aboutDifficult to generalize about
the environmental and healththe environmental and health
effectseffects
► There areThere are so manyso many of them,of them,
so many usesso many uses, and they can, and they can
produceproduce so manyso many differentdifferent
kindskinds of effectsof effects
► Pest control,Pest control,
pharmaceuticals, foodpharmaceuticals, food
additives, and otheradditives, and other
consumer productsconsumer products

4. ToxicologyToxicology
RadiationRadiation
► Nuclear radiation isNuclear radiation is
considered as a category ofconsidered as a category of
pollution because exposurepollution because exposure
to nuclear radiation is linkedto nuclear radiation is linked
to serious health problems,to serious health problems,
includingincluding cancercancer
Thermal PollutionThermal Pollution
► Changes the average waterChanges the average water
temperature andtemperature and
concentration of dissolvedconcentration of dissolved
oxygen, changing the riversoxygen, changing the rivers
speciesspecies compositioncomposition
ParticulatesParticulates
► Released into the atmosphere by manyReleased into the atmosphere by many
natural processes and human activitiesnatural processes and human activities
► Chemical toxins, such as heavy metals,Chemical toxins, such as heavy metals,
enter the biosphere as particulatesenter the biosphere as particulates
AsbestosAsbestos
► Asbestos refers to a group ofAsbestos refers to a group of fibrousfibrous
silicate mineralssilicate minerals
► UsedUsed as insulation materialas insulation material aroundaround
pipes and for brake linings ofpipes and for brake linings of
automobilesautomobiles
► WhenWhen inhaledinhaled it may causeit may cause asbestosisasbestosis
(a pneumonia condition),(a pneumonia condition),
bronchogenicbronchogenic carcinomacarcinoma (lung(lung
cancer)cancer)

5. ToxicologyToxicology
Electromagnetic FieldsElectromagnetic Fields
(EMFs)(EMFs)
► Electromagnetic fields areElectromagnetic fields are
part of our everyday urbanpart of our everyday urban
lifelife
► Children exposed to EMFsChildren exposed to EMFs
from power lines have anfrom power lines have an
increasedincreased risk ofrisk of
contracting leukemia,contracting leukemia,
lymphomas, and nervouslymphomas, and nervous
system cancerssystem cancers
Noise PollutionNoise Pollution
Personal pollutantsPersonal pollutants
► Most common of these areMost common of these are tobacco,tobacco,
alcohol, and other drugsalcohol, and other drugs
► Use and abuse lead to a variety ofUse and abuse lead to a variety of
human illshuman ills ranging from sufferingranging from suffering
and/or dying from chronic disease,and/or dying from chronic disease,
criminal activity such as recklesscriminal activity such as reckless
driving or manslaughter, streetdriving or manslaughter, street
crime, loss of careerscrime, loss of careers
► 30% of all cancers30% of all cancers in the US arein the US are
tied to smoking-related disorderstied to smoking-related disorders

6. Fundamentals of ToxicologyFundamentals of Toxicology
AA poison or toxicantpoison or toxicant is a substance that is harmful to livingis a substance that is harmful to living
organismsorganisms
ToxicologyToxicology is the science that studiesis the science that studies poisons (or toxinspoisons (or toxins))
► AA basic concept ofbasic concept of toxicology istoxicology is thatthat any synthetic or naturalany synthetic or natural
chemical (even water) can be harmful if ingested in a large enoughchemical (even water) can be harmful if ingested in a large enough
quantityquantity
• Environmental toxicologyEnvironmental toxicology concerned withconcerned with how environmentalhow environmental
toxicantstoxicants, through their interaction with humans, animals, and, through their interaction with humans, animals, and
plants,plants, influence the health and welfareinfluence the health and welfare of humans, animals, andof humans, animals, and
plants, as well asplants, as well as ways to prevent or minimizeways to prevent or minimize adverse effectsadverse effects

7. ToxicologyToxicology
ToxicityToxicity measures how harmful a substance ismeasures how harmful a substance is
ToxicityToxicity depends ondepends on severalseveral factors:factors:
► DoseDose
► Frequency ofFrequency of exposureexposure
► Who is exposedWho is exposed
► How wellHow well the body’sthe body’s detoxification systemsdetoxification systems ((liver, lungs, andliver, lungs, and
kidneys)kidneys) workwork
► Genetic makeupGenetic makeup that determines an individual’sthat determines an individual’s sensitivitysensitivity to ato a
particular toxinparticular toxin
SeveralSeveral other factorsother factors cancan affectaffect thethe harm causedharm caused by a substance,by a substance,
such assuch as

8. ToxicologyToxicology
 Whether a toxicant isWhether a toxicant is solid, liquidsolid, liquid, or, or gasgas,, organicorganic oror inorganicinorganic,,
ionizedionized oror nonionizednonionized;; solubilitysolubility (whether in water or fat);(whether in water or fat);
persistencepersistence;; bioaccumulation, biomagnification, chemicalbioaccumulation, biomagnification, chemical
interactionsinteractions
TheThe effecteffect of toxicants following exposure can be immediate (of toxicants following exposure can be immediate (acuteacute
toxicitytoxicity) or prolonged () or prolonged (chronic toxicitychronic toxicity))
Acute toxicityAcute toxicity, which ranges from, which ranges from dizziness and nausea to deathdizziness and nausea to death,,
occurs immediately to within several days following aoccurs immediately to within several days following a singlesingle
exposureexposure
Chronic toxicityChronic toxicity generally produces damage to vital organs, such asgenerally produces damage to vital organs, such as
the kidneys or liver, following athe kidneys or liver, following a long-term, low-level exposurelong-term, low-level exposure toto
toxicantstoxicants

9. ToxicologyToxicology
Concept of Dose and ResponseConcept of Dose and Response
► Dose is the most important factorDose is the most important factor affecting the toxicityaffecting the toxicity
► DoseDose or concentrationor concentration is the amount of a harmful substance ais the amount of a harmful substance a
personperson ingests, inhales, or absorbsingests, inhales, or absorbs
► The effect of a certain chemical on an individual depends on theThe effect of a certain chemical on an individual depends on the
dose or concentrationdose or concentration of the toxic factor—of the toxic factor—dose-responsedose-response

10. Concept of Dose and ResponseConcept of Dose and Response
► Usually when we think of dose, we think in terms of taking oneUsually when we think of dose, we think in terms of taking one
vitamin capsule a day or two aspirin every four hours, orvitamin capsule a day or two aspirin every four hours, or
something like thatsomething like that
► Contamination of food or water with chemicals can alsoContamination of food or water with chemicals can also
provide doses of chemicals each time we eat or drinkprovide doses of chemicals each time we eat or drink
► Some commonly used measures for expressing levels ofSome commonly used measures for expressing levels of
contaminants are listed incontaminants are listed in Table 1Table 1
► These measures tell us how much of the chemical is in food,These measures tell us how much of the chemical is in food,
water or airwater or air
► The amount we eat, drink, or breathe determines the actualThe amount we eat, drink, or breathe determines the actual
dose we receivedose we receive

11. Table 1. Measurements for Expressing Levels of Contaminants
in Food and Water
Dose
Abbre
v
Metric
equivalent
Abbre
v
Approx. amt. in water
parts per
million
ppm
milligrams per
kilogram
mg/k
g
1 teaspoon per
1,000 gallons
parts per
billion
ppb
micrograms per
kilogram
ug/kg
1 teaspoon per
1,000,000 gallons

12. ToxicologyToxicology
ResponseResponse is the effect upon an organism resulting fromis the effect upon an organism resulting from
exposure to a toxicantexposure to a toxicant
► ResponseResponse variesvaries greatlygreatly with duration of exposurewith duration of exposure
► TheThe modemode of exposureof exposure, whether, whether continuous or intermittentcontinuous or intermittent
► Activity level of an exposed organismActivity level of an exposed organism
► Normally,Normally, continuous exposurecontinuous exposure isis more injurious thanmore injurious than
intermittentintermittent exposureexposure
► Individuals differIndividuals differ in theirin their responseresponse to environmental toxins,to environmental toxins,
just as they do in response to all environmental conditionsjust as they do in response to all environmental conditions

13. Dose-Response CurveDose-Response Curve
► The relationship of doseThe relationship of dose
to response can beto response can be
illustrated as a graphillustrated as a graph
called acalled a dose-responsedose-response
curvecurve
► The dose is representedThe dose is represented
on theon the xx-axis-axis andand
response is representedresponse is represented
on theon the yy-axis-axis
► The following graphThe following graph
shows a simple exampleshows a simple example
of a dose-response curveof a dose-response curve
for an individual with afor an individual with a
single exposure to thesingle exposure to the
chemical ethanolchemical ethanol
(alcohol), with graded(alcohol), with graded
responses between noresponses between no
effect and deatheffect and death
Individual Dose-Response
Curve

14. Dose-Response CurveDose-Response Curve
► An important aspect of dose-responseAn important aspect of dose-response
relationships is the concept ofrelationships is the concept of
thresholdthreshold, below which there are no, below which there are no
adverse effects from exposure to theadverse effects from exposure to the
chemicalchemical
► The human body has defenses againstThe human body has defenses against
many toxic agentsmany toxic agents
► Cells in human organs, especially inCells in human organs, especially in
the liver and kidneys, break downthe liver and kidneys, break down
chemicals into nontoxic substanceschemicals into nontoxic substances
that can be eliminated from the bodythat can be eliminated from the body
in urine and fecesin urine and feces
► In this way, the human body can takeIn this way, the human body can take
some toxic insult (at a dose that issome toxic insult (at a dose that is
below the threshold) and still remainbelow the threshold) and still remain
healthyhealthy
► It is important for toxicologists toIt is important for toxicologists to
identify a level exposure to a chemicalidentify a level exposure to a chemical
at which there is no effect and toat which there is no effect and to
determine thresholds when possibledetermine thresholds when possible

15. ► The most commonly used measure, linked to the dose-The most commonly used measure, linked to the dose-
response curve, is theresponse curve, is the amount of exposure require foramount of exposure require for
50%50% of a population or observed subjects to show aof a population or observed subjects to show a
responseresponse
► The dose at which 50% of the population dies is called theThe dose at which 50% of the population dies is called the
median lethal dose 50median lethal dose 50, or, or LDLD5050 (lethal dose)(lethal dose)
► TheThe EDED5050 ((effective dose 50%effective dose 50%) is the dose that causes an) is the dose that causes an
effect in 50% of the population or observed subjectseffect in 50% of the population or observed subjects
► For example, theFor example, the EDED5050 of aspirin would be the dose thatof aspirin would be the dose that
relieves headaches in 50% of the peoplerelieves headaches in 50% of the people
► TheThe TDTD5050 ((toxic dose 50%toxic dose 50%) is defined as the dose that is) is defined as the dose that is
toxic to 50% of the populationtoxic to 50% of the population
ToxicologyToxicology

16. Health Risk AssessmentHealth Risk Assessment
TheThe four steps involvedfour steps involved in risk assessmentin risk assessment
are:are:
(1) Hazard Identification(1) Hazard Identification
(2) Dose-response assessment(2) Dose-response assessment
(3) Exposure assessment(3) Exposure assessment
(4) Risk characterization(4) Risk characterization

17. Step What It Answers
1.Hazard
Identification
Does exposure to a substance cause an increased
likelihood of an adverse health effect such as cancer or
birth defects?
2. Dose-response
assessment
What is the relationship between amount of exposure
(dose) and the seriousness of the adverse health effects?
3.Exposure
assessment
How much, how often, and how long are humans
exposed to the substance in question? For hazardous air
pollutants, emissions are measured and analyzed to
determine the relationship between emissions and
concentrations in the environment. Where humans live
relative to the emissions is also considered.
4.Risk
characterization
What is the probability of an individual or population
having an adverse health effect? Risk characterization
combines and evaluates data from dose-response
assessment and exposure assessment (step 2 & 3).

18. Health Risk AssessmentHealth Risk Assessment
► Once a risk assessment has been performed, its results areOnce a risk assessment has been performed, its results are
evaluatedevaluated
► Evaluation, which includes the development and implementationEvaluation, which includes the development and implementation
of laws to regulate hazardous substances, is known asof laws to regulate hazardous substances, is known as riskrisk
managementmanagement
Risk assessment helps us to estimate the probability that an eventRisk assessment helps us to estimate the probability that an event
will occur and enables us to set priorities and manage risks in anwill occur and enables us to set priorities and manage risks in an
appropriate wayappropriate way

19. Conceptual Framework
Hazard Assessment
Toxicity Assessment
Acute & Chronic Toxicity
Exposure
Chemical and physical
transformation
Risk Characterization
Risk Management

20. End of SlidesEnd of Slides