introduction toxicology, general information on some basic toxins used in day to day life and also unknown toxins we are always in contact with but little do we know about them

1. 4/24/2020
REGIONAL INSTITUTE OF EDUCATION, BHOPAL
TOXICOLOGY
Basic concept, types of toxicants, toxicity testing, LC-50, LD-50, acute
and chronic toxicity
Prepared by:
RATNA PANDEY B.SC. B.ED. VIII SEMESTER

2. HISTORY AND BACKGROUND
PARACELSUS: “All substances are poisons; it’s the dose that makes the poison”.
He determined that specific chemicals were responsible for the toxicity of a plant or
chemical poison. He also documented that the bodies response to those chemicals
dependedupon the dose received. His study revealed that small doses of a substance
might be harmless or beneficialwhereas larger doses could be toxic this is known as
dose-response relationship, a major concept of toxicology.
Orfila, a Spanish physician,is often referred to as the founder of toxicology.
He demonstrated effects of poison on specific organs by analyzingautopsy materialsfor
poison and their associated tissue damage. It is recognized that virtuallyall toxic effects
are caused by changes in specific cellularmolecules and biochemicals.
Xenobioticis the general term that is used for a foreign substance taken into the body.
Xenobioticsmay produce beneficialeffects (pharmaceuticals) or they may be toxic (such
as lead). A xenobiotic in small amountsmay be non-toxic and even beneficialbut when
the dose is increased, toxic and lethal effects may result.

3. BASIC CONCEPT OF TOXICOLOGY
TOXICOLOGY: The study of the adverse effects of chemicals or physical agents on living organism.
(The science of poison)
Adverse effects may occur in many forms, ranging from ranging from immediate death to subtle
changes not realized until months or years later.
They may occur at various levels within the body:
 An organ
 A type of cell
 Or a specific biochemical
 Toxinology, a specialized area of study, looks at microbial, plant and
animal venoms, poisons, and toxins.
Types of toxicology: Analyticaltoxicology
 Appliedtoxicology
 Clinicaltoxicology
 Veterinary toxicology
 Forensic toxicology
 Environmentaltoxicology

4. TOXICOLOGY TERMINOLOGY
TOXICANTS Substances that produce adverse biological effects of any nature
Maybe chemical or physical in nature,
Affects maybe of various types (acute or chronic, etc.)
TOXINS Specific protein produced by living organisms
(mushroom toxin or tetanus toxin)
Most exhibit immediate effects.
POISONS Toxicants that cause immediate death or illness when experienced in very
small amounts.
Toxicants, toxins and poisonare often interchangeablyused in the literature;however,
there are subtle differences as indicatedin the table and the images shown as below

5. Pesticide chemicals are toxicants Amanita muscaria mushroom
contains a neurotoxin Black Widow spiders produce a
Toxicants:
 Substances producing adverse biological effects of any kind.
 May be chemical or physical in nature.
 Effects may be acute or chronic.
Toxins:
 Peptides or proteins produced by living organisms.
 Venoms are toxins injected by a bite or sting.
Poisons:
 Toxins produced by organisms.

6. TOXIC AGENTS
A toxic agent is anything that can produce an adverse biological effect. It may be chemical,
physical, or biological in form. For example, toxic agents may be:
Chemical (such as cyanide) Physical (such as radiation) Biological (such as snake venom)
The toxicity of the agent is dependent on the dose.
A distinction is made for diseases people get from living organisms. Organisms that invade and
multiply within another organism and produce their effects by biological activity are not classified

7. as toxic agents but as biological agents. An example of this is a virus that damages cell
membranes resulting in cell death.
If the invading organisms excrete chemicals which are the basis for their toxicity, the
excreted substances are known as biological toxins. In that case, the organisms are called toxic
organisms. A specific example is tetanus. Tetanus is caused by a bacterium, Clostridium tetani. The
bacteria C. tetani itself does not cause disease by invading and destroying cells. Rather,
a toxin (neurotoxin) that the bacteria excrete travels to the nervous system and produces
the disease.
Group of Clostridium tetani bacteria

8. TOXIC SUBSTANCES (TOXICANTS)
A toxic substance is simply a material that has toxic properties. It may be a discrete
toxic chemical or a mixture of toxic chemicals. For example, lead chromate, asbestos,
and gasoline are all toxic substances. More specifically:
 Lead chromate is a discrete toxic chemical.
 Asbestos is a toxic material that does not have an exact chemical compositionbut
comprises a variety of fibers and minerals.
 Gasoline is a toxic substance it containsa mixture of many chemicals. The
compositionof gasoline varies with octane level, manufacturer, time of season, and
other factors.
LEAD CHROMATE ASBESTOS GASOLINE

9. SYSTEMATIC AND ORGAN TOXICANTS
Toxic substances may be systemic toxicants or organ toxicants.
A systemic toxicant affects the entire body or many organs rather than a specific site.
For example, potassium cyanide is a systemic toxicant in that it affects virtually
every cell and organ in the body by interfering with the cells’ abilityto use oxygen.
Toxicants may also affect only specific tissues or organs while not producing damage to
the body as a whole. These specific sites are known as the target
organs or target tissues.
 Benzene is a specific organ toxicant in that it is primarily toxic to the blood-
forming tissues.
 Lead is also a specific organ toxicant; however, it has three target
organs: the central nervous system, the kidneys, and the hematopoieticsystem.
A toxicant may affect a specific type of tissue (such as connective tissue) that is present
in several organs. The toxic site is then considered the target tissue.
Toxic substance may be systematic toxins or organ toxins.

10. A systematic toxin is one that affects the entire body or many organs rather than a
specific site. For example, potassium cyanideis a systematic toxin in that it affects
virtuallyevery cell and organ in the body by interfering with the cells abilityto utilize
oxygen.

11. Natural and Man-Made Chemicals
Often, people mistakenly assume that all man-made chemicals are harmful and
natural chemicals are beneficial.In reality, natural chemicals can be just as harmful to
human health as man-made chemicals, and in many cases, more harmful.
Following figure compares the toxicity of several naturaland man-made chemicals.

12. CHEMICAL TOXICITYIS A SLIDING SCALE,NOT BLACK AND WHITE-AND WHETHER A
CHEMICAL IS OCCURING NATURALLYOR MAN MADE TELL US NOTHING ABOUT TOXICITY.

13. TOXICITY TESTING
Toxicity testing, is the process of determining the degree to which a substance of
interest negatively impacts the normal biologicalfunctionsof an organism, given a
certain exposure duration,route of exposure, and substance concentration.
Toxicity testing is required for new chemicals being introduced into markets.
Toxicologicalscreening is very important for the developmentof mew drugs and for the
extension of the therapeutic potentialof existing molecules.
Toxicity tests are mostly used to examine specific adverse event or specific end point.
Toxicity tests are categorized by test duration,life stage and end points.
Toxicity testing also helps calculatethe No Observed Adverse Effect Level (NOAEL)dose
and is helpful for clinicaltrials.

14. SOURCES OF TOXIC SUBSTANCES
 Classified based on their – chemical nature, mode of action, class (exposure and
use class).
 Exposure class: food, air, water and soil.
 Use class: drugs as drug of abuse, therapeutic drugs, agriculture chemicals, food
additives,pesticides, plant toxins and cosmetics.

15. NECESSITIES OF TOXICOLOGICAL STUDIES
 Benefit – risk ratio can be calculated
 Prediction of therapeuticindex
Therapeuticindex= maximum tolerance/ minimum curative dose
 Smaller ratio better safety of drugs.

16. TYPES OF TOXICITY STUDIES
 Acute toxicity/ single dose studies
 Sub-acute or chronic/ repeated dose studies
 Local toxicity studies
 Allergenicity/ hypersensitivity
 Genotoxicity
 Carcinogenicity/Oncogenicity

17. ACUTE TOXICITY
Preliminary
 Maximum Non-Lethal Dose determined
(MNLD)
Definitive
 MTD (max. tolerated dose) and MLD
determined
 Evaluateeffects
 Target organ of toxicity may be determined

18.  Acute toxicity testing- study the effect of single dose on a particularanimalspecies.
 Acute toxicity testing be carried out with two different animalspecies (one rodent
and one non-rodent).
 In acute toxicologicaltesting, the investigationalproduct is administeredat
different dose levels, and the effect is observed for 14 days. All mortalities caused
by the investigational productduring the experimental period are recorded and
morphological,biochemical,pathologicaland histologicalchanges in dead animals
are investigated.
 The LD50 was used as an indicatorof acute toxicity previously. The determinationof
LD50 involves large numbers of animals, the mortality ratio is high. (24 hours
testing)
 Graphicalmethod
 Arithmetical method (Kerber’s method). When number of animalsis
small.
 Because of these limitations,modified methodswere developed:
 The fixed dose procedure
 The acute toxic category method
 The up-and-downmethod

19. SUB-ACUTE OR CHRONIC TOXICITY
 Two mammalianspecies (one should be non-rodent)
 Long durationstudies (30-180 days)
 Dose is dependenton dose-escalating studies
 Drug administered by clinicalroute
 Parameters monitored and recorded are:
 Behavioral
 Physiological
 Biochemical
 Microscopic observation
 Rodents and non-rodentsare used to study the chronic toxicity of a substance.
 Dose: expected therapeutic level (daily) or expected therapeutic level to increase
dose phase-wise manner.
 The test substance is administered orally for =/>90 days, and regular body weight
variations,biochemicaland cardiovascularparameters changes, and behavioral
changes are observed.
 Used to determine the maximum tolerabledose and nature of toxicity.

20.  During the study period, the animalsare observed for normal physiological
functions, behavioralvariationsand alterationsin biochemicalparameters at
regular intervals(at least every 14 days).
 At the end of the study, tissues are collected from all parts of the animaland
subjected to histologicalanalysis.

21. DOSE
 High dose: produce significant retardationof growth or some pathologicalchanges
(10 times the expected maximum clinicaldose).
 The Low dose is about twice the expected maximum clinicaldose
 Medium dose fixed midway between the high and low dose.
 LD50: the median lethal dose= the effect may be defined as specific toxic event
(tremors) and sometimes defined as lethality
 ED50: the median effective dose= the dose for which half (50%) of the animals’
exhibit (E) and half of animalsexhibit no effect.
 ED10and ED90 are doses at which 10% and 90% of the animalsrespectively
demonstrate effect.
 LC50 is the lethal concentrationrequired to kill 50% of the population.

23. TYPES OF LOCAL TOXICITY STUDIES
Dermal toxicity  Rats and rabbit
 Local signs (erythema, oedema)
 Histologicalexamination
Dermal photo toxicity  Guinea pig
 Used in treatment of leukoderma
 Examinationof erythema and oedema
formation
Vaginaltoxicity  Rabbit or dog
 Observation of swelling
 Histopathologyof vaginalwall

24. Rectal tolerance  Rabbit or dog
 Signs of pain,blood or mucous
 Histology examinationof rectal mucosa
Oculartoxicity  Albinorabbit
 Changes in cornea, iris and aqueous
humor
 Histologicalexaminationof eye
Parenteral drugs  For intravenous/ intra muscular/
subcutaneous/ intra-dermal injection
 Sites of injectionexamined grossly and
microscopically

25. Inhalationtoxicity  One rodent and non-rodent specie
 Acute and chronic studies performed
 Observation of respiratory rate
 Histologicalexaminationof respiratory
passages, lung tissue

26. GENOTOXICITY
In vitro tests:
 Test for gene mutationin Bacteria
 Cytogenetic evaluationof chromosomal damage in mammaliancells
E.g., Ames’s Salmonella Assay detects increased number of aberrationsin
metaphase chromosomes
 DNA strand breaks, DNA repair or recombination,measurements of DNA adduct

27. In vivo tests:
 In vivo test for chromosomal damage using mammalianhematopoieticcells.
 Chromosomal damage in rodent hematopoieticcells
E.g., Micronucleus Assay

28. The use of animalsin evaluatingchemical safety is costly and time consuming.
Furthermore, there is the ethical need to developalternative methodsto reduce the
required number of animals.The new in-vitro assays offer numerous advantagessuch as
speed, reproducibilityandcontrol of test conditions,and increased sensitivity.

29. REFRENCES:
Casarett & Doull’sTOXICOLOGY the basic science of poison- Curtis D. Klaassen
https://toxtutor.nlm.nih.gov/01-002.html - U.S. NATIONAL LIBRARYOF MEDECINE(NIH)
http://pbs.twimg.com/media/CTn6HlDWwAEB1Jc.png:large, I STOCK PHOTOS- IMAGESOURCE
https://www.agriculture.purdue.edu/pesp/rowmanual/chapter_9/1.shtml#top
www.slideshare.net
Google images
Wikipedia