This document discusses dose-response relationships and toxicity studies. It provides details on:
- Acute and chronic toxicity studies which determine lethal doses, target organs, and appropriate doses for further studies.
- Factors that influence toxicity like dose, exposure route, chemical properties, and individual variability in things like genetics, age and sex.
- Dose-response curves which illustrate the relationship between dose and effect and are used to determine safe exposure levels.
- Various terms used in toxicity assessments like NOAEL, LOAEL, BMD, RfD, and ADI.
The aim of this lecture is to provide
an overview of the management of various toxic exposures.
emergency medical services that should be immediately contact to provide advanced life support for patient with unstable vital signs resulting from a poisoning exposure.
Ecotoxicology is the science devoted to the study of the adverse effects of chemicals on ecosystems structure, functions, and biodiversity. It is a modern discipline, just developed during the last four decades, directly associated to the need to identify, predict, control, and minimize the negative environmental consequences of the recent human industrial development. Ecotoxicology has always been connected to toxicology, and is in part an extension of human/veterinary toxicology to the investigation of effects on wildlife. In parallel, it also linked ecotoxicology to ecology, from both conceptual and methodological viewpoints.
Toxicology deals with the study of the harmful effects of chemicals on living beings. This branch of science has been equally recognised in medical as well as scientific field
Ecotoxicology is the study of the effects of toxic chemicals on biological organisms, especially at the population, community, ecosystem, and biosphere levels.
This short presentation describes the principles of measuring lipophilicty and bio-mimetic properties, such as protein and phospholipid binding by HPLC. These data can be used to model compound's in vivo distribution.
The aim of this lecture is to provide
an overview of the management of various toxic exposures.
emergency medical services that should be immediately contact to provide advanced life support for patient with unstable vital signs resulting from a poisoning exposure.
Ecotoxicology is the science devoted to the study of the adverse effects of chemicals on ecosystems structure, functions, and biodiversity. It is a modern discipline, just developed during the last four decades, directly associated to the need to identify, predict, control, and minimize the negative environmental consequences of the recent human industrial development. Ecotoxicology has always been connected to toxicology, and is in part an extension of human/veterinary toxicology to the investigation of effects on wildlife. In parallel, it also linked ecotoxicology to ecology, from both conceptual and methodological viewpoints.
Toxicology deals with the study of the harmful effects of chemicals on living beings. This branch of science has been equally recognised in medical as well as scientific field
Ecotoxicology is the study of the effects of toxic chemicals on biological organisms, especially at the population, community, ecosystem, and biosphere levels.
This short presentation describes the principles of measuring lipophilicty and bio-mimetic properties, such as protein and phospholipid binding by HPLC. These data can be used to model compound's in vivo distribution.
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
Polycyclic aromatic hydrocarbons and their effects on the environmentDipo Elegbs
The aim of this presentation is to review
contemporary information on PAH pollution,
PAH degradation, the fate and risk associated
with the presence of these compounds in the
environment and also to enlighten on some
well-known possible remediations.
Pharmacophore Mapping and Virtual Screening (Computer aided Drug design)AkshayYadav176
Pharmacophore Mapping and Virtual Screening (Computer aided Drug design)
Concept of pharmacophore, Pharmacophore mapping, Identification of pharmacophore features and pharmacophore modeling, Conformation search used in pharmacophore mapping, Virtual screening.
Chemical risk assessment is often limited by the lack of experimental toxicity data for a large number of diverse chemicals. In the absence of experimental data, potential chemical hazard is often predicted using data gap filling techniques such as quantitative structure activity relationship (QSAR) models. QSARs are theoretical models that relate a quantitative measure of chemical structure to a physical property or a biological effect. QSAR tools are a widely utilized alternative to time-consuming clinical and animal testing methods, yet concerns over reliability and uncertainty limit application of QSAR models for regulatory chemical risk assessments. The reliability of a QSAR model depends on the quality and quantity of experimental training data and the applicability domain of the model. This talk will describe the basics concepts and best practices in QSAR modeling, principles associated with validation of QSAR models, summary of available QSAR tools, limitations and challenges in the acceptance of QSAR models, and the current status and prospects of QSAR modeling methods in the medical devices community.
INTRODUCTION
Toxicology is the science of the poisons. It also studies the nature, effects, detection, assessment and treatment of their effects on biological material.
Toxicology is a multidisciplinary science. The ultimate objective of the combined research is to determine how an organism is affected by exposure to an agent.
This includes an understanding of:
How the agent moves and interact with living cells and tissues of the organism;
What parts of the organism are affected by its presence and health outcomes of this exposure.
Evaluation of the toxicity of substances whose biological effects may not have been well characterized.
The influence of chemical toxicity is mainly
determined by the dosage, duration of exposure,
route of exposure, species, age, sex, and environment.
The goal of toxicology is to contribute to the
general knowledge and harmful actions of
chemical substances.
2. to study their mechanisms of action,
3. and to estimate their possible risks to humans
HISTORY
Dioscorides, a Greek physician in the court of the Roman emperor Nero, made the first attempt to classify plants according to their toxic and therapeutic effect. Poisonous plants and animals were recognized and their extracts used for hunting or in warfare.
In 1500 BC people used hemlock, opium, arrow poisons, and certain metals to poison enemies or for state executions.
Theophrastus Phillipus Auroleus Bombastus von Hohenheim (1493–1541) (also referred to as Paracelsus, a Roman physician from the first century) is considered "the father" of toxicology.
He stated that "All things are poisonous and nothing is without poison; only the dose makes a thing not poisonous.“
Mathieu Orfila (1813) is considered the modern father of toxicology.
In 1850, Jean Stas became the first person to successfully isolate plant poisons from human tissue.
Hippolyte Visart de Bocarmé used nicotine to kill his brother-in-law. He extracted nicotine from tobacco leaves.
The 20th and 21st Centuries have marked by great advancements in the level of understanding of toxicology. DNA and various biochemicals that maintain body functions have been discovered. Our level of knowledge of toxic effects on organs and cells has expanded to the molecular level.
Mey Akashah, "Risk Assessment and Improved Decision-Making," Harvard School of Public Health, Harvard Medical School, and Harvard Extension School, April 5 2012.
Course: Human Health and Global Environmental Change
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
Polycyclic aromatic hydrocarbons and their effects on the environmentDipo Elegbs
The aim of this presentation is to review
contemporary information on PAH pollution,
PAH degradation, the fate and risk associated
with the presence of these compounds in the
environment and also to enlighten on some
well-known possible remediations.
Pharmacophore Mapping and Virtual Screening (Computer aided Drug design)AkshayYadav176
Pharmacophore Mapping and Virtual Screening (Computer aided Drug design)
Concept of pharmacophore, Pharmacophore mapping, Identification of pharmacophore features and pharmacophore modeling, Conformation search used in pharmacophore mapping, Virtual screening.
Chemical risk assessment is often limited by the lack of experimental toxicity data for a large number of diverse chemicals. In the absence of experimental data, potential chemical hazard is often predicted using data gap filling techniques such as quantitative structure activity relationship (QSAR) models. QSARs are theoretical models that relate a quantitative measure of chemical structure to a physical property or a biological effect. QSAR tools are a widely utilized alternative to time-consuming clinical and animal testing methods, yet concerns over reliability and uncertainty limit application of QSAR models for regulatory chemical risk assessments. The reliability of a QSAR model depends on the quality and quantity of experimental training data and the applicability domain of the model. This talk will describe the basics concepts and best practices in QSAR modeling, principles associated with validation of QSAR models, summary of available QSAR tools, limitations and challenges in the acceptance of QSAR models, and the current status and prospects of QSAR modeling methods in the medical devices community.
INTRODUCTION
Toxicology is the science of the poisons. It also studies the nature, effects, detection, assessment and treatment of their effects on biological material.
Toxicology is a multidisciplinary science. The ultimate objective of the combined research is to determine how an organism is affected by exposure to an agent.
This includes an understanding of:
How the agent moves and interact with living cells and tissues of the organism;
What parts of the organism are affected by its presence and health outcomes of this exposure.
Evaluation of the toxicity of substances whose biological effects may not have been well characterized.
The influence of chemical toxicity is mainly
determined by the dosage, duration of exposure,
route of exposure, species, age, sex, and environment.
The goal of toxicology is to contribute to the
general knowledge and harmful actions of
chemical substances.
2. to study their mechanisms of action,
3. and to estimate their possible risks to humans
HISTORY
Dioscorides, a Greek physician in the court of the Roman emperor Nero, made the first attempt to classify plants according to their toxic and therapeutic effect. Poisonous plants and animals were recognized and their extracts used for hunting or in warfare.
In 1500 BC people used hemlock, opium, arrow poisons, and certain metals to poison enemies or for state executions.
Theophrastus Phillipus Auroleus Bombastus von Hohenheim (1493–1541) (also referred to as Paracelsus, a Roman physician from the first century) is considered "the father" of toxicology.
He stated that "All things are poisonous and nothing is without poison; only the dose makes a thing not poisonous.“
Mathieu Orfila (1813) is considered the modern father of toxicology.
In 1850, Jean Stas became the first person to successfully isolate plant poisons from human tissue.
Hippolyte Visart de Bocarmé used nicotine to kill his brother-in-law. He extracted nicotine from tobacco leaves.
The 20th and 21st Centuries have marked by great advancements in the level of understanding of toxicology. DNA and various biochemicals that maintain body functions have been discovered. Our level of knowledge of toxic effects on organs and cells has expanded to the molecular level.
Mey Akashah, "Risk Assessment and Improved Decision-Making," Harvard School of Public Health, Harvard Medical School, and Harvard Extension School, April 5 2012.
Course: Human Health and Global Environmental Change
Modeling Dose Response for Risk Assessment, George GrayOECD Governance
Presentation by Prof. George Gray, Director of the Centre for Risk Science and Public Health, George Washington University, at the Workshop on Risk Assessment in Regulatory Policy Analysis (RIA), Session 11, Mexico, 9-11 June 2014. Further information is available at http://www.oecd.org/gov/regulatory-policy/
Extrapolation of in vitro data to preclinical and.pptxARSHIKHANAM4
Extrapolation of in vitro data to preclinical.
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micro teaching on communication m.sc nursing.pdfAnurag Sharma
Microteaching is a unique model of practice teaching. It is a viable instrument for the. desired change in the teaching behavior or the behavior potential which, in specified types of real. classroom situations, tends to facilitate the achievement of specified types of objectives.
Ethanol (CH3CH2OH), or beverage alcohol, is a two-carbon alcohol
that is rapidly distributed in the body and brain. Ethanol alters many
neurochemical systems and has rewarding and addictive properties. It
is the oldest recreational drug and likely contributes to more morbidity,
mortality, and public health costs than all illicit drugs combined. The
5th edition of the Diagnostic and Statistical Manual of Mental Disorders
(DSM-5) integrates alcohol abuse and alcohol dependence into a single
disorder called alcohol use disorder (AUD), with mild, moderate,
and severe subclassifications (American Psychiatric Association, 2013).
In the DSM-5, all types of substance abuse and dependence have been
combined into a single substance use disorder (SUD) on a continuum
from mild to severe. A diagnosis of AUD requires that at least two of
the 11 DSM-5 behaviors be present within a 12-month period (mild
AUD: 2–3 criteria; moderate AUD: 4–5 criteria; severe AUD: 6–11 criteria).
The four main behavioral effects of AUD are impaired control over
drinking, negative social consequences, risky use, and altered physiological
effects (tolerance, withdrawal). This chapter presents an overview
of the prevalence and harmful consequences of AUD in the U.S.,
the systemic nature of the disease, neurocircuitry and stages of AUD,
comorbidities, fetal alcohol spectrum disorders, genetic risk factors, and
pharmacotherapies for AUD.
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June 20, 2024, Prix Galien International and Jerusalem Ethics Forum in ROME. Detailed agenda including panels:
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Tom Selleck Health: A Comprehensive Look at the Iconic Actor’s Wellness Journeygreendigital
Tom Selleck, an enduring figure in Hollywood. has captivated audiences for decades with his rugged charm, iconic moustache. and memorable roles in television and film. From his breakout role as Thomas Magnum in Magnum P.I. to his current portrayal of Frank Reagan in Blue Bloods. Selleck's career has spanned over 50 years. But beyond his professional achievements. fans have often been curious about Tom Selleck Health. especially as he has aged in the public eye.
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Introduction
Many have been interested in Tom Selleck health. not only because of his enduring presence on screen but also because of the challenges. and lifestyle choices he has faced and made over the years. This article delves into the various aspects of Tom Selleck health. exploring his fitness regimen, diet, mental health. and the challenges he has encountered as he ages. We'll look at how he maintains his well-being. the health issues he has faced, and his approach to ageing .
Early Life and Career
Childhood and Athletic Beginnings
Tom Selleck was born on January 29, 1945, in Detroit, Michigan, and grew up in Sherman Oaks, California. From an early age, he was involved in sports, particularly basketball. which played a significant role in his physical development. His athletic pursuits continued into college. where he attended the University of Southern California (USC) on a basketball scholarship. This early involvement in sports laid a strong foundation for his physical health and disciplined lifestyle.
Transition to Acting
Selleck's transition from an athlete to an actor came with its physical demands. His first significant role in "Magnum P.I." required him to perform various stunts and maintain a fit appearance. This role, which he played from 1980 to 1988. necessitated a rigorous fitness routine to meet the show's demands. setting the stage for his long-term commitment to health and wellness.
Fitness Regimen
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Tom Selleck health and fitness regimen has evolved. adapting to his changing roles and age. During his "Magnum, P.I." days. Selleck's workouts were intense and focused on building and maintaining muscle mass. His routine included weightlifting, cardiovascular exercises. and specific training for the stunts he performed on the show.
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In recent years, Selleck has emphasized the importance of flexibility and mobility in his fitness regimen. Understanding the natural decline in muscle mass and joint flexibility with age. he includes stretching and yoga in his routine. These practices help prevent injuries, improve posture, and maintain mobilit
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Cardiac conduction defects can occur due to various causes.
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- Video recording of this lecture in English language: https://youtu.be/lK81BzxMqdo
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2. Introduction
• The need to establish some criteria to base the relative safety of
chemicals is essential.
• Several methods are used to obtain data in order to establish safe
levels and provide information about the relative toxicity of
chemicals.
3. Acute Toxicological Studies (1)
• Information concerning the toxicity of a substance is obtained
primarily from either acute or chronic toxicity studies.
• Acute toxicity studies are the most commonly performed studies for
obtaining information on the effects of chemical exposure. They are
short-term, relatively inexpensive tests with death of the test animal
being the useful observed effect.
• Information obtained from acute toxicity tests can be used to
– determine the relative toxicity of different chemicals comparing the respective LD50
values, which are the doses that prove to be lethal for 50 percent of the test animals;
– identify the target organs (heart, liver, kidneys, etc.) that are affected as a result of
exposure; and
– determine the appropriate doses for long term, chronic studies.
4. Acute Toxicological Studies (2)
• To perform acute toxicity studies the test animal population is divided
into several groups, with an equal number of individuals (usually 10 to
50) in each group. One group of test animals –referred to as the
control group – is exposed to all the same experimental conditions
except exposure to the toxic substance.
• The groups are observed for 14 days, and the number of deaths in each
group is recorded.
5. Acute Toxicological Studies (3)
• LC50 is a measure of chemical toxicity resulting from inhalation. LC
means “lethal concentration” and the subscript has the same meaning as
described previous for LD. The unit of measure for the LC50 is usually
expressed as part per million (ppm).
6. Chronic Toxicological Studies (1)
• Chronic toxicity tests may be performed over a period of months, years,
or the lifetime of the test animal. Doses of the toxic substance are
selected to assure that most of the animals will survive the entire time
the study is performed.
• Different species of test animals may be more or less sensitive to the
same toxic chemical.
• Males and females of the same species may respond differently to the
same substance.
• Although acute and chronic studies provide useful information in
evaluating chemical toxicity, it is important to understand that they are
not truly representative of the environment to which people are exposed
in everyday life.
7. Chronic Toxicological Studies (2)
• Characteristics of animal studies
– A single dose
– A single route of exposure
– The number of animals exposed is small.
– The genetic make-up of the population is not very diverse.
– Only individuals in good health and/or of the same sex are selected.
• In reality
– Several different routes
– Exposure to more than one chemical at a time
– Greater genetic variability in a larger population – the range of
responses to a given chemicals more diverse.
– The collective interactive effect of all these factors on toxicity
makes it difficult to establish a cause-effect relationship.
8. Dose-Response Curves (1)
• The major purpose for performing acute and chronic toxicity studies is
to establish a cause-effect relationship between exposure to a toxic
substance and an observed effect in order to determine a safe exposure
level.
• A curve can be drawn that illustrates the relationship between the dose
administered and the observed response. This curve is referred to as
the dose-response curve.
• A dose-response curve can be developed form most chemicals. From
these curves the threshold level and the relative toxicity of chemicals can
be obtained to help establish safe levels of chemical exposure.
9. Dose-Response Curves (2)
• The threshold is the dose below which no effect is detected
or above which an effect is first observed.
• The threshold information is useful information in
extrapolating animal data to humans and calculating what
may be considered a safe human dose for a given toxic
substance.
• The threshold dose (ThD0.0) is measured as mg/kg/day. It
is assumed that humans are as sensitive as the test animal
used. To determine the equivalent dose in man the ThD0.0
is multiplied by the average weight of a man, which is
considered to be 70 kg.
10. Dose-Response Curves (3)
• The calculation used to determine the safe human dose
(SHD) is as follows:
substance
toxic
of
mg/day
Amount
SF
(kg)
70
ThD
SHD 0.0
Where
SHD = Safe Human Dose
ThD0.0 = Threshold dose at which no effect is observed.
70 Kg = Average weight of a man
SF = Safety factor (ranges from 10 to 1000, which varies
according to the type of test and data used to
obtain the ThD0.0.
11. Terminology Associated with
Dose-Response Curves (1)
• No observed effect level (NOEL)
– The highest tested dose of a substance that has been
reported to have no harmful (adverse) health effects on
people or animals.
• No observed adverse effect level (NOAEL)
– It denotes the level of exposure of an organism, found by
experiment or observation, at which there is no
biologically or statistically significant (e.g. alteration of
morphology, functional capacity, growth, development
or life span) increase in the frequency or severity of any
adverse effects in the exposed population when
compared to its appropriate control.
12. Terminology Associated with
Dose-Response Curves (2)
• lowest-observed-effect-level (LOEL)
– Lowest concentration or amount of a substance, found
by experiment or observation, that causes any alteration
in morphology, functional capacity, growth, development,
or life span of target organisms distinguishable from
normal (control) organisms of the same species and
strain under the same defined conditions of exposure
• lowest-observed-adverse-effect-level (LOAEL)
– Lowest concentration or amount of a substance, found
by experiment or observation, which causes an adverse
alteration of morphology, functional capacity, growth,
development, or life span of a target organism
distinguishable from normal (control) organisms of the
same species and strain under defined conditions of
exposure.
13. Terminology Associated with
Dose-Response Curves (3)
• Frank-effect level (FEL)
– Level of exposure that produces unmistakable and
irreversible effects (such as impairment or mortality)
at statistically significant increased severity or
frequency.
– The level where overt effects are observed is referred to
as the Frank-effect level.
14. Threshold Dose
• Dose below which no adverse effects are observable in a
population of exposed individuals.
• Threshold dose approximated by a NOAEL (No Observed
Adverse Effect Level)
16. Safe Dose for Threshold Effect
• NOAEL approach
– Identify the adverse effect that occurs at the lowest dose
– Determine the NOAEL or LOAEL for that endpoint
– Divide NOAEL/LOAEL by uncertainty factors
17. Acceptable Daily Intake
• ADI estimated (maximum) amount of an agent, expressed
on a body mass basis, to which a subject may be exposed
over his lifetime without appreciable health risk (also TDI,
tolerable daily intake)
• ADI derived from NOAEL by the use of uncertainty
factors UFs (or safety factors SFs)
18. Reference Dose (RfD)
• RfD is an estimate of the daily exposure that is likely
to be without appreciable health effect even if
continued exposure occurs over a lifetime.
20. Additional Uncertainty Factors
• Sometimes applied:
– UFLOAEL-NOAEL = 3 or 10
– UFsubchronic-chronic = 3 or 10
– UF database insufficiences = up to 10
• MF, modifying factor for professional judgement: up
to 10
• RfD = NOAEL (or LOAEL) / UF1 UF2 UF3 MF
21. Benchmark Dose Approach (1)
• NOAEL approach uses only single points, shape of
dose-response is ignored.
• Bench mark dose (BMD) is calculated from the curve
fitted to the dose-reponse data, so all information is
used.
• BMD can only be used when available data are
suitable for modelling.
• Not replacement for NOAEL, but additional tool
22. Benchmark Dose Approach (2)
1. A mathematical model is applied to the
experimental data to produce a dose-response curve
of best fit.
2. By statistical calculation an upper 95% confidence
limit of the curve is determined
3. The Benchmark Response is defined as 10% (or 5%,
or 1%).
4. The Benchmark Dose corresponds to the bench
mark response on the upper confidence limit curve.
24. Non-threshold?
• Absence of a detectable effect at low doses is either
because the dose is below a threshold or because the
response is below the level that can be detected by the
test sytem.
25. Threshold or Non-threshold
• Presence of a threshold cannot be proven from
experimental data.
• Conclusions about existence of a threshold are based
on biological plausibility and expert judgement.
• Genotoxic effects (DNA dammage leading to cancer)
are thought to be possible at any level of exposure, so
no threshold.
27. Calculated Risk or Safe Dose
• Extrapolation may be used to calculate:
– the risk associated with a known intake.
– intake associated with a de minimis risk, e.g. an
increased life time risk of developing cancer of 1
in 106 (‘virtually safe dose’, VSD).
30. From LED10 to VSD
• If LED10 = 57 mg/kg/day (response 10% or 0,1)
• then VSD (virtual safe dose, response 1 in 106 or 10-6)
= 57 x 10-6 / 0,1 = 5,7 x 10-4 mg/kg/day
31. ALARA Approach
• For genotoxic carcinogens (non-threshold effects)
also the ALARA-approach may be followed:
exposure to be reduced to as low as reasonably
achievable (ALARA) or as low as reasonably
practical (ALARP)
32. Relative Toxicity (1)
• A comparison of the dose-response curves for two or more different
chemicals – administered to the same type of test animal – can be used
to determine the relative toxicity of the chemicals.
• The LD50 for chemical A is less than the LD50 for chemical B.
Therefore, chemical A is considered more toxic than chemical B.
33. Relative Toxicity (2)
• Chemical A is more toxic than chemical B at the higher
doses, but at the lower doses chemical B is more toxic than
chemical A.
34. Relative Toxicity (3)
• Relative toxicity also be evaluated by comparing the slope
of each dose-response curve. A steep dose-response curve
is indicative of a chemical that is rapidly and extensively
absorbed and slowly detoxified: therefore, the chemical is
more toxic.
35. Variables Influencing Toxicity
• These factors include:
– the dose-time relationship,
– the route of exposure,
– the physical and chemical properties of the toxic substance,
– the chemical interactions,
– the interspecies and intraspecies variability,
– genetics,
– age,
– sex, and
– health of the individual collectively.
• The toxicity of a given substance is the net result of the
complex interaction between all of these various factors.
36. Dose-Time Relationship
• Not only is the dose of a toxic substance important in
determining toxicity, but so is the frequency and length of
exposure.
• The rapid elimination of the substance from the blood
stream decreases the probability of an adverse effect.
• Gradual accumulation increases the probability that an
adverse effect will occur.
– Symptoms of acute exposure to sublethal quantities of chlorinated
solvents, such as chloroform or carbon tetrachloride, are primarily
associated with the nervous system, such as excitability, dizziness
and narcosis.
– Chronic exposure to these solvents is primarily associated with
liver damage.
37. Routes of Exposure
• LD50 values for various organochlorine and
organophosphate pesticides resulting from ingestion and
skin exposure.
• The different absorption rates for various regions of the
skin in the human male
38. Physical and Chemical Factors
• Chemical toxicity can be affected by the arrangement of
the atoms in a molecule.
• The structural differences can result in different toxic
effects being observed as a result of exposure.
– The LD50 for 1,1-dichloroethylene is 5,750 mg/kg and the LD50 for
the 1,2-dichloroethylene isomers is 770 mg/kg.
– Based on animal studies, 1,1-dichloroethylene is a suspected human
carcinogen. Its structure is similar to a known human carcinogen,
vinyl chloride.
– The 1,2-dichloroethylene isomers are not carcinogenic, but they do
have different effects. The cis isomer is an irritant and acts as a
narcotic (causes drowsiness). The trans isomer affects the central
nervous system (brain and spinal cord) and the gastrointestinal
system causing weakness, tremors, cramps, nausea; it may also
cause liver and kidney damage.
39. Interspecies and Intraspecies Variability
• Interspecies variability
– The variability in response between species is primarily the result
of the evolution of different biological mechanisms involved in the
metabolism of toxic substances.
– The differences in toxicity may be due to the rate at which
metabolism occurs, or whether metabolism produces chemical
intermediates more toxic than the parent compound.
• For example, the pesticide malathion is metabolized at a different rate in
mammals than in insects. In mammals, the chemical intermediates are rapidly
metabolized to deliver end products that are excreted from the body. In insects
metabolize malathion more slowly and produce a chemical intermediate ---
malaoxon --- that is toxic to the insect.
• Methanol intoxication results in ocular damage and blindness. However, in
other species methanol is less toxic and the symptoms associated with human
intoxication are not observed.
• Rats do not have a vomiting reflex. Rodenticides, such as squill, are more
effective if they are ingested because the rat can not discard the substance by
vomiting.
40. Intraspecies (individual) variability
• Individuals within a population ---exposed to a single dose
--- will demonstrate a wide array of responses.
• This type of variability can be caused by differences
associated with individual genetics and sex of the
individuals within the population.
41. Genetics
• The differences in genetics makeup both within species and
between species markedly influence the disposition and the
metabolism of toxic substances.
– For example, some individuals have an enzyme (glucose-6-
phosphate dehydrogenase) deficiency resulting in their red blood
cells being more fragile than normal. Consequently, red blood cells
of these individuals are more susceptible to chemicals such as
phenylhydrazine and primaquine, which cause hemolysis.
– The enzyme aryl hydrocarbon hydroxylase (AHH) transforms the
chemical benzo[a]pyrene to its carcinogenic metabolite. Some
individuals produce lower amounts of AHH; benzo[a]pyrene is
therefore less toxic to these individuals. Similarly, low AHH
individuals may be less likely to develop cancer from cigarette
smoke.
42. Age
• In general, younger and developing individuals are more
sensitive to toxic substances than older individuals. The
difference can be primarily attributed to differences in
metabolisms; specially to differences in the functioning of
the liver.
• In younger individuals the mechanisms for detoxifying
substances are less developed than in older individuals.
However, some substances are less toxic to the young than
to adults.
• The lead absorption rate is four to five times greater in
young individuals than in adults; the cadmium absorption
rate is 20 times greater than in adults.
43. Sex
• The difference in toxicity between genders seems to be
primarily influence by the sex hormones (estrogen and
testosterone), which can affect metabolism.
• Some organophosphate pesticides are more toxic to
females than males.
– Parathion is metabolized more rapidly in females resulting in a
higher concentration of the more toxic intermediate, paraoxon.
– Male rats are 10 times more susceptible to liver damage than
female rats as a result of chronic oral exposure to DDT.
44. State of Health
• The liver and the kidney are important organs for
detoxifying and removing toxic substances. Therefore,
conditions that lead to liver or kidney disease enhance the
toxic effects of substances normally detoxified by these
organs.
45. Chemical Interactions (1)
• The interaction between two or more chemicals and their
subsequent effects have not been widely studied; not
because these interactions are not important, but rather
because the results are difficult to interpret and
extrapolate, and also because the studies are longer and
costlier.
• The presence of other chemicals at the time of exposure or
as a result of previous exposure can affect the response to
the specific toxicant being studied. These effects can be
additive, synergistic, antagonistic, or they may
demonstrate the characteristics associated with
sensitization or potentiation
46. Chemical Interactions (2)
• Additive effects
– An additive effect occurs when the combined effect of
the two chemicals is equal to the sum of the effects of
each individual chemical.
• Synergistic effect
– A synergistic effect occurs when the observed effects are
greater than what would be predicted by simply
summing the effects of each individual chemical.
47. Chemical Interactions (3)
• Antagonistic effects
– Antagonistic effects are the basis on which antidotes are
developed to counteract the effects of toxic substances
that enter the body.
– Antagonistic effects occur when the sum of the effects of
each individual chemical is less than the sum of the
effects for both chemicals.
48. Chemical Interactions (4)
• Four major types of antagonism
– Functional antagonism
• It refers to a type of reaction two chemicals have on a specific
physiological function in the test organism, usually producing
counterbalancing or opposite effects.
– Chemical antagonism
• It may be referred to as chemical inactivation. This type of
interaction is the result of a reaction between two chemicals to
produces a less toxic product.
– Dispositional antagonism
• The toxic substance is either transformed into a less toxic
substance or it is eliminated from the body more rapidly, then
the observed effects will be less than the expected ones.
49. Chemical Interactions (5)
– Receptor antagonism
• It occurs when two chemicals require binding to the same
receptor in order to exert their effect. The result is that when
the two chemicals are administered together the observed effect
is less than the sum of the effects for each chemical.
– Sensitization
• Initial exposure to toxic chemicals does not always result in an
observable or measurable effect. However, subsequent
exposure to the same chemical may result in an observable or
measurable effect.
• Sensitization occurs as a result of the interaction of the body’s
immune system with the toxic chemical during the initial
exposure.
50. Chemical Interactions (6)
– Potentiation
• At first glance it would appear that synergism and potentiation
are the same. In A potentiation, only one of the chemicals has
an observable effect when administered alone.
• Chemical A has no effect on mortality (0%). Chemical B
causes 25% mortality. When the two chemicals are
administered together the effect is greater than the sum of their
individual effects (0% + 25% = 100 %).
51. LD50 of
Chemicals
Substance Animal, Route LD50 Reference
Sucrose (table sugar) rat, oral 29,700,000,000 ng/kg [7]
Vitamin C (ascorbic acid) rat, oral 11,900,000,000 ng/kg [8]
Grain alcohol (ethanol) rat, oral 7,060,000,000 ng/kg [10]
Melamine rat, oral 6,000,000,000 ng/kg
Table Salt rat, oral 3,000,000,000 ng/kg [12]
Paracetamol (acetaminophen) rat, oral 1,944,000,000 ng/kg [13]
Metallic Arsenic rat, oral 763,000,000 ng/kg [15]
Aspirin (acetylsalicylic acid) rat, oral 200,000,000 ng/kg [17]
Caffeine rat, oral 192,000,000 ng/kg [18]
Cadmium oxide rat, oral 72,000,000 ng/kg [22]
Nicotine rat, oral 50,000,000 ng/kg [23]
Strychnine rat, oral 16,000,000 ng/kg [24]
Arsenic trioxide rat, oral 14,000,000 ng/kg [25]
Metallic Arsenic rat, intraperitoneal 13,000,000 ng/kg [26]
Sodium cyanide rat, oral 6,400,000 ng/kg [27]
Beryllium oxide rat, oral 500,000 ng/kg [30]
Aflatoxin B1 (from Aspergillus flavus) rat, oral 480,000 ng/kg [31]
Dioxin (TCDD) rat, oral 20,000 ng/kg [33]
Polonium-210 human, inhalation 10 ng/kg (estimated) [37]
Botulinum toxin (Botox)
human, oral,
injection, inhalation
1 ng/kg (estimated) [38]
Ionizing radiation human, irradiation 6 Gy