Toxicology Toxicology the study of how natural or

Toxicology

Toxicology: the study of how natural or manmade poisons cause undesirable effects in living organisms. Undesirable Effects: damaging to either the survival or normal function of the individual.

Addresses a variety of questions: EX: in agriculture, toxicology determines the possible health effects from exposure to pesticides or herbicides, or the effect of animal feed additives, such as growth factors, on people. -In laboratory experiments on animals to establish dose-response relationships. - deals with the way chemicals and waste products affect the health of an individual.

Basic Terminology Toxin: toxic substances produced naturally. A toxin is any poisonous substance of microbial (bacteria or other tiny plants or animals), vegetable, animal or non-synthetic chemical origin that reacts with specific cellular components to kill cells, alter growth or development, or kill the organism.

Toxicant: any chemical that can injure or kill humans, animals, or plants; a poison. - used when talking about toxic substances that are produced by or are a by-product of human-made activities. EX: dioxin (2, 3 -7, 8 -tetrachlorodibenzo-p-dioxin {TCDD}), produced as a by-product of certain chlorinated chemicals Arsenic, a toxic metal, may occur as a natural contaminant of groundwater OR may contaminate groundwater as a by-product of industrial activities. If the second case is true, such toxic substances are referred to as toxicants, rather than toxins.

Toxic: poisonous or deadly effects on the body by inhalation (breathing), ingestion (eating), or absorption, or by direct contact with a chemical Toxicity describes the degree to which a substance is poisonous or can cause injury.

Depends on a variety of factors: 1. Dose: the actual amount of a chemical that enters the body. The amount of exposure and the type of toxin will determine the toxic effect. Acute (short term) exposure occurs over a very short period of time, usually 24 hours. Chronic exposures occur over long periods of time such as weeks, months, or years.

l l Dose-response is a relationship between exposure and health effect, that can be established by measuring the response relative to an increasing dose. Threshold dose: a dose or exposure level below which the harmful or adverse effects of a substance are not seen in a population.

also referred to as the no observed adverse effect level (NOAEL), or the no effect level (NEL). - for substances causing cancer (carcinogens), no safe level of exposure exists, since any exposure could result in cancer. LOAEL – least observed adverse effect level – when negative results are first seen in a test population

2. Duration - how long – chronic or acute 3. Shape and structure of the chemical itself: determines how it will interact with cells and other chemicals Effect of p. H on Absorption

4. Route of exposure: dermal, oral, respiratory Gastrointestinal Tract: - absorption depends on structure of chemical

Respiratory Tract: - inhalation or aspiration of gas, liquid or solid particles - absorption depends on solubility of the substance into the blood or the size of the particles Size of Particulate Matter: Dust, soot - particle > 10 micrometers generally don’t enter the respiratory tract – deposited in nose and sinus cavity – trapped in mucus and expelled - particles < 0. 01 micrometers – exhaled - particles between 0. 01 and 10 micrometers can be lodged in respiratory tract – the smaller the particle the deeper in the lungs they travel

Skin – relatively impermeable due to the compact dead cells at the surface - permeable to non-polar substances like chemical solvents - substances may (although in small amounts) be absorbed through the hair follicles, sweat glands and sebaceous glands

5. Barriers to Absorption: Blood brain barrier: Located in the capillary wall of the blood vessels in the brain – tightly joined and don’t let charged materials into the brain – allows lipid soluble (fat like substances) into the brain Placenta – made up of layers of tissue derived both from the mother and child – usually prevents the transfer of most toxicants Exception: methyl mercury – higher in fetuses than mothers because of a less effective (developed) blood brain barrier

6. Binding and Storage: site of toxin/toxicant storage - Permanent binding or Reversible binding – depends on the type of chemical bond - covalent bonds tend to be permanent - ionic or weak molecular bonds tend to be reversible Changes in Toxicant Levels in a Body - can be problematic in the future if the storage site is broken down and releases the toxicant at a future date - site depends on nature of the chemical Adipose tissue – binding of lipid soluble chemicals (DDT and DDE) Bone – mineral toxicants such as lead – replace the mineral matrix in the bone

7. Excretion and Elimination: - principle routes: urine, biliary (liver), respiratory - urine: water soluble substances are usually excreted through the kidneys – one of the roles of the kidney and liver is to convert non-water soluble substances into excretable forms - biliary – toxicants in the blood and those bound to blood proteins are removed by the liver and become part of the bile which is then excreted into the small intestine and eventually leave with feces – some may be metabolized by the intestinal flora and then be reabsorbed - lungs – gases dissolved in the blood can diffuse out through the lungs - other routes: gastrointestinal, mother’s milk, sweat and saliva

8. Biotransformation and Bioactivation: Toxicants can undergo chemical change in the organism to produce products called metabolites - this process is called biotransformation – usually organisms biotransform toxicants into less harmful products in order to excrete them - if the metabolite is more toxic than the original chemical then the chemical is said to have undergone bioactivation – some chemicals in the body that are actually harmless become toxic through bioactivation

Benzo[a]pyrene Polycyclic Aromatic Hydrocarbon (PAH) Polycyclic - 5 Rings Aromatic – contains a benzene ring Hydrocarbon – composed of C & H

Ba. P is a Genotoxicant • Capacity to interact with and damage DNA

Sources of Ba. P Inefficient burning of any carbon source Burning of fossil fuels Energy Production Engines Coal and Petroleum Processing Bacterial and Plant Synthesis Weathering of Rock Volcanoes and Wildfires Charbroiled Foods Cigarette Smoke

Prevalence of Ba. P in environment make the probability of contact very high. IMPORTANCE? Possible Mutagenic Effects of Ba. P

Cellular Metabolism of Ba. P stimulates the production of Cytochrome p 450 • Cyt p 450 is a detoxification enzyme

The Paradox • Cyt p 450 bioactivates Ba. P causing it to be an active genotoxicant

Stimulation of Cytochrome p 450 Ba. P enters organism - respiration - dermal absorption - ingestion Ba. P Cytoplasm Ba. P migrates across cellular membrane

Stimulation of Cytochrome p 450 Ba. P enters organism - respiration - dermal absorption - ingestion Cytoplasm Ba. P migrates across cellular membrane Ba. P

Stimulation of Cytochrome p 450 Ba. P binds to a protein complex called Aryl Hydrocarbon Hydroxylase (Ah) Ba. P Ah hsp 90

Stimulation of Cytochrome p 450 Ba. P binds to a protein complex called Aryl Hydrocarbon Hydroxylase (Ah) Ba. P Ah hsp 90

Stimulation of Cytochrome p 450 Causes the release of a heat shock protein (hsp 90) Ba. P Ah hsp 90

Stimulation of Cytochrome p 450 Hsp 90 is replaced by another protein called Aryl hydrocarbon receptor nuclear transferase (Arnt) Ba. P Ah hsp 90 Arnt

Stimulation of Cytochrome p 450 Allows for the Ba. P complex to be translocated into the nucleus Ba. P Ah Arnt Nucleus

Stimulation of Cytochrome p 450 Allows for the Ba. P complex to be translocated into the nucleus Nucleus Ba. P Ah Arnt

Stimulation of Cytochrome p 450 In the nucleus • Ba. P complex stimulates the production of Cyt p 450

Stimulation of Cytochrome p 450 In the nucleus • Ba. P complex stimulates the production of Cyt p 450 • Cyt p 450 acts on Ba. P in cell

Bioactivation of Ba. P by Cyt p 450 adds oxygen to Ba. P to form Ba. P-7, 8 -epoxide

Bioactivation of Ba. P by Cyt p 450 Another enzyme breaks the epoxide bond by adding water forming Ba. P-7, 8 -diol

Bioactivation of Ba. P by Cyt p 450 adds another oxygen forming Ba. P-7, 8 -diol-9, 10 -epoxide

Bioactivation of Ba. P by Cyt p 450 Ba. P-7, 8 -diol-9, 10 -epoxide is the major carcinogenic form of Ba. P Binds covalently to DNA, RNA and proteins Binds preferentially to guanine

Bioactivation of Ba. P by Cyt p 450

Effects of Ba. P-DNA Adducts Normally guanine binds to cytosine Ba. P-DNA adduct with guanine disrupts hydrogen bonding with cytosine

Normal Bonding in DNA

Effects of Ba. P-DNA Adducts Results of G – C Disruption: • Single Strand Breakage • Replication problems • G: C T: A mutations • Possible precursors to Cancer

Importance of Studying Ba. P • Major pollutant easily incorporated into tissues that has the potential to lead to mutations and cancer • Biomarker for human health risk assessment

9. Individual human factors: - individual susceptibility the differences in types of responses to hazardous substances between people. Each person is unique, and because of that, there may be great differences in the response to exposure. Exposure in one person may have no effect, while a second person may become seriously ill, and a third may develop cancer.

- sensitive sub-population those persons who are more at risk from illness due to exposure to hazardous substances than the average, healthy person. These persons usually include the very young, the chronically ill, and the very old. It may also include pregnant women and women of childbearing age. Depending on the type of contaminant, other factors (e. g. , age, weight, lifestyle, sex) could be used to describe the population.

Toxic Symptom: any feeling or sign indicating the presence of a poison in the system. Toxic Effects: the health effects that occur due to exposure to a toxic substance; also known as a poisonous effect on the body. Selective Toxicity: a chemical will produce injury to one kind of living matter without harming another form of life, even though the two may exist close together.

Types of Toxic substances: 1. Heavy Metals: Pb, Hg, Cd 2. Solvents and Vapors Nearly everyone is exposed to solvents. Occupational exposures can range from the use of "white-out" by administrative personnel, to the use of chemicals by technicians in a nail salon. When a solvent evaporates, the vapors may also pose a threat to the exposed population.

3. Radiation and Radioactive Materials

4. Dioxin/Furans Dioxin, (or TCDD) was originally discovered as a contaminant in the herbicide Agent Orange. Dioxin is also a by-product of chlorine processing in paper producing industries.

Dioxin Poisoning

5. Pesticides The EPA defines pesticide as any substance or mixture of substances intended to prevent, destroy, repel, or mitigate any pest. EX: insecticide, fungicide, rodenticide, piscocide, herbicide

6. Plant Toxins Different portions of a plant may contain different concentrations of chemicals. Some chemicals made by plants can be lethal. For example, taxon, used in chemotherapy to kill cancer cells, is produced by a species of the yew plant. 7. Animal Toxins These toxins can result from venomous or poisonous animal releases. Venomous animals are usually defined as those that are capable of producing a poison in a highly developed gland or group of cells, and can deliver that toxin through biting or stinging. Poisonous animals are generally regarded as those whose tissues, either in part or in their whole, are toxic.

All chemicals (or any chemical) may be poisonous at a given dose and through a particular route. For example, breathing too much pure oxygen, drinking excessive amounts of water, or eating too much salt can cause poisoning or death

Many toxins and toxicants are ENDOCRINE DISRUPTORS - disrupt the functioning of the endocrine system - a complex network of glands and hormones that regulates many of the body's functions, including growth, development and maturation, as well as the way various organs operate.

l Endocrine glands -- including the pituitary, thyroid, adrenal, thymus, pancreas, ovaries, and testes -- release carefully-measured amounts of hormones into the bloodstream that act as natural chemical messengers, traveling to different parts of the body in order to control and adjust many life functions

An endocrine disruptor is a synthetic chemical that when absorbed into the body either mimics or blocks hormones and disrupts the body's normal functions. This disruption can happen through altering normal hormone levels, halting or stimulating the production of hormones, or changing the way hormones travel through the body, thus affecting the functions that these hormones control. EX: Estrogen disruptors – send false signals to the body and disrupt the normal functions of estrogen

Exposure to endocrine disruptors: 1. direct contact with pesticides and other chemicals 2. ingestion of contaminated water, food, or air. 3. found in insecticides, herbicides, fumigants and fungicides that are used in agriculture as well as in the home 4. Industrial workers can be exposed to chemicals such as detergents, resins, and plasticizers 5. enter the air or water as a byproduct of many chemical and manufacturing processes 6. when plastics and other materials are burned. 7. can leach out of plastics, including the type of plastic used to make hospital intravenous bags 8. Many endocrine disruptors are persistent in the environment and accumulate in fat, so the greatest exposures come from eating fatty foods and fish from contaminated water.

Results of Endocrine Disruption: Feminization/masculinization Changes in fertility Hormonally related cancer Birth Defects Premature puberty

MEASURING TOXICITY: 1. Lethal dose-50% (LD 50): the dose lethal to 50% of the test population - usually reported in milligrams of chemical toxicant per kilogram of body weight (mg/kg) - toxicity and LD 50 are inversely related – the greater the toxicity, the lower the LD 50 – PAGE 155 2. Lethal concentration-50% (LC 50): the lethal concentration of the toxic substance in air or water for 50 % of the test population 3. Effective dose-50% (ED 50): the dose of toxic substance that is 50% successful (effective) in producing a specific response

Measurements are reported as doseresponsive curves which shows the effect of different doses on a population scientists typically start with high doses and work down to the threshold levels (maximum dose with no visible effect)

LD 50 (mg of toxicant per kg of test organism)

SPECIAL CONSIDERATIONS Children Greater susceptibility: 1. still developing - changes in early development affect all subsequent changes 2. not as effective at dealing with toxic substances 3. weigh less 4. behaviors: crawling, chewing

Carcinogens: cancer causing agents “suspected carcinogens” – those determined by feeding extremely large doses (unreasonable exposure) to rats Why? Too long/expensive to work with small amounts and large numbers of test animals PROBLEM: once a chemical is “suspect”, scientist work backward and extrapolate the harmful dose - the body works with low dosages of toxicants differently than large doses (chronic vs. acute) and some studies indicate that very low doses may stimulate the body to fight the effects of the chemicals

Chemical Mixtures: - exposure is not always simple but a complex mixture of chemicals chemical mixtures interact several ways Additive: the chemicals work together and the result is cumulative Synergistic: the chemicals work together in an enhanced method – greater than simply adding the effects together Antagonistic: the chemicals hinder one another and the combined effect is less than the added, anticipated effect

Disposal Issues: “DILUTION IS THE SOLUTION TO POLLUTION” wash it down with plenty of water…. . Problem? Longer term effects, interactions, accumulations Countered by the Boomerang Paradigm – what you throw away will come back to you (or the following generations)

Leads to RISK ASSESSMENT: statistical method to quantify the risks of a particular action Adverse Human Health Risk Assessment 1. Hazard Identification - identify the possible risk substance 2. Dose-Response Assessment – how much is required to cause problems? 3. Exposure Assessment – how long, how much, where? 4. Risk Characterization – running the math – what is the likely hood of an individual or population to have an adverse effect?

Risk is then controlled by RISK MANAGEMENT – laws and regulations for the development and use of the hazardous substances

PRECAUTIONARY PRINCIPLE: anything new should be analyzed with a high level of scrutiny until proven safe may slow down progress, but may save lives Ecological Risk Assessment: same basic process as human health risk assessment except on a much wider scale – includes many more variables and unpredictability Cost Benefit Analysis: sometimes addressing a problem is very expensive and the benefit to addressing it must outweigh the cost – usually if human health is concerned the cost is outweighed by the benefit, but if the benefit is considered to low for the cost the problem may not be addressed in an adequate way