Introduction to Toxicology Chapter 5 PDF

INTRODUCTION  ON THE DAY OF THE PATIENT’S VICTORY AT COURT, SOMEONE WROTE A HEADLINE: “ THE DAY THAT TOMOKO SMILED”. SHE COULDN’T POSSIBLY HAVE KNOWN. TOMOKO UEMURA, BORN IN 1956, WAS ATTACKED BY MERCURY IN THE WOMB OF HER OUTWARDLY HEALTHY MOTHER. NO ONE KNOWS IF SHE IS AWARE O...

INTRODUCTION  ON THE DAY OF THE PATIENT’S VICTORY AT COURT, SOMEONE WROTE A HEADLINE: “ THE DAY THAT TOMOKO SMILED”. SHE COULDN’T POSSIBLY HAVE KNOWN. TOMOKO UEMURA, BORN IN 1956, WAS ATTACKED BY MERCURY IN THE WOMB OF HER OUTWARDLY HEALTHY MOTHER. NO ONE KNOWS IF SHE IS AWARE OF HER SURROUNDINGS OR NOT. SMITH AND SMITH ( 1975)  In 1932, when Chisso started making vinyl chloride and acetaldehyde, people didn't know that methyl mercury would be a byproduct, or what methyl mercury would do to people, or how it would behave in the environment. Some people may have known that it was flowing, along with other heavy metals, from the factory into the bay, but if so, it was not considered a problem great enough to do anything about. Chisso was more interested in saving the factory (with its associated jobs), their profits, and their business reputation than in fixing the problems and helping the victims. Although some of the people in Minamata were horribly hurt, many of the people were not hurt, and those were often afraid of losing their jobs should the factory be deemed responsible for the town's problems. The issue was causing serious rifts in the community.  Toxicology Toxicology is the study of adverse effects of chemicals on living systems, including: Mechanisms of action and exposure to chemicals as a cause of acute and chronic illness. Understanding physiology and pharmacology by using toxic agents as chemical probes. Recognition, identification, quantification of hazards from occupational exposure to chemicals. Discovery of new drugs and pesticides. Development of standards and regulations to protect humans and the environment from adverse effects of chemicals.  Branches of Toxicology 1. Mechanistic—cellular, biochemical and molecular mechanisms by which chemicals cause toxic responses 2. Forensic—cause of death, legal aspects 3. Clinical—treatments for poisonings and injuries caused by xenobiotics 4. Environmental—environmental pollutants, effects on flora and fauna 5. Food—adverse effects of processed or natural food components 6. Regulatory—assigns risk to substances of commercial importance.  Origins of Toxicology Earliest humans used animal venoms and plant extracts for hunting, warfare and assassination. 400 BC: Hippocrates compiled a listing of a number of poisons and outlined some clinical toxicology principles. 1493-1541: Paracelsus—physician and philosopher All substances are poisons; the right dose differentiates a poisons from a remedy. “Dose determines toxicity.” 1775: Percival Pott found that soot caused scrotal cancer in chimney sweeps. Much later the carcinogens in soot found to be polycyclic aromatic hydrocarbons. 1972: Rachel Carson/EPA led to ban of insecticide DDT for environmental and health concerns  Examples of Toxicological Cases 399 B.C. Socrates, a Greek Philosopher died of Hemlock poisoning (according to Plato) Coniine is the active toxic ingredient Antagonist for the nicotinic acetylcholine receptor, leading to cessation of neurotransmission, muscular and respiratory collapse and death coniine October 20th, 1740 Charles VI, Holy Roman Emperor, King of Bohemia, Hungary, and Croatia died from eating death cap mushrooms Active ingredient is alpha-amanitin that inhibits RNA polymerase inhibiting protein synthesis leading to hepatocellular lysis, liver failure, kidney failure, coma, respiratory failure, and death Alpha-amanitin  Examples of Toxicological Cases April 30th, 1945, Eva Braun, long-time companion of Hitler committed suicide with a cyanide capsule Inhibitor of cytochrome c oxidase, part of complex IV of the electron transport chain and inhibits ATP production leading to brain death and heart cessation, hypoxia, and death Jan 16th, 1975 Bando Mitsugoro VIII, a famous Japanese Kabuki actor died from eating 4 livers of pufferfish Active toxic ingredient is tetrodotoxin Tetrodotoxin blocks voltage-gated sodium channels leading to suppression of neurotransmission, numbness, bronchospasms, coma, respiratory failure, death tetrodotoxin  Examples of Toxicological Cases 1932-1968: Minamata disaster—caused by methylmercury toxicity from industrial wastewater from Chisso Corporation in Minamata City in Japan 2265 victims Caused neurological syndrome associated with methyl mercury poisoning including ataxia, numbness, insanity, muscle weakness, hearing and speech loss, birth defects, paralysis, coma, death Methyl mercury Alters neurochemistry and neurotransmission through multiple mechanisms sarin Environmental toxicology Environmental Toxicology is the multidisciplinary study of the effects of manmade and natural chemicals on health and the environment. This includes the study of the effects of chemicals on organisms in their natural environments and in the ecosystems to which they belong Environmental toxicology is the study of the impacts of chemical substances (potential and actual pollutants) upon the structure and function of ecological system, including man. Environmental toxicology uses typical species chosen from the ecosystem or laboratory test organisms to examine their answer for the chemicals. Toxicology Beginnings—Most early toxicology tests were human oriented, then agricultural species, then desirable species—not based on ecosystems As ecosystems are fragmented, resilience declines. They need more protection from stressors Many definitions of one word Environmental Toxicology Ecotoxicology Effect of toxic substances ocurring in "the branch of toxicology concerned both natural and man-made with the study of toxic effects, caused environments by natural or synthetic pollutants, to the constituents of ecosystems, animal (including human), vegetable and microbial, in an integral context”  Why did we need ecotoxicology in the past? After WWII Dilution Paradigm ended “The solution to pollution is dilution” Boomerang Paradigm started “What you throw away can come back and hurt you!”  This book’s definition The science of contaminants in the biosphere and their effects on constituents of the biosphere, including humans Individual population community ecosystem landscape ecoregion continent hemisphere biosphere Individual organ/tissue cellular biomolecular https://superfund.oregonstate.edu/teacher-resources-mercury-my-community-and-me CHAPTER 1 Environmental Contaminants  Toxicology is arguably the oldest scientific discipline, as the earliest humans had to recognize which plants were safe to eat. Humans are exposed to chemicals both deliberately and inadvertently. Most exposure of humans to chemicals is via naturally occurring compounds consumed in the diet from food plants.  Chemicals are natural, biological, or synthetic in origin – Natural (food, metals, minerals) – Biological (toxins from bacteria) – Synthetic—manufactured through chemical processes Approximately 100,000 chemicals are currently in use worldwide. 500 new formulations enter the marketplace annually.  Problem The Great Chemical Unknown [Scientific American October 28, 2010] Fraction of chemicals whose hazards have been characterized dredging: removal of sediments and debris from the bottom decomposition of leads lakes, rivers, to chemical  Contaminants of interest Organic Inorganic Living organisms Mineral sources Natural Examples: Anthropogenic sources Carbon monoxide Examples: Carbon dioxide Main characteristic—C-H bond Nitrogen oxides Exceptions-- CCl4—carbon Sulfur dioxides tetrachloride Nitrogenous wastes Phosphates Metallic elements Classification of Environmental Contaminants  When does a compound or When does a contaminant element become an becomes a pollutant? environmental contaminant? Contaminant Pollutant Anthropogenic Condition: Xenobiotic higher than Ecotoxicants background The same concentration affects diff. sp. differently have an adverse affect A. Inorganic Contaminants B. Organic Contaminants 1. Hydrochlorofluorocarbons and Chlorofluorocarbons 1. Metal and Metalloids 2. Organochlorine alkenes 2. Organometallic compounds 3. PAHs 3. Inorganic Gases 4. Polyhalogenated Benzenes, Phenols and Biphenyls 4. Anionic Contaminants Including Nutrients 5. Polychlorinated Naphthalene's 6. Dioxins/Furans 7. Pesticides C. Radiations 8. Herbicides 9. Oxygen demanding compounds 1. Radioactivity 10. Other important compounds 2. Radionuclides 11. Emerging contaminants of concern 3. UV radiation 4. IR radiation 5. Genetic Contaminants A. Inorganic Contaminants 1. Metal and Metalloids 2. Organometallic compounds 3. Inorganic Gases 4. Anionic Contaminants Including Nutrients Metals & Metalloids Naturally occurring elements that become contaminants when human activity raises their concentrations in the environments above natural levels. Once released in the atmosphere metals can be transported in a gaseous phase or sorbed particles. Aquatic & Terrestrial sources: ( through wet or dry atmospheric deposition) Inorganic chemical manufacturing industries Mining Agricultural pesticides Atmospheric sources Mining & non-ferrous metal production Steel & iron manufacturing Coal combustion Oil combustion Waste incineration Phosphate fertilizers Cement production Wood combustion Characteristics to understand Metals lose electrons when reacting with non metals. Normal biological processes can be affected by uptake of metals or metal species from the environment. Bonding tendencies need to be understood. Essentiality of the element to life Inorganic Gases Coal power plants & vehicles CO2 from combustion, linked to global warming NOX SO2 Leads to acid rain May cause pulmonary diseases among others SO2 can causes plant damage Nutrients Nitrogen & Phosphorous nutrients Cultural eutrophication ((is the process that speeds up natural eutrophication because of human activity) “overfertilization of lakes with nutrients and the changes that occur as a result”) Source: fertilizer runoff & sewage discharge Methemoglobinemia “blue-baby syndrome” Baby ingests nitrate in drinking water Nitrate turns to nitrite in anaerobic stomach conditions NO2- reacts with hemoglobin, so it can’t carry oxygen Ammonia is pH dependent Nitrite, ammonia, & nitrosamines—highly toxic to aquatic biota near sewage discharges  http://www.youtube.com/watch?v=Y7ZJkd2d8vQ http://www.dailymail.co.uk/news/article-2239040/Crimson-tides-Tourists-flee- Bondi-Beach-Red-Sea-rare-algae-bloom-turns-water-colour-blood.html http://www.youtube.com/watch?v=kLtTOmvTqrk  Organic Compounds What are they? An organic compound is any member of a large class of chemical compounds whose molecules contain carbon. What do they include? Unintentional Poisons Insecticides & herbicides Products, by-products, or wastes of industry Natural & synthetic compounds https://www.atsdr.cdc.gov/features/toxicsubstances/index.html Polycyclic Aromatic Hydrocarbons (PAHs) Accidentally formed chemicals Organometallic Compounds Organolead Tetraalkyllead, gasoline additive Important in areas with lots of traffic Can cause neurological problems Organomercury Natural processes or synthesis. Biocides ( seed coatings) Elemental mercury is methylated by bacteria—biomethylation Sorbs to particulates, bioaccumulates in muscles and tissues. Neurological problems Organotins Catalysts, polymer stabilizers, insecticides, fungicides, bactericides, wood preservatives & antifouling agents Mostly synthesized for industrial use of product of biomethylation. TMT TET (tri-methyl & tri-ethyl) are neurotoxins TBT (tri-butyl) used as biocide in antifoulant paints for barnacles on boats, highly toxic to aquatic invertebrates (crustaceans & mollusks) Half-life in water of days to weeks TBT sorbs to sediments, half-life in aerobic sediments of months, in anaerobic sediments of years—being banned in US  Radionuclides Radionuclides (or radioactive materials) are a class of chemicals where the nucleus of the atom is unstable. They achieve stability through changes in the nucleus (spontaneous fission, emission of alpha particles, or conversion of neutrons to protons or the reverse). This process is called radioactive decay or transformation, and often is followed by the release of ionizing radiation (beta particles, neutrons, or gamma rays). https://wwwn.cdc.gov/TSP/substances/ToxChemicalListing.aspx?toxid=27 https://www.radioactivity.eu.com/site/pages/Radioactive_Toxicity.htm  UPTAKE, BIOTRANSFORMATION, DETOXIFICATION, ELIMINATION AND ACCUMULATION CHAPTER 3  Solubility is the most important - disposal, where in the env can it be Fate of Chemicals found, can it be diluted, how should we test it, Research provides a basic understanding of the biologic, chemical, and hydrologic processes that affect partitioning into various environmental media (e.g. water, sediment and tissue) and chemical and microbial transformation. These processes can have a significant effect on the potential toxicity of a contaminant. Environmental Fate of contaminants Two main factors determining contaminant fate 1. Physical/chemical properties Affect persistency and distribution 2. Conditions of the surrounding ecosystem Difficult to obtain, can vary depending season & scale of the system  Steps for determining the Condition of the surrounding ecosystem 1. Define the scale and boundaries organism lake atmosphere biosphere 2. Define the system under study To understand contaminant fate Processes can be important in one ecosystem and unimportant in another 3. Characterization of environmental condition To understand the fate of metals and metalloids Speciation could be affected by element chemistry and condition  Contaminant accumulation Concentrations in target organs or tissues Basic Processes resulting in Bioaccumulation: Uptake Biotransformation Elimination  Contaminant partitioning Contaminant Transport : Influenced by partitioning of the compound or element between the various phases or compartments. Gaseous & aqueous phases Aqueous & sediment/particulate phases Dissolved & liquid/solid phases  Contaminant Partitioning When the contaminant is released to one compartment and moves to another, where it builds up in concentration Assume steady-state system & use equilibrium equations Partition coefficient (Distribution coefficient) at equilibrium X(phase a) X(phase b) Kd or Kp= X(phase b) / X(phase a) Sorption Coefficient = aqueous (a) & particulate (b) phases Adsorption if associated with surface of particulate only Analytical methods generally are rigorous & represent both adsorption & absorption, so we generally use sorption  Important points Sorption coefficients are determined empirically under lab conditions for some contaminants and particulate phases. Useful tools for: comparing the relative tendency for contaminants to accumulate in sediments or soils Give insight into potential fate of contaminants Might not always be accurate predictors of concentrations of contaminants in sediment and water under environmental circumstances ( system not at equilibrium, variability of structure and quality)  Factors affecting partitioning of contaminant Vapor Pressure (P) Water solubility (C) Used to calculate: Henry’s law coefficient (H or KH) aqueous & vapor phases KH = P/C H increases as P increases or C decreases High H = steady state, accumulate in atmosphere, contaminant will decrease in water & accumulate in the atmosphere & then may move globally Weathering Changes in relative concentrations of individual compounds in the mixture over time. When a group of contaminants (PAHs or PCBs) are released in mass from a source, they each partition uniquely according to their specific coefficients, changing their concentrations, can determine the ratios PCBs—unique mix to each source—if you can characterize the weathering pattern, you can determine the source of the PCBs  Sewage: 1. remove large objects. 2. add O2 to encourage microbial degradation (decomposition) Degradation Environmental degradation is caused due to institutional, socio- economical and technological activities. It is the deterioration of the environment through the depletion of resources like water, air, and soil. Here both biotic and abiotic processes contribute to the degradation of the environment. Degradation Abiotic Degradation: It is a prominent process that mainly occurs under the influences of hydrolysis and photolysis. Hydrolysis: Hydrolytic reaction is the reaction of water with another chemical compound to form two or more products involving usually splitting the other compound. In simple terms when water combines with heat or light energy it can break chemical bonds, this process is known as hydrolysis. Photolysis: It mainly occurs on surface waters or in the atmosphere where the intensity of light is at its highest. Photolysis is a chemical process by which molecules are broken down into smaller parts or units through the absorption of light. Photodegredation—Photolysis—light is absorbed & bonds are broken and the contaminant is degraded, needs UV (most energy) to vis light Direct photolysis—contaminant absorbs light & degrades ( fragments or oxidizes) Indirect photolysis—other chemical absorbs light & forms a reactive species that reacts with the contaminant facilitating degradation Oxidation: direct reaction with oxygen pharmaceuticals and personal care products includes caffeine Results from these studies showed that the rate and extent of ibuprofen degradation is greatly influenced by the presence of clay particles and solar radiation. The results from the biological assays show that primary PPCP is more toxic than the mixture of secondary products. Degradation Biotic Degradation: Microorganisms such as fungi and bacteria are prime factors responsible for biotic degradation. These microorganisms degrade chemicals to obtain energy from these sources. It occurs at a highly accelerated rate, far exceeding abiotic degradation. It is a process that can completely lead to the mineralization of chemicals to carbon dioxide, water, and other basic inorganic constituents. Bioremediation is a process wherein microorganisms are used to mitigate environmental contaminants. Biotic degradation ( biologically mediated) Within organisms, catalyzed by enzymes Detoxification, activation, and elimination of contaminants Can enhance degradation due to catalytic effect of enzymes  Degradation of organics Mineralization—from organics to carbon dioxide, water, and inorganic salts Complete degradation CxHxX CO2 + X Incomplete degradation CxHxX Metabolite A & B... CxHxX Metabolite C & D... Xenobiotics, not similar to natural compounds, tend to be microbially resistant, they do not degrade biologically very well, because there are no enzymes adapted to their break down Toxicity decreases biological degradation, too  half life, Bioaccumulation solubility, Bioaccumulation: It is a process where organisms accumulate themselves with chemicals from dietary sources or from an abiotic environment. And through passive diffusion, these organisms take in these toxic chemical substances. Bioaccumulation refers to the net accumulation of contaminants, in an organism. Some of the primary organs that uptake this toxic include the gastrointestinal tract, gills, and lungs. But other organs such as scales, skin, feathers, fur, etc. act as a protective barrier against various chemical toxic. Sources: Water, air, and solid phases( food, soil, sediment, fine particles) in the environment Mathematical model Provides only details essential to understanding and accurately predicting the behaviors or the system.  Hg is the only metal that can bioaccumulate Bioconcentration and biomagnify all others bioaccumulates and bioconcentrates Bioconcentration is a related but more specific term, referring to uptake and net accumulation of a contaminant in an organism from water alone. Potential influence of microplastics on mercury bioconcentration and bioaccumulation by fish. bioaccumulation: in 1 organism over time bioconcetration: from multiple env sources Bioaccumulation Biotransformation Water Food Loss from urine & feces Loss from gills Uptake and Elimination process at saturation, all uptake is eliminated Concentration U = E Steady State U > E Duration of Exposure E2 X A 4 0 Source-to-Effect Continuum 8 Stressor Domain Receptor Domain Source/stressor Effect/outcome formation Fate and transport Biological event Environmental Target tissue Concentration dose Exposure = f (concentration, behavior, time) E3 X A 4 0 Exposure Assessment 8 Using Biomonitoring Biomonitoring data can be used to: Better estimate Reduce some Measure total intake dose types of internal dose (in conjunction uncertainty with PK models) E5 X A Biomonitoring, Biomarkers, 4 0 and Body Burdens 8 Biomarker: Biologic indicator of exposure; used to measure chemical, metabolites, or product of interaction between chemical and target molecule or cell Body burden: Total amount of a contaminant in the body; a type of biomarker Biomonitoring: Method for assessing human exposure to chemicals, their metabolites, or their byproducts; the act of collecting biomarker and body burden data  Concentration vs. Body Burden concentration * mass of tissue / kg individual Concentration Mass contaminant per mass organism (mg/kg tissue) only tissue of the sample fish Body burden Mass or total amount of contaminant in or on person eating the fish the individual (g/individual) whole organism consuming the concentration Body burden refers to the accumulation of synthetic chemicals – found in substances like household cleaners, fabrics, cosmetics, pest repellants, computers, cell phones – which helped “modernize” our lives in the post World War II chemical age and which are now found in our own bodies.  Biomonitoring Advantages and Limitations Advantages Limitations Measures all aggregate exposure Not source- or pathway-specific (all sources, all routes) where did the individual become contaminated Reflects uptake and accumulation Requires permissions for collection of human specimens May be able to correlate internal Can be costly dose with effects Difficult to interpret potential health risks  Biomarkers Used to measure: Direct amount of a compound (i.e., body burden) Biological interaction of the compound with the body Physiological changes in an organism as a result of interaction with the compound Collected using biomonitoring methods Can be used to reconstruct past exposures Reflect internal dose but may not indicate risk EXA 408 8 Modeling Uptake Uptake Movement of a contaminant into or onto an organism Involves dermis, pulmonary surfaces, gut, or gills Starts with interaction with cell of tissues Ingest ion Enters cell by Lipid route Aqueous route Endocytic route Mechanisms for uptake Mechanisms Adsorption Passive diffusion Active transport Facilitated diffusion or transport Exchange diffusion Endocytosis  Pharmacokinetics The study of the time course of ADME of a substance in an organism’s body Chemical in environment into sth, as Chemical enters body Absorption opposed to adsorption on the surface Distribution Chemical in blood and tissues Metabolism Chemical impact on health is usually investigated via the concept of ADME. This is how a chemical is Absorbed, Distributed, Metabolized, or Eliminated Excretion in living systems. EXA 408 21 INTERACTIONS WITH ORGANISM SURFACE BEFORE UPTAKE  1st Step—Adsorption Can be modeled with linear adsorption equations Freundlich and Langmiur Isotherm Equations absorbent - what is the surface saturation mass of absorbant amount adsorbed/ Concentration  Adsorption Isotherms Freundlich Equation - developed to describe gas adsorption on solids. q = KC1/n where q = adsorbed quantity ( amount adsorbed/ mass adsorbent) C = Concentration of solute in solution after adsorption K = distribution coefficient ( derived constant) n = correction factor ( derived constant) Freundlich Plots Adsorption Isotherms Langmuir Equation -developed to describe gas adsorption on planar surfaces q = kCb/ (1 + kC) Where q and C defined in Freundlich k = constant related to bonding strength b = adsorption maximum Langmuir Equation occurs on planar surfaces, fixed number of identical site, each site only one molecule adsorption is reversible no lateral movement of molecules on surface adsorption energy same for all site and independent of surface coverage little interaction between adsorbate molecules Langmuir Plots Adsorption isotherm This equations have been successfully used to define toxicant movement onto diverse biological surfaces: Unicellular algae Fish gills Periphyton Zooplankton 2nd Step—Across the cell Diffusion : Movement of the contaminant Active Transport down an electrochemical gradient Uses energy to move Lipophilic compound through the lipid contaminant up the bilayer electrochemical gradient Nonpolar organics or uncharged inorganics Uses carrier molecule Charged ion through a channel protein Subject to saturation kinetics Charged metals & protons and competitive inhibition Depends on ion charge & size (including Cation transport with ATP-ase hydration sphere) (adenosine triphosphate) Gated & ungated channels, influenced by chemistry of cell Ions & hydrophilic compounds Facilitated diffusion Endocytosis Down electrochemical gradient through a carrier protein without energy Brought into cell alone or in Faster than simple diffusion particulate Subject to saturation kinetics Pinocytosis & phagocytosis Exchange diffusion Exchange ions across the membrane Across the Cell Membrane Reaction Order—Kinetics of Uptake & Elimination imp because: how was is its metabolism and elimination, what is its fate Reaction rate equation dC/dt=kCn Zero Order Reaction, n=0 First Order Reaction, n=1 Michaelis-Menten Kinetics Saturation kinetics Enzyme-mediated processes Active transport Facilitated diffusion Above threshold concentration, Zero Order Reaction Rate (Vmax) Below threshold concentration, First Order Reaction Rate  Biotransformation Biotransformation is the process by which substances that enter the body are changed from hydrophobic to hydrophilic molecules to facilitate elimination from the body. This process usually generates products with few or no toxicological effects. Change in contaminant due to enzymatic catalysis Subject to saturation kinetics & competitive inhibition Detoxification Change to more hydrophilic, increases elimination Change to nontoxic form Change to form retained & sequestered Activation Change from nontoxic to more toxic form Change from less toxic to more toxic form Ex. Dichlorodiphenyltrichloroethane (DDT) an insecticide (used to help eradicate malaria) that was found to be toxic due to its transformation into Dichlorodiphenyldichloroethylene (DDE)  Mechanisms of Biotransformation & Detoxification Organic Compound Metals & Metalloids hydrophobic hydrophilic Phase I Phase I Biomethylation Metabolism Metabolism or Biomineral- Biotransformation ization Phase II Binding to Metabolism Metallothionein or Another Ligand Elimination or Sequestration Compound Elimination (capture it and isolate it - causes accumulation)  Metals and Metalloids Biotransformation results in elimination and sequestration Addition of methyl or ethyl groups by microbes of metal contaminated sites. Bound by amino acids Metallothioneins Phytochelatins ( metal binding polypeptides) Sequestered in bone, exoskeleton, shells, or nails in place of calcium Eliminated with molting or loss of nail Sequestered by incorporation into variety of granules or concretions  Organic compounds Options: Eliminated rapidly Subjected to metabolism ( with excretion of metabolites) Phase I Reactions Make compound more hydrophilic Add –COOH, –OH, –NH2, –SH in proteins Oxidation, hydrolysis & reduction reactions MFOs (mixed function oxygenases) put Oxygen onto the compound Phase II Reactions Make compounds even more hydrophilic Bind with acetate, cysteine, sulfate, glycine, glutamine, or glutathione Enzymatic Subject to saturation kinetics, inhibition & induction  smallest PAH https://www.nottingham.ac.uk/nmp/sonet/rlos/bioproc/liverdrug/page_one.html  Elimination Mechanisms Excretion or biotransformation of contaminant can be Depuration—release of contaminant into clean environment transferred into other areas of Clearance—rate of contaminant movement between compartmentsthe body normalized to concentration Growth dilution—as organisms grow, concentration decreases, but body burden remains constant  Plants Leaf dropping, leaching & evaporation from leaves, root exudation, herbivore grazing Animals Across gills, exhalation, secretion of bile (gall bladder), secretion from hepatopancreas, intestinal mucosa, molting, kidney excretion, egg deposition, loss in hair, feathers, skin, sweat, saliva, Main routes: gills, kidney, liver bile  Elimination Mechanisms Enterohepatic Circulation In liver, compound can be excreted in bile into feces, in the small intestine, compound is reabsorbed and transported to liver Reabsorption Kidney excretion Gastrointestinal excretion Renal elimination Others VOCs in breath Deposition of lipophilic compounds Modeling Elimination First Order kinetics are the most common Zero order – less frequently Saturation kinetics – less frequently Compartment models Rate constant Clearance-volume Fugacity models consideration of all possible body compartments  Forward & Backward Analysis Compile data on exposure Compile data on body media concentration burdens B F A O C R Develop representative Develop representative K W profile in the media body burden profile W A A R R D D Combine media Use PK models to convert: concentrations with intake dose to body burden exposure factors to body burden to intake dose estimate intake dose EXA 408 29  Pharmacokinetic Models Pharmacokinetic (PK) models evaluate the internal dose of a compound Simple – one-compartment, first-order First-order: Rate of elimination of chemical is dependent on the amount of chemical present continued exposure from same source or exposure from multiple sources Steady state: Assuming no net change in amount of chemical one time exposure Complex – multi-compartment, physiologically-based pharmacokinetic How can PK models be used in exposure assessment? Characterize internal dose Route-to-route extrapolation of the internal dose Exposure reconstruction from epidemiological studies EXA 408 22  One-Compartment, First-Order PK Models applies to some drugs injection is fastest, followed Chemical by inhalation Compartment C sat d. Cmax = Dose - kC Digestive Tract Chemical Degradation Time Elimination/Clearance C is the pollutant concentration (mass/volume) k is the first-order elimination rate constant (time-1) EXA 408 23  Steady-State One-Compartment, First-Order PK Model ADD ln(2) ADD × t1/2 Css = k= Css = k×V t1/2 V × ln(2) Where: Css is the steady-state pollutant concentration (mg/L, ng/g-lipid weight) ADD is the average daily dose (mg/day, ng/day) standari zed k is the first-order elimination constant (day-1, sec-1) V is the volume of distribution (L) varia ble t1/2 is the half life for elimination (day, sec) EXA 408 24  k C Rate constant based models One compartment model First order rate constants Elimination of contaminant from an organism to clean environment. Elimination predicted from initial concentration (Co) dC dX dt = -kC dt = -kX Ct=Coe-kt – Biological half-life (t½) Time to reduce concentration in compartment by 50% t½ = (Ln2)/k – Mean residence time Time a particle would be in the compartment ( ) =1.44 t½ or k=1/  Non-Steady-State PK Model ADDt 1 – e-kt C(t) = C(0)e-kt + × Vt k Where: C(t) is the pollutant concentration at time, t (mg/L, ng/g-lipid weight) C(0) is the initial pollutant concentration at time, 0 (mg/L, ng/g-lipid weight) ADD is the average daily dose (mg/day, ng/day) k is the first-order elimination constant V is the volume of distribution (L) EXA 408 25  k1 1 2 k2 Modeling Elimination 2 compartment model 2nd+ order Elimination 2 or more elimination mechanisms -kit -kit Ct=Co i Xt=Xo i Effective half-life (keff) = (Ln2)/ ki The slower mechanism will control elimination  kE 1 k k Modeling Elimination 2 Multiple compartment model Clearance-volume based models Apparent volume of distribution ( Vd) Used to determine the dose within the organism (Dt) Used in Pharmacokinetics & Toxicokinetics Physiologically based pharmacokinetics (PBPK) ( physiological and anatomical features in describing kinetics) Dt=CoVo + CiVi Bioaccumulation Net concentration after uptake, biotransformation & elimination processes within an individual Simplest model: 1st order uptake & 1st order elimination dC dt = kuC1-keC Bioconcentration factor (BCF) Bioaccumulation factor (BAF) Bioaccumulation factor from sediment (BSAF) Accumulation factor  if not in env but present in BCF organism, assume its not coming from the env Bioconcentration factor is the concentration of a particular chemical in a tissue per concentration of chemical in water (reported as L/kg). This physical property characterizes the accumulation of pollutants through chemical partitioning from the aqueous phase into an organic phase, such as the gill of a fish. In the context of setting exposure criteria it is generally understood that the terms "BCF" and "steady-state BCF"' are synonymous. A steady-state condition occurs when the organism is exposed for a sufficient length of time that the ratio does not change substantially. does not consider the possibility of the organism eating contaminated food, only looks at is the environment contaminated  lipid content - amount of fat in an organism Accumulation body burden = alpha* R Models can incorporate: Multiple uptake sources—food, water Estimated assimilation efficiency alpha = amount absorbed / amount ingested from food Specific ration R = amount of food consumed/mass of organism Biotransformation Multiple elimination mechanisms fugacity model - [ ] in different compartments Molal World Volumes Air, water, sediment, soil Soil: 9x10^3 m3 substance is defined by its ability to escape a physical Air 10^3 m3 compartment Water 7 x 10^6 m3 f = c/z Sediment and biota 2x10^4 m3 z is fugacity capacity constant n = cv - mol/compartment c is concentration in given compartment nx = f Zx Vx Cx = fx zx n tot = f * (SUM ZxVx) in a compartment, C will remain the same but Z will shift f = n tot/SUM ZxVx The lifespan of an organism determiens how long they will be exposed to a contaminant Molal World Volumes A pesticide has a 96hr LC50 pf 3ppb for rainbow trout. near a lake, Soil: 9x10^3 m3 200g of pesticide are sprayed, and 35% of it leeches into the lake Air 10^3 m3 after rain. Lake is 30,000m2, depth 0.5m. does this [ ] exceed Water 7 x 10^6 m3 LC50? Sediment and biota 2x10^4 m3 FACTORS mass in water = 200*0.35 = 70g V of lake = 30,000*0.5 = 15,000 m3 mass of water = 15,000 (10^6 cm/1m3)(1g/cm3 -> density) = 1.5x10^10g INFLUENCING Lc = 70 g / 1.5x10^10 g = 4.7 ppb -> poses a risk to kill 50% at least of fish, because it is more thna LC50 BIOACCUMULATION Z air = 4x10^-4 mol/atm*m3 Chapter 4 Z water = 0.03 Z sediment = 10000 using molal world volumes, calc eqm c where 1 mol is distributed among air, water and sediment f = n tot / (SUM ZxVx) = 1 mol / ( (4x10^-4 * 10^3) + (0.03*7x10^6) + (1000*2x10^4) = 4.90 x 10^-9 atm C = f Zx air = 2.00x10^-12 mol/m3 water = 1.50x10^-10 sedi = 4.9x10^-5 if you want to analyze pcbs, look at sediments, highest [ ] Contaminant accumulation Contaminant Chemistry what partition? Organism intake and excretion Environmental conditions of interaction Temp affecting evaporation rate, pH of env affecting bioavailability habitats affecting what contaminats are even present Contaminant–solid interactions Association, Retention, or Sorption: The binding of a species without implication to the mechanism (which may include adsorption, absorption, precipitation, and surface precipitation). Adsorption: The binding of an ion or small molecule to a surface at an isolated site—a two-dimensional surface complex. Binding can be electrostatic, chemical, or hydrophobic. Absorption: The uptake of a species within another material (analogous to water uptake into a sponge).Partitioning: The distribution of a population of molecules of a given compound between any two phases, determined by the compound’s relative compatibility with each medium (Schwarzenbach et al., 1993). Precipitation: The formation of a three-dimensional structure without the association of a substrate (sorbent) material. This process occurs in solution directly and leads to discrete particles. Surface precipitation: a heterogeneous mechanism, refers to nucleation on previously existing particles. Both are important processes for metal and metalloid retention but generally do not contribute to organic compound retention in soils and sediments.  Bioavailability The fraction of chemical present in the environment that is or may become available for biological uptake by passage across cell membranes. ex. Al(OH)3 (s) + acid rain -> Al 3+ which can be uptaken by plants Bioavailability relates to a series of processes, ranging from processes external of organisms, towards internal tissues, and fully internal to the biological response site. Redrawn from Ortega- Calvo et al. (2015) by Wilma IJzerman.  Absolute vs Relative Bioavailability non-intravenous Intraveneously unknown how much is intaken (out of dose administered)  Bioavailability Absolute Bioavailability routes of exposure—oral vs. IV AUC comparisons (area under the curve) multiple pathways Relative Bioavailability two different sources, one is the reference- food 1 vs. food 2 AUC comparisons (area under the curve) Other things to measure: urine & bile only 1 pathway  Bioavailability Relative Bioavailability Compare organism concentration in different sources—eg. Filter feeders in Abu Dhabi & Dibba sediments for oil contaminants Compare different food sources for fish—measure blood concentration of individuals fed the different foods Compare exposure concentrations Effective Dose in pharmacokinetics Drugs or Toxicants: Give drug orally, measure blood C Give drug IV, measure blood C Determines amount of drug & rate of uptake Estimation of absolute bioavailability of an ingested dose by comparison of AUCs for ingestion and intravenous injection (top panel), and relative bioavailability by AUC comparison for the same dose administered in two different foods (bottom panel). All measurements need exposure studies Statistical measurements Mean residence time Mean time of a drug residence in a compartment (MRT) Mean absorption time Tells us how quickly contaminant gets into blood after exposure (MAT) Chemical Qualities Influencing Bioavailability—inorganic From Water Water chemistry modifies the species and sites uptake Weak acids: NH3 + H+ NH4+ H+ + CN- HCN H2S HS- S-2 Water Chemistry—Metals Dissolved Metals and metalloids (affected by speciation) changing form of metals (ex. methylation) or Binding to ligands & anions Cr 3 and Cr 6 -> only hexavalent is toxic, or methyl-Hg being toxic but Hg not toxic Ligand DOC (fulvic & humic acids) & inorganic compounds Anions Anoxic waters: NH3, HS-, S2- Oxygenated waters: B(OH), B(OH)4-, Cl-, CO32-, HCO3-, F-, HPO42-, NH3, OH- , Si(OH)4, SO42- Hydration spheres Around cations  Free-ion activity model (FIAM) The free ion activity model (FIAM) of metal- organism interaction was initially developed to rationalize experimental observations and to explain what was initially perceived as ‘‘the universal importance of free metal ion activities in determining the uptake, nutrition and toxicity of cationic trace metals’’ States that only free metal ions are taken up by organisms Developed in model solutions incorrect, Hg is taken in the organic (methylated) form Water Chemistry Modifies competition at uptake sites H+, Ca2+, Mg2+, Na+ concentration To model bioavailability, need to factor in competing cations, pH, ligand concentrations, temperature, & ionic strength Water chemistry of the microlayer at a biological surface is also important.  Bioavailability in solids An important step that limits the bioavailability of contaminants is their retention onto solids that compose soils and sediments. A wide range of solids exists in natural systems that vary in their reactivity toward organic and inorganic contaminants  Chemical Qualities Influencing Bioavailability—inorganic From Solid Phases Solids: aerosols, particulates, food, soils, sediments Aerosols & particulates Distribution within Near surface vs. distributed throughout vs. all deep within Particle size—small particles get farther into lung  Bioavailability—inorganic—solids Food Particle size and chemical form Diet Middle East: chronic dwarfism due to Zn deficiency Zn is less available from Cereal diet Protein diet enhances Zn, but decreases Ca absorption sediment - bottom of water soil - dry outside Solids ( soils and sediments) Solids within both soils and sediments are a composite of inherited material termed primary minerals (which are minerals formed by geological processes) and solids developed in place (authogenic). Such solids also have a balance of inorganic and organic fractions.  Bioavailability—inorganic—solids Sediments Aquatic sediments are an open, dynamic, structured biogeochemical system typically composed of an oxic zone overlying anoxic materials. Mixture of solid particles & interstitial water Sediment biota Difficult to model sediment bioavailability Used sequential extraction to determine availability Bioavailability—inorganic—solids Oxic Sediments Exchangeable metals> carbonates> Fe-Mn oxides> DOC & Sulfide bound metals Anoxic sediments AVS—acid volatile sulfide Sulfide is mostly bound to Fe or Mg in sediments, other metals have greater binding coefficients, so they tend to replace iron As metals mix with the sediments, they replace the iron Cd2+ + FeS CdS + Fe2+ Decreases interstitial water concentration of metals If SEM/AVS < 1, then metal precipitates & is unavailable Organic Contaminants Bioavailability from water Structure-activity relationship (SAR) and quantitative structure-activity relationship (QSAR) models are mathematical models that can be used to predict the physicochemical, biological and environmental fate properties of compounds from the knowledge of their chemical structure.  Partitioning between water and organism Octanol/water partition coefficient is very important index in Biological, toxicological and environmental area. The human body is made from water and lipids. If you know the distribution ratio of the chemicals to the octanol, you can estimate bioaccumulations. The octanol/water partition coefficient (Kow) is defined as the ratio of a chemical's concentration in the octanol phase to its concentration in the aqueous phase of a two-phase octanol/water system. Bioavailability decreases with increasing log Kow Bioconcentration factor: experimental concentration distribution = [ ] organism or sediment/ [ ] water (instead of octanol/water)  Persistency of some chemicals in soil >100 days - persistent, 30-100 - moderately persistent, plants (100% of E from sun) 2nd -> herbivoes (10%) 3rd -> primary carnivores (1%) 4th -> etc Why are concentrations higher In predators than prey Predators Accumulate more Prey larger pop living for a shorter time not eating More dilution effect much contaminant cus they dont eat much food Difficulties in defining trophic status can be determined by C measurements Water or food exposure? source of contaminant? Outcomes of trophic transfer of contaminants Biomagnification Similar concentrations in predator and prey Concentration decreases as trophic level increases bioconcentration feathers - hair in human, human sample colection From Chapter 4 can also have sediment for bottom feeders no bioaccumualtion: excretion=egestion Quantifying bioaccumulation from food Assimilation from food Estimate of contaminant transfer between members of trophic levels Quantified as bioavailability from food Assimilation efficiency Steady-state concentration Twin Tracer Technique Trophic Transfer Identifying trophic level Bioaccumulation study done as a laboratory experiment controlling level In field survey Twin-tracer technique Introduces radiotracer of the substance to be assimilated simultaneously with an inert radiotracer to which assimilation is compared. A radionuclide such as 14 C is used and assumed to behave identically to its nonradioactive nuclide in chemical and biological processes. Assimilation Efficiency using radiotracer Organism is fed a radioisotope and the difference between the amount of the isotope ingested and egested over a time period gives Assimilation Efficiency. phytoplankton can determine ecosystem health Trophic Position Defining Trophic Position Changes in stable nitrogen isotope composition is the best indicator.  Quantifying bioaccumulation from food Quantifying trophic status Isotopic discrimination Ratios of C, N & S isotopes changes with trophic transfers Lighter isotopes are eliminated easier than heavy 12C to 13C 32S to 34S 14N to 15N CHO meter to measure ratios  14N to 15N Discrimination Ratio ( 15N) Compare organism ratio to air ratio Changes with trophic level & animal age, but nothing else 15 N of ~3.4 o/oo per trophic transfer Allows for intermediate trophic levels Combination of N & C ratios Gives estimate of trophic level and sources of vegetable biomass tropic enrichment factor EXAMMM Quantifying bioaccumulation from food Estimating trophic transfer Simplest way Biomagnification Factor (B) B = C at level n / C at level n-1 › Bioaccumulation Factor (BF) BF= Corganism/Csource Concentration Factor (CF) CF= Cn/Cwater 15N Bowes and Thorp, 2015) trophic level using aa Fig. 1. (a) Trophic position is calculated from bulk-tissue stable isotope analysis using the producer ) 4 3.4] þ 1. (b) Trophic position using amino acid compound specific isotope analysis – 3.4) 4 7.6] þ 1.  Model using trophic structure ( 15N) to determine bioaccumulation C=aeb( 15N) where C is concentration in organism in food web & b is the biomagnification power Shorter chain, less magnification  Biomagnification of Contaminants Inorganic contaminants Metals and metalloids Radionuclides Organic Contaminants phytoplankton  Biomagnification of PCBs 209 forms Log Kow above 6.1 subject to biomagnification Higher trophic levels had more Cl in congeners more lipophilic persistent, do not degrade, bioaccumulate, biomagnify Cod young seals polar bear & older seals 3&4 5&6 6&7 Older vs young seals: slow elimination Due to slower elimination of more highly Cl PCBs Diet of young seals Log Kow > 7-8 -> accumulate in sediment or soil (does not exclude food chain passing) log Kow between 4-7 -> accumulate in organisms log Kow < 4 -> water