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BIOL 354 (7)


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University of Waterloo
BIOL 354
Vivian Dayeh

BIOL 354 MIDTERM 1 NOTES INTRODUCTION  Toxicology – study of toxic substances (toxicants/contaminants); study of poisons  Xenobiotic – foreign substances to an organism; anything not endogenous  Anthropogenic – caused or produced by humans; describes origin or compound which otherwise would not occur naturally.  Toxicants – poisonous agent that produces adverse biological effects; can be organic or inorganic e.g., metals, PAHs, PCBs etc.  Toxin – toxic substance produced by a living organism e.g., snake venom, tetrodotoxin (found in puffer fish – shuts down nervous system and you die) History of toxicology  Paracelsus  everything is toxic; it’s the dose that makes the poison  Viability decreases as dose increases. Environmental toxicology  It’s the study of harmful effects of chemicals on ecosystems.  If there’s no exposure, there’s no effect.  In order for effect to occur, toxicant must: o Be released into environment e.g., rain storm o Be exposed to the target organism e.g., fish has to swim downstream to contaminated area. o Be taken up by target organism  may be modified from original form o Cause a response in the target organism  Different classes of environmental toxicants: o Radiation  e.g., Japan’s Fukushima Daiichi nuclear plant release o Inorganic  metals, ammonia o Organic  dioxins, furans, PAHs o Pesticides  insectides, fungicides, herbicides o Complex affluents  STP, mine, pulp and paper  Historical examples o Chimney sweeps  PAHs formed from incomplete combustion and led to an increase in scrotal cancer (link discovered by Percival Pott) o Mad hatters  used solutions containing Hg to make hats, and inhaled the vapor due to poor ventilation; caused neuropathy. Historical need for ecotoxicology  Changes in human behaviour o Pre-industrial revolution  small rural communities; receiving environment was able to cope with the wastes produces (baby diaper analogy) o Post-industrial revolution  developing countries shifted from rural to industrialized civilization; receiving environment could no longer cope.  Pollution – substances in environment that produce adverse effects; not all necessarily toxicants (e.g., P  eutrophication) but many are (e.g., PAHs, PCBs).  Paradigm shift o From dilution (solution to pollution is dilution) to boomerang (what you throw away can come back and hurt you) CONTAMINANTS FROM SOURCE TO RECEPTOR  Contaminants – tend to migrate in environment from high to low concentration  Elements of a toxicity event involves o Generation of a contaminant o Release of the contaminant (can be intentional or non intentional) o Movement of the contaminant to a receptor (organism of some sort) o Exposure at a high enough concentration for a long enough period o A response  Entry of contaminants into the environment o Direct /point source discharge  you can pinpoint exactly where discharge occurs e.g., industrial waste, sewage discharge etc. o Indirect /nonpoint source discharge  cant see a pipe e.g., agricultural & urban runoff. Experiment: effect of toxicants on fish (juvenile rainbow fish)  Once in the environment, you need to exposure to get a response.  In clean water  no toxicant thus no response  Add a toxicant  exposure may have a response but depends on organism, time and amount of exposure. o When exposed to a high dose/conc, it takes little time to get a response o At low dose/conc., you need to increase time to get a response.  Exposure routes o Oral  organism is given a specific dose (amount) of toxicant by mouth/diet. Unit for dose expresses as weight of toxicant/weight of organism [1 mg/kg = 1 ppm; 1g/kg = 1 ppb]. o Injection  organism exposed to the dose via intravenous, subcutaneous, or intraperitoneal injection (abdomen). o Topical  toxicant/drug is applied to the skin e.g., patches. o Respiratory  from air (inhalation via lungs); from water (uptake via gills). Organism exposed to specific concentration of toxicant; units expressed as weight of toxicant/volume of air or water [1 mg/L = 1 ppm] Measuring toxicity  Done using a bioassay, which is designed to determine the effects of a toxicant on an organism e.g., lethality bioassay is used to determine if chemical is toxic and how toxic it is relative to other chemicals.  Important bioassay parts other than the test organism o Exposure time  time to allow for the response to occur at the dose/conc of the toxicant o Dose/concentration or toxicant  amount of toxicant to develop a response within a given time period. Classifying toxicity responses  Based on the degree of response o Lethal  response that results in death of an organism o Sublethal  response under the level that directly causes death  Individual  Biochemical – enzyme inhibition  Hormonal – changes in cortisol levels due to stress  Physiological – changes in growth or reproduction  Species – changes in population structure  Community – changes in diversity and abundance of a species  Based on the timing of response o Acute – severe stimulus to quickly bring about response (can be lethality or sublethal); short term (response within 96 hrs); common endpoint. o Chronic – stimulus slowly bring about response; exposure occurs for long period of time; long term test (at least 10% of organisms life). o Sub-acute – less severe stimulus than acute; response takes longer to develop. o Cumulative – response occurs because stimulus has been repeated several times; exposure can be identical as previous one or different. o Delayed – response does not emerge until well after the exposure to the stimulus. Bioassay results  Keep time constant and vary dose or concentration o LC50- conc causing lethality in 50% of the test organisms in a given time. o LD50- dose causing lethality in 50% of the test organisms in a given time.  Keep dose or concentration constant and vary time. o LT50- time to cause lethality in 50% of the test organisms at a given dose/conc.  Measure endpoints that do not result in death  sublethality o ED50, EC50, ET50  E= effective.  E.g., enzyme induction, inhibition of growth etc. Modifying factors  Can adjust the toxicity of a given chemical to an organism.  During the bioassay, you want to keep all conditions constant other than [toxicant].  2 types of modifying factors: o Biological/biotic  species, sex, age, size, nutrition o Abiotic  exposure route, partitioning, pH, oxygen, temperature, light. INORGANIC POLLUTANTS Metals  Elements thus, cant be created or destroyed; lustrous appearance; malleable  Can be require, toxic or both depending on the metal and the concentration.  Bioavailability and toxicity can be affected by chemical speciation Speciation  the form taken by an element in an environmental sample.  In solution, metals may exist as free metal ions (e.g., Cu2+) or metal ligand complexes. Ligand may be: o Inorganic  complex with hydroxide, carbonate, fluoride ions o Organic  citrate, EDTA or natural organic humic or fluvic acid Classification of metals (based on density)  Heavy metals – greater density of iron e.g., Hg, Pb, Cd  Metalloids – nonmetallic elements that have properties similar to metals, but are less lustrous and are semi-conductors e.g., Se, As.  Metals of concern: As, Cu, Cd, Ch, Pb, Hg. Metal functions in biota  Many metals are required by organisms Fe, Cu, Zn  Essential metals can be incorporated into macromolecules or may act as enzyme cofactors e.g., Hb (Fe3+), chlorophyll (Mg2+), Mitochondria (Cu2+)  Important metal ions: Na+ (osmoregulation), K+ (memb potential), Ca2+ Classification of metals (based on preferential binding of metal to specific ligands)  Class A  complex with O > N > S  oxygen-seeking (group I and II metals) o Associated with carboxyls, carbonyls, alcohols, phosphates o Target phospholipids, nucleic acids, ATP, and ADP  Class B  complex with S > N >> O  S or N-seeking (Cu, Cd, Hg, Ag, Au) o Associate with sulphydryls, disulphides, thioethers, and amines o Target amino acids, proteins, free nucleotides Metal occurrence  Anthropogenic activity has increased metals in environment e.g., mining.  This makes them more bioavailable and alters their distribution & availability. Sources of metal pollution  They persist in the environment because they are not biodegradable.  Ubiquitous in environment  found in soils, sediment, surface water at low conc. o Weathering of metal-bearing rock & soil plays role in distributing metals.  Anthropogenic sources: o Industry – metal mining, refining/smelting o Urban waste – disposal of metals from garbage, solid waste etc o Agriculture – from use of metal based pesticides (may contain As or Hg) o Other sources:  Ash, cinder – plants/animals take up metals, and once burned, the metals remain and may be found in conc. levels.  Paints – Pb and tin based paints; marine boat hulls, residential painting  Lumber – pressure treated wood (contain Ch, Cu and As – CCA)  Tannery – processing leather uses Cu and Cd solutions Examples of metal toxicity  Binding to molecules in organisms and altering their function e.g., block enzyme binding site  Interfering with uptake of essential metals – due to blocked uptake in cell  Generation of reactive oxygen species (ROS) – oxidizes lipid bilayer, which decreases membrane fluidity, and can damage DNA. Organometals –more likely to enter organisms and are more toxic than their parent metals.  Tributyl tin  antifouling compound used in water environments. o Paints contain TBT; prevents buildup of material on bottom of boats  Tetraethyl lead  anti-knock compound found in gasoline. Source of Pb in city dust.  Methyl mercury  occurs due to biomethylation (most toxic forms of Hg). o Hg is released as inorganic Hg from mining and processing, landfill leaching etc o Sulphate-reducing bacteria transform inorganic Hg into methylmercury (in both aerobic and anaerobic condition), and produces mono and di-methylated Hg. o Neurotoxin that can easily bioaccumulate in organisms. Non-metallic inorganics  Ammonia – common cause of fish kills, burn of plants  2 forms: ammonia (unionized) – NH3, and ammonium (ionized) – NH4+  Sources  landfills, farms, fertilizers, pulp and paper, steel mills, STP  Discharge can either be point source (E.g., STP), or nonpoint source e.g., farms Ammonia biological activity  Toxicity mostly contributed to the unionized form NH3, whose amount is dependent on: o pH and temperature.  % NH3 increases with increased temp and increased pH.  More dependent on pH than temp.  Movement of ammonia across the fish gills o Free diffusion direction determined by pressure gradient  determined by combination of total ammonia and pH on either side o Active transport out in exchange for Na (NH4+ has same ionic radius as K+) o Ammonium cant diffuse across the memb.  NH4+ mimics K+ and goes through the Na/K pump and this leads to an increase in K+ levels in the cell.  Ammonia toxicity to fish expresses itself as a neurological disorder  toxicity due to the disturbance of electrochemical gradients, inhibiting enzymatic reactions, intracellular pH changes. Other inorganics  Chlorine – highly toxic and reactive; used by industry and for water treatment  Cyanide – produced in large amounts in mining and metals processing. Effects oxidative phosphorylation used to produce ATP in mitochondria. ORGANIC POLLUTANTS  Carbon compounds with generally low persistence (exception  POPs and PAHs) o POP  persistent organic pollutants e.g., PCBs, dioxins, furans, pesticides.  Extremely diverse & new compounds are continuously being invented & mass produced Petroleum hydrocarbons  Crude oil  unrefined oil made of numerous different aromatic & aliphatic compounds  Recovered from ground but spillage may occur during storage or transportation.  Highly lipophilic and abundant in environment.  Most are of low or moderate toxicity: o Low MW compounds  volatile and more toxic (also valuable & consumed) o High MW  adsorb onto sediments/soils – reduce bioavailability but persist. PAHs - Polycyclic/Polynuclear Aromatic Hydrocarbon  2+ fused aromatic rings e.g., naphthalene (simplest PAH found in mothballs)  Produced whenever organic material is burned  by product of combustion  Natural sources  volcanoes, forest fires  Anthropogenic sources  fossil fuels, burning wood, car exhaust, tobacco smoke o Increase levels of PAHs in environment  increase potential for exposure  16 priority PAHs; very low water solubility; lipophilic; low volatility for larger PAHs  Rapidly partitions into sediments; metabolized & excreted rapidly in higher vertebrates  Main environmental sink are soils and sediments  less bioavailable but can be altered PCBs –Polychlorinated Biphenyls  All of anthropogenic origin  no natural formation.  Very stable, inflammable, non-conduncting man made products  Uses: insulating fluid in electrical equipment, hydraulic fluid, flame retardants  Use has been reduced because they are persistent and hydrophobic  Low acute toxicity  instead often chronic effects are observed  Interfere with endocrine system of vertebrates and affects reproduction & evolution. Dioxins & furans – Polychorinated dibenzodioxins (PCDDs) / dibenzofurans (PCDFs)  Chlorinated organic that are by-products of chlorination/bleaching processes.  Persistent and hydrophobic; not readily metabolized & excreted due to high chlorination  Specific isomers are toxic to mammals e.g., TCDD (know structure)  interferes with endocrine system and is a contact carcinogen.  Sources: pulp & paper mills, metal refineries, manufacture of PCBs, pesticides, forest fire Pesticides  Any biological/chemical agent that kills unwanted pests (plant or animal pest)  You want it to be highly toxic but only to kill desired target.  Perfect pesticide would: kill quickly, persistent to be effective, cheap manufacture Organochlorine insecticides e.g., DDT, methocychlor, chlorinated cyclodioenes, and HCH  All are neurotoxins; persistent, low water solubility; liophilic; volatile  DDT  para-dichlorodipheyltrichloroethane o Penetrates waxy cuticle of insects & kills nerve cells by disrupting Na balance o It’s less bioavailable to vertebrates thus relatively non-toxic to humans o Banned in Canada due to its effects on wildlife, particularly fish-eating birds:  Food web: Birds (reproductive failure + death)  carnivorous fish  few plankton  phyto plankton  DDT, DDE, DDD o It was found to inhibit a Ca-dependent ATPase in the shell gland of birds, which resulted in thin egg shells that were laid which could easily be damaged. o Impact of DDT on birds helped the paradigm shift. Other insectides  Organophosphorous compounds and phosphorothionates e.g., diazinon, malathion o Nerve toxins inhibit acetylcholinesterase o Lipophilic, volatile & toxic to vertebrates  less persistent than organochlorines o Includes herbicides (e.g., glyphotase) & potent chemical weapons (e.g., sarin)  Carbamates  similar mode of action to organophosphorous insecticides. o More diverse in properties and use.  Pyrethroid insecticides  neurotoxic and lipophilic but not persistent in environment o Synthetic variations based on natural product (pyrethrin) –from chrysanthemum Herbicides  Phenoxyherbicides – e.g., 2,4-D and 2,4-T (agent orange made from these and dioxin) o Organochlorines that mimic plant hormones & interfere with growth regulation o Not persistent; variable in solubility depending on formulation  Glyphosphate  N-(phosphonomethyl)glycine o Widely used to treat broadleaf weeds and grasses o Vertebrates exhibit high tolerance o Sorption & microbial degradation Emerging chemicals of concern  Pharmaceuticals  diverse; biologically active; not regulated with environmental health in mind  Endocrine disruptors & mimics  may interfere with animal reproductive performance RADIOACTIVITY Radioactive elements & isotopes  Come from: natural sources, mining (e.g., U-235), nuclear reactors & power plants, nuclear accidents, radioactive effluents, medical or industrial use.  Unstable isotopes will spontaneously decay releasing radiation  subatomic particles and electro-magnetic radiation.  Decay is exponential  rate of decay quantified as half-life of isotope (<<1 sec to years) Radiation  Form of energy characterized by electromagnetic spectrum Non-ionizing - Low energy photons Ionizing -  or  particles Radio Microwave Infrared Visible light UV X-ray Gamma ray Thermal Optical Broken bonds Heating Excites electrons Damages DNA  Ionizing photons result from the nuclear decay of unstable isotopes of an element which has the same # of protons in nucleus but different # of neutrons.   particles  contain 2 protons and 2 neutrons  relatively large mass. Chunks of nucleus ejected from radioactive atom carrying a +2 charge. o Cannot penetrate most matter (concern only if absorbed)   particles  high speed particles  electrons
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