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