Lecture 3 - RH Flashcards
What are the classes of metal?
Class A - oxygen - seeking metals
Class B - Sulfur or nitrogen - seeking (these are typically highly toxic)
Borderline
These classes are based on lewis acid-base properties
What are metals like in relation to essentiality and non-essentiality?
Essential metals are needed in small amounts and toxic in large amounts
Non-essential metals are tolerable up to a certain amount but toxic at a large amount
What must be a characteristic of a chemical for it to be considered as a toxicant?
It must be bioavailable
What is the reference toxicant for inorganic chemicals?
Copper
What is the reference toxicant for organic chemicals?
Phenol
What are trace metals?
Metals required in trace amounts
How does the body manipulate metal toxicants to diminish their toxicity?
Metals can be stored in some body parts using proteins to avoid their toxicity.
What is the issue with inorganic phosphate fertilizer?
Causes lots of cadmium to contaminate the soil affecting marine (such as crayfish)
What is the function of metal ions?
Enzyme cofactors
Structural components of organic molecules
Ultra trace essentiality (Li, Al, Sn)
What does bioavailability refer to?
Portion/fraction of a substance that an organism absorbs or accumulates
What influences the bioavailability of metals?
Concentration
pH
Redox potential
Complexation
Organic content
Environmental factors: temperature, salinity, complexing substances
How can temperature affect toxicity?
Increased toxicity
How does salinity affect toxicity?
Decreased due to complexing with Cl- ions or SO4 ions
How do complexing substances affect toxicity?
Decreases toxicity
What are some factors related to speciation that affect metal toxicity?
Ionic state (Divalent and trivalent cations are most biologically active)
Molecular state (Toxicity determined by rate of uptake and degradation of the molecule)
Form (organic forms more toxic than inorganic forms)
What does the strength of the bond indicate about toxicity?
Stronger bonds result in greater toxicity
How does a divalent/trivalent metal cause toxicity?
It binds to functional groups of amino acids or purines/pyramidines in nucleic acids
What are some biological impacts of metal binding reactions?
Block essential function of biomolecules
Displace essential metal ions in biomolecules
Alter or modify the configuration of biomolecules
How is lead toxic?
Interferes with production of ALAD resulting in impaired haemoglobin synthesis
How is mercury toxic?
Interferes with breakdown of catecholamines resulting in CVD and Heart failure
How is arsenic toxic?
Disrupts normal aerobic metabolism resulting in oxidative stress and formation of ROS
How can configuration be altered by metals?
Tertiary structure can be altered in enzyme proteins
Polynucleotides can alter genetic information
Biomembranes can be altered by binding to lipoprotein membranes (Hg alters axon)
How do organisms typically get rid of toxins?
Complexing metal ions with cysteine rich proteins called metallothioneins
Depositing the metals as insoluble granules in tissues
Excretion via faeces
What are metallothionenes?
Cysteine-rich proteins used to complex metallic toxins.
Are metals typically biomagnified?
No, however organometallic compounds can be biomagnified
What are the methods by which metals are measured?
Atomic Absorbtion Spectroscopy
Neutron activation
Mass spectroscopy
Gas chromatography + mass spectrometry
Pulse polarigraphy - gives quantity and ionic state
What are the advantages and disadvantages of investigating total metals?
Easy, less expensive however less meaningful
What are the advantages and disadvantages of investigating individual types of metals?
Harder, more expensive, however more meaningful and environmentally relevant
In what form is Hg mostly released into the environment?
Most is released as inorganic Hg
Where does environmental Hg come from?
Gold production, coal and oil combustion
Major inputs from the chlor-alkali industry
Slimicides used in timber and paper pulp industries to prevent fungal growth
antifouling paint for ship hulls
pesticides
seed dressings
Weathering of mercury bearing rocks, released volcanoes and geothermal vents
What are some commercial uses for mercury?
Thermometers
Medicine
Dentistry (amalgam in the past)
Fluorescent lamps
Which organisms typically contain mercury?
Most fish species contain approx 0.15 p.p.m
Birds accumulate mercury in their feathers and livers
What caused minamata disease?
Mercury pollution of minamata bay in Japan causing accumulation of toxic mercury in the food chains and in turn affecting 2000 people and killing 43 people while injuring 700 others.
Where is environmental cadmium sourced from?
Cadmium is produced as a byproduct of zinc smelting
Does cadmium biomagnify? Why or why not?
No, because the fishes and mammals that ingest it are able to excrete it. However molluscs accumulate cadmium more readily
What causes Itai Ita?
Cadmium toxicity which causes severe bone deformities (it replaces calcium). Contaminated rice paddies was the source
What forms of cadmium are most common?
Cd2+>Cd1+ (ranked according to abundance)
What are the commercial uses of cadmium?
Batteries
Pigments
Plastics
What are the sources of lead in the environment now? Rate in order of abundance.
Mining
Smelting
Gasoline = Natural weathering
Refining
What are the uses of lead today?
Dentistry
Medicine
Radiation protection
What are the forms of toxic lead?
Pb2+ (major problem)
Tetraethyl Pb and tetramethyl Pb these are very bioavailable and cross the blood brain barrier
How does lead affect organisms?
In aquatic systems 16 different chemical species can occur. Low pH and low water hardness favours Pb2+ and in turn toxicity
What are the physiological effects of lead on humans?
Children’s mental development is impaired
Neurological defects
Kidney dysfunction
Anemia
What causes anemia during lead poisoning?
Shortened blood cell life span
Impaired haemoglobin synthesis
What causes neurological defects from lead?
Blocks impulse transmission and acetylcholine release
Which organisms bioconcentrate Lead?
Mussels
The extent to which toxicity is amplified by hardness and pH is shown in this example:
at pH 7.1, hardness 50 mg/L as CaCO3 -> 1.1mg/L
at pH 8.1, hardness 360 mg/L as CaCO3 -> 398 mg/L
What are the sources of copper release into the environment?
Pesticides (Bourdeux mixture)
Mining and Smelting (3rd most common metal in use)
What are some commercial uses of copper?
Plumbing, electrical conductors, cookware, coins, medicine
What are the forms of copper that can be toxicants? Rate in order of abundance.
Cu2+
Cu+
Cu3+
Cu4+
What are the biological effects of copper?
Copper is essential as an important cofacter in many enzymatic reactions
hemocyanin
What are the sources of Zinc?
Fungicides
Mining and smelting and 4th most commonly used
What forms of zinc are toxicants?
Zn2+
ZnO - zinc oxide
What are some commercial uses of zinc?
Galvanisation
Pigments
Catalyst in rubber manufacture
Medicine
Coins
What are the biological effects of zinc?
Zinc is an essential element and used as a cofactor in many important enzymatic reactions
What are the forms of tin?
Sn2+ more commonly than Sn4+
What are the sources of tin in the environment?
Mining/Smelting
Former use as a marine antifoulant
What are the commercial uses of tin?
Coating other metals to reduce corrosion
Dentistry
Glass production
What are the biological effects of tin? What is an important effect of TBT on snails?
Tributyl tin (TBT) is extremely toxic and lethal to a variety of planktonic organisms
TBT causes gross distortion of oyster shells rendering them unmarketable
Female marine snails exposed to TBT developed a penis and sperm duct
This condition is known as imposex due to imposing opposite sexual characteristics
What are the forms of Aluminum that are toxic?
Al+, Al2+, Al3+
What are the sources of aluminum?
Mining and smelting
Increased use of Al pots and Al paint
Acidification due to acid rain increasing solubility of Al in H2O causing an increased bioavailability of Al
What are some commercial uses of aluminum?
Aerospace industry
Various alloys
electrical conductors
Constructio
What are some proposed biological effects of aluminum?
Implicated in Alzheimer’s disease but no evidence as of yet
Damages plant roots and reduces growth in acid soils due to increased bioavailability of Al3+ ions
What are the forms of arsenic?
As3-, As0, As3+, As5+, organoarsenicals, AsH3 (arsenic gas which is most toxic)
What are the commercial uses of arsenic?
Alloys
Agricultural products (pesticides, etc)
Electronics
Pigments
What are some biological effects of arsenic?
Sublethal toxic effect on reproduction in several fish
Reproductive impairment in crustaceans
Toxic to sensitive algae
Associates with erythrocytes causing rapid membrane breakdown
Enters blood and associates with serum proteins
What is biomethylation?
A process by which inorganic metal forms change into organic metal forms
How does biomethylation affect toxins?
Increases toxicity and bioconcentration
How does biomethylation occur?
Bacteria
