5 metals and metalloids I Flashcards
what are the general properties of metals?
-metals can neither be created nor destroyed
-metals are naturally occurring
what else can be said about metals, which can neither be created nor destroyed?
-problematic environmental contaminants (do not degrade, so very persistent)
-however, chemical form of the metal can be altered
what can be said about metals which are naturally occurring?
anthropogenic activities increase metal bioavailability either because:
-metals are moved from biologically inaccessible to accessible compartments in the biosphere
-form of the metal is changed to more bioavailable or toxic form
what are the anthropogenic sources of environmental metal pollution?
what are metals/metalloids?
-heavy metals: atomic density >5g/cm3, or specific gravity >5
-less often used nowadays
-trace metals: in trace amount, <ppb levels
-metalloids- share properties of both metals and non-metals (ex: selenium, arsenic)
what is the classification of metals?
based on chemistry
-affinity to bind to oxygen, sulfur and nitrogen
-class A (O seekers): O>N>S
-class B (S/N seekers): S>N>O
-borderline: in-between/ambivalent
what is the graph of the classification of all metals?
what is the graph of metal-ion binding sites in proteins (functional groups)?
toxicity mainly arises from binding to proteins (enzymes)
-proteins have functional groups on their side: which class B wants to bind to N or S which causes denaturation or inactivation
what is the graph of toxicity sequence of metal ions in a range of organisms?
ranked based on toxic potency (left are the most toxic)
-class B metals are more toxic
what are the major abiotic factors influencing metal bioavailability and toxicity in water?
hardness (Ca and Mg concentration) in water
-hard water has more Ca and Mg (water cations)
pH/alkalinity of the water
-alkaline is when there is a higher pH and there are more carbonates, hydroxide ions and bicarbonates
-acidic=less carbonate, OH and bicarbonate
concentration of inorganic and organic ligands in water
-ions can forms complexes
-if want to increase solubility of a metal=make water more acidic
-if pH is higher=less amount of free metal ions in solution
what is the graph of the factors influencing metal bioavailability in natural water?
-if water is harder, there is a higher degree of competition= therefore decrease uptake of the free toxic metal
-when increased competition= why metals are more toxic in soft water
-if water has increased organic matter=more organic complexation so less toxic metal available for uptake
-more alkaline=more OH and HCO3 so increased degree of organic complexation so less free metals ions
-acidic waters=metals are more toxic
-hardness and alkalinity have a direct relationship (if one goes up, so does the other)
what is the graph of speciation of Cu in freshwater?
free ion is most important
-availability goes down as pH increases (so it becomes less toxic)
what are the graphs of the effects of hardness, pH and DOC (NOM) on acute Cu toxicity?
calcium is the primary hardness cation
-goes up, meaning Cu uptake is going down (less toxic because there is more competition)
DOC=dissolved organic carbon
-more organic matter, the less toxic it is
would metals (e.g. Cd) be more bioavailable/toxic or less bioavailable/toxic in seawater relative to freshwater? what would be the basis of this difference?
saltwater would be less toxic
-more ions so more competition (like Na and Cl)
-freshwater: 1.8 ppb (acute), 0.72 ppb (chronic)
-saltwater: 33 ppb (acute), 7.9 ppb (chronic)
-we must have much more Cd in seawater to have same toxicity
what is the graph of chemical speciation of Cd in seawater?
cadmium is most important
-more salinity=decrease in free ions (becomes complex with chloride)
what are the major abiotic factors influencing metal bioavailability and toxicity in soil/sediment?
soil: solid (minerals and organic matter), water and air
factors
-pH
-inorganic ligands
-natural organic matter (NOM)
what is the graph of a sample and the categories a metal is put into?
when taken all metals from sample
-fraction will occur in pore water (important due to uptake)
-low pH will increase solubility of metals=more ions in pore water
-if increased hardness in pore water=less toxic
questions need to ask to decide toxicity
1. what amount of metals are found in pore water?
2. what is the chemistry of the pore water (hardness, alkalinity, ions, etc)
what is the environmental exposure to animals to metals?
trophic transfer of metals
-efficiency varies with each metal (Hg, Se, etc are more efficient)
