Top 10 Toxicants are as follows:
1. Copper (Cu)
- In ionic form (Cu+, Cu2+), used as pesticide, since antiquity
- essential micronutrient
- complex speciation, bioavailability depends on pH, salinity and humic acid concentration
- Common uses: electronics, plumbing, antifouling, wood preservative.
2. Phosphorus (P4)
- yellow form very reactive and therefore highly toxic
- red form found in matches
- Essential nutrient (mostly in the form of phosphate: PO43-); key element in DNA, RNA, ATP.
- Phosphine (PH3) is common insecticide and rodenticide
- Covalently bond to organic compounds: pesticides, fire retardants.
3. Sulfur (Sx)
- in various forms used as fungicide, since antiquity
- S containing compounds have typical smell
- essential nutrient (S containing amino acids)
- Common uses: gun powder, sulphuric acid, preservative (sulfite in wine suppresses yeasts).
4. Arsenic (As)
- in various forms used as pesticide, since antiquity
- famous poison: killed Napoleon
- used as wood preservative, pesticide and in metal alloys
- sometimes present in natural environments at relatively high levels
- Some ores have high as content; smelting releases this As.
5. Selenium (Se)
- Essential micronutrient but toxic at low levels (mind your supplements!)
- mimics S in biochemical reactions, hence its toxicity
- used in semi-conductors, pigments
6. Lead (Pb)
- most widely distributed toxic element, mostly because of its use in the past (lead based paint, tetraethyl lead in gasoline, lead arsenate as insecticide, solder, piping – now all obsolete in the West)
- still used in batteries, lead crystal, ceramics, ammunition and as weights (fisheries, wheel balancing) and released during smelting of ores
- Pb2+causes anemia and neurological dysfunction
7. Cadmium (Cd)
- closely associated with zinc (a micronutrient), which it (as Cd2+) mimics biochemically, hence its toxicity (also a carcinogenic)
- forms complexes with ligands, especially S containing
- Common uses and sources: by product of zinc mining, nickel-cadmium batteries, plastic stabilizers, pigment, vulcanized rubber.
8. Chromium (Cr)
- essential micronutrient, occurring predominantly as Cr(III) and Cr(VI)
- hexavalent form is especially toxic (carcinogenic, kidney necrosis)
- toxicant in ‘Erin Brokovitz’ movie
- Used in chrome plating, tanning, pigments, wood preservation.
9. Nickel (Ni)
- common element in earth crust
- Nickel compounds (Ni2+) are very toxic and carcinogenic; in elemental form, it causes contact dermatitis in sensitized individuals
- Used in alloys to prevent corrosion (stainless steel, coins), ni-cd batteries.
10. Aluminum (Al)
- after iron, most common metal in earth crust
- free Al3+ is toxic, but sufficiently high concentrations only occur at low pH (acid main drainage, acid rain mobilizing free Al3+ in soils)
- Widely used in elemental form in construction, sheet metal.
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