Top 10 Toxicants

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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