Top 10 Toxicants

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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Sajid Ali is environmental columnist at

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