Environmental impacts II

Question 1

Arsenic

Answer 1

• Average concentration in crust - 2ppm
• Associated with gold and sulphide deposits (FeAsS2)
• Main component of >200 minerals
• Chemical forms: As3-, As0, As3+ and As5+
• Forms organic compounds (e.g. arsenobetaine)
• Acute poisoning above 100gdL-1 in blood (inorganic As and metabolites)

Question 2

Sources of arsenic

Answer 2

• As is abundant in many common rock types
• Sulphide minerals (pyrite, galena sphalerite) - these are common ore minerals and gangue minerals so mining releases As to environment
• Coals (can be extremely high in As)
• Fe formation

Question 3

Speciation and As Toxicity

Answer 3

• Toxicity of As varies with form (speciation) - bioactivity varies.
• Reduced forms (arsine, organo-arsine) extremely toxic
• Arsenite (As(III)) very toxic. 0.1g As2O3 may be lethal
• Arsenate (As5+) several times less toxic
• Elemental arsenic (As0)is not considered poisonous