Chemistry Reference
In-Depth Information
(4)
Toxic or persistent organic compounds of silicon
and substances that may cause the formation of
such compounds in water, excluding those that
are biologically harmless or are converted
rapidly in water into harmless substances.
(5)
Inorganic compounds of phosphorus and ele-
mental phosphorus.
(6)
Fluorides and cyanides.
(7)
Substances that have an adverse effect on the
oxygen balance, particularly ammonia and
nitrates.
plant, or a non-point source, e.g. farm run-off, con-
struction site, land disturbance or mine.
The Chemical Industries Association
Indicators of
Performance
2000 report [6] claims that total dis-
charges of Red List substances have been reduced by
96% since 1990, with some 14 t being discharged in
1999.
Effects of pollution
Acidification.
Acidification of the terrestrial envi-
ronment takes place via the deposition of acids
derived from aerial SO
2
and NO
x
pollution (see
Section 2.2) and from industrial acid discharges,
particularly acid mine drainage. In underground
coal and metal mines the pumping of groundwater
exposes pyrite (FeS
2
) in the lower strata, which
becomes subject to aerial oxidation:
The UK publishes priority lists of dangerous
chemicals: the Red List and First Priority Candidate
Red List (Table 3.4), for which the control regime is
more stringent than for the Black List, containing
a precautionary element and requiring Best Avail-
able Technology Not Entailing Excessive Cost
(BATNEEC).
Pollution may emanate from a point source, e.g. a
pipe or channel from a factory or sewage treatment
2FeS
2
+ 2H
2
O + 7O
2
Æ 2FeSO
4
+ 2H
2
SO
4
Additionally, when the water returns to the mine
after extraction and pumping cease, the sulfuric
acid and iron(II) sulfate dissolve. The iron(II) is oxi-
dised slowly by bacteria to iron(III) in the acidic
conditions:
Table 3.4
Red List priority toxic chemicals
First Priority
Red List
Candidate Red List
4Fe
2+
+ O
2
+ 4H
+
Æ 4Fe
3+
+ 2H
2
O
which liberates more acid by reaction with the now
covered pyrite:
Aldrin
2-Amino-4-chlorophenol
Atrazine
Anthracene
Azinphos-methyl
Azinphos-ethyl
Cadmium and its compounds
Biphenyl
FeS
2
+ 14Fe
3+
+ 8H
2
O Æ 15Fe
2+
+ 2SO
4
2-
+ 16H
+
DDT (including metabolites
Chloroacetic acid
When the iron(II)- and acid-bearing water reaches
the surface it oxidises rapidly, depositing orange
ferric hydroxide (Fe(OH)
3
) and oxyhydroxide
(FeOOH) precipitates and releasing further acid:
DDD and DDE)
1,2-Dichloroethane
2-Chloroethanol
Dichlorvos
4-Chloro-2-nitrotoluene
Dieldrin
Cyanuric chloride
Endosulfan
2,4-Dichlorophenoxyacetic
acid (including salts
and esters)
4Fe
2+
+ O
2
+
4H
+
Æ 4Fe
3+
+ 2H
2
O
Fe
3+
+ 2H
2
O Æ Fe(OH)
3
+
3H
+
Endrin
Demeton-O
Fe
3+
+ 2H
2
O Æ FeOOH
+
3H
+
Fenitrothion
1,4-Dichlorobenzene
Hexachlorobenzene
1,1-Dichloroethylene
The acids released leach toxic metals from mine
spoil, particularly Cu, Pb, Cd, Sn and As, and carry
them to streams and groundwater.
Acidification of soil can overcome the natural car-
bonate buffering, lowering the pH by as much as two
units. Phosphate and nitrate anions may become
remobilised and aluminium, manganese and zinc
leach from the soil.
Acid rain also leaches nutrient cations Ca
2+
, K
+
and
Mg
2+
previously held as complex ions in the soil,
replacing them with H
+
Hexachlorobutadiene
1,3-Dichloropropan-2-ol
g
-Hexachlorocyclohexane
1,3 Dichloropropene
Malathion
Dimethoate
Mercury and its compounds
Ethylbenzene
PCBs
Fenthion
Pentachlorophenol
Hexachloroethane
Simazine
Linuron
Trichlorobenzene (all isomers)
Mevinphos
Trifluralin
Parathion (including
parathion-methyl)
Triorganotin compounds
Pyrazon 1,1,1-Trichloroethane
with resulting reductions in
