Geology Reference
In-Depth Information
and behaviour of young children, steps were taken in the mid-1970s to
reduce the lead content of tap water in Glasgow and other susceptible
areas, which often exceeded the WHO maximum guideline at the time of
100 mgL
1
. The method chosen was adjustment of pH to 8-9 by lime
dosing. The effects of liming the Glasgow water supply were quite
dramatic. Whereas pre-1978, when the pH was 6.3, only 50% of random
daytime samples were
o
100 mgL
1
in lead, the figure increased to 80%
during 1978-1980, when the adjusted pH was 7.8. After 1980, when the
pH was increased further to 9.0, 95% of samples were
o
100 mgL
1
.
80
It
appears that carbonate and hydroxycarbonate lead compounds present
in the coatings on the pipes were stabilized. Significant reductions in
blood lead levels of key exposed groups (e.g. pregnant women) were also
observed.
Since 1989, as regulatory upper limits for lead in drinking water have
fallen, e.g. to 50 mgL
1
(EC) and now to 10 mgL
1
(WHO), orthopho-
sphate has been added to the water supply in Glasgow to precipitate
insoluble lead compounds such as Pb
3
(PO
4
)
2
and Pb
5
(PO
4
)
3
OH. This has
resulted in a fall in the proportion of households with water lead 410 mg
L
1
from 49% in 1981 to 17% in 1993.
81
Despite this improvement, an
estimated 13% of infants were still exposed via bottle feeds to tap water
lead concentrations in excess of 10 mgL
1
and it seems very unlikely that
further treatment of the water supply will be able to guarantee water lead
concentrations
o
10 mgL
1
.
Occasionally, elevated concentrations of lead in tap water arise from
the illegal use of lead solder in capillary joints to join copper pipes.
Cu
21
þ
2e
E
0
H
¼
0.337 V
"
Cu
(s)
(3.93)
Cu
21
þ
Pb
(s)
Cu
(s)
þ
Pb
21
E
0
H
¼
0.463 V (3.94)
"
In Washington DC, USA, where the water disinfection programme was
recently modified from chlorine to chloramines, an unexpected appear-
ance of high levels of lead in the tap water has been partly attributed to
similar galvanic corrosion when copper pipes are connected to lead-
containing brass fittings in the presence of chloramines. With the shift to
chloramines, the oxidizing potential of Washington DC's water was
lowered and not only could the brass become highly anodic and the
copper cathodic, but also the previously deposited PbO
2
scales on the
inside of lead service pipes began to dissolve.
82
3.3.2.3 Cadmium in Irrigation Water. In the 1950s in Japan, many
people, especially menopausal women suffering from malnutrition, low
