sea areas is larger than usual, and phosphate is present in such large quantities that
it is not depleted by the plankton algae in the summer (McIntyre and Johnston
1975).
Where there are strong tides, such far-reaching changes do not take place on the
ocean floor. That is the case with London's sludge,S million m 3 of which are annually dumped in the mouth of the Thames, and with the sludge from the ManchesterLiverpool area, about 0.6 million m 3 in 1971, with about 40,000 t of dry material
per year, which is dumped in Liverpool Bay, Irish Sea. A working group concluded
that even an increase to 250,000 t of solids is unlikely to produce changes beyond a
tolerable limit (Department of the Environment 1972). Great Britain dumps 25 times
as much sludge as the Federal Republic of Germany. Since 1962, approximately
0,3 million m 3 per year of treated sludge have been dumped by the city of Hamburg
in an area northeast of "Elbe 1" light ship in the Helgoland Bight. Nearly every day
a barge was loaded with 1200 m 3 of sludge containing about 8% solids, towed for
about 11 h to the site, and emptied. Unloading took about 2 h so that the sludge is
spread over a larger area. The costs of this procedure are said to have been DM 7 per
m 3 . An investigation of the area, in 1971, showed an increase of organic matter in
the sediment, and high concentrations of the clam Abra alba, and of the polychaete
Pectinaria (Caspers 1975). But in the summer of 1975, a large part of the bottom
fauna died out. It is still not certain whether sludge is mainly responsible for this, or
whether a natural phenomenon is involved and a lack of oxygen extended in wide
eddies in Helgoland Bay during the especially placid summer weather (Fig. 40). The
basic situation seems to be similar to New York Bight (Fig. 39). From 1980 on, the
sludge disposal so close to the mouth of the Elbe river has no been longer tolerated,
sludge disposal in 1981 took place west of Helgoland, in deeper water. The policy in
the Federal Republic of Germany is to prohibit dumping of sludge in coastal waters.
This means that the city of Hamburg either has to bring the sludge to the edge of
the continental shelf, or find means to dispose of it on land (Dethlefsen 1981).
Sewage sludge is a micture of substances - including clay particles, organic remnants,
and trace elements of the most varied sorts, that have very different effects. With
anaerobically treated sludge from Hamburg sewage treatment plants, about 50 t of
solid material was introduced into the region of the light ship "Elbe 1" every day;
about half of this amount is organic matter, and it contains, per year, about 500 t of
zinc, 18 t of copper, 13 t of chromium, 11 t of lead, 2.4 t of nickel, 0.5 t of cadmium, 0.5 t of silver, and between 36 kg and 270 kg of mercury. These amounts will
double when a new sewage treatment plant comes into operation, in 1981, and if
dumping should continue. Sewage sludges have different concentrations of heavy
metals; in general, calculated by dry weight, they contain 10 times more copper,
30-50 times more lead, zinc, and cadmium, and 200 times more silver than average
Earth crust material or unpolluted marine sediments. Where industrial effluents are
included in sewage, concentrations may be 10-100 mg/kg of mercury and cadmium,
20-200 mg/kg of nickel, 1-4 g/kg of lead and chromium, and 1-15 g/kg of copper
and zinc (National Academy of Sciences 1975a). Sludge dredged from the bottom of
harbors and from heavily polluted estuaries may have even higher heavy metal concentrations. This is the reason for rather high concentrations in the sediment of
dumping areas (Fig. 35 and 74).
66
it is not depleted by the plankton algae in the summer (McIntyre and Johnston
1975).
Where there are strong tides, such far-reaching changes do not take place on the
ocean floor. That is the case with London's sludge,S million m 3 of which are annually dumped in the mouth of the Thames, and with the sludge from the ManchesterLiverpool area, about 0.6 million m 3 in 1971, with about 40,000 t of dry material
per year, which is dumped in Liverpool Bay, Irish Sea. A working group concluded
that even an increase to 250,000 t of solids is unlikely to produce changes beyond a
tolerable limit (Department of the Environment 1972). Great Britain dumps 25 times
as much sludge as the Federal Republic of Germany. Since 1962, approximately
0,3 million m 3 per year of treated sludge have been dumped by the city of Hamburg
in an area northeast of "Elbe 1" light ship in the Helgoland Bight. Nearly every day
a barge was loaded with 1200 m 3 of sludge containing about 8% solids, towed for
about 11 h to the site, and emptied. Unloading took about 2 h so that the sludge is
spread over a larger area. The costs of this procedure are said to have been DM 7 per
m 3 . An investigation of the area, in 1971, showed an increase of organic matter in
the sediment, and high concentrations of the clam Abra alba, and of the polychaete
Pectinaria (Caspers 1975). But in the summer of 1975, a large part of the bottom
fauna died out. It is still not certain whether sludge is mainly responsible for this, or
whether a natural phenomenon is involved and a lack of oxygen extended in wide
eddies in Helgoland Bay during the especially placid summer weather (Fig. 40). The
basic situation seems to be similar to New York Bight (Fig. 39). From 1980 on, the
sludge disposal so close to the mouth of the Elbe river has no been longer tolerated,
sludge disposal in 1981 took place west of Helgoland, in deeper water. The policy in
the Federal Republic of Germany is to prohibit dumping of sludge in coastal waters.
This means that the city of Hamburg either has to bring the sludge to the edge of
the continental shelf, or find means to dispose of it on land (Dethlefsen 1981).
Sewage sludge is a micture of substances - including clay particles, organic remnants,
and trace elements of the most varied sorts, that have very different effects. With
anaerobically treated sludge from Hamburg sewage treatment plants, about 50 t of
solid material was introduced into the region of the light ship "Elbe 1" every day;
about half of this amount is organic matter, and it contains, per year, about 500 t of
zinc, 18 t of copper, 13 t of chromium, 11 t of lead, 2.4 t of nickel, 0.5 t of cadmium, 0.5 t of silver, and between 36 kg and 270 kg of mercury. These amounts will
double when a new sewage treatment plant comes into operation, in 1981, and if
dumping should continue. Sewage sludges have different concentrations of heavy
metals; in general, calculated by dry weight, they contain 10 times more copper,
30-50 times more lead, zinc, and cadmium, and 200 times more silver than average
Earth crust material or unpolluted marine sediments. Where industrial effluents are
included in sewage, concentrations may be 10-100 mg/kg of mercury and cadmium,
20-200 mg/kg of nickel, 1-4 g/kg of lead and chromium, and 1-15 g/kg of copper
and zinc (National Academy of Sciences 1975a). Sludge dredged from the bottom of
harbors and from heavily polluted estuaries may have even higher heavy metal concentrations. This is the reason for rather high concentrations in the sediment of
dumping areas (Fig. 35 and 74).
66