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EC number: 233-334-2
CAS number: 10124-43-3
In the control aquarium, no cobalt added, the observed mortality was
very low. Only one dead nymph was collected in the last week of the
experiment. It was observed that the nymphs were growing rapidly and
emergence of sub-imagines started the 14th of July. Emerging specimens
were then collected almost every day until the end of the experiment.
Fifty per cent of the stocked population emerged within 22 days. After
28 days 64 per cent had emerged, and 9 large nymphs were found alive in
In sum 58 specimens were found again after four weeks which corresponds
to a recapture of 77%. The number of lost individuals was 17 (23%). As
the animals could not escape this loss must be regarded as non-observed
mortality. It is known that nymphs of the genus Ephemerella exhibit
cannibalism which may explain the non-observed mortality.
In the 5.2 ppb concentration the survival was almost as good as in the
control, 71%. The emergence was a little retarded in comparison with the
control, the time for 50% emergence coming 4 days later. The observed
mortality was low but higher than in the control. It is interesting to
note that one of the subimagines was not able to fly. It was floating
around on the water surface for more than one hour before it was picked
up. As such specimens never reproduce the handicapped individual was
classified as dead. The non-observed mortality was 24%.
Some emergence was noted in the 32.6 ppb aquarium. It was, however, very
much retarded. Only 15 nymphs were found at the end of the experiment
and 50% of the stocked population did not survive the experimental
period. Four subimagines not capable of flying were found. The number of
observed dead nymphs was high, and the non-observed mortality was 34%.
In the 470 ppb aquarium all animals died and 50% mortality was reached
within 20 days. It was observed that the nymphs grew very poorly before
they died. Non-observed mortality was 32%. In the highest concentration,
3950 ppb, all animals died. Dead animals occurred within a week but not
within 96 hours. 50% of the population was dead after nine days.
Non-observed mortality was 13%. In all aquaria with addition of cobalt
the mortality was greater than in the control.
The mean weight of nymphs from the 32.6 ppb concentration was
considerably lower than in the smaller concentrations. Using Student's
t-test it was seen that the difference was statistically significant
(P<< 0.001). There was no significant difference in weight of nymphs in
the control and in the 5.2 ppb aquarium (0.50> P> 0.30). Analysis of
variance showed that the weight of preserved subimàgines was significant
difference between sexes, females being heavier than males. As the sex
ratios were not the same in the different aquaria, the sexes had to be
separated in the further calculations. When student's t-test was used it
was seen that the males in the control were heavier than the males in
both the 32.6 and 5.2 ppb concentrations (P-<0.02). The females in the
control were heavier than the females in the 32.6 ppb aquarium
(P<0.001). Between the females in the control and in the 5.2 ppb
concentration there was no statistical difference (0.70> P> 0.50) when
the whole material was considered.
In the Rickleå River in northern Sweden, salmon (Salmo salar
L.) are present in the lowermost 15 km. The salmon population has been
studied since 1961. In 1965 the density of salmon and trout parr
decreased in some of the rapids and a drastic reduction of the numbers
of sea-migrationg salmon smolts was recorded in 1966. In recent years
the juvenile salmon population has decreased still more, and it is now
very hard to find salmon parr by electro-fishing. It was not reasonable
to believe that the decrease was caused by organic pollution or failure
of spawning. Trout (Salmo trutta L.) has decreased to a Lesser
extent than salmon, and sculpin (Cottus gobio L.) is still very
abundant in the rapids.
Simultaneously there has been a drastic impairment of the invertebrate
fauna. Some of the insect species important as food for salmon parr are
now absent or reduced in number. This has been shown by drift sampling
and investigations on the Fontinalis community in the rapids. Although
nymphs of the mayflies, Baetis rhodani and Ephemerella ignita, and
blackfly larvae are present in the mosses during summer, the
winter-growing nymphs of Ephemerella mucronata and Baetis
rhodani and winter-growing blackfly larvae are absent or reduced in
number in the area of salmon habitat. Most of the Plecoptera species are
still present. The reduction of the invertebrate fauna explains the
decreased population of salmon parr in recent years.
In 1963 a diamond factory began operation in the upper end of the area
accessible to the salmon. Here nickel was used from 1963 to 1967, and
since 1967 cobalt was used instead. In the process the metals have been
dissolved in acids and the wastes were discharged into the river after
neutralization with slaked lime. A laboratory investigation has shown
that the treatment with lime did not prevent the metals from
dissociating in the acidid river water. The consumption and the
discharge of heavy metals has increased from year to year since 1963. A
purification plant was not installed and in operation before November
1973. The decrease of the salmon population and the impairment of the
invertebrate fauna are well synchronized with the activities at the
diamond factory. An electroplating plant was also in operation in the
same place in the years 1964-1969.
Due to varying discharge, and water flow in the river the concentration
of cobalt in the water, fluctuated in the years 1972-1973. When the
factory was closed in summer the concentration was below the detection
limit of the analytical method (Atomic absorbtion =<1 ppb) . In May and
June the content of cobalt was low, 2-5 ppb, due to the spring flood.
The highest concentrations prevailed during autumn and winter, 10-43
ppb, when the water discharge of the river was low. The yearly
fluctuation was in accordance with the elimination of mayfly nymphs and
blackfly larvae in the mosses in winter.
In the superficial layer of the sediments the concentrations of cobalt
were higher below the discharge (14-24 ppm) than above (4-8 ppm). These
values are not very high in comparison with other watercourses. In
Fontinalis, however, the accumulation of cobalt was much more
pronounced; 41-43 above and 770-820 mg/kg dry weight below the discharge
The sensitivity of the mayfly, Ephemerella ignita, to cobalt was
investigated in a four week running water test. The nymphs were living
on their natural substrate. Cobalt nitrate was administered constantly.
Drastic effects were recorded in sub-acute concentrations. In
concentrations of 3950 and 470 ppb added to the water, all nymphs died
within three weeks. With 32.6 ppb the mortality was higher and the
emergence of subimagines was retarded in comparison with the control.
The growth of the nymphs was slow and the appearance of handicapped
subimagines was frequent at this concentration. The differences in
development in 5.2 ppb and in the control were small but always in
favour of the control.
The experimental running water investigation suggests that heavy metal
discharge from the diamond factory is the cause of the ecological damage
noted in the river.
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