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additional ecotoxicological information
Type of information:
experimental study
Adequacy of study:
weight of evidence
Study period:
3 (not reliable)
Rationale for reliability incl. deficiencies:
documentation insufficient for assessment
Justification for type of information:
Multiple single-species toxicity studies are available for cobalt; however, population/community level studies are limited. These tests offer the ability to simultaneously investigate potential environmental effects on organism populations and ecosystems not typically observed in “single-species” laboratory tests and provide an empirical validation of predicted environmental fate processes. In this capacity, field evaluations examine the validity and ecological relevance of effects observed under real-world conditions, are required to reduce extrapolation uncertainties, and will ultimately influence the application factors (AFs) applied in the PNEC derivation process under current regulatory strategies.

Data source

Reference Type:
other: Academic thesis/dissertation
Sam Södergren
Bibliographic source:
Section of Ecological Zoology, Department of Biology, University of Umeå, Sweden
Report date:

Materials and methods

Type of study / information:
This report is a comination of field assessment and field/laboratory investigation. The lab tests were conducted with Ephemerella mucronata and were conducted at a field station. While the field investigation were an analysis of field monitioring investigations.

Test material

Constituent 1
Reference substance name:
Cobalt nitrate
Cobalt nitrate
Test material form:
not specified
Specific details on test material used for the study:
Co(NO3)2 Source and purity undefined

Results and discussion

Any other information on results incl. tables


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 the aquarium.

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.

Applicant's summary and conclusion

Executive summary:

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 (April 1973).

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.