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Toxicity to terrestrial arthropods

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Reference
Endpoint:
toxicity to terrestrial arthropods: long-term
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
ISO 11267 (Inhibition of Reproduction of Collembola by Soil Pollutants)
Qualifier:
according to
Guideline:
other: OECD guideline No 232
GLP compliance:
yes
Application method:
contact
Analytical monitoring:
no
Vehicle:
no
Test organisms (species):
Folsomia candida
Animal group:
Collembola (soil-dwelling springtail)
Details on test organisms:
Species: Folsomia candida (Willem)
Source:Combined limit/range-finding test: In-house laboratory culture with known history.
Final test: Faculty of Earth and Life Sciences (Animal Ecology), VU University Amsterdam, The Netherlands.
Reason for selection:This system has been selected as an internationally accepted species.
Characteristics:For the test, synchronous, 10 to 13-day old juvenile springtails were used.
Start of each batch: Adult springtails were placed in small containers with plaster of Paris base. Batches were split up in case of overcrowding. Springtails were transferred to fresh medium regularly. Breeding medium was humidified regularly with RO-water.
Composition of culture medium:Mixture of plaster of Paris (Knauf B.V., Utrecht, The Netherlands) and activated charcoal (Sigma Aldrich, The Netherlands). Plaster of Paris provides highly moist substrate, while the charcoal adsorbs waste gases and excretion products.
Temperature:20 ± 1°C
Feeding: Twice a week with dry yeast (Dr.Oetker).
Light: 16 hours photoperiod daily; 400-800 lux.
Test duration: 28 days
Study type:
laboratory study
Limit test:
no
Total exposure duration:
28 d
Test temperature:
20°C +-1 with a range of 20 +- 2°C
pH (if soil or dung study):
Parameter Day 0 Day 28
pH
Control 8.0 8.2
10 mg/kg d.s. 7.8 8.3
32 mg/kg d.s. 8.0 8.3
100 mg/kg d.s.8.0 8.3
320 mg/kg d.s.8.0 8.4
1000 mg/kg d.s.8.0 8.4
Humidity:
Parameter Day 0 Day 28
Control 47 46
10 mg/kg d.s. 45 45
32 mg/kg d.s. 46 46
100 mg/kg d.s.46 46
320 mg/kg d.s.45 44
1000 mg/kg d.s.44 44
Photoperiod and lighting:
Parameter Day 0 Day 28
Light intensity (lux) 560 529
Details on test conditions:
Test vessels: Volume: approximately 100 ml glass jar, covered with a plastic lid.
Synchronization of a batch: 25 days prior to the test adult springtails were placed in small containers with plaster of Paris base and allowed to lay eggs over a two-day period. After this time adults were removed. Thirteen days after the first juveniles emerge from the eggs they were used for the test.
Artificial soil: According to the guideline. Weight of components based on dry mass:
5% sphagnum peat, no visible plant remains, finely ground (Lentse Potgrond, Lent, The Netherlands);
20% kaolin clay (China Clay Ast, source Silex Pottenbakkersmaterialen, ‘s-Hertogenbosch, The Netherlands);
~74% industrial sand, >50% of particles between 50 and 200 microns (Zilverzand M32, source Eurogrit B.V., Nieuwegein, The Netherlands);
<1.0% calcium carbonate (analytical grade, Merck KGaA, Darmstadt, Germany) to obtain an initial pH of 6.0 ± 0.5;
The dry constituents are mixed thoroughly before addition of the test substance.
Number of replicates: 8 for the control, 4 for each test concentration.
Loading: 10 springtails per vessel (containing approximately 30 g of wet soil).
Temperature: 20 ± 1°C with a temperature range of 20 ± 2°C.
pH: 6.0 ± 0.5
Aeration: Twice a week by briefly opening the lid.
Light: 16 hours photoperiod daily, intensity 400 - 800 lux.
Feeding: Weekly with approx. 2 mg dry yeast (Dr. Oetker).
On day 14 test vessels were weighted in order to check for loss of moisture. If the difference in weight between day 0 and day 14 was higher than 2% an appropriate amount of Mili-RO water was added.
After preparation of the test media springtails were tapped from the breeding containers and introduced in the test containers
Reference substance (positive control):
no
Duration:
28 d
Dose descriptor:
LC50
Effect conc.:
> 1 000 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Remarks:
CdTe
Basis for effect:
mortality
Remarks:
adults
Duration:
28 d
Dose descriptor:
EC10
Effect conc.:
11 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Remarks:
CdTe
Basis for effect:
reproduction
Remarks on result:
other: CI = 0.63-205
Duration:
28 d
Dose descriptor:
EC50
Effect conc.:
> 1 000 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Remarks:
CdTe
Basis for effect:
reproduction
Duration:
28 d
Dose descriptor:
NOEC
Effect conc.:
1 000 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Remarks:
CdTe
Basis for effect:
mortality
Duration:
28 d
Dose descriptor:
NOEC
Effect conc.:
10 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Remarks:
CdTe
Basis for effect:
reproduction
Reported statistics and error estimates:
When the difference in the number of young springtails was smaller than 20% then an average was calculated and the integer number was used forfurther analyses. Otherwise, additional counting was performed by these two persons at the same time and the results was taken for further analysis.
For the final test springtails were counted by one person. As no significant mortality (>20%) was observed in any of the concentrations tested, nostatistical analysis was performed. The EC10 and EC50 for reproduction was based on log-linear regression analysis of the percentages of reproduction inhibition versus the logarithms of the corresponding nominal exposure concentrations of the test substance.
For determination of the NOEC data of the limit concentration was statistically compared with data from the control treatment (Bonfferoni t-test) after checking for normality and homogeneity of variation (TOXSTAT Release 3.5, 1996, D.D. Gulley, A.M. Boelter, H.L. Bergman).

Total mortality of adult springtails observed in the control treatment was 5%. Mortality obseved in test groups ranged from 2.5 to 10% and was considered biologically not significant. Moreover, the observed mortality was not related to the dose applied.

Mean mortality in the final test

 CdTe (mg/kg dw) replicate number of springtails day 0 number of adult springtails day 28   moratlity day 28  mortality day 28 (%)  mortality (group mean) day 28 (%) 
 control 10  20 
control  10  10 
control 10  10  0 0
Control  10  10  0
control  E 10  10 
Control   10  10 
control  10  10
 Control 10  20 
10  10  10 
10  B 10 9 1  10
 10  C 10 10  0
10  10  10 
32  11  11 
32  10  10 
32 10  20 
32  10  10 
 100 10  10 
100 10  10  0  0
 100 10  10 
100  10  10 
320  10  20 
320  10  20 
320  C 10  10 
320   D  10  10  0  0
1000  10  10 
1000  10  10 
1000  10  10 
1000  10   9  1  0

On average 844 instars per replicate were found in the control. The coefficient of variation was 12%. Effects on reproduction ranged from 10 to 40% reduction and were related to applied doses at 10 through 320 mg/kg dw. The effects observed at 10,100 and 100 mg/kg dw were in agreement with the results of the combined limit/range finding test. Note that the effect observed at the highest concentration was lower than one observed 32 mg/kg dw and it was statistically not different from the control. For the worst-case scenario NOEC was set to 10 mg/kg dw. In the view of the fact that the EC10 for reproduction was 11 mg/kg dw the NOEC of 10 mg/kg dw seems to be a good estimate.

 CdTe concentration (mg/kg dw) replicate  number of instars (reproduction) day 28  reduction in reproduction (%)  group mean reduction in reproduction (%) 
 control 911     
 control 1004     
control  696     
 control  D 888     
 control 878     
 control 728     
 control 876     
 control 768     
 10 602  29   10
 10 828  1.9   
 10 C 876  -3.8   
 10 747  11   
 32 728  14   19*
 32 625  26   
 32 630  25   
 32 744  12   
 100 512  39   25 *
 100 735  13   
100  690  18   
100  585  31   
320  588  30   40*
 320 532  37   
320  521  38   
320  393  53   
1000  597  29  14 
1000  670  21   
1000   884  -4.8  
1000  751  11   

* statistically signficant (p<0.01)

Validity criteria fulfilled:
yes
Conclusions:
Test done according standard protocol.
Executive summary:

Under the conditions of the study CdTe had no effect on reproduction of adult springtails (Folsomia candida) at 10 mg/kg dw (NOEC). The NOEC for mortality was 1000 mg/kg dw. The LC50 for mortality of adult springtails was beyond the range tested, i.e. exceeded 1000 mg/kg dw. The EC10 for reproduction was 11 mg/kg dw with a 95% CI between 0.63 -205 mg/kg dw. The EC50 for reproduction was beyond the range tested, ie exceeded 1000 mg/kg dw.

Description of key information

An ecotoxicity study was performed using Folsomia candida as test species.

No effects were seen up to a concentration of 10 mg CdTe/kg DW.
As Cd2+ ion determines ecotoxicity, the PNEC deriviation will be based on the Cd 2+ ion as determined in the RA (ECB 2007).

Key value for chemical safety assessment

Short-term EC50 or LC50 for soil dwelling arthropods:
1 000 mg/kg soil dw
Long-term EC10, LC10 or NOEC for soil dwelling arthropods:
10 mg/kg soil dw

Additional information

Under the conditions of the study CdTe had no effect on reproduction of adult springtails (Folsomia candida) at 10 mg/kg dw (NOEC). The NOEC for mortality was 1000 mg/kg dw. The LC50 for mortality of adult springtails was beyond the range tested, i.e. exceeded 1000 mg/kg dw. The EC10 for reproduction was 11 mg/kg dw with a 95% CI between 0.63 -205 mg/kg dw. The EC50 for reproduction was beyond the range tested, ie exceeded 1000 mg/kg dw.