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Ecotoxicological information

Long-term toxicity to aquatic invertebrates

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Reference
Endpoint:
long-term toxicity to aquatic invertebrates
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Qualifier:
no guideline followed
Principles of method if other than guideline:
The test was a pre-guideline 21-day reproduction study with neonate (<24 h) Daphnia magna, at least five concentrations were tested in five-fold including a blank control. Ten daphnids were used for each replicate sample. The test solutions were renewed three times a week and were prepared fresh at each renewal. The number of surviving females and number of neonates were recorded daily, the neonates being removed from the test vessels after counting.
GLP compliance:
no
Analytical monitoring:
no
Vehicle:
no
Details on test solutions:
The test medium used was 50-µm filter UV-sterilised Lake IJssel water. Stock solutions were prepared in the test medium. The test solutions were renewed three times a week and were prepared fresh at each renewal. The ration of concentrations was 1.8; actual concentrations were not verified during the experiments. At least five concentrations were tested in five-fold including a blank control.
Test organisms (species):
Daphnia magna
Details on test organisms:
The experiment was started with newborn (< 24 h) daphinds from a laboratory stock culture. These were fed daily with 3E+08 cells/L of the unicellular green alga Chlorella pyrenoidosa.
Test type:
semi-static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
21 d
Post exposure observation period:
None
Hardness:
225 mg/L (as CaCO3)
Test temperature:
20 +/- 0.5 °C
pH:
8.1
Dissolved oxygen:
Not reported
Salinity:
Not relevant
Nominal and measured concentrations:
Nominal and measured concentrations not given.
Details on test conditions:
The experiments were carried out in a temperature room at 20 ± 0.5 °C with a 12-h photoperiod. The tests were conducted in 800-ml vessels to which 500 ml of the test solution was added. The pooled neonates were randomly distributed into cohorts of ten animals each and transferred to the test vessels. The daphnids were fed daily 3E8 cells of the unicellular green algae Chlorella pyrenoidosa. The number of surviving females and number of neonates were recorded daily, the neonates being removed from the test vessels after counting. When daphnids appeared to be males, these animals were excluded from both fecundity and survival analysis. Oxygen concentrations and pH were measured at regular intervals.
Reference substance (positive control):
no
Key result
Duration:
21 d
Dose descriptor:
NOEC
Effect conc.:
<= 3.2 µg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth
Duration:
21 d
Dose descriptor:
LOEC
Effect conc.:
10 µg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
reproduction
Duration:
21 d
Dose descriptor:
LC50
Effect conc.:
14 µg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
mortality
Remarks on result:
other: 13-15
Details on results:
The survival pattern of the daphnids was clearly related to the exposure concentration and a gradual decline of the LC50 with time was observed. Generally, the lower rate of population increase caused by certain concentrations of test compounds was due to both increased mortality and fewer clutches per female. The latter was also due to reduced parental survival.
Reported statistics and error estimates:
The results were summarized in life-table form. The intrinsic rate of natural increase, rm, was calculated for each cohort of ten animals by successive approximation from the equation:

Sum of lx.mx.e^-rm.x = 1

Where lx is the proportion of individuals surviving to age x, mx is the age-specific fecundity (number of females produced per surviving female at age x), and x is days. As rm calculated after 21 days is indistinguishable from rm estimated for the entire life-span, due to the great importance of early reproduction, all calculations were based on 21-day experiments. Finally, means and errors were calculated.
Differences in mean survival and rm between treatments and blank control were tested using the Willimas’ test. After verification of differences between blank and solvent control (Student’s t-test). Prior to the Willimas’ test, the data were tested for homogeneity of variances using the Bartlett test. Normailty was verified by means of a Shapiro-Wilk test, or graphivcally, by plots of ordered data against the normal order statistic. It should be noted that in case of survival data the arcsin square root transformation of the proportion of survivorsin each test vessel was used. The lowest concentration which was significantly different from the control was denoted as LRCT (lowest rejected concentration tested; similar to the LOEC). Differences were considered significant at the p < 0.01 level. From the LOEC the NOEC was derived by applying a factor of 1.8. The LC50 values and their 95% confidence limits were determined according to Kooijman (1981).
Kooijman SALM (1981). Parametric analyses of mortality rates in bioassays. Water Res. 15: 107-119.

Description of key information

The value of 3.2 µg/L derived in the 21-day toxicity study in Daphnia magna is considered to be a NOEC and used in the risk assessment. 

Key value for chemical safety assessment

EC10, LC10 or NOEC for freshwater invertebrates:
3.2 µg/L

Additional information

One long-term toxicity study with Daphnia magna is available for the test substance. The test is a semi-static non-GLP, pre-guideline 21-day reproduction study with neonate (<24 h) Daphnia magna, without analytical monitoring (van Leeuwen et al., 1985c). At least five concentrations (with a ratio of 1.8) were tested in five-fold including a blank control. Ten daphnids were used for each replicate sample. The test solutions were renewed three times a week and were prepared fresh at each renewal. The number of surviving females and number of neonates were recorded daily, the neonates being removed from the test vessels after counting. The survival pattern of the daphnids was clearly related to the exposure concentration and a gradual decline of the LC50 with time was observed. Generally, the lower rate of population increase caused by certain concentrations of test compounds was due to both increased mortality and fewer clutches per female. The latter was also due to reduced parental survival. The LRCT (lowest rejected concentration tested; similar to the LOEC) was 10 µg/L. The NOEC was derived from the LOAEC by applying a factor of 1.8, resulting in a value of ≤ 3.2 µg/L.