Chromium trioxide

Long-term toxicity to aquatic invertebrates

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

long-term toxicity to aquatic invertebrates

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

The EU RAR summarises the results of a number of aquatic invertebrate toxicity studies which, individually, have limitations regarding study design and reliabilty. However the results of these studies when taken as a whole, provide an adequate assessment of chronic toxicity to aquatic invertebrates. The data are considered to fulfil the criteria laid down in Annex XI to Regulation 1907/2006: adequate for classification and labelling, adequate coverage of key parameters (survival, reproduction and growth), exposure duration comparable or longer that Article 13(3) methods, adequate documentation provided: EU RAR, of which parts have been copied to this endpoint record. Reliability for endpoint also increased based on test results from several species.

Qualifier:

no guideline followed

Guideline:

other: range of studies

Principles of method if other than guideline:

Several studies, collectively, provide a weight-of-evidence to address the endpoint of chronic toxicity

GLP compliance:

no

Analytical monitoring:

yes

Details on sampling:

Various sampling procedures based on multiple studies

Vehicle:

no

Details on test solutions:

Various test media prepared based on multiple studies

Test organisms (species):

other: range of species tested

Test type:

other: range of test designs used

Water media type:

freshwater

Limit test:

no

Remarks on exposure duration:

Range used from several studies

Post exposure observation period:

None reported

Hardness:

Range from several studies

Test temperature:

Range from several studies

pH:

Range from several studies

Dissolved oxygen:

Range from several studies

Salinity:

Not applicable

Nominal and measured concentrations:

Range from several studies

Details on test conditions:

Range from several studies

Reference substance (positive control):

no

The results of the chronic aquatic invertebrate toxicity studies evaluated in the DAR are summarised below.

Species	Endpoint	Value (mg/L)	Reference
Crustacea
Ceriodaphnia dubia	7-day NOEC (survival) 7-day NOEC (reprod)	8.4 4.7	De Graeve et al. (1992) De Graeve et al. (1992)
Daphnia carinata	NOEC (reprod)	50	Hickey (1989)
Daphnia magna	21-day NOEC (mortality) 21-day NOEC (reprod) 21-day NOEC (mortality) 21-day NOEC (reprod) 21-day NOEC (survival) 21-day NOEC (growth) 21-ay NOEC (yield) 14-day NOEC (reprod) 14-day NOEC (reprod)	18 18 35 35 200 60 350 25 0.5a	Kuhn et al. (1989) Kuhn et al. (1989) Sloof and Canton (1983) Sloof and Canton (1983) Van Leeuwen et al. (1987) Van Leeuwen et al. (1987) Van Leeuwen et al. (1987) Hickey (1989) Elnabarawy et al. (1986)
Coelenterate
Hydra littoralis	11-day NOEC (reprod)	35	Dannenberg (1984)
Hydra oligactis	21-day NOEC (growth)	1,100	Sloof and Canton (1983)
Insect
Culex pipiens	25-day NOEC (survival) 25-day NOEC (development)	1,100 1,100	Sloof and Canton (1983) Sloof and Canton (1983)
Mollusc
Lymnaea stagnalis	40-day NOEC (reprod) 40-day NOEC (mortality) 7-day NOEC (hatchability)	110 3,500 350	Sloof and Canton (1983) Sloof and Canton (1983) Sloof and Canton (1983)

Results are from tests with potassium dichromate except for a - sodium dichromate. All concentrations as Cr.
De Graeve et al., (1992): this paper reported the results of a ring test, in which 18 determinations of the NOEC values were made.   The values in the table here are the geometric mean of the NOEC values reported for each endpoint.

Validity criteria fulfilled:

yes

Conclusions:

Based on a review of existing data, an adequate assessment of the chronic toxicity of Cr(VI) to aquatic invertebrates has been achieved.

Executive summary:

From a review of the long-term effects of potassium and sodium dichromate on aquatic invertebrates, a range of results is presented based on several endpoints and durations of exposure. As well as effects on survival and reproduction of invertebrates, sublethal effects of exposure to chromium (VI) have been reported. Adult grass shrimp, Palaemonetes pugio, were exposed to levels of chromium (VI) (as sodium chromate) ranging from 0.5 to 4.0 mg/l over 28 days. Approximately 41% of surviving shrimp possessed cuticular lesions, usually associated with articulations of the appendages and abdomen, after exposure to 0.5 mg/l. Increasing exposure

concentrations lead to a proportionate increase in the loss of limbs such that nearly 50% of limbs were lost at the highest exposure concentration. It was proposed that the organisms experienced chromium-induced exoskeletal deficiencies resulting in a viaduct for pathogenic organisms and direct chromium influx that perpetuated lesion development (Doughtie et al., 1983).

Reference 2

Endpoint:

long-term toxicity to aquatic invertebrates

Type of information:

experimental study

Adequacy of study:

key study

Study period:

not specified

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

test procedure in accordance with national standard methods

Qualifier:

according to guideline

Guideline:

other: Provisional Procedure: extended toxicology test with Daphnia magna (determination of NOEC for reproduction rate, mortality and the time of the first appearance of offspring; 21 d)

Version / remarks:

as of 1 January 1984, issued as the "Recommendation of the Federal Environmental Agency on the Performance of Testing according to Section 5, paragraph 1 no. 3of the Regulation on Application Documents and Evidence under the Chemicals Act"

GLP compliance:

not specified

Analytical monitoring:

yes

Details on sampling:

- Sampling method: Samples were taken twice from selected concentration levels of the test series during the test period and analysed chemically: the first sampling took place on one of the transfer days before the 7th day, i.e. in the period during which no offspring appeared; the second sampling took place between the 16th and 21st day.
For the corresponding dilution levels, the following parameters were determined:
the concentrations of the initial preparations in order to check the solution behaviour and the dilution steps; the concentrations in the test and control preparations after an interval of 48/72 h in order to determine the fate of the substance.

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: The stock solution was prepared by diluting 100 mg potassium dichromate in 1 L dilution water using a magnetic stirrer. From the stock solution of the substance to be tested, graduated dilutions with dilution water were produced. The dilution steps corresponded to a ratio of 1:2.
- Controls: yes, dilution water only
- Test concentration separation factor: 2

Test organisms (species):

Daphnia magna

Details on test organisms:

TEST ORGANISM
- Common name: water flea
- Strain/clone: IRCHA strain
- Age at study initiation (mean and range, SD): - Method of breeding: 20-30 specimens were placed in forty 2 L beakers which had been filled with at least 1.6 L Berlin tap water (temperature controlled, declorinated, oxygen saturated, hardness: 16°, pH: 7.6-7.7). Before collecting the water, the tap was turned on fully and left to run for at least 1 h. After collecting, it was left to stand for 24 hrs. All beakers were covered with watch glasses and placed on a white supporting surface. Feeding with dry algae of the Scenedesmus genus took place daily. 9 g of feed were suspended in 1 L tap water and 2 mL of the suspension were added to each beaker. The temperature of the culture area was regulated thermostatically at 20°C. Under exclusion of daylight, the area was lit by fluorescent lamps (Philips TL 65/33W) for 9 h between 7 a.m. and 4 p.m. On Monday and Thursday of each week the tap water in all beakers was renewed as were the beakers themselves on Mondays. On Mondays, the offspring which had appeared between Thursday or Friday and Monday were concentrated using the 0.315 mm DIN sieve and separated according to size using the 0.630 mm DIN sieve. Daphnia in the different size categories were used separately for further cultivation.
- Source: laboratory culture
- Feeding during test: yes
- Food type: Tetramin-Hauptfutter (fish feed) and activated sludge
- Amount: 15-20 mg/L COD as daily feed amount
- Frequency: daily

METHOD FOR PREPARATION AND COLLECTION OF EARLY INSTARS OR OTHER LIFE STAGES, INCLUDING CULTURING CONDITIONS:
In order to obtain 24 h-old animals on the potential preparation days in a 21 d test series - Wednesdays or Fridays - it was necessary to remove the offspring from the cultivation beakers on Tuesday and/or Thursday. The daphnids which were at most 24 h old were removed by pipette and concentrated on a 0.25 mm DIN sieve, placed in as small amount of dilution water as possible and used as test organisms.

Test type:

semi-static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

21 d

Test temperature:

25 +/- 1 °C

Dissolved oxygen:

at water saturation level

Nominal and measured concentrations:

Nominal concentration range: 4.6-142 µg/L Cr(VI) and 13-400 µg/L K2Cr2O7, respectively.
As the results of the chemical analysis revealed a recovery of >80%, only nominal concentration values were given.

Details on test conditions:

TEST SYSTEM
- Test vessel: beakers
- Type (delete if not applicable): open
- Material, size, headspace, fill volume: 400 mL beakers filled with 250 mL
- Aeration: no
- Renewal rate of test solution (frequency/flow rate): 3 times a week (Monday, Wednesday and Friday)
- No. of organisms per vessel: 5
- No. of vessels per concentration (replicates): 4
- No. of vessels per control (replicates): 4
- Biomass loading rate: 1 animal/50 mL

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: 25 mL of each of the four salt solutions (concentration stated below in section 'overall remarks') was pipetted into a graduated flask and completed to 1 L with deionised water.
- pH: 8.0 +/- 0.2
- Amount of Ca/mg: 2.5 mmol/L
- Na/K ratio: 10:1
- Conductivity: >1 µS/cm (When conductivity of the deionised water was <1 µS/cm, dilution water was diluted with 10% tap water.)

OTHER TEST CONDITIONS
- Adjustment of pH: no
- Photoperiod: from 7 a.m. to 4 p.m.
- Light intensity: not specified, only lamp type given (Philips TL 40/25W)

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
The immobilisation or mortality of parent animals and the total number of offspring per test vessel was observed 3 times a week with every renewal of test solutions and recorded. the day of first offspring appearance. Beside, the test and control preparations were observed daily in
order to record the day on which the first offspring appeared.

TEST CONCENTRATIONS
- Spacing factor for test concentrations: 2
- Range finding study: yes, 3 d Daphnia test under the same conditions as the 21 d reproduction test
- Test concentration range: 4.6-142 µg/L Cr(VI) and 13-400 µg/L K2Cr2O7, respectively
- Results used to determine the conditions for the definitive study: yes

Duration:

24 h

Dose descriptor:

EC50

Remarks:

determined in preliminary acute Daphnia test before the 21d-reproduction test

Effect conc.:

0.93 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

Potassium dichromate

Basis for effect:

immobilisation

Duration:

24 h

Dose descriptor:

EC50

Remarks:

determined in preliminary acute Daphnia test before the 21d-reproduction test

Effect conc.:

0.35 mg/L

Nominal / measured:

nominal

Conc. based on:

element

Remarks:

Cr(VI)

Basis for effect:

immobilisation

Duration:

21 d

Dose descriptor:

NOEC

Effect conc.:

0.05 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

Potassium dichromate

Basis for effect:

other: parent animal mortality and reproduction rate

Key result

Duration:

21 d

Dose descriptor:

NOEC

Effect conc.:

0.018 mg/L

Nominal / measured:

nominal

Conc. based on:

element

Remarks:

Cr(VI)

Basis for effect:

other: parent animal mortality and reproduction rate

Details on results:

The parameters for fixing the NOEC of the substance were the mortality of the parent animals, the reproduction rate and the appearance of the first offspring during the test period.
As the results of the chemical analysis revealed a recovery of >80%, only nominal concentration values were given.

Reported statistics and error estimates:

The Student's t-test and the U-test were the statistical methods used to calculate the mortality and the reproduction rate.

Validity criteria fulfilled:

not specified

Conclusions:

A chronic reproduction study was conducted with potassium dichromate exposed toDaphnia magna at several concentrations for a test period of 21 days using semi-static test conditions. The study design according to a national test guideline is well documented and the test conditions as well as the observed effect parameters are identical to those in international test guidelines (e.g. OECD 211). Adequate statistical methods were used for calculation of the results, which can be considered as reasonable. Hence, the study is considered to be acceptable for the assessment of the chronic toxicity of the registered substance to aquatic invertebrates.
Based on the obtained results, a 21 -d NOEC of 0.05 mg/L for the parameters parental mortality and reproduction was determined for potassium dichromate and for chromium(VI) a 21 -d NOEC of 0.018 mg/L was derived for the parameters parental mortality and reproduction.

Executive summary:

Investigations were carried out in order to determine the NOEC of potassium dichromate and other environmentally relevant substances in the 21 d Daphnia reproduction test. The test was conducted in line with the provisional procedure proposed by the German Federal Environmental Agency (as of 1 January 1984). Daphnia magna Straus was used as the test organism. Evaluation parameters for fixing the NOEC were the mortality of the parent animals, the reproduction rate and the appearance of the first offspring during the test period. The concentrations of substances in the test preparations were chemically quantified. The test substance was fully dissolved (both quantitatively and optically) in dilution water using a magnetic stirrer (stock solution). From the stock solution of the test substance, graduated dilutions with dilution water were produced in the concentration range in which effects were to be expected in accordance with the results from the acute 24 h Daphnia test and a preliminary 3 d Daphnia test. The dilution steps corresponded to a ratio of 1:2. The tested concentration range was 4.6-142 µg/L for potassium dichromate and 13-400 µg/L for chromium(VI), respectively. During the process of medium renewal (3 times a week), dead parent animals or those incapable of swimming were removed. The offspring were counted and the total number for each test vessel was recorded. Then, the pH value and the oxygen concentration were measured in two test vessels per concentration level. Based on the obtained results, a 21 -d NOEC of 0.05 mg/L for the parameters parental mortality and reproduction was determined for potassium dichromate and for chromium(VI) a 21 -d NOEC of 0.018 mg/L was derived for the parameters parental mortality and reproduction.

Reference 3

Endpoint:

long-term toxicity to aquatic invertebrates

Type of information:

experimental study

Adequacy of study:

key study

Study period:

not specified

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 211 (Daphnia magna Reproduction Test)

Deviations:

yes

Remarks:

Missing information: description of analytical method, composition of medium, frequency of test solution renewal, individual results for effect parameter

GLP compliance:

not specified

Specific details on test material used for the study:

SOURCE OF TEST MATERIAL
- Source (i.e. manufacturer or supplier) and lot/batch number of test material: supplied by Baker
- Purity, including information on contaminants, isomers, etc.: >= 96%

Analytical monitoring:

yes

Details on sampling:

Samples for determination of the test substance concentration were taken at various times.

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: Direct dissolution in Aqua dest.
- Controls: yes, preparation not further specified
- Test concentration separation factor: 1.8

Test organisms (species):

Daphnia magna

Details on test organisms:

TEST ORGANISM
- Common name: water flea
- Strain/clone: not specified
- Age at study initiation (mean and range, SD): 0-24 hrs
- Source: laboratory stock
- Feeding during test: yes
- Food type: unicellular green algae Chlorella pyrenoidosa
- Amount: 3x10^8 cells/litre/day
- Frequency: daily

Test type:

semi-static

Water media type:

freshwater

Remarks:

from Lake IJssel

Limit test:

no

Total exposure duration:

21 d

Hardness:

225 mg/L as CaCO3

Test temperature:

20 +/- 0.5 °C

pH:

8.1 +/- 0.1

Nominal and measured concentrations:

Measured Concentrations: 0.06, 0.11, 0.20, 0.35, 0.64, 1.13 mg Cr/L

Details on test conditions:

TEST SYSTEM
- Test vessel: jars
- Material, size, headspace, fill volume: 800 mL jars, filled with 500 mL medium
- Aeration: Before adding the test solutions and the algal suspension the waterwas aerated.
- Renewal rate of test solution (frequency/flow rate): intermittent-flow system; the flow through the 20-liter test vessels was 667 mL/hr.
- No. of organisms per vessel: 10
- No. of vessels per concentration (replicates): 5
- No. of vessels per control (replicates): 5

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Lake IJssel water, filtered through 50 µm plankton gauze and sterilized by means of a Wedeco M2-6 UV apparatus

OTHER TEST CONDITIONS
- Adjustment of pH: no
- Photoperiod: 12 hrs
- Light intensity: not specified

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
Mortality and reproduction were recorded every day.

TEST CONCENTRATIONS
- Spacing factor for test concentrations: 1.8
- Number of test concentrations: 6

Duration:

21 d

Dose descriptor:

LOEC

Remarks:

stated as LRCT (lowest rejected concentration tested)

Effect conc.:

0.11 mg/L

Nominal / measured:

meas. (not specified)

Conc. based on:

element

Remarks:

Cr

Basis for effect:

other: carapace length

Duration:

21 d

Dose descriptor:

LOEC

Remarks:

stated as LRCT (lowest rejected concentration tested)

Effect conc.:

0.64 mg/L

Nominal / measured:

meas. (not specified)

Conc. based on:

element

Remarks:

Cr

Basis for effect:

mortality

Remarks:

stated as survival

Duration:

21 d

Dose descriptor:

LC50

Effect conc.:

0.5 mg/L

Nominal / measured:

meas. (not specified)

Conc. based on:

element

Remarks:

Cr

Basis for effect:

mortality

Remarks on result:

other: 99%-confidence limits: 0.2-1.1 mg/L

Key result

Duration:

21 d

Dose descriptor:

NOEC

Effect conc.:

0.06 mg/L

Nominal / measured:

meas. (not specified)

Conc. based on:

element

Remarks:

Cr

Basis for effect:

other: carapace length

Duration:

21 d

Dose descriptor:

NOEC

Effect conc.:

0.35 mg/L

Nominal / measured:

meas. (not specified)

Conc. based on:

element

Remarks:

Cr

Basis for effect:

mortality

Remarks:

stated as survival

Reported statistics and error estimates:

The LC50 value was determined by graphical interpolation. The concentrations at which 0 and 100% mortality occur were be regarded as a 99% confidence interval. The intrinsic rate of natural increase (r_m) for each replication was calculated by substitution of the daily observed effects on survival and reproduction. Differences in mean survival, r_m, and carapace length between the controls and test concentrations were tested by the method of Williams (1971, 1972). The survival data were first subjected to the arcsine square root transformation. The low- test concentration differing significantly from the control is denoted as the LRCT (lowest rejected concentration tested).

Validity criteria fulfilled:

not applicable

Conclusions:

A chronic reproduction study was conducted with potassium dichromate exposed to Daphnia magna at several concentrations for a test period of 21 days in a semi-static experiment comparable to an OECD 211 study. The study is well documented and meets generally accepted scientific principles, wherefore it is considered to be reliable and acceptable for the assessment of the long-term toxicity of the registered substance to aquatic invertebrates.
The experiment was started with young daphnids (0-24 hr) from a laboratory stock and the parameters mortality and reproduction were observed daily throughout the test. After 3 weeks the experiment was ended and the Carapace length of all surviving adults was determined. The 21-d LC50 value was determined by graphical interpolation as 0.5 mg/L (99% CI: 0.2-1.1 mg/L). The 21-d LRCT (Lowest rejected concentration tested) based on survival as well as the 21-d LRCT based on growth (carapace length) were determined to be 0.11 mg/L and 0.64 mg/L, respectively. A steep decline in survival rate between the third- and second-highest concentration was observed, therefore the results can be considered reasonable.

Executive summary:

In semi-static experiments with cohorts of Daphnia magna survival appeared to be a dominant factor in exponential population growth. Specific inhibition of reproduction as a result of toxic stress was not observed for potassium bichromate, but individual growth (carapace length) was found to be a sensitive parameter. The test item had a purity of >=96% and was dissolved in destilled water for application. The concentrations were analytically controlled by atomic absorption spectrophotometry. The experiments were performed in a constant temperature room of 20+/-0.5°C with a photoperiod of 12 hrs. The experiments were started with young daphnids (0-24 hr) from a laboratory stock. Young daphnids were distributed at random, in cohorts of 10, among the test concentrations and controls. Mortality and reproduction were recorded every day. Neonates were counted and then removed. After 3 weeks the experiments were ended and the Carapace length of all the surviving adult daphnids was measured. The 21-d LC50 value was determined by graphical interpolation as 0.5 mg/L (99% CI: 0.2-1.1 mg/L). The 21-d LRCT (Lowest rejected concentration tested) based on survival as well as the 21-d LRCT based on growth (carapace length) were determined to be 0.11 mg/L and 0.64 mg/L, respectively. Correspondingly, the 21 -d NOEC on survival as well as the 21-d NOEC based on growth (carapace length) were determined to be 0.06 mg/L and 0.35 mg/L, respectively. A steep decline in survival rate between the third- and second-highest concentration was observed, therefore the results can be considered reasonable.

Description of key information

1) Key_ Long-term toxicity to aquatic invertebrates by summary of data from European Union Risk Assessment Report: chromium trioxide, sodium chromate, sodium dichromate, ammonium dichromate and potassium dichromate

3rd. Priority List; Volume 53: NOEC = 0.5 - 3,500 mg/L (nominal) for several species from various studies with different test durations ranging from 7 to 40 days

2) Key_Long-term toxicity to aquatic invertebrates: NOEC (21d) = 0.35 mg/L for survival and 0.06 mg/L for growth (Carpace length) of Daphnia magna exposed to potassium dichromate (semi-static, freshwater, test design comparable with OECD 211)

3) Key_Long-term toxicity to aquatic invertebrates: NOEC (21d) = 0.05 mg/L for parental mortality and reproduction of Daphnia magna exposed to potassium dichromate (semi-static, freshwater, test design according to national test guideline)

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates

Dose descriptor:

NOEC

Effect concentration:

0.05 mg/L

Additional information

1) From a review of the long-term effects of potassium and sodium dichromate on aquatic invertebrates, a range of results is presented based on several endpoints and durations of exposure. As well as effects on survival and reproduction of invertebrates, sublethal effects of exposure to chromium (VI) have been reported. Adult grass shrimp, Palaemonetes pugio, were exposed to levels of chromium (VI) (as sodium chromate) ranging from 0.5 to 4.0 mg/l over 28 days. Approximately 41% of surviving shrimp possessed cuticular lesions, usually associated with articulations of the appendages and abdomen, after exposure to 0.5 mg/l. Increasing exposure

concentrations lead to a proportionate increase in the loss of limbs such that nearly 50% of limbs were lost at the highest exposure concentration. It was proposed that the organisms experienced chromium-induced exoskeletal deficiencies resulting in a viaduct for pathogenic organisms and direct chromium influx that perpetuated lesion development (Doughtie et al., 1983).

2) In semi-static experiments with cohorts of Daphnia magna survival appeared to be a dominant factor in exponential population growth. Specific inhibition of reproduction as a result of toxic stress was not observed for potassium bichromate, but individual growth (carapace length) was found to be a sensitive parameter. The test item had a purity of >=96% and was dissolved in destilled water for application. The concentrations were analytically controlled by atomic absorption spectrophotometry. The experiments were performed in a constant temperature room of 20+/-0.5°C with a photoperiod of 12 hrs. The experiments were started with young daphnids (0-24 hr) from a laboratory stock. Young daphnids were distributed at random, in cohorts of 10, among the test concentrations and controls. Mortality and reproduction were recorded every day. Neonates were counted and then removed. After 3 weeks the experiments were ended and the Carapace length of all the surviving adult daphnids was measured. The 21-d LC50 value was determined by graphical interpolation as 0.5 mg/L (99% CI: 0.2-1.1 mg/L). The 21-d LRCT (Lowest rejected concentration tested) based on survival as well as the 21-d LRCT based on growth (carapace length) were determined to be 0.11 mg/L and 0.64 mg/L, respectively. Correspondingly, the 21 -d NOEC on survival as well as the 21-d NOEC based on growth (carapace length) were determined to be 0.06 mg/L and 0.35 mg/L, respectively. A steep decline in survival rate between the third- and second-highest concentration was observed, therefore the results can be considered reasonable.

3) Investigations were carried out in order to determine the NOEC of potassium dichromate and other environmentally relevant substances in the 21 d Daphnia reproduction test. The test was conducted in line with the provisional procedure proposed by the German Federal Environmental Agency (as of 1 January 1984). Daphnia magna Straus was used as the test organism. Evaluation parameters for fixing the NOEC were the mortality of the parent animals, the reproduction rate and the appearance of the first offspring during the test period. The concentrations of substances in the test preparations were chemically quantified. The test substance was fully dissolved (both quantitatively and optically) in dilution water using a magnetic stirrer (stock solution). From the stock solution of the test substance, graduated dilutions with dilution water were produced in the concentration range in which effects were to be expected in accordance with the results from the acute 24 h Daphnia test and a preliminary 3 d Daphnia test. The dilution steps corresponded to a ratio of 1:2. The tested concentration range was 4.6-142 µg/L for potassium dichromate and 13-400 µg/L for chromium(VI), respectively. During the process of medium renewal (3 times a week), dead parent animals or those incapable of swimming were removed. The offspring were counted and the total number for each test vessel was recorded. Then, the pH value and the oxygen concentration were measured in two test vessels per concentration level. Based on the obtained results, a 21 -d NOEC of 0.05 mg/L for the parameters parental mortality and reproduction was determined for potassium dichromate and for chromium(VI) a 21 -d NOEC of 0.018 mg/L was derived for the parameters parental mortality and reproduction.