Registration Dossier

Ecotoxicological information

Endpoint summary

Administrative data

Description of key information

Additional information

Acute data:

For fish, the lowest reliable data point for ammonium molybdate was put forward for hazard assessment purposes:

- 96h-LC50 of 237 mg Mo/L for the fish O. mykiss (HRC, 1994); Mo-salt was (NH4)2Mo2O7,

 

For invertebrates (test organism: Daphnia magna) the lowest reliable data points for ammonium molybdate was put forward for hazard assessment purposes:

- 48h-LC50 of 79 mg Mo/L for the cladoceran D. magna (HRC, 1994); Mo-salt was (NH4)2Mo2O7

No algal toxicity data were generated with ammonium molybdate. Therefore read-across from reliable data that were generated with sodium molybdate were considered for this trophic level. For the most sensitive strain of P. subcapitata that was used in reliable study reports, 4 acute data points were availabe. The geometric mean of those 4 data points was 333.1 mg/L. This value is considered as a reliable acute algal toxicity reference value for hazard assessment purposes (e.g., classification).

No reliable EC50-values with ammonium molybdate were reported for any other freshwater or marine algal species.

 

Chronic freshwater data

A Species Sensitivity Distribution (SSD) has been developed for the assessment of molybdenum in the freshwater compartment, using the reliable species-specific chronic toxicity effect levels that have been identified. An overview of these species-specific data is given below. All toxicity tests were performed using sodium molybdate as test substance.

 

Overview of most sensitive species-specific K1-NOEC/EC10 -values for molybdenum in the freshwater environment

Species

Trophic level

NOEC/EC10-value

(mg Mo/L)

Reference studies

Oncorhynchus mykiss

Fish

43.2

Parametrix, 2008

Pimephales promelas

Fish

60.2

Parametrix, 2007; GEI, 2009

Ceriodaphnia dubia

Crustacea

63.0

De Schamphelaere et al, 2008; GEI, 2009

Pseudokirchneriella subcapitata -CIMM strain

Algae

74.3

Rodriguez, 2008; De Schamphelaere and Janssen, 2008

Daphnia magna

Crustacea

89.5

De Schamphelaere et al, 2008

Rodriguez, 2007 ; GEI, 2009

Xenopus laevis

Amphibia

115.9

De Schamphelaere et al, 2008

Chironomus riparius

Insecta

121.4

De Schamphelaere et al, 2008

Brachionus calyciflorus

Rotifera

193.6

De Schamphelaere et al, 2008

Lymnaea stagnalis

Gastropoda

221.3

De Schamphelaere et al, 2008

Lemna minor

Aquatic plant

241.5

De Schamphelaere et al, 2008

 

 

No-effect levels for dissolved molybdenum were situated between 43.2 mg Mo/L and 241.5 mg Mo/L, i.e., a difference of a factor of 5.6 between the most and least sensitive species. Fish appear to be the most sensitive trophic level, representing the two lowest no-effect concentrations, followed by the algal speciesP. subcapitata and the two cladoceransD. magnaandC. dubia.  The lowest sensitivity was found with duckweed (L. minor).

 

As mentioned before, these data have been used for the construction of a Species Sensitivity Distribution (SSD) from which the following parameter was derived:

- the median 5thpercentile, i.e. the HC5,50%with 5%-95%-confidence interval. The confidence interval is calculated using a Monte Carlo analysis on the log-normal distribution that was fitted through the 10 data points. The outcome of this analysis allows the derivation of the HC5,50%with 5%-95% confidence interval, and this value should be used for PNEC-derivation (i.e., PNECaquatic= HC5,50%/ Assessment Factor).   

 

The HC5,50%(± 95%CL) that was associated with this distribution was 38.2 mg Mo/L (95%CL: 18.7 – 57.3 mg Mo/L).  Application of an assessment factor between 1 and 5 on this HC5,50% results in the final PNEC for molybdenum in the aquatic environment. The value of this assessment factor depends on the uncertainty analysis that is conducted on the dataset that is presented below.

 

Composition of the test media that were used for the development of the Mo-effects database.

Species

Test duration

Endpoint

pH

Hardness(1)

mg/L as CaCO3

mg Ca/L

mg Mg/L

Pimephales promelas

34 d

Biomass

7.5±0.05

98.4

22.3

10.4

Oncorhynchus mykiss

78/84 d

Biomass

7.4±0.1

81.0

18.3

8.6

Pseudokirchneriella subcapitata -CIMM strain

72 h

Growth rate

8.0-8.1

24.1

4.9

2.9

Ceriodaphnia dubia

7 d

Reproduction

7.6-7.9

180

Not specified

Daphnia magna

21 d

Reproduction

7.4-8.2

168 - 250

27.9-80.1

12.2-24.2

Xenopus laevis

4 d

Malformation

7.8

110.7

19.4

15.1

Chironomus riparius

14 d

Growth

6.9-7.1

84.7

14

12.1

Brachionus calyciflorus

48 h

Reproduction

7.5

84.7

14

12.1

Lymnaea stagnalis

28 d

Length

7.8-8.2

140

40.1

9.7

Lemna minor

7 d

Growth rate

6.5-6.7

54.9

9.8

7.4

(1): derived from nominal/measured Ca/mg content

 

 The uncertainty analysis revealed that the effects database for molybdenum fulfils all requirements that were stipulated at the London workshop (2001) for the application of the statistical extrapolation method (SSD-method) when deriving a PNECaquatic:

-  High quality (Klimisch 1) no-effects data are available for 10 different species;

-  From an ecological point of view all species and evaluated endpoints (growth, reproduction, developmental malformations) are relevant for the aquatic environment;

-  The eight different trophic levels that were defined in the London workshop (2001) are represented in the database;

-  Test media are relevant for EU-surface water conditions, and the variation in physicochemical parameters (e.g., pH, hardness) is representative for EU freshwaters;

-  All tests were performed in artificial test media which are considered to promote metal bioavailability (i.e., worst-case conditions) due to the absence of natural compounds in the water that can form metal complexes and, hence, reduce metal bioavailability and toxicity (e.g., dissolved organic matter);

-  The HC5,50% is based on a conservative (Log-normal) fitted distribution.

 

Each of these findings supports the conclusion that the HC5,50%that is calculated with this dataset is sufficiently protective of the aquatic environment. This value of 38.2 mg Mo/L is below the lowest NOEC is the dataset (43.2 mg Mo/L;Oncorhynchus mykiss), and therefore protects all species that are included in the species sensitivity distribution.

 

There are, however, some arguments that may promote the application of an additional assessment factor in the HC5,50%for the determination of the PNECaquatic:

- No mesocosm studies with molybdenum are available, therefore creating some uncertainty with regard to the lab-to-field translation of Mo-related effects.

- There are two reliable unbounded NOEC-values below the HC5,50%- one of them for a species that is not included in the species sensitivity distribution (Oncorhynchus kisutch(Ennevor, 1993)). The difference between the HC5,50%and these unbounded NOECs are a factor of 2.25 or less;

- The 95% confidence limit that is associated with the HC5,50%is 18.7 – 57.3 mg Mo/L; the lower 95%-CL is a factor of 2.05 below the HC5,50%.


Based on all of these arguments – and taking sufficient conservatism into account - an Assessment Factor of 3
on the HC5,50%is put forward for the derivation of an aquatic PNEC, resulting in a PNECaquatic of 12.7 mg Mo/L.The use of an AF of 3 results in a PNECaquatic that is below the reported reliable unbounded NOECs and the 95% CL that is associated with the HC5,50%. An assessment factor of 3 is sufficient to cover the uncertainty with regard to the lab-to-field translation of Mo-related effects.

Marine freshwater data:

A Species Sensitivity Distribution (SSD) has been developed for the assessment of molybdenum in the marine compartment, using the reliable species-specific chronic toxicity effect levels that have been generated in various research studies. An overview of these species-specific data is given in the table below. All toxicity tests were performed using sodium molybdate as test substance.

Overview of most sensitive species-specific K1-NOEC/EC10-values for molybdenum in the marine environment

Species

End parameter

Endpoint

Value (mg Mo/L)

Reference 

Mytilus edulis

Embryonal development

48h-EC10

4.4

Morgan et al, 1986 

Acartia tonsa

Development

20d-EC10

7.96

Aquasense, 2009 

Cyprinodon variegatus

Larval dry weight

28d-EC10

84.1

Parametrix, 2010 

Menidia beryllina

Standard length, blotted wet weight

37d-NOEC

 139

Dinehart, 2013 

Americamysis bahia

Reproduction

28d-NOEC

116

Lehman, 2010 

Phaeodactylus tricornutum

Growth rate (cells)

72h-ErC10

170

Aquasense, 2009

Dendraster excentricus

Larval development

48h-EC10

223.6

Parametrix, 2008a 

Strongylocentrotus purpuratus

Larval development

48h-EC10

421.3

Parametrix, 2008b 

Ceramium tenuicorne

Growth rate (length)

7d-NOEC

641

Le Page et al, 2010 

Dunaliella tertiolecta

Growth rate (cells)

72h-ErC10

881

Le Page and Hayfield, 2010
 Crassostrea gigas  Larval development 48h-EC10 1174  Aquasense, 2009

No-effect levels for dissolved molybdenum were situated between 4.4 mg Mo/L and 1174 mg Mo/L, i.e., a difference of a factor of 267 between the most and least sensitive species. The musselM. edulisand the copepodA. tonsawere the most sensitive trophic level, The least sensitive species were the oysterC. gigasand two algal species (microalgaD. tertiolectaand macroalgaC. tenuicorne).

As mentioned before, these data have been used for the construction of a Species Sensitivity Distribution (SSD) from which the median 5thpercentile was derived, i.e. the HC5,50%with 5%-95%-confidence interval. This value is further used for PNEC-derivation (i.e., PNECmarine= HC5,50%/ Assessment Factor).

Using the RIVM software package ETX, a Log-Normal Distribution was plotted through this data set. The HC5,50%(± 95%CL) that was associated with this distribution was 5.74 mg Mo/L (95%CL: 0.58 – 21 mg Mo/L), respectively. Application of an assessment factor between 1 and 5 on this HC5,50%will result in the final PNECmarinefor molybdenum in the marine environment. The value of this assessment factor depends on the uncertainty analysis that is conducted on the chronic marine toxicity dataset.

Based on the outcome of the uncertainty analysis, an assessment factor (AF) of 1-5 should be applied on the HC5,50%for the determination of the PNECmarine. The uncertainty analysis revealed that the effects database for molybdenum fulfils all requirements that were stipulated at the London workshop (2001) for the application of the statistical extrapolation method (SSD-method) when deriving a PNECmarine:

- High quality (Klimisch 1) no-effects data are available for 10 different species

- Eight different trophic levels were included in the data set, each representing a trophic level that is typical for the marine environment; the London Workshop (2001) defined for the freshwater environment 8 different taxonomic groups that should be included in the effects database, and this guidance was adopted in RIP 3.2 , Chapter R10 (ECHA, 2008). It was ensured that the marine data set also covered 8 different trophic levels that were relevant for the marine environment and had additional ecologic and/or economic value: fish (two species), a calanoid copepod, an opossum shrimp (mysid), echinoderms (two species), molluscs (two species), a diatom, a microalga, and a macroalga.

- From an ecological point of view all species and evaluated endpoints (growth, reproduction, developmental malformations) are relevant for the aquatic environment. All chronic toxicity tests are performed using sensitive life stages (e.g. fish test used an early life stage, the tests with crustaceans were started with newly born organisms, tests with echinoderms and molluscs were conducted with freshly fertilized embryos). Absence of adverse effects on these lifestages is considered a good indicator when deriving safe exposure concentration levels;

- Covering ‘chronic’ exposure times is achieved for all trophic levels in the Mo database. What comprises “chronic exposure” depends on the exposure duration and is also a function of the life cycle of the test organisms. The duration should therefore be related to the typical life cycle and to the recommended exposure duration from standard ecotoxicity protocols. Typical reported exposure time for algae is 3 days, and 7 days for higher plants, which is in accordance with international guidelines (e.g. OECD, ASTM, USEPA). Larval developmental tests with echinoderms or mollusc should have a duration of 48h, i.e., until the typical D-shaped larval stage has been reached. The early life stage test with fish has an exposure duration of 28 days which is also in line with OECD standard guidelines. Exposure duration of tests with the marine invertebrates (A. bahia,A. tonsa) were also in line with the recommendations given in international guidelines for these organisms.

- All tests were conducted according to standard guidelines that have been published for these organisms, or that were acceptable for regulatory purposes

- Test media are relevant for the marine environment, covering different salinities that are relevant for the marine environment (20 -35 ppt);

- All tests were performed under laboratory conditions in media which are considered to promote metal bioavailability (i.e., worst-case conditions) due to the absence of natural compounds in the water that can form metal complexes and, hence, reduce metal bioavailability and toxicity (e.g., dissolved organic matter);

- All reported effects data (EC10, NOEC) are based on measured Mo-values;

- According to the guidelines presented in the TGD (EC, 2003) and RIP 3.2, Chapter 10 (ECHA, 2008) the 50 % confidence interval (or median confidence interval) is considered in deriving the PNEC. This percentile was calculated by conducting an analysis according to the methodology presented by Aldenberg and Jaworska (2000). The resulting HC5,50%with 95% CL, based on the log-normal distribution, was 6.85 mg Mo/L (95% CL: 0.92 – 22.1 mg Mo/L);

- It should be noted, however, that no mesocosm studies with molybdenum is available for the marine environment, therefore creating some uncertainty with regard to the lab-to-field translation of Mo-related effects. However, the lack of such data does not imply that field testing might generate lower NOEC values

Based on all of these arguments – and taking sufficient conservatism into account - an Assessment Factor of 3 on the HC5,50% is put forward for the derivation of an aquatic PNEC,resulting in a PNECmarineof 2.28 mg Mo/L. An assessment factor of 3 is considered sufficient to cover the uncertainty with regard to the lab-to-field translation of Mo-related effects.