Zinc hydroxide

Endpoint summary

Description of key information

ecotoxicity reference values (erv)

The erv are based on the ecotoxicity of the Zn⁺⁺ion. They are (for data and full analysis, see document "Ecotoxicity of zinc", IUCLID section 13):

for acute aquatic effect :

-at low pH (<7.0): 0.413 mg Zn/l (Ceriodaphnia dubia)

-at neutral/high pH (7.0 -8.5): 0.136 mg Zn/l (Selenastrum capricornutum (=Pseudokirchneriella subcapitata)

-for chronic aquatic effect:

-at pH 8.0: 19 µg Zn/l (Pseudokirchneriella subcapitata)

-at pH 6.0: 82µg Zn/l (Daphnia magna)

Additional information

1. Aquatic toxicity: freshwater, short-term

establishing the dataset

In accordance to the approach followed in the RAR, only acute data from standardised test protocols were considered in the analysis for setting the reference value for classification. This is possible because numerous data are available, and it ensures that the tests were performed under rather well defined and standard conditions.

Still, the quality and some aspects of relevancy should be checked in a critical way when using the extensive datasets from the open literature, available for zinc. It is e.g. important to know the conditions under which the organisms were tested and cultured, because these conditions may result in acclimatisation and deviating toxicity response. The information on these test conditions is often scarce in non-standardised test reports.

The short-term aquatic ecotoxicity data base for zinc was reviewed according to the following principles:

• the data accepted for setting the acute aquatic reference value in the RA (ECB 2008, Annex 1.3.2a, table 1) were as such also accepted and used for the present analysis. Prescriptions from standard protocols were strictly followed, e.g. data from an acute Daphnia test exceeding 48 hrs were not used.
• Data that were rejected for use in the RA (ECB 2008, Annex 1.3.2a, table 2) were also not used for the present analysis. In this respect, data from studies that were accepted for use in the chronic database, but rejected for use in the acute toxicity database were reconsidered; this resulted in the acceptance of a few additional data.
• In accordance to the approach followed in the RA, acute data obtained in natural waters that contained e.g. significant amount of DOC, were not used. Exception to this rule were data obtained on the N.-American Great Lakes waters, which were used, in accordance to the RA.
• Fish data mentioned in the RA under “EHC 1996” were not used, since they were from a review, not from original study reports. These data are not influencing the outcome of the analysis, since they are all at the higher concentration level.
• More recent (obtained after 1996 to the present) short-term acute toxicity data on standard organisms were included in the database.

After checking and updating the data base, the data are grouped per species as follows:

-pH: low (6 -<7) - neutral/high (7 -8.5)

-hardness: low/medium (<100mg CaCO3/l) and medium/high (>100 mg CaCO3/l).

If 4 or more data points were available on a same species, the geomean was calculated and used for the analysis.

 

Acute data – results

The short-term acute aquatic toxicity database covers 10 species (1 algae, 4 invertebrates and 5 fish species). The full set of EC50 values are presented together with the pH and hardness of the test media in the CSR. A significant number of data are available at both low and neutral/high pH.

 

Discussion: reference values for short term aquatic ecotoxicity

Table above presents an overview of the information available for short-term aquatic toxicity for zinc. It can be seen that significant number of data are available at both low and neutral/high pH.

At low pH, 2 values are available for 2 daphnia species. The values are similar. They were obtained at lower hardness, where the highest sensitivity is expected, which is confirmed by the value >530 µg/l, obtained on Ceriodaphnia dubia at high hardness. Algae are as a rule not tested under standardised conditions at low pH, but from chronic algae data (72 hrs NOECs), it is known that the sensitivity of algae is much lower at lower pH. Simulation with the biotic ligand model gives an aquatic ecotoxicity value for algae at pH 6 which is about 5 times higher than the one observed at neutral/high pH. Fish toxicity at low pH is also not critical in this respect, so the values for the daphnids are representative for the sensitivity of organisms to zinc at low pH. The lowest value observed for Ceriodaphnia dubia is used for the classification at low pH.  

At neutral/high pH, the value obtained on the algae Selenastrum capricornutum is the lowest of the dataset. This value is taken forward as reference value for classification at this pH. This value is obtained at low hardness conditions, where sensitivity is highest. The same algae species is also the most sensitive in the chronic aquatic toxicity database (see below) so this sensitivity pattern is consistent. Among the daphnids, Ceriodaphnia dubia is also here the most sensitive, and the lowest value comes close to the one for the alga. From the paired data, it follows that the Daphnids are more sensitive at lower hardness than at the higher hardnesses. The fish are also at this pH less sensitive to zinc, although the lowest value observed on O. Mykiss also comes close to the reference value. All together, the lowest values among the species show also here a consistent pattern, supporting the lowest value identified.

In conclusion, the reference values for the Zn⁺⁺ion that are used for the aquatic toxicity hazard assessment of Zn⁺⁺are:

• for low pH: 0.413 mg Zn/l (based on single lowest value for Ceriodaphnia dubia)
• for the neutral/high pH: 0.136 mg Zn/l (based on single lowest value for Selenastrum capricornutum (=Pseudokircherniella subcapitata)

 

2. Aquatic chronic toxicity: 

 

Chronic data - establishing the dataset

A vast database on chronic ecotoxicity of zinc to freshwater and marine organisms is available. Based on that, a Species Sensitivity Distribution (SSD) approach has been developed for the assessment of zinc in the freshwater and marine compartment, using the reliable species-specific chronic toxicity effects.

 

The chronic freshwater and marine toxicity dataset for zinc was checked according to the general criteria for data quality:

- toxicological endpoints, which may affect the species at the population level, are taken into account. In general, these endpoints are survival, development, hatching, growth and reproduction,

- whether or not toxicity values are considered chronic is not determined exclusively by exposure time, but also by the generation time of the test species, e.g., for unicellular algae and other microorganisms (bacteria; protozoa), an exposure time of four days or less already covers one or more generations thus for these type of species, chronic NOEC values may be derived from relatively short experiments. For PNEC derivation a full life-cycle test, in which all relevant toxicological endpoints are studied, is normally preferred to a test covering not a full life cycle and/or not all relevant endpoints. However, NOEC values derived from tests with a relatively short exposure time may be used together with NOEC values derived from tests with a longer exposure time if the data indicate that a sensitive life stage was tested in the former tests,

- test media should be relevant: both artificial and natural marine waters are selected,

- for freshwater tests pH, hardness and temperature should be reported. In case pH or hardness is not reported, the composition of the test medium or type of test medium should be provided. DOC should be measured or robustly estimated; for marine toxicity tests pH, salinity (preferably, although it is expected that pH (±8) /salinity (±30 ppt) does not substantially change in marine test media) and test temperature should be reported,

-for bioavailability normalization puroposes in the freshwater compartment, the physico-chemistry of the test media should be within the boundaries of the bioavailability models (pH 5.7 – 8.4, and Ca 4.8 – 156 mg/L; see Table 10),

- Zn concentrations should be measured in test media (or as a minimum in stock solutions),

- only the results of tests in which the organisms were exposed to zinc alone are used, thus excluding tests with metal mixtures,

- statistically derived EC10 or NOEC values are retained; in cases where both the NOEC and EC10 values are available from the same experiment, preference is given to the EC10. If the EC10 was used as NOEC equivalent, the EC10 should not be more than 3.2-times lower than the lowest concentration used in the test, and the confidence intervals should not be too wide (and it is proposed that the confidence interval should not exceed a factor of ±10),

- unbounded NOEC values (i.e., no effect was found at the highest or lowest concentration tested) are not used.

For the purpose of PNEC setting the lowest toxicity value for the most sensitive endpoint observed on the species is selected. The lowest value is determined on the basis of the geometric mean if more than one value for the same endpoint is available. An overview of these species-specific toxicity data for the freshwater compartment is given in Table 1, while Table 2 provides an overview for the marine environment. It should be emphasized that for freshwater PNEC derivation purposes, all individual chronic toxicity value are first normalized to the specific water chemistry of European surface waters using bioavailability models.

 

Freshwater:

 

The 41 distinct chronic species ecotoxicity values from 17 taxonomic groups that were used for the SSD in the present analysis are summarised in the CSR, and in table below. The “species mean” NOEC values used for PNEC derivation (freshwater PNEC_{add, aquatic}), range from 13.9 to 1310 µg/l.

The following table gives an overview of the geometric mean and most sensitive freshwater species-specific chronic K2-NOEC/EC10-values for zinc (values as reported in references; non-normalized for bioavailability)

Test organism	Taxonomic group	Endpoint	Geometric mean EC10/NOEC (µg/L)	Lowest EC10/NOEC (µg/L)
Acipenser transmontanus	Fish (Acipenseridae)	Growth (length)	195	104.2
		Growth (weight)	104.2
		Mortality	136.6
Alathyria profuga	Mollusc (Bivalvia)	Mortality	29.6	29.6
Anuraeopsis fissa	Rotifer	Gross reproductive rate	35.1	30.8
		Life span	31.8
		Net reproductive rate	30.8
		Rate of population increase	43.7
Brachionus calyciflorus	Rotifer	Growth Rate	215.1	215.1
Brachionus rubens	Rotifer	Gross reproductive rate	98.7	39.0
		Life span	68.9
		Net reproductive rate	39.0
		Rate of population increase	64.0
Bryocamptus zschokkei	Crustacean (Copepoda)	Mortality	300.0	300.0
		Reproduction	300.0
Ceriodaphnia dubia	Crustacean (Cladocera)	Mortality	87.1	51.8
		Reproduction	51.8
Chlorella sp. (isolate 12)	Alga (Chlorophyta)	Growth rate	136.0	136.0
Cirrhinus mrigala	Fish (Cyprinidae)	Growth (weight)	100.0	100.0
Cottus bairdi	Fish (Cottidae)	Biomass	37.0	27.0
		Growth (length)	27.0
		Growth (weight)	37.0
		Mortality	69.6
Cucumerunio novaehollandiae	Mollusc (Bivalvia)	Mortality	13.9	13.9
Cyprinus carpio	Fish (Cyprinidae)	Mortality	1183.7	1183.7
Danio rerio	Fish (Cyprinidae)	Hatching	666.1	666.1
Daphnia longispina	Crustacean (Cladocera)	Mortality	1587.0	181.0
		Reproduction (number of juveniles)	181.8
		Reproduction (brood size)	181.0
Daphnia lumholtzi	Crustacean (Cladocera)	Mortality	24.9	24.9
		Reproduction	42.8
Daphnia magna	Crustacean (Cladocera)	Intrinsic growth rate	263.0	107.5
		Mortality	125.0
		Reproduction	107.5
Dreissenia polymorpha	Mollusc (Bivalvia)	Mortality	382	382
Echyridella menziesii	Mollusc (Bivalvia)	Mortality	148.2	148.2
Ephoron virgo	Insect Ephemeroptera	Mortality	718.0	718.0
Euchlanis dilatata	Rotifer	Mortality	31.0	31.0
		Reproduction	92.4
Gobiocypris rarus	Fish (Cyprinidae)	Mortality	78.0	78.0
Hyalella azteca	Crustacean (Amphipoda)	Reproduction,	42.0	42.0
		Mortality	42.0
Hyridella australis	Mollusc (Bivalvia)	Mortality	15.4	15.4
Hyridella depressa	Mollusc (Bivalvia)	Mortality	22.8	22.8
Hyridella drapeta	Mollusc (Bivalvia)	Mortality	23.2	23.2
Jordanella floridae	Fish (Cyprinodontidae)	Growth	26.0	26.0
Lampsilis siliquoidea	Mollusc (Bivalvia)	Growth (length)	32.7	32.7
		Mortality	126.0
Lemna gibba	Plant (Araceae)	Frond numbers	2120.0	1310.0
		Growth (weight)	1310.0
Lithobates chiricahuensis	Amphibia	Development	62.0	62.0
		Growth (length)	62.0
		Growth (weight)	62.0
Lymnaea stagnalis	Mollusc (Gastropoda)	Development	530.0	223.0
		Growth Rate (length)	506.8
		Growth rate (weight)	223.0
Microcystis aeruginosa	Cyanobacteria	Growth (cell density)	1000.0	1000.0
Navicula pelliculosa	Alga ((Diatomaea)	Growth rate	280.0	280.0
Oncorhynchus mykiss	Fish (Salmonidae)	Biomass	150.0	150.0
		Growth (length)	300.0
		Growth (weight)	199.0
		Mortality	152.9
Phoxinus phoxinus	Fish (Cyprinidae)	Mortality, Growth	50.0	50.0
Pimephales promelas	Fish (Cyprinidae)	Reproduction	78.0	78.0
Planothidium lanceolatum	Cyanobacteria	Growth (cell density)	234.0	234.0
Potamopyrgus jenkinsi	Mollusc (Gastropoda)	Growth	72.0	72.0
Pseudokirchneriella subcapitata	Alga (Chlorophyta)	Growth Rate	24.1	24.1
Salmo trutta	Fish (Salmonidae)	Hatching	119.4	119.4
Salvelinus fontinalis	Fish (Salmonidae)	Hatching	534.0	534.0
Velesunio ambiguus	Mollusc (Bivalvia)	Mortality	28.9	28.9

 

The data in the above table (the geometric mean for the most sensitive endpoint) have been used for the construction of a Species Sensitivity Distribution (SSD) from which the median 5^th percentile was derived. This value represents the HC5,50% with 5%-95%-confidence interval. 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., PNEC_aquatic= HC5,50%/Assessment Factor). For the purpose of PNEC setting, the lowest value normalised for bioavailability for the most sensitive endpoint is selected for the freshwater compartment. The lowest value is determined on the basis of the geometric mean if more than one value for the same endpoint is available.

Since chronic toxicity of Zn depends on the physico-chemistry of the test medium, all chronic toxicity data (i.e., NOEC/EC10 values) from the database were normalized to the various combinations of specific physico-chemical conditions occurring in European surface waters, as reflected by the conditions monitored in the individual monitoring sites from the FOREGs database  (http://weppi.gtk.fi/publ/foregsatlas/index.php). All freshwater chronic toxicity data were normalized to each of the different environmentally relevant water chemistries documented in this extensive  dataset (see BOX 1). After this bioavailability normalization, the geometric mean value of the most sensitive endpoint per species is used as input data for the calculation of the HC5,50% related to each of the different physico-chemistries occurring in the FOREGs dataset. The distribution of all these HC5,50% values is finally used for setting the  PNEC value for Zn. The different steps in this process are described in more detail in the background document.

 

For each sampling site from the FOREGs database, a separate normalized SSD is constructed through fitting of the log-normal transformed normalised toxicity data to 7 different distributions, ie. cauchy, exponential, gamma, log-normal, logistic, normal, weibull and gumbel. Best fitting statistic such as Anderson-Darling was used to select the best fitting distribution for each of the 546 datapoints from the FOREGs database, after which HC5,50% values were derived for each sampling site from the FOREGs database. In the last step, a distribution of all 546 bioavailabilty normalized HC5,50%’s were plotted and the 10^th percentile of that distribution is proposed as final HC5,50% value (Figure 2), resulting in a value of 14.4 µg Zn/L (as normalised dissolved value). The 10^th percentile is proposed to represent reasonable worst-case conditions of bioavailability in PNEC derivation in analogy with the use of the 90^th percentile of reasonable worst-case setting in the PEC derivation (ECHA 2008).

 

Based on the weight of evidence from the different considerations provided by the extensive uncertainty analysis, combined with the inherent conservatism resulting from the setting of the HC5,50% value with reference to realistic worst case conditions of bioavailability, an Assessment Factor of 1 on the HC5,50% is applied for the derivation of the PNEC, resulting in a PNEC_freshwater of 14.4 µg Zn/L.

For a detailed discussion on the uncertainty related to the SSD and the HC5, and the derivation of the PNEC, seethe background document on environmental risk assessment of zinc in the aquatic compartment, attached to section 13 of IUCLID.

 

 

 

 

Marine:

 

The 32 distinct chronic species ecotoxicity values from 18 taxonomic groups that were used for the SSD in the present analysis are summarised in the CSR, and in table below. The “species mean” NOEC values used for PNEC derivation (freshwater PNEC_{add, aquatic}), range from 4.2 to 2074 µg/l.

 

 

The following table gives an overview of the geometric mean and most sensitive marine species-specific chronic NOEC/EC10-values for zinc (all values Klimish 2 score)

Test organism	Taxonomic group	Endpoint	Geometric mean EC10//NOEC (µg/L)	Lowest EC10//NOEC (µg/L)
Allorchestes compressa	Crustacean (Amphipoda)	Mortality	63.0	63.0
Apostichopus japonicus	Echinoderm (Holothuroidea)	Mortality	444.0	18.8
		Growth rate (weight)	18.8
Capitella capitella	Annelid (Polychaeta)	Reproduction	108	108.0
Ceramium tenuicorne	Macrophyte (Rhodophyta)	Growth (length)	11.9	11.9
Conticriba weissflogii	Alga (Thalassiosirales)	Growth rate	430.0	430.0
Cryothecomonas armigera	Alga  (Cryomonadida)	Growth rate	366.0	366.0
Crassostrea gigas	Mollusc (Bivalvia)	Mortality	254.0	192.9
		Growth (length)	192.9
Etroplus suratensis	Fish (Cichlidae)	Mortality	1480.0	1480.0
Evechinus chloroticus	Echinoderm (Echinacea)	Growth (length)	10.0	9.7
		Development	9.7
Gaimardia trapesina	Mollusc (Bivalvia)	Mortality	2074.0	2074.0
Galeolaria caespitosa	Annelid (Polychaeta)	Fertilization	134.8	134.8
Haliotis diversicolor supertexta	Mollusc (Gastropoda)	Growth rate (length)	64.0	64.0
Haliotis iris	Mollusc (Gastropoda)	Development	4.2	4.2
Haliotis rufescens	Mollusc (Gastropoda)	Development	15.3	15.3
Harpacticus sp.	Crustacean (Copepoda)	Mortality	122.6	122.6
Holmesimysis costata	Crustacean (Mysida)	Mortality	7.1	7.1
Hyale longicornis	Crustacean (Amphipoda)	Mortality	970.0	970.0
Hydroides elegans	Annelid (Polychaeta)	Development (larvae settlement)	23.2	23.2
		Development (from eggs to trochophore larvae)	37.0
Macrocystis pyrifera	Macroalga (Lessoniaceae)	Growth (length of germination tubes)	190.2	190.2
Melita awa	Crustacean (Amphipoda)	Mortality	480.0	480.0
Melita matilda	Crustacean (Amphipoda)	Mortality	230.0	230.0
Mysidopsis juniae	Crustacean (Mysida)	Growth (length)	75.0	64.5
		Mortality	64.5
Mytilus galloprovincialis	Mollusc (Bivalvia)	Development	54.0	54.0
Mytilus trossolus	Mollusc (Bivalvia)	Development	48.0	48.0
Neanthes arenaceaodentata	Annelid (Polychaeta)	Reproduction	108.5	108.5
Nitzschia closterium	Alga (Bacillariales)	Growth	85.5	85.5
Penaeus monodon	Crustacean (Decapoda)	Mortality	8.6	8.6
Phaeocystis antarctica	Alga (Phaeocystales)	Growth rate	450.0	450.0
Pleurochrysis roscoffensis	Alga (Syracosphaerales)	Growth rate	100.0	100.0
Sepia officinalis	Mollusc (Cephalopoda)	Growth rate (length)	53.0	53.0
		Mortality	185.0
Strongylocentrotus purpuratus	Echinoderm (Echinacea)	Development	29.0	29.0
Thalassiosira pseudonana	Alga (Thalassiosirales)	Growth (cell density)	350.0	350.0
Tigriopus angulatus	Crustacean (Copepoda)	Mortality	1190.8	1190.8

 

 

 

The data in the above table(the geometric mean for the most sensitive endpoint) have been used for the construction of a Species Sensitivity Distribution (SSD) from which the median 5^th percentile was derived. This value represents the HC5,50% with 5%-95%-confidence interval. 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., PNEC_aquatic= HC5,50%/Assessment Factor). For the purpose of PNEC setting the lowest toxicity value for the most sensitive endpoint is selected for the marine compartment. The lowest value is determined on the basis of the geometric mean if more than one value for the same endpoint is available.

 

The SSD was constructed through fitting of log-normal transformed toxicity data to 7 different distributions using the bootstrapping method, ie. exponential, gamma, log-normal, logistic, normal, weibull, and gumbel. 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). Using this analysis, the Weibull distribution was defined as the optimal distribution considering the Anderson-Darling goodness-of-fit statistics, which emphasizes the tails of the distributions. The HC5,50% (± 95%CL) that was associated with this distribution was 7.2 µg Zn/L (95%CL: 4.4– 12.5 µg Zn/L; see Table 16). Application of an assessment factor between 1 and 5 on this HC5,50% results in the final PNEC for zinc in the aquatic environment. The value of this assessment factor depends on the uncertainty analysis. Based on the weight of evidence from all the different considerations provided by this extensive analysis  an Assessment Factor of 1 on the HC5,50% is applied for the derivation of the marine water PNEC,  resulting in a PNEC_marine of 7.2 µg Zn/L. 

For a detailed discussion on the uncertainty related to the SSD and the HC5, and the derivation of the PNEC, see the background document on environmental risk assessment of zinc in the aquatic compartment, attached to section 13 of IUCLID.