Registration Dossier

Administrative data

Hazard for aquatic organisms


Hazard assessment conclusion:
PNEC aqua (freshwater)
PNEC value:
20.6 µg/L
Assessment factor:
Extrapolation method:
sensitivity distribution

Marine water

Hazard assessment conclusion:
PNEC aqua (marine water)
PNEC value:
6.1 µg/L
Assessment factor:
Extrapolation method:
sensitivity distribution


Hazard assessment conclusion:
PNEC value:
52 µg/L
Assessment factor:
Extrapolation method:
assessment factor

Sediment (freshwater)

Hazard assessment conclusion:
PNEC sediment (freshwater)
PNEC value:
117.8 mg/kg sediment dw
Assessment factor:
Extrapolation method:
sensitivity distribution

Sediment (marine water)

Hazard assessment conclusion:
PNEC sediment (marine water)
PNEC value:
56.5 mg/kg sediment dw
Assessment factor:
Extrapolation method:
equilibrium partitioning method

Hazard for air


Hazard assessment conclusion:
no hazard identified

Hazard for terrestrial organisms


Hazard assessment conclusion:
PNEC soil
PNEC value:
35.6 mg/kg soil dw
Assessment factor:
Extrapolation method:
sensitivity distribution

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:
no potential for bioaccumulation

Additional information

Weight of evidence approach

In the assessment of the ecotoxicity of naphthenic acids, zinc salts, basic, a weight of evidence approach from data for the metal cation and the organic anion is followed. This strategy is based upon the assumption that upon release to the environment and dissolution in aqueous media, naphthenic acids, zinc salts, basic will dissociate and only be present in its dissociated form, i.e. as zinc cation and naphthenate anion.

A basic assumption made in this hazard assessment and throughout the CSR (in accordance to the same assumption made in the EU RA process) is that the ecotoxicity of zinc and zinc compounds is due to the Zn++ ion. As a consequence, all aquatic, sediment and terrestrial toxicity data in this report are expressed as “zinc”, not as the test substance as such, because ionic zinc is considered to be the causative factor for toxicity. A further consequence of this is that all ecotoxicity data obtained on different zinc compounds, are mutually relevant for each other. For that reason, the available ecotoxicity databases related to zinc and the different zinc compounds are combined before calculating the PNECs. The only way zinc compounds can differ in this respect is in their capacity to release zinc ions into (environmental) solution. That effect is checked eventually in the transformation/dissolution tests and may result in different classifications.

Upon dissolution in water, it is indeed predicted that metal carboxylates dissociate completely into the metal cation and the organic anion at environmentally relevant conditions. No information is available on the stability constants of naphthenic acids, zinc salts, basic, but predictions of stability of other zinc carboxylates (Zn propionate, Zn valerate, Zn isovalerate and Zn benzoate) in a standard ISO 6341 medium (2 mM CaCl2, 0.5 mM MgSO4, 0.77 mM NaHCO3 and 0.077 mM KCl, pH 6 and 8) clearly show that monodentate ligands such as carboxylic acids have no potential for complexing zinc ions in solution (Visual minteq. Version 3.0, update of 18 October 2012.

The fate and behaviour (e.g. partitioning) in the environment for Zn2+ and naphthenate anion are predicted to be significantly different from each other, resulting in a different distribution over the environmental compartments (water, air, sediment and soil). Because the relative exposure to both constituent ions is hence predicted to be different from the original composition of naphthenic acids, zinc salts, basic, data for the ecotoxicological properties of naphthenic acids, zinc salts, basic tested as such are considered less relevant for effects and risk assessment and a read-across approach to separate data for both the zinc cation and naphthenate anion is preferred.

For most metal-containing compounds, it is the potentially bioavailable metal ion that is liberated (in greater or lesser amounts) upon contact with water that is the moiety of ecotoxicological concern. The solubility of naphthenic acids, zinc salts, basic (see IUCLID section 4.8 or chapter 1.3 of the CSR) is above the range of effects concentrations for dissolved Zn in the aquatic environment (lowest acute and chronic reference values: 136 and 19 µg Zn/L, respectively, PNECfreshwater for Zn = 20.6 µg Zn/L) and therefore ecotoxicity data for soluble Zn salts can be directly used in a weight of evidence approach for naphthenic acids, zinc salts, basic. As a conservative approach also the ecotoxicological properties of the carboxylic acid are considered.

According to the REACH Guidance on information requirements and chemical safety assessment, chapter B.8 Scope of exposure assessment, an environmental exposure and risk assessment is mandatory for a substance if it is classified as hazardous to the aquatic environment or if it has another classification and an aquatic PNEC can be derived. The threshold for PNEC derivation is not reported in the guidance, and was set at the limit test concentration for acute toxicity tests with fish, daphnids and algae, i.e. 100 mg/L. Therefore if a substance is not classified as dangerous for the aquatic environment, but meets the criteria for at least one of the other hazard classes or categories and has L(E)C50 values < 100 mg/L, it was still considered for the environmental exposure assessment.

For naphthenic acids, zinc salts, basic both the Zn2+ ion and the naphthenate anion are considered for the environmental exposure and risk assessment. Zinc is classified as hazardous to the aquatic environment (as Aquatic Acute 1, Aquatic Chronic 1), while naphthenic acid is not classified as hazardous to the aquatic environment, but are classified for other endpoints (Skin Irrit. 2, Skin Sens. 1 and Eye Irrit. 2) and has some key L(E)C50 values for effects on aquatic organisms < 100 mg/L. In case both moieties require a risk assessment, the dose additivity approach is used to explain the ecotoxicological effects of the metal carboxylate based on the data for the individual moieties as stated in a toxicity assessment of chemical mixtures opinion for the European Commission (Scientific Committee on Consumer Safety (SCCS), Scientific Committee on Health and Environmental Risks (SCHER), and Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR). 2011. Preliminary opinion on Toxicity and Assessment of Chemical Mixtures;, the dose/concentration addition method should be preferred over the independent action approach if no mode of action information is available. Reliable ecotoxicological data for naphthenic acids, zinc salts, basic are only available for a standard OECD 201 algae test with Pseudokirchneriella subcapitata (Cheshire EcoSolutions, 2013). The algae test was selected because the zinc moiety is predicted to be the driver for toxic effects of naphthenic acids, zinc salts, basic in the environment and algae are the most sensitive aquatic organisms to zinc. Reference to the corresponding toxicity data for effect of zinc and naphthenic acid on algae growth rate and the dose additivity approach (based on the assumption of complete dissolution and a worst-case zinc content of 20% in naphthenic acids, zinc salts, basic) results in a predicted ErC50 for naphthenic acids, zinc salts, basic that is lower than the experimentally derived ErC50 for this substance (Eqn. 1; Table 1). EC50ZnNaphB = 1 / {(weight % Zn / EC50 Zn) + (weight % Naph / EC50 Naph)} It is therefore concluded that an weight of evidence approach to consider the data on individual moieties is conservative. Zinc is the main driver for toxic effects to aquatic organisms and the ecotoxicity data for naphthenic acid do not add significantly to the predicted toxicity for naphthenic acids, zinc salts, basic.

Table 1: Acute toxicity data for effects of naphthenic acids, zinc salts, basic and its moieties to aquatic organisms (only most sensitive species per trophic level).  Trophic level  Endpoint  Naphthenic acids, zinc salts, basic (CAS: 84418 -50 -8) Naphthenic acid (CAS: 13328 -24 -5)  Zinc ion

 Trophic level  Endpoint  Naphthenic acids, zinc salts, basic (CAS: 84418 -50 -8) Naphthenic acid (CAS: 13328 -24 -5)  Zinc ion
 Algae  72h ErC50  3.62 mg/L (experimental, Pseudokirchneriella subcapitata); 0.68 mg/L (based on read across to Zn only); 0.67 mg/L (based on read across to both Zn and naphthenic acid)  29.6 mg/L (Pseudokirchneriella subcapitata )  0.136 mg Zn/L (Pseudokirchneriella subcapitata)
 Fish  96h LC50  No reliable experimental data  5.62 mg/L (Pimephales promelas)  0.169 mg Zn/L (Oncorhynchus mykiss)
 Aquatic invertebrates  48h EC50  No reliable experimental data 20 mg/L (Daphnia magna)  0.147 mg Zn/L (Ceriodaphnia dubia)

Zn_Marine and freshwater toxicity

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 acuteDaphniatest 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 (<100 mg CaCO3/l) and medium/high (>100 mg CaCO3/l).

If 4 or more data points were available on a same species, the geometric mean 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 2Daphniaspecies. 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 onCeriodaphnia dubiaat 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 dubiais used for the classification at low pH.  

At neutral/high pH, the value obtained on the algaeSelenastrum capricornutumis 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 dubiais 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. Altogether, 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: freshwaterChronic data - establishing the dataset

In this analysis, like in the RAR, the results of the chronic aquatic toxicity studies are expressed as either the actual (measured) concentration or as thenominal (added) concentration (Cn). The actual concentrations include thebackground concentration (Cb) of zinc. Because of the “added risk approach”, the results based on actual concentrations have been corrected for background, if possible. This correction for background is based on the assumption that only the added concentration of zinc is relevant for toxicity. In case both actual and nominal concentrations were reported, the results are expressed in the RAR (and in this CSR) as nominal concentrations, provided the actual concentrations were within 20% of the nominal concentrations.

Many of the reported aquatic toxicity data (either actual or nominal) represent total-zinc concentrations, i.e. the dissolved plus particulate fraction. However, the results are regarded as being dissolved-zinc concentrations, because under the conditions that were used in the laboratory tests, it is assumed that the greater part of zinc present in the test waters was in the dissolved fraction. This is especially true for the long-term studies, e.g. by using flow-through systems, in which particulate matter (suspended inorganic material and/or organic matter) was removed from the artificial test waters or natural waters. The fact that in ecotoxicity testing the nominal added concentration of zinc is very close to the actually measured zinc concentration, is also demonstrated by the many data reported in the papers of the chronic aquatic ecotoxicity database. Also in static and flow-through acute toxicity studies with several saltwater species, dissolved zinc was greater than 93% of the total zinc. Therefore, the PNECadd values derived from the aquatic toxicity studies are considered to be relevant for dissolved zinc.

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

-study design preferably conform to OECD guidelines or equivalent

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

- whether or not NOEC 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 considerably less already covers one or more generations, especially in water, thus for these kinds 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.  

-If for one species several chronic NOEC values (from different tests) based on the same toxicological endpoint are available, these values are averaged by calculating the geometric mean, resulting in the “species mean” NOEC.

-If for one species several chronic NOEC values based on different toxicological endpoints are available, the lowest value 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.

-In some cases, NOEC values for different life stages of a specific organism are available. If from these data it appeared that a distinct life stage was more sensitive, the result for the most sensitive life stage is selected. The life stage of the organisms is indicated in the tables as the life stage at start of the test (e.g. fish: yearlings) or as the life stage(s) during the test (e.g. eggsàlarvae, which is a test including the egg and larval stage).

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

-Like in the RAR, unbounded NOEC values (i.e. no effect was found at the highest concentration tested) arenotused.

-If the NOEC was <100 µg/l, the separation factor between the NOEC and LOEC should not exceed a factor of 3.2.

-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.

-Like in the RAR, only the results of tests with soluble zinc salts are used, thus excluding tests with “insoluble” zinc salts (ZnO, ZnCO3), unless dissolved zinc is measured.  


Referring to the EU RA on zinc (ECB 2008), all the data that were accepted for deriving the freshwater PNEC in the RA (ECB 2008, Annex 3.3.2.A. part I) were as such also accepted for the present analysis. On the other hand, the data that were considered not useful for the purpose of PNEC derivation in the RA (ECB 2008, Annex 3.3.2.A. part II), were also not used for the present analysis.

The relevancy of the long-term aquatic ecotoxicity data base for PNEC derivation was further checked in accordance to the same principles as those applied in the RA (ECB 2008). Relevancy was checked

1) related to the zinc background: in accordance to the RA (ECB 2008), a level of 1µg/l Zn was set as a cut-off for this.

2) related to test medium conditions: Zinc ecotoxicity to aquatic organisms is a function of the physicochemical characteristics of the water. Parameters such as hardness, pH, dissolved organic carbon (DOC) are well-known drivers for zinc ecotoxicity. For this reason, it was considered important in the EU RA to select ecotoxicity data that were obtained under test conditions similar to the conditions observed in EU waters. Based on information related to the parameters mentioned above in EU waters, the following boundaries for EU relevancy for pH, hardness have been used in the RA (ECB 2008) and also in the present analysis for data selection, also considering OECD test guidelines:

pH:                             minimum value: 6

                                   maximum value: 9

Hardness:                   minimum value: 24 mg/l (as CaCO3)

                                   maximum value: 250 mg/l (as CaCO3)          

As indicated above, background zinc concentration was also considered in the RA to be a factor influencing the toxicity response of organisms to zinc; to avoid influence of acclimatisation towards very low or very high zinc concentrations (not occurring in the EU waters), a minimum value for soluble zinc was also set in the RAR for data

selection: “around 1 µg/l” (ECB 2008).

Data obtained under conditions failing these relevancy criteria were not used for PNEC derivation in the present analysis. For a detailed description of the relevancy criteria and their application in the RA, see the RAR (ECB 2008).

It is realised that the selected ranges of the three criteria will not cover all European aquatic systems, e.g. specific aquatic systems in the Scandinavian countries. In particularly, hardness is much lower in the Scandinavian countries, although also other abiotic parameters differ from the ‘average’ situation in European freshwaters. Therefore, a “soft water PNECadd, aquatic” has been derived in the RA process, in addition to the generic PNECadd, aquatic.The present analysis however relates to the development of a generic PNEC for EU waters.

DOC: Tests have been considered relevant for the present analysis if DOC concentrations in the test media are between 0 mg/l and 13 mg/l. In most test solutions, DOC is not present.


The extensive dataset on chronic aquatic toxicity in the RA (ECB 2008) was also updated with new information. This information was screened for the same criteria as those described above.

For details on data selection see the CSR zinc.


The 23 distinct chronic species ecotoxicity values that were used for the SSD in the present analysis are summarised in the CSR. The “species mean” NOEC values used for PNEC derivation (freshwater PNECadd, aquatic), range from 19 to 530 µg/l.


PNEC derivation

PNEC freshwater

All adequate chronic data on fish, invertebrates, algae and plants were considered together in a species sensitivity distribution (SSD), and the PNECwas calculated by means of statistical extrapolation, using all available chronic NOEC values as input. The database is indeed sufficiently large and answers the basic requirements to use an SSD, since it covers the required 8 different taxonomic groups and > 10 test organisms.

Since the log-normal distribution significantly fits the data, this distribution was used for the SSD (like in the RAR). Other conditions to apply statistical extrapolation were also met (see CSR, discussion on the safety factor to be applied to the HC5). 


Because of the inclusion of 6 additional species, the species sensitivity distribution (SSD) that was calculated for the present analysis is slightly different from the one of the RAR (2008). For a detailed discussion on the uncertainty related to the SSD and the HC5, and the derivation of the PNEC, see the CSR.

As a result of the analysis, a PNEC freshwater of 20.6 µg Zn/l was derived.

3. Aquatic chronic toxicity: marine waters

For zinc, a specific effects assessment was made and a specific PNEC was derived for the marine environment, since there is a vast dataset available on marine ecotoxicity. This specific approach is also more reflective of the toxicity of zinc in the marine environment given the different speciation and bioavailability of zinc in salt – and freshwater, and differences in physiology of saltwater organisms. Given the vast amount of available toxicity data, statistical extrapolation was used to derive the marine PNEC. This marine effects assessment is following an added risk approach, as applied for the freshwater.


 Sources of data

The ecotoxicological data were derived from original papers, published in peer-reviewed international journals. Literature and environmental databases, including AQUIRE (US EPA), MARITOX, ECETOC, and BIOSIS, as well as review articles covering zinc in marine waters were searched and reviewed for sources of relevant and reliable chronic toxicity data on zinc. Only original literature was used.


Data reliability and relevancy

Selection of ecotoxicity data for quality was done according to a systematic approach as presented by Klimisch et al. 1997. Standardized tests, as prescribed by organizations such as ASTM, OECD and US EPA, are used as a reference when test methodology, performance and data treatment/reporting are considered. A detailed description of data reliability and relevancy is provided in the CSR.


PNEC marinewater

Ecotoxicity database for zinc on species of the marine aquatic environment

The marine zinc database largely fulfils the species and taxonomic requirements for input chronic toxicity data as explained in the RIP R. 10 guidance (at least 10 species NOECs and 8 taxonomic groups). Indeed, 39 species mean NOECs based on 48 NOEC values, from 9 taxonomic groups covering three trophic levels were found to fulfil the relevancy and reliability requirements as explained by Klimisch et al. 1997. The marine zinc database includes 4 micro- and 5 macro-algae species, 4 annelid species, 6 crustacean species, 5 echinoderm species, 9 mollusc species, 1 nematod species, 1 cnidarian species and 1 fish species. The geometric mean values of the species NOECs are presented in the CSR.


Statistics on the species sensitivity distribution (SSD)

Given the multitude of relevant high quality toxicity data, statistical extrapolation was used for PNEC determination. As the approach taken is based on added risks, the results of the toxicity tests based on measured concentrations were corrected for background zinc concentration. Given the wealth of experimental data, no alternative method i.e. assessment factor approach was applied for the PNEC determination. 

Following the RIP R. 10 guidance, different distributions may be used for the SSD. Fitting of the chronic zinc toxicity data was assessed towards the log-normal frequency distribution (default distribution). To be conform with the approach taken in the Zn RAR 2008, it is the lognormal distribution which was used to provide a basis for setting the PNEC saltwater, in spite of a better fit with the Weibull statistical distribution. It is noted also that the PNEC is a PNECadd., i.e. the background concentration needs to be considered in the compliance assessment exercise. The 5thpercentile value of the SSD (the HC5), set at 50% confidence value, using the lognormal distribution function, results in a value of6.09 µg zinc/L.For further details on the setting of the PNEC from the SSD, see the CSR zinc.


Naphthenic acid: Aquatic toxicity

Additional information:

The substance used for the key studies for fish,Daphniaand algae, is a good representative for the NA of this dossier because of equal specifications. Table 1 presents the unsaponifiable fraction, the acid value and the water fraction of the NA used in the ecotoxicity key studies and the NA in current dossier. Results for the latter can be found in IUCLID chapter 1.

The effect of the water accommodated fraction (WAF) of naphthenic acids (NA) on the aquatic organismsPseudokirchneriella subcapitata,Daphnia magnaandPimephales promelaswere measured. The test protocols were according to OECD guidelines and the tests were performed according to GLP principles. The quality of the test and test results are highly reliable.

The NA mixture that was used as a test substance was relevant for the present dossier. 

For algae a static set up was used, forDaphniaand fish a semi static set up was used with medium renewal every 24 hours. Analytical results are available for all 3 studies. Effect values are expressed both in loading rate and in measured dissolved concentration. 

Also data on microbial toxicity (Vibrio fisheri) are reported In literature for NA surrogates. In the microtox assay the EC50 for cyclohexane carboxylic acid was 0.07 mM ( 13.0 +/- 1.6 mg/L).

From biodegradation tests it can also be concluded that NA are not toxic to microbial communities.

Enrichment cultures, obtained from an active tailings settling pond, using commercially available NAs as the sole carbon source, resulted in the isolation of a co-culture containingPseudomonas putidaandPseudomonas fluorescens. These microorganisms are not affected by the presence of naphthenic acid.

Also in other biodegradation tests using naphthenic enrichement cultures show the survival ofPseudomonas stutzeriandAlcaligens denitrificans. And in yet another enriched cultureAcinetobacter calcoaceticusand a member of thePseudomonasfluorescensgroup were demonstrated. From these tests it can be concluded that microbial populations are able to survive naphthenic acid exposure.

Conclusion on classification

The classification as hazardous to the aquatic environment of naphthenic acids, zinc salts, basic is based on a weight of evidence approach, taking into account the data for naphthenic acids, zinc salts, basic itself and the classification of its moieties (zinc and naphthenic acid):

•Only an acute ErC50 value for the effect of naphthenic acids, zinc salts, basic on algae growth rate is available (ErC50 of 3.62 mg/L; Cheshire EcoSolutions, 2013). Algae are considered as the most sensitive aquatic organisms for toxicity of naphthenic acids, zinc salts, basic because i) algae are the most sensitive aquatic organisms for zinc and ii) naphthenic acid is less toxic to aquatic organisms compared to zinc. Therefore it is concluded that data on toxicity of naphthenic acids, zinc salts, basic to fish and aquatic invertebrates are not critical for classification and the value of 3.62 mg/L is taken forward as the acute Exotoxicity Reference Value (ERVacute) for this substance. This ERVacute is > 1 mg/L and therefore does not result in an acute 1 classification for naphthenic acids, zinc salts, basic.

•Assessment of chronic effects based on the acute data for naphthenic acids, zinc salts, basic results in a chronic 2 classification for a substance that is not rapidly degradable. The zinc moiety is identified as the main driver for toxic effects of naphthenic acids, zinc salts, basic to aquatic organisms and the ecotoxicity of naphthenic acid is predicted not to add significantly to the predicted toxicity for naphthenic acids, zinc salts, basic. The concept of “degradability” was developed for organic substances and is not applicable to inorganic substances like zinc. As a surrogate approach for assessing “degradability”, the concept of “removal from the water column” was developed to assess whether or not a given metal ion would remain present in the water column upon addition (and thus be able to exert a chronic effect) or would be rapidly removed from the water column. In this concept, “rapid removal” (defined as >70% removal within 28 days) is considered as equivalent to “rapidly degradable”. Under IUCLID section 5.6, the rapid removal of zinc from the water column is documented. Consequently, zinc is considered as equivalent to being ‘rapidly degradable” in the context of classification for chronic aquatic effects. Following this line of reasoning, it can be concluded that the acute toxicity data would not justify a chronic classification for naphthenic acids, zinc salts, basic.

•The substance naphthenic acids, zinc salts, basic has no official Annex VI classification and will dissociate into zinc and naphthenate ions after dissolution in water and hence can be regarded as a mixture of both constituent ions. Zinc has an official Aquatic Acute 1 and Aquatic Chronic 1 classification (M factor 1; Annex VI of CLP Regulation EC No 1272/2008), while naphthenic acid is not classified as hazardous to the aquatic environment. For the reasons mentioned above, the zinc constituent is however considered as equivalent to being ‘rapidly degradable” in the context of classification for chronic aquatic effects. Considering this, in combination with the chronic ecotoxicity reference value for zinc of 19 µg/L, the classification of the zinc constituent for chronic aquatic effect should be “Aquatic Chronic 2”, rather than the previously mentioned official Aquatic Chronic 1 classification. Taking into account the weight of zinc in naphthenic acids, zinc salts, basic (12-20%), the summation method results in an Aquatic Chronic 3 classification for naphthenic acids, zinc salts, basic.

It is concluded that an Aquatic Chronic 3 classification for hazards to the aquatic environment is appropriate for naphthenic acids, zinc salts, basic.