Naphthenic acids, zinc salts, basic

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

6.39 µg/L

Assessment factor:

1 000

Extrapolation method:

assessment factor

PNEC freshwater (intermittent releases):

63.86 µg/L

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

0.64 µg/L

Assessment factor:

10 000

Extrapolation method:

assessment factor

PNEC marine water (intermittent releases):

6.39 µg/L

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

147.73 µg/L

Assessment factor:

100

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

31.93 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

3.19 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Hazard for air

Air

Hazard assessment conclusion:

no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

PNEC soil

PNEC value:

6.38 mg/kg soil dw

Extrapolation method:

equilibrium partitioning method

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Additional information

Read-across

Metal carboxylates are substances consisting of a metal cation and a carboxylic acid anion. Based on the solubility of naphthenic acids, zinc salts, basic in water, a complete dissociation of naphthenic acids, zinc salts, basic resulting in zinc cations and naphthenate anions may be assumed under environmental conditions ultimately. The respective dissociation is reversible, and the ratio of the salt /dissociated ions is dependent on the metal-ligand dissociation constant of the salt, the composition of the solution and its pH.

A metal-ligand complexation constant of naphthenic acids, zinc salts, basic could not be identified. According to the Irving-Williams series, stability constants formed by divalent first-row transition metal ions generally increase to a maximum stability of zinc (Mn(II) < Fe(II) < Co(II) < Ni(II) < Cu(II) > Zn(II)). Based on an analysis by Carbonaro et al. (2007) of monodentate binding of zinc to negatively-charged oxygen donor atoms, including carboxylic functional groups, monodentate ligands such as naphthenate anions are not expected to bind strongly with zinc, especially when compared to polydentate (chelating) ligands. The metal-ligand formation constants (log KML) of zinc with other carboxylic acids, i.e. acetic, formic and benzoic acid, range from 0.6 to 1.59, (Bunting and Thong, 1970) and point to a lowly-moderately stable complexation. 

The analysis by Carbonaro & Di Toro (2007) suggests that the following equation models monodentate binding to negatively-charged oxygen donor atoms of carboxylic functional groups:

log KML= αO* log KHL+ βO; where

KML is the metal-ligand formation constant, KHL is the corresponding proton–ligand formation constant, and αO and βO are termed the slope and intercept, respectively. Applying the equation and parameters derived by Carbonaro & Di Toro (2007) and the pKa of naphthenic acid of 4.72 results in:

log KML= 0.301 * 4.72 + 0.015

log KML= 1.44 (estimated zinc-naphthenate formation constant).

Thus, in the assessment of environmental fate and pathways of naphthenic acids, zinc salts, basic, read-across to the assessment entities naphthenate and soluble zinc substances is applied since the individual ions of naphthenic acids, zinc salts, basic determine its environmental fate. Since zinc ions and naphthenate ions behave differently in the environment, regarding their fate and toxicity, a separate assessment of each assessment entity is performed. Please refer to the data as submitted for each individual assessment entity. For a documentation and justification of that approach, please refer to the separate document attached to section 13, namely Read Across Assessment Report for naphthenic acids, zinc salts, basic.

 

Reference:

Carbonaro RF & Di Toro DM (2007) Linear free energy relationships for metal–ligand complexation: Monodentate binding to negatively-charged oxygen donor atoms. Geochimica et Cosmochimica Acta 71: 3958–3968.

Bunting, J. W., & Thong, K. M. (1970). Stability constants for some 1: 1 metal–carboxylate complexes. Canadian Journal of Chemistry, 48(11), 1654-1656.

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 that naphthenic acids, zinc salts, basic dissociates and releases zinc cations and naphthenate anions, and applying aquatic toxicity data of naphthenic acids, zinc salts, basic and aquatic toxicity data of its moieties zinc cations and naphthenate anions:

 

Short-term toxicity:

Short-term toxicity data of naphthenic acids, zinc salts, basic are available for algae (RL2), invertebrates (RL4) and fish (RL4) and the lowest EC/LC50 has been identified for algae with the 72-h ErC50 of 3.62 mg/L. Thus, LC/EC50 values are well above the classification cut-off value for acute (short-term) aquatic hazard Category 1 of 1 mg/L according to Regulation (EC) No 1272/2008, Table 4.1.0 (a).

Regarding naphthenate, reliable data are available for algae, invertebrates and fish with the lowest LC/EC50 reported for fish with 5.62 mg/L.Thus, LC/EC50 values are well above the classification cut-off value for acute (short-term) aquatic hazard Category 1 of 1 mg/L according to Regulation (EC) No 1272/2008, Table 4.1.0 (a).

Regarding the acute (short-term) aquatic toxicity, naphthenic acids, zinc salts, basic is further evaluated by comparing the dissolved zinc ion level resulting from the T/Dp after 7 d at a loading rate of 1 mg/L with the acute ecotoxicity reference values (ERVs) as determined for the (soluble) zinc ion. The ERV is based on the lowest acute EC50/LC50 for algae, invertebrates and fish.

The short-term ecotoxicity reference values for the zinc ion used for the aquatic toxicity hazard assessment amount to 0.413 mg Zn/L (based on single lowest value for Ceriodaphnia dubia) at low pH and 0.137 mg Zn/L (based on single lowest value for Pseudokirchneriella subcapitata) at neutral/high pH.

Dissolved zinc concentrations of 0.149 mg/L at pH 6 (low pH) and 0.118 mg/L at pH 8 (neutral/high pH) in the T/Dp after 7 days are significantly lower than the derived short-term ERVs. Hence, naphthenic acids, zinc salts, basic is not sufficiently soluble to cause short-term toxicity at the level of the acute ERV (expressed as the EC/LC50) of zinc.

In accordance with Figure IV.4 “Classification strategy for determining acute aquatic hazard for metal compounds” of ECHA Guidance on the Application of the CLP Criteria (Version 5.0, July 2017) and section 4.1.2.10.2. of Regulation (EC) No 1272/2008, naphthenic acids, zinc salts, basic is poorly soluble and does not meet classification criteria for acute (short-term) aquatic hazard.

In sum, naphthenic acids, zinc salts, basic does not meet classification criteria of Regulation (EC) No 1272/2008 as Acute (short-term) aquatic hazard.

 

Chronic (long-term) toxicity:

Regarding long-term toxicity, data of naphthenic acids, zinc salts, basic are available for the trophic level algae/aquatic plants with the 72-h ErC10 of 1.09 mg/L. Thus, the ErC10 value is above the classification cut-off values for long-term aquatic hazard of 1 mg/L according to Regulation (EC) No 1272/2008, Table 4.1.0 (b).

According to the QSAR-based outcome of the model ECOSAR v.1.11, naphthenates have a very low potential for chronic toxicity to aquatic invertebrates and fish with the lowest chronic values (ChV = 10^([log (LOEC x NOEC)]/2)) of 31.6 mg/L for daphnids indicating that chronic toxicity up to the classification cut-off values for long-term aquatic hazard of 1 mg/L according to Regulation (EC) No 1272/2008 is highly unlikely. Applying the surrogate approach according to Table 4.1.0 (b) (iii) of Regulation (EC) No 1272/2008, using the lowest acute toxicity value for invertebrates and fish, i.e. the 96-h LC50 of 5.62 mg/L for fish (Pimephales promelas), and taking into account that naphthenates are considered readily biodegradable and do not bioaccumulate, naphthenates would also not meet classification criteria for long-term aquatic hazard (as concluded for the self-classification of naphthenic acids, CAS # 1338-24-5).

Therefore, the long-term (chronic) assessment of naphthenic acids, zinc salts, basic is based on the most toxic moiety, i.e. the zinc cation. The long-term reference values for the zinc ion that used for the aquatic toxicity hazard assessment amount to 82 µg Zn/L (for Daphnia magna) at low pH and 19 µg Zn/L (for Pseudokirchneriella subcapitata) at neutral/high pH. Dissolved zinc concentrations of 0.188 mg/L at pH 6 (low pH) and 0.154 mg/L at pH 8 (neutral/high pH) in the T/Dp after 28 days are not lower than the derived long-term ERV and naphthenic acids, zinc salts, basic can be considered soluble regarding the chronic aquatic hazard classification.

Thus, chronic ecotoxicity reference values of zinc (as derived in the CSR of zinc oxide attached in section 13) are recalculated for naphthenic acids, zinc salts, basic based on the average and maximum (worst case) zinc contents of 15 % and 18.5 % (respectively). The chronic ecotoxicity reference value for P. subcapitata of 0.019 mg Zn/L is applied, corresponding to 0.127 mg/L for naphthenic acids, zinc salts, basic with an average zinc content of 15 % and 0.103 mg/L for the maximum (worst case) zinc content of 18.5 %. Thus, naphthenic acids, zinc salts, basic meets classification criteria of long-term aquatic hazard of Regulation (EC) No 1272/2008. The chronic ecotoxicity reference values of 0.127 mg/L for naphthenic acids, zinc salts, basic with an average zinc content of 15 % and 0.103 mg/L for the maximum (worst case) zinc content of 18.5 % are compared with the criteria for long-term aquatic hazard classification, taking into account if zinc, the toxic moiety of concern (due to the biodegradability of naphthenate), is considered rapidly degradable or not. The concept of “Degradability” was developed for organic substances and is not applicable to inorganic zinc substances. As a surrogate approach for assessing “degradability”, the concept of “removal from the water column” was developed to assess if a specific 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”. The rapid removal of zinc from the water column is documented in the section „Environmental fate“. Consequently, zinc is considered as equivalent to being ‘rapidly degradable” in the context of classification for chronic aquatic effects. Based on the chronic ecotoxicity reference values of 0.127 mg/L for naphthenic acids, zinc salts, basic with an average zinc content of 15 % and 0.103 mg/L for the maximum (worst case) zinc content of 18.5%, naphthenic acids, zinc salts, basic meets classification criteria of long-term aquatic hazard Category 3 in accordance with Table 4.1.0 (b) (ii) of Regulation (EC) No 1272/2008.

Naphthenic acids, zinc salts, basic does not meet classification criteria of Regulation (EC) No 1272/2008 as Acute (short-term) aquatic hazard but meets criteria of Long-term aquatic hazard Category 3.