Naphthenic acids, zinc salts

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

0.004 mg/L

Assessment factor:

1 000

Extrapolation method:

assessment factor

PNEC freshwater (intermittent releases):

0.04 mg/L

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

0 mg/L

Assessment factor:

10 000

Extrapolation method:

assessment factor

PNEC marine water (intermittent releases):

0.04 mg/L

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

689.7 µg/L

Assessment factor:

1

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

0.015 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

0.002 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:

0.001 mg/kg soil dw

Extrapolation method:

equilibrium partitioning method

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Additional information

Zinc naphthenate is a complex UVCB with a large number of constituents. As such, ecotoxicity studies were undertaken following a WAF method, with results reported as loading rates, in line with the OECD guidance 23 for difficult to test substances. Based on water accommodated fraction loading rates (WAF), naphthenic acids, zinc salts has a 96-hour LC50 for fish of >100 mg/L and a 48-hour EL50 for Daphnia magna of 35 mg/L. The 72h-NOELR for algae growth rate inhibition is 1.0 mg/L, when based on biological relevance, and the 72h-EL50 is 4.0 mg/L.

Zinc naphthenate is a UVCB containing a large number of constituents, each of which could potentially have properties varying from other constituents in the salt. Zinc naphthenate consists of 70-95% zinc salts of naphthenic acids, C8-C20 with 0-3 rings, and 5-30% petroleum fraction, C12-C22, which remains unreacted from the naphthenic acid raw material. Therefore, properties have been provided for representative structures which bracket the range of potential constituents present in zinc naphthenate with regard to the molecular weight and number of cyclic groups.

As the constituents in the UVCB vary in size and physico-chemical properties, two sets of sediment and soil PNECs were derived for use in the risk assessment. Equilibrium partitioning was used to calculate the sediment and soil PNECs using Koc values calculated from the highest and lowest of the partition coefficient results (Log Kow 0.8 – 5.4). These sediment and soil PNECs have been calculated using equilibrium partitioning, with a Koc value of 1.792 L/kg and a Henry’s constant of 0.0016 Pa/m3/mol. The Henry’s constant was calculated based on a vapour pressure of 0.026 Pa, a water solubility of 163.17 mg/L and a molecular weight of 204.6 g/mol.

A separate set of sediment and soil PNECs have been derived using a Koc value of 48560 L/kg, a vapour pressure of 1.3 Pa, a water solubility of 44.01 mg/L and a molecular weight of 376.9 g/mol.

Conclusion on classification

Zinc naphthenate is a complex UVCB with a large number of constituents. As such, ecotoxicity studies were undertaken following a WAF method, with results reported as loading rates, in line with the OECD guidance 23 for difficult to test substances. Based on water accommodated fraction loading rates (WAF), naphthenic acids, zinc salts have a 96-hour LC50 for fish of >100 mg/L and a 48-hour EL50 for Daphnia magna of 35 mg/L. The 72h-NOELR for algae growth rate inhibition is 1.0 mg/L, when based on biological relevance, and the 72h-EL50 is 4.0 mg/L.

On the basis of the lowest short-term ecotoxicity result being 4.0 mg/L, the substance does not meet the criteria for classification as acute category 1 (EC50 ≤1 mg/L). On the basis of the lowest long-term ecotoxicity result being 1.0 mg/L and the substance being not rapidly biodegradable, the substance meets the criteria for classification as chronic category 2 (NOEC ≤1 mg/L). On the basis of the short-term ecotoxicity results and the substance not be rapidly biodegradable, the substance would not meet the criteria for classification as it is considered not to bioaccumulate (BCF <500 L/kg).

On the basis of the worst-case classification applicable, zinc naphthenate would be classified as aquatic chronic category 2 (H411: toxic to aquatic life with long lasting effects).