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PBT assessment

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PBT assessment: overall result

Reference
Name:
zinc distearate
Type of composition:
boundary composition of the substance
State / form:
solid: bulk
Reference substance:
Composition 1
PBT status:
the substance is not PBT / vPvB
Justification:

Classification of Zinc distearate for effects in the environment:

 

The chemical Zinc distearate (CAS no. 557-05-1) is used to manufacture drugs, lacquers, and plastics. It is used as a dietary supplement, waterproofing agent, heat and light stabilizer, and lubricant. It is also used in cosmetic powders for its adhesive properties. The aim was to assess whether the PBT criterion within Annex XIII was fulfilled forZinc distearate. The PBT criterion was herein assessed based on experimental data in conjunction with standardized environmental fate models. Here follows a description of the PBT assessment.

 

Persistence assessment

The tested substance does not fulfil the P criterion within Annex XIII based on the assessment that here follows:

 

Biotic degradation

42-days Closed Bottle test following the OECD guideline 301 D was performed to determine the ready biodegradability of the test chemical. The study was performed at a temperature of 20°C. The test system included control, test item and reference item. Polyseed were used for this study. 1 polyseed capsule were added in 500 ml D.I water and then stirred for 1 hour for proper mixing and functioning of inoculum. This gave the bacterial count as 10E7 to 10E8 CFU/ml. At the regular interval microbial plating was also performed on agar to confirm the vitality and CFU count of microorganism. The concentration of test and reference item (Sodium Benzoate) chosen for both the study was 4 mg/L, while that of inoculum was 32 ml/l. OECD mineral medium was used for the study. ThOD (Theoretical oxygen demand) of test and reference item was determined by calculation. % degradation was calculated using the values of BOD and ThOD for test item and reference item. The % degradation of procedure control (reference item) was also calculated using BOD & ThOD and was determined to be 70.48%. Degradation of Sodium Benzoate exceeds 45.18 % on 7 days & 70.48 % on 14th day. The activity of the inoculum was thus verified and the test can be considered as valid. The BOD42 value of test chemical was observed to be 0.6 mgO2/mg. ThOD was calculated as 2.6 mgO2/mg. Accordingly, the % degradation of the test item after 42 days of incubation at 20 ± 1°C according to Closed Bottle test was determined to be 23.07%. Based on the results, the test item, under the test conditions, was considered to be primary inherently biodegradable in nature.

 

Thus, based on the above available information, it has been concluded Zinc distearate is likely to be not persistent (notP) in nature.

 

Environmental fate

According to the fugacity model levels III, the most likely environmental fate for this test chemical is soil (i.e.estimated to 83.9%). In soil,Zinc distearatewas expected to have slow mobility based upon a Log KOC value of 3.179. The half-life in soil (75 days estimated by EPI suite) indicates that the chemical is not persistent in soil and the exposure risk to soil dwelling animals is moderate to low.

 

If released in to the environment, 15.9 of the chemical will partition into water according to the Mackay fugacity model level III in EPI suite version 4.1 (2017). However, the half-life (37.5 days estimated by EPI suite) indicates that the chemical is not persistent in water and the exposure risk to aquatic animals is moderate to low.

 

Moreover, its persistent characteristic is only observed in the sediment compartment but Fugacity modelling shows that sediment is not an important environmental fate (less than 1% i.e reported as 0.00575% when estimated by EPI Suite version 4.1).

 

Hence it has been concluded that chemical Zinc distearate is not persistent in nature.

 

 

Bioaccumulation assessment

The tested substance does not fulfil the B criterion within Annex XIII based on the assessment that here follows:

 

Theestimated BCF value from authoritative database was evaluated to be 3.162 L/Kg, respectively and theoctanol water partition coefficient of the test chemical ranges was determined to be 4.64, respectively, which is close to the threshold of 4.5. If this chemical is released into the aquatic environment, there should be a low risk for the chemical to bioaccumulate in fish and food chains.

 

Toxicity assessment

The tested substance does not fulfil the T criterion within Annex XIII based on the assessment that here follows:

 

Mammals

The tested chemical is regarded to be not classified for carcinogenicity, mutagenicity and reprotoxicity, Further, there is no evidence of chronic toxicity, as identified by the classifications STOT (repeated exposure), category 1(oral, dermal, inhalation of gases/vapours, inhalation of dust/mist/fume) or category 2 (oral, dermal, inhalation of gases/vapours, inhalation of dust/mist/fume).

 

Aquatic organisms

As per Column 2 (Annex VIII) of the REACH regulation,testing for this end point is considered scientifically unjustified since there are mitigating factors indicating that aquatic toxicity is unlikely to occur as the substance is highly insoluble in water (solubility: 0.0046 mg/L at 25° C). The chemical Zinc distearate was therefore not considered as hazardous to aquatic environments as per the criteria set out in Annex XIII.

 

Conclusion

Based on critical, independent and collective evaluation of information summarized herein, the tested compound does not fulfil the P, B and T criterion and has therefore not been classified as a PBT compound within Annex XIII.