Antioxidant 168: Pollution and Degradation

Introduction

Antioxidant 168 (LENOX) is a water-soluble organophosphate that reacts with the hydroperoxides in polymers during processing. This compound can help extend the performance of other primary antioxidants. It is available in several formulations, including tackifier resins and engineering plastics. Its high-performance solid phosphite ester can improve the thermo-stability of polymer processing.

Antioxidant 168 Induced Plastic pollution

Plastic pollution is a source of chemical to the environment and wildlife. Despite the ubiquity of plastic pollution and thus plastic additive in the environment, plastic additives have been studied to a limited extend. As a prerequisite to a study aiming to evaluate the leaching of a common additive used as an antioxidant (Antioxidant 168) from polyethylene microparticles, an inventory of the potential background contamination of the laboratory workplace was done. In this study, Antioxidant 168 (tris(2,4-ditert-butylphenyl) phosphite) and its oxidized form (tris (2,4-ditert-butylphenyl) phosphate) were quantified in different laboratory reagents, including the plastic packaging and the powders, using Pyrolysis-GC/MS. At least one form of Antioxidant 168 was detected in all tested laboratory reagents with higher concentrations in caps and bottles as compared to the powders. Additionally, oxidized Antioxidant 168 was also found in the reverse osmosed and deionized water container used in the laboratory. The same profile of contamination, i.e. higher concentration of the oxidized form and higher concentrations in acidic reagents, was observed when comparing the reagent and their respective containers suggesting that the additive is leaching from the container into the powder. Overall, this study demonstrates that the antioxidant additive Antioxidant 168 is ubiquitous in the laboratory workplace. Plastic additives such as Antioxidant 168 can therefore largely interfere and biased ecotoxicological and toxicological studies especially using environmentally relevant concentrations of microplastics. The source, fate and effects of plastic additive from plastic debris should be carefully considered in future studies that require setting up methods to overcome these contaminations.[1]

In conclusion, the present study demonstrates that a plastic additive used as an antioxidant, Antioxidant 168, was detected in different laboratory materials including plastic packaging and more problematically reagents powders. Reduced and oxidized forms of Antioxidant 168 were ubiquitous in the laboratory workplace at high concentrations, which prevented further study of that leaching from plastics in realistic conditions.

Degradation of Antioxidant 168

Antioxidant 168 (tris(2,4-di-tert-butylphenyl) phosphite) is a widely used antioxidant in the polyolefin industry, but it may degrade and generate NIAS during polymer processing. Studies from our group and the literature have shown that under UV irradiation Antioxidant 168 can degrade into several degradation products; two of them are 2,4-di-tert-butylphenol and tris(2,4-di-tert-butylphenyl)phosphate, via the chemical reaction. For simplicity, hereafter these two degradation products, 2,4-di-tert-butylphenol and tris(2,4-di-tert-butylphenyl)phosphate, are abbreviated DP1 and DP2, respectively. DP1 has been subjected to several toxicity studies, but there is limited information about DP2. Simoneau et al.  studied 449 baby bottles and found that 90% of them had a DP1 level >400 mg kg–1. Hirata-Koizumi reported that the revealed no-observed adverse-effect levels (NOAEL) of DP1 were 5 and 20 mg kg–1 for newborn and young rats, respectively, indicating that DP1 is more toxic than Antioxidant 168 as shown by the acute toxicity of Antioxidant 168 on rats that there was no obvious adverse effect even at the concentration of >2000 mg kg–1. With regard to regulation of Antioxidant 168 and its degradation products, the specific migration limit (SML) of Antioxidant 168 is 60 mg kg–1 based on EU 10/2011; however, there are no SML specifications for DP1 and DP2. Despite the limited regulation on the two degradation products, it is important to investigate the degradation of Antioxidant 168 and the migration of Antioxidant 168 and these two degradation products because of their potential health risk. [2]

The effects of ultraviolet (UV) irradiation on the degradation of Antioxidant 168 and the migration of its two degradation products, 2,4-di-tert-butylphenol and tris(2,4-di-tert-butylphenyl)phosphate, from polypropylene (PP) were investigated. A blown film machine was used to extrude PP films containing Antioxidant 168, the films were stored in the dark for 45 days, two UV treatments and sunlight exposure were applied to the films, and GC-MS was used for degradation and migration studies. Extrusion, storage, UV treatments, and sunlight exposure significantly affected concentrations of Antioxidant 168 and the degradation products. 2,4-Di-tert-butylphenol was the major degradation product produced by UV irradiation, but tris(2,4-di-tert-butylphenyl)phosphate was the major degradation product produced by extrusion, storage, and sunlight exposure. The degradation products have no or little health risk, because migration study and threshold of toxicological concern (TTC) analysis show that experimental maximum migration of 2,4-di-tert-butylphenol and tris(2,4-di-tert-butylphenyl)phosphate are only 2 and 53% of the theoretical maximum migration amounts, respectively.[3]

References

[1] Hermabessiere, L., Receveur, J., Himber, C., Mazurais, D., Huvet, A., Lagarde, F., Lambert, C., Paul-Pont, I., Dehaut, A., Jezequel, R., Soudant, P., & Duflos, G. (2020). An Irgafos? 168 story: When the ubiquity of an additive prevents studying its leaching from plastics. Science of The Total Environment, 749, 141651.

[2] Fouyer, K.; Lavastre, O.; Rondeau, D. Direct monitoring of the role played by a stabilizer in a solid sample of polymer using direct analysis in real time mass spectrometry: the case of Irgafos 168 in polyethylene Anal. Chem. 2012, 84, 8642– 8649

[3] Yang, Y., Hu, C., Zhong, H., Chen, X., & Yam, K. L. (2016). Effects of Ultraviolet (UV) on Degradation of Irgafos 168 and Migration of Its Degradation Products from Polypropylene Films. Journal of Agricultural and Food Chemistry, 64(41), 7866-7873.

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