ADDITIVES OF GLOBAL CONCERN: PHENOLIC BENZOTRIAZOLES UV -326, UV-327 AND UV-328
Stabilizer additives have not received as much attention in the literature as some other additives but have recently been the subject of increased concern. Ultraviolet (UV) light stabilizers function by preventing degradation of plastic through competitive absorption of UV light. In the past the main concern has been associated with heavy metal-based UV stabilizers in PVC such as lead and cadmium with readily leach into the environment and rightly so.
However, another group of UV stabilizers, based on phenolic benzotriazole (BT) are of growing concern to chemical regulators. This is mainly because they share a phenolic structure which is the necessary structure for molecules to bind with the human estrogen receptors and therefore have the potential to exert endocrine disrupting activity. The BT family, including UV-326, UV-327 and UV -328 also demonstrate persistent, bioaccumulative and toxic properties.
The benzotriazole stabilizer UV-328 (2-(2H-benzotriazol-2-yl)-4,6-ditertpentylphenol ) has been found to exhibit persistent, bioaccumulative and toxic (PBT) properties to such as extent that it may be a POP substance meeting the Stockholm Convention criteria. This has resulted in a proposal by Switzerland (UNEP 2020) to list UV-328 on Annex A of the Stockholm Convention which, if successful, would result in its classification as a POP and subject it to global elimination.
UV-328 has also been identified by the Member State Committee of the European Chemicals Agency (ECHA)4 as a Substance of Very High Concern (SVHC) and added to Annex XIV ‘Authorisation list’ of the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) Regulation, with a sunset date of November 27th, 2023. All uses after this date requires a formal authorization by ECHA.
Other similar stabilizers from the phenolic benzotriazole group have also been added to the Authorisation List including UV-320, UV-327 and UV350. These stabilizers all meet the REACH criteria of PBT and very Persistent and very Bioaccumulative (vPvB) substances and were confirmed on the Authorisation List in February 2020.5 UV-328 is highly hydrophobic, adsorbs and/or absorbs strongly to organic material, and has a low tendency to volatilise. When released to water, it will likely partition to particles and organic matter, suspended or deposited. Experimental and estimated data indicate that UV-328 does not degrade rapidly in water, soil, or sediment. It has been measured in sediment (along with UV-327) near an industrial release site in Narragansett Bay, USA decades after release stopped. It has been detected in multiple studies in aquatic life, foodstuffs and human adipose tissue (UNEP 2020)
UV-328 and related benzotriazoles (i.e., UV-326 and UV-327) can be transported long distances in plastic resin pellets and plastic fragments especially in aquatic environments, resulting their detection in plastics on remote islands (IPW 2020). They have also been detected in plastic fragments ingested by seabirds (Tanaka et al., 2019). Furthermore, they were also found to accumulate in preen gland oil of wild seabirds from remote islands from plastic ingestion, indicating their bioaccumulative nature. UV-328 and associated BT are considered to be toxic for mammals, endangering human health and the environment, as it may cause damage to liver and kidneys through prolonged or repeated oral exposure (UNEP 2020). The Swiss proposal to the Stockholm Convention also notes that that pharmacokinetic modelling indicates that BT based UV stabilizers such as UV-326, UV-327 and UV-328 are absorbed into the gastrointestinal tract, metabolised in the liver, and excreted via kidneys and that this leads to liver and kidney toxicity (UNEP 2020).
There are high levels of concern about UV-328, UV-326 and UV-327 both because of their PBT properties but also because of their widespread use in common plastics allowing for high levels of human and environmental exposure. UV-328 is a high production volume (ten of thousands of tonnes globally) chemical used as a UV stabilizer in plastics. The range of polymer types and plastic types incorporating UV-328 is broad and includes: polyolefin and plastic shrink films (e.g. food contact shrink wrap), plastic outdoor furniture, ABS resin, epoxy resin, fibre resin, PVC (e.g. construction materials and food packaging), unsaturated polyesters, polyacrylates (e.g. paints, textiles, leather finishing) and polycarbonates. It is particularly recommended as UV absorber for polyolefins (e.g. bottle caps, plastic bottles, plastic wrap), polyurethanes, PVC, polyacrylate, epoxy and elastomers.6 UV-328 as a high-volume plastic additive with production and/or importation in the European Economic Area in the range of 100- 1000 t/a and 450–4,500 t/a in the US.7
The ubiquitous nature of BT UV stabilizers in plastic was supported by a recent study8 from International Pellet Watch who sampled marine litter plastic fragments collected in remote coastal locations and analysed the fragments for UV stabilizer additives. The results demonstrated that while UV-328 was detected in many samples, even higher concentrations of UV-326 and UV-327 were present in most of the fragments (see Figures 8 and 9).
Regulatory agencies for chemical management are increasingly concerned about the persistent, bioaccumulative and toxic properties of benzotriazole UV stabilizers. While some of the benzotriazole UV stabilizers exhibit PBT characteristics to a lesser or higher degree (with UV-328 currently assessed as the most hazardous) the precautionary principle should apply and lead to the rapid phase out of this family of UV stabilizers.
If UV-328 is assessed as a POP and added to the annexes of the Stockholm Convention the plastic recycling industry will need to develop detection systems to ensure that this chemical does not contaminate the recycling stream and recirculate into new products made from recycled plastic. In addition, the management of plastic waste contaminated by POPs requires that it be destroyed or irreversibly transformed so that it does not exhibit POP characteristics. Given the high-volume production and use as additives in a wide variety of polymers it is important that the process of evaluation and phase out of the BT family of stabilizers be accelerated.