MANAGEMENT OF POPs CONTAMINATED PLASTIC

Plastics that are contaminated with persistent organic pollutants (POPs) because they have been deliberately added to impart a property to the plastic (fire retardancy, etc.), or because they have been inadvertently added because the POP is a trace contaminant of another additive, or because the plastic in its waste form has become contaminated by POPs (as is the case for some marine plastic litter), in most cases need to be considered separately from most other forms of plastic waste. The Stockholm Convention on Persistent Organic Pollutants requires all parties to destroy or irreversibly transform POPs waste (including POPs-contaminated plastic) so that it no longer exhibits POPs characteristics. These characteristics include toxicity in tiny amounts, persistence in the environment, ability to travel long distances, and bioaccumulation in fatty tissues of living organisms causing food chain contamination.

To be defined as POPs waste and subject to Stockholm Convention Article 6 measures, the plastic must contain one or more POPs that for each POP exceeds a prescribed concentration level known as the Low POP Content Level (LPCL). These levels are reviewed periodically, and are sometimes reduced as science demonstrates that POPs are harmful at lower levels than previously understood. So, if a piece of plastic contains a POP or a mixture of POPs at a concentration exceeding the LPCL, it must be destroyed and not recycled, unless the POP can be removed and managed separately (there are some cases where this is possible).

WHY MUST POPS-CONTAMINATED PLASTIC BE DESTROYED AND NOT RECYCLED?

Plastics contaminated with POPs should not be recycled. The Stockholm Convention prohibits the recycling of POPs waste to prevent the highly toxic chemicals from entering other products and causing unintended and dangerous exposures. However, from time to time, under political pressure, the Convention has granted time-limited exemptions to allow the recycling of materials contaminated with some POPs, such as the brominated flame retardants, commercial PentaBDE and commercial OctaBDE. In January 2020, the European Union announced it will revoke its exemption for recycling of plastics and other materials containing polybrominated diphenyl ethers (PBDE), a brominated flame retardant used widely in plastics. The exemption to allow recycling of this POP has proven to be a costly mistake.

Studies conducted by IPEN have demonstrated that plastic contaminated with PBDEs (usually from electronic waste and automotive plastics) has bled into the recycling chain of non-contaminated plastics. As a result, consumer goods with high exposure potential, such as children’s toys and cooking utensils, manufactured from recycled plastic have been found to contain elevated levels of these POPs. Other POPs are also entering the plastic recycling chain contaminating goods made from recycled plastic with short-chained chlorinated paraffins (SCCPs), dioxins, brominated dioxins, hexabromocyclododecane (HBCD), and other highly toxic POPs chemicals.

The ongoing contamination of the plastic recycling chain with highly toxic persistent organic pollutants threatens to poison the circular economy before it emerges from its infancy. So before any discussion about the relative merits of different ‘solutions’ to end-of-life plastic waste takes place, it must be acknowledged that POPs-contaminated plastic must be identified and removed from the general recycling system, then destroyed or treated in such a way that POPs are removed or so that the plastic exhibits no POPs characteristics, thereby allowing the remaining polymer to be recycled by other means. There are some very limited examples where POPs can be removed or separated (such as solvent regeneration and SCWO). The rest of POPs-contaminated plastic must be destroyed in the most environmentally sound manner, according to Convention guidelines.

TECHNIQUES FOR THE ENVIRONMENTALLY SOUND MANAGEMENT OF POPS-CONTAMINATED PLASTICS

This section only considers environmentally sound technologies for destruction of POPs-contaminated plastic, and a few specific technologies where the POPs can be separated from the plastic and allow recycling of the remaining polymer. One of the requirements of environmentally sound technology is that it destroys or irreversibly transforms POPs without unintentionally generating further POPs in the process. Unintentional POPs or UPOPs are the by-products of combustion technologies where waste chlorine and carbon are among the feedstock (the precursor formation pathway) and de novo synthesis where polychlorodibenzo-p-dioxins (PCDD) and polychlorod ibenzofurans (PCDF), known commonly as dioxins and furans, form in the post-combustion phase. The Stockholm Convention lists UPOPs in Annexes C, Part I to the Stockholm Convention:

· Hexachlorobenzene (HCB);

· Hexachlorobutadiene (HCBD)

· Pentachlorobenzene (PeCB);

· Polychlorinated biphenyls (PCB);

· Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/ PCDF); and

· Polychlorinated naphthalenes (PCN).

Combustion and other incineration processes, such as waste to energy incinerators, pyrolysis, gasification, cement kilns, metallurgy blast furnaces, and plasma arc units, have a strong tendency to form UPOPs in emissions and in residues from their filters such as fly ash, cement kiln dust (CKD), bottom ash, and scrubber water effluent where wet scrubbers are engaged to strip flue gases. IPEN does not regard these technologies as environmentally sound due to their propensity to generate highly hazardous UPOPs54, thereby perpetuating the POPs-contamination cycle. These technologies are not discussed further in this report for treatment of POPs-contaminated plastics.

SEPARATION OF POPs-CONTAMINATED PLASTIC WASTES FROM OTHER POLYMERS

Managing POPs-contaminated plastic waste in an economically efficient manner requires the separation from non-impacted waste. This presents some challenges, as testing for POPs can be complex and expensive in the general absence of labelling of plastics containing POPs additives. For example, hard casings (High Impact Polystyrenes - HIPs) for computers and electrical products are likely to contain brominated flame retardants that have been identified as octa-BDE, penta-BDE, and deca-BDE subsets of the PBDE group. POPs such as SCCPs are used as plasticizers in different types of plastics, but especially PVC. However, some techniques have been developed to simplify identification.

Some electronic screening methods have been developed to separate brominated POPs-contaminated plastics from other polymers including imaging and XRF technology.

Figure 26. Unisort Blackeye by Steinert for separation of brominated black plastics.

One type of imaging equipment that can sort plastic by type of polymer (including black plastic) is UniSort BlackEye from STEINERT.

The UniSort BlackEye uses hyper spectral imaging (HSI) technology. The UniSort BlackEye sorts black plastics such as PE, PP, PVC, and styrenes, and recovers recyclates from materials that were previously sent for processes like thermal recovery.

XRF (X-RAY FLUORESCENCE) SEPARATION

The use of XRF to detect materials on the basis of chemical composition is an effective method to screen brominated flame retardants in plastics, but may also have application for fluorinated plastics in the future due to the ability of XRF to detect halogenated elements, such as bromine, chlorine, and fluorine. One example of this application for separation of brominated plastics is the Redwave company.56 They have incorporated an XRF-based sensing technology into a conveyor belt, and separation technology for mass screening of plastics to separate outputs into brominated and bromine-free plastics. An alternative to fixed separation systems includes hand-held XRF devices that may be applied to screening of incoming plastic batches for recycling that are suspected of brominated POPs contamination. They can also be used to detect potential brominated POPs-contamination of surfaces in recycling and plastics processing centers where brominated plastics have been handled. Portable XRF devices can be calibrated to detect and measure a range of elements including bromine and chlorine. An example of this widely available device is produced by Olympus57 (who also partner with Redwave on component supplies for fixed systems), and is designed for testing consumer goods, analysing metals and alloys, and surface contamination by elements such as lead and mercury.

Figure 27. Redwave XRF-based plastic separator

Figure 28. Post-separation plastics divided into brominated and non-brominated plastic using the Redwave XRF system.

IPEN uses this device for screening of plastics and consumer goods (including children’s toys) suspected of contamination with brominated POPs as a result of being produced from recycled plastics where PBDEs have entered the recycling chain. Subsequent laboratory analysis of those articles identified as contaminated can then produce a lower quantification limit and differentiate individual BFR congeners, if required, for additional quality assurance. The XRF device can be a cost-effective screening method of excluding non-impacted articles instead of using more expensive laboratory analysis on each item.