Evaluation of hand-held XRF for screening waste articles for exceedances of limit values for brominated flame retardants

Abstract

Recent research has demonstrated the presence of restricted persistent organic pollutant (POP) brominated flame retardants (BFRs) in items such as children s toys and food contact articles. As the presence of these contaminants in such items serves no useful purpose, they are thought to originate from the use of recycled plastics that were originally treated with BFRs. To address this issue, European Union (EU) Regulation 850/2004 specifies low POP concentration limit (LPCL) values such that articles containing such BFRs [selected polybrominated diphenyl ethers (PBDEs) and hexabromocyclododecane (HBCDD)] at concentrations exceeding the LPCL (1000mg/kg) cannot be recycled and must be treated so that the BFR content of such articles is destroyed. Existing LPCLs for PBDEs cover PBDEs present in the penta- and octa-brominated diphenyl ether (BDE) formulations, with an LPCL for deca-BDE at a similar concentration scheduled for implementation from March 2019. Given the widespread use of PBDEs and HBCDD in applications such as electrical and electronic goods, polystyrene building insulation foam, seating foam and fabrics in homes, offices and cars, monitoring compliance with LPCLs represents a substantial undertaking, compounded by conventional methods for measuring PBDEs and HBCDD being destructive, timeconsuming, expensive and incompatible with being conducted in situ at waste handling sites. Our principal objective was thus to evaluate the feasibility of using hand-held X-ray fluorescence (XRF) spectrometers to determine bromine in waste articles as a surrogate indicator of exceedance of LPCLs. Of particular concern is the incidence of false positives (where the concentration of bromine but not PBDEs or HBCDD exceeds the LPCL) and false negatives (where the concentration of PBDEs or HBCDD exceeds the LPCL but this is not indicated by the bromine concentration recorded by XRF). False positives may occur when a BFR other than a PBDE or a HBCDD (e.g. tetrabromobisphenol A) is present at a concentration above 1000mg/kg. We measured bromine in 769 waste articles and PBDEs and HBCDD in 538 of the same articles collected in Ireland between 2015 and 2016. These articles comprised waste electronic and electrical equipment (WEEE), polystyrene building insulation and end-of-life vehicle foams and fabrics, as well as waste carpets, curtains, furniture foams and fabrics. Measurements revealed concentrations of PBDEs and HBCDD exceeding existing LPCLs in 29 of 538 articles (5.4%). Anticipating the introduction of an LPCL for deca-BDE (BDE-209), we found that the proportion of articles exceeding either existing LPCLs or the anticipated LPCL of 1000mg/kg for BDE-209 was 8.7% (47/538). By comparison, false positives numbered 52 (9.7%) when existing LPCLs only were considered, reducing to 34 (6.3%) when the anticipated LPCL for BDE-209 was accounted for. No false negatives were detected. Based on our data, enforcement of existing LPCLs would prevent 97.9% of the estimated 17,721kg/year of HBCDD, penta-BDEs and octa-BDEs generated currently in Ireland, as well as 13.0% of the 15,284kg/year of BDE-209 generated, from being recycled. Enforcement of an LPCL of 1000mg/kg for BDE-209 would prevent recycling of 98.1% of the 33,004kg/year of PBDEs and HBCDD currently generated in Ireland. Although false positives will lead to some articles being incorrectly prevented from being recycled, the absence of false negatives in this study, combined with the cost- and time-effectiveness of hand-held XRF relative to conventional methods for measuring PBDEs and HBCDD, renders hand-held XRF potentially feasible for large-scale monitoring of LPCL compliance. Despite this, use of hand-held XRF to screen individual waste articles may still be considered overly time-consuming by waste treatment professionals. Consequently, automation of the screening process using a fixed/bench-top XRF instrument in conjunction with a conveyor belt carrying waste articles is considered a feasible approach for large-scale waste handling operations, albeit one requiring greater capital outlay. Short-term approaches to minimise the number of articles requiring checking for compliance with LPCLs merit consideration. These involve using data from this project that show very low BFR concentrations and no exceedances of current or anticipated LPCLs for some waste categories such as extruded polystyrene (XPS) building insulation foam. On-site separation of XPS from expanded polystyrene (EPS) foam (for which 35% of samples were found to exceed the LPCL for HBCDD) to allow recycling or reuse of XPS without checking for LPCL compliance would reduce the monitoring burden placed on the waste management industry.