Authenticating bioplastics using carbon and hydrogen stable isotopes – An alternative analytical approach

Abstract

Rationale A combination of stable carbon (δ13C) and hydrogen (δ2H) isotope ratios and carbon content (% C) was evaluated as a rapid, low‐cost analytical approach to authenticate bioplastics, complementing existing radiocarbon (14C) and Fourier transform infrared (FTIR) analytical methods. Methods Petroleum‐ and bio‐based precursor materials and in‐market plastics were analysed and their δ13C, δ2H and % C values were used to establish isotope criteria to evaluate plastic claims, and the source and biocontent of the samples. 14C was used to confirm the findings of the isotope approach and FTIR analysis was used to vertify the plastic type of the in‐market plastics. Results Distinctive carbon and hydrogen stable isotope ratios were found for authentic bio‐based and petroleum‐based precursor plastics, and it was possible to classify in‐market plastics according to their source materials (petroleum, C3, C4, and mixed sources). An estimation of C4 biocontent was possible from a C4‐petroleum isotope mixing model using δ13C which was well correlated (R2 = 0.98) to 14C. It was not possible to establish a C3‐petroleum isotope mixing model due to δ13C isotopic overlap with petroleum plastics; however, the addition of δ2H and % C was useful to evaluate if petroleum‐bioplastic mixes contained C3 bioplastics, and PLS‐DA modelling reliably clustered each plastic type. Conclusions A combined dual stable isotope and carbon content approach was found to rapidly and accurately identify C3 and C4 bio‐based products from their petroleum counterparts, and identify instances of petroleum and bio‐based mixes frequently found in mislabelled bioplastics. Out of 37 in‐market products labelled as bioplastic, 19 were found to contain varying amounts of petroleum‐based plastic and did not meet their bio‐based claims.

Assessing microbial plastic degradation requires robust methods

“…Fossil fuels –from the Carboniferous (360–300 million years ago) – were generated long before the evolution of C4 plants during the Oligocene (34–23 million years ago) and, hence, have a typical C3 carbon isotopic signature. The δ 13 C signature has been suggested for tracing bio‐based vs petroleum‐based plastics (Berto et al., 2017 ; Rogers et al., 2021 ). We propose measuring the transfer of the light δ 13 C signature of petroleum‐based plastics into microbial biomass by using IRMS as a simple and cost‐effective method for confirming plastic biodegradation, as demonstrated previously (Zadjelovic et al., 2022 ) and illustrated in Figure 2B .…”

RADIOCARBON AND ATMOSPHERIC14CO2PIONEER ATHOL RAFTER

“…The measurements of the rapid changes in atmospheric 14 CO 2 content since 1950 mean that samples can be aged quite precisely, often to within a single year. A wealth of applications include authentication of art objects; testing confiscated elephant ivory for violations of the CITES agreement (Uno et al 2013;Cerling et al 2016) and other wildlife forensic studies (Uno et al 2013); authentication of bioplastic source (Telloli et al 2019;Rogers et al 2021); and even as a tool for determining the age of human remains for forensic investigations.…”

INTERCOMPARISON EXERCISE ON FUEL SAMPLES FOR DETERMINATION OF BIOCONTENT RATIO BY 14C ACCELERATOR MASS SPECTROMETRY

“…The liquid scintillation counting (LSC) based method could be cheaper than the AMS, but burdened with many difficulties, such as quenching in the fuel blend samples which are not transparent liquids (Doll et al 2017;Krajcar Bronic ´et al 2017). Radiocarbon-based biocontent ratio measurement is also used for the determination of the biocomponent ratio in plastics and other materials that can be produced also from bio and fossil sources (Quarta et al 2013;Palstra and Meijer 2014;Santos et al 2019;Rogers et al 2021).…”