###### Abstract  
Fourier-transform infrared (FTIR) spectroscopy has been extensively used in plastic pollution research, since it has the advantages of great simplicity, rapidity, and low cost, being widely employed in the fingerprint identification of molecular composition and structure. The present study evaluates attenuated total reflection (ATR)-FTIR spectroscopy as a sensitive and effective assay for the identification of deoxyribonucleic acid (DNA) isolated from experimental animals. Various composite materials based on recycled polyethylene temepthhalate (PET) as the main component, along with high-density polyethylene (HDPE), polypropylene (PP), and aluminum nanopowder obtained using an injection-molding machine, were used as substrate contaminants. The contamination was performed using quantified nucleic acid solution added in droplets to the clean, decontaminated samples, which were then dried and kept in a protective environment until the analysis. ATR-FTIR (with an FTIR spectrometer equipped with an ATR accessory) spectroscopy was used to analyze the bare composite materials' substrates and the DNA-contaminated samples. To the best of our knowledge, the evaluation of PET packaging contamination with DNA species by FTIR has not been reported previously. This study demonstrated that FTIR spectroscopy could provide a rapid, sensitive, and reliable approach for screening of biochemical contaminants on composite materials based on recycled PET. A 2022 25 April 2022 25 April  
Plastics, such as polyethylene terephthalate (PET), high- and low-density polyethylene (HDPE, LDHE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), and polycarbonate (PC), are considered the most common, durable, and relatively cheap synthetic materials used in industry, reported to continually produce general municipal solid waste in Europe [5]. Among this variety of plastics, PET occupies an essential role in the packaging industry, mainly because of its durability and thermal stability [6]. However, these features come with an extremely high cost, with its existence causing a major environmental issue, since around 100 million plastic bottles are produced and discarded worldwide every day [7]. Fortunately, PET packaging is 100% recyclable. Globally, of approximately 30 million tons of plastic waste collected in 2020, more than one-third (34.6%) was sent for recycling, and 23.4% ended up in landfalls [3; 8]. Less than half of the plastic packaging waste was recycled in Europe in 2019, as announced by the European Environment Agency. Lithuania has the highest recycling rate of plastic waste (about 70%), while Malta is at the other end of the scale, with only 11% [9]. Currently, there are different methods generally used to manage PET pollution--namely, mechanical, thermal, and chemical-based treatments--leading to recycling of the material. In short, PET is gathered, sorted, washed, transformed into smaller pieces, decontaminated, and processed into PET pellets. These pellets can be used either in fully recycled content (100%) or as a blend of the recycled plastic with the virgin one (50/50) [10; 11]. While mechanical recycling involves melting, chemical recycling is based on depolymerization. Chemical recycling is now used in many industrial and commercial applications, including food contact applications [12]. Before any recycled PET (rPET) is placed on the market, it goes through an authorization practice overseen by the European Food Safety Authority (EFSA), which ensures that the recycling process meets the required standards [13]. The main criterion is the cleaning efficiency of the PET recycling process, measuring the technical capability of the process to remove potential contaminants from recollected PET [14]. Any existing contaminant must be at acceptably low levels, whether it originates from the material in contact with the plastic article, the original plastics, or the recycling process itself.