Microplastics May Sabotage Forensic DNA Evidence, Study Warns

Polystyrene microplastics, the tiny fragments shed from everything from disposable coffee cups to packaging foam, have now been caught interfering with one of the most sensitive tools in modern criminal justice: forensic DNA profiling. In a study published in the International Journal of Legal Medicine, researchers from Centurion University of Technology and Management, the State Forensic Science Laboratory in Bhubaneswar, and partner institutions in India report that even modest concentrations of polystyrene particles can distort DNA quantification, suppress the amplification of key genetic markers, and degrade the quality of the DNA profiles that courts rely on. The finding lands at an uncomfortable moment, because microplastics are no longer an exclusively environmental problem. They have been detected in human blood, sputum, skeletal tissue, and organs, which means they can now travel inside the very biological samples—bloodstains, tissue, saliva—that forensic scientists collect at crime scenes.

The team began with a computational question: does polystyrene physically interact with the molecular machinery of DNA analysis? Using in-silico docking, they modeled how polystyrene binds to Taq DNA polymerase, the heat-stable enzyme that copies DNA during the polymerase chain reaction, or PCR. The predicted binding energy was a favorable −4.57 kilocalories per mole, suggesting the polymer does not merely float passively beside the enzyme but engages with it in ways that could disrupt its catalytic work. The researchers then turned to the DNA itself, docking polystyrene against the mitochondrial DNA HVI region, a workhorse target in forensic sequencing, and against four short tandem repeat markers that anchor human identification: D8S1179, D13S317, D21S11, and D2S1338. The interaction energies ranged from −1.95 to −1.53 kilocalories per mole, with D8S1179 showing the strongest association. In plain terms, the plastic showed a measurable chemical affinity for the exact genetic regions forensic laboratories amplify every day.

Computational predictions, however, are only as good as their experimental confirmation. To probe what happens to DNA at the molecular level when polystyrene is present, the team used attenuated total reflectance Fourier-transform infrared spectroscopy, or ATR-FTIR, on calf thymus DNA mixed with the polymer. The spectra told a precise story. The deoxyribose C–O stretching peak shifted from 1066 to 1047 wavenumbers per centimeter, the asymmetric phosphate stretch moved from 1242 to 1260, and the purine ring C–N stretching band drifted from 671 to 737. Each of these shifts indicates that polystyrene is not a bystander: it perturbs the sugar-phosphate backbone and the nitrogenous bases of DNA, the very structures that primers must recognize and polymerases must read. A forensic assay depends on those molecular contacts happening cleanly and repeatedly; a plastic particle wedging itself into the chemistry undermines the entire chain of events.

The consequences showed up immediately in DNA quantification, the step that tells a laboratory how much human DNA a sample contains and therefore how to process it. When the researchers spiked known quantities of control DNA with polystyrene at concentrations between 25 and 100 micrograms per milliliter, the readings collapsed. A sample containing 0.5 nanograms of DNA was estimated at just 0.027 nanograms, and a 1.0-nanogram sample registered as 0.046 nanograms—underestimations by factors of roughly eighteen and twenty-two respectively. Part of the explanation lies in fluorescence interference. Real-time PCR instruments quantify DNA by reading fluorescent signals, and polystyrene is known to fluoresce and to absorb or scatter light in ways that scramble those readings. Notably, the internal positive control’s cycle threshold value barely moved, shifting from 27.83 in controls to 27.72 in treated samples, which suggests the problem was not classic PCR inhibition at the quantification stage but optical distortion—the instrument was effectively being blinded by the plastic.

Quantification errors alone would be serious, because an analyst who believes a sample contains almost no DNA may choose an aggressive low-template strategy or may even decline to test it at all. But the study found that polystyrene also attacks the amplification stage directly. When DNA spiked with 25 micrograms per milliliter of polystyrene was run through STR profiling, the markers D10S1248, TH01, and D12S391—all part of the expanded European and international standard sets—amplified poorly or dropped out. At 100 micrograms per milliliter, the quality-sensing markers within the quantification kit showed a heterozygote peak height balance of just 0.44, far below the balanced ratios expected in a clean reaction, which the authors interpret as significant PCR inhibition. The mechanism is likely multifaceted: polystyrene can sequester DNA strands and primers through the same binding interactions predicted in silico, compete with the polymerase, and interfere with the fluorescent chemistry that reports amplification progress.

The downstream effect on DNA profiles was consistent across every concentration the team tested. Short tandem repeat profiling, the backbone of human identification, depends on every locus amplifying reliably and symmetrically. When some markers fail, drop out, or produce imbalanced peaks, the resulting profile becomes harder to interpret, harder to match against a suspect or a database, and more vulnerable to challenge in court. The authors emphasize that such compromised profiles are especially dangerous for low-template DNA samples—the faint traces from a single touched surface, a fingerprint residue, or a hair—and for mixture samples containing DNA from multiple contributors, where every lost allele complicates the already delicate task of deconvoluting who contributed what. In other words, microplastic contamination hits hardest precisely where forensic science is already operating at its limits.

What makes the study timely is the growing recognition that microplastics are inside us. Recent reviews have documented polystyrene and other polymers in human blood, sputum, skeletal tissues, and a widening list of organs, and research on laboratory animals has linked polystyrene exposure to mitochondrial disruption and genotoxic effects. For forensic practitioners, this reframes contamination risk. It is no longer sufficient to think of sample contamination purely in terms of handling errors, environmental bacteria, or chemical inhibitors like humic acids and indigo dye. A victim’s or perpetrator’s own body may carry polymer particles into a bloodstain or tissue sample, and clothing, packaging, and plastic evidence bags may shed additional fragments onto exhibits during storage. The study’s authors, who have previously examined how metal contaminants interfere with STR analysis, position microplastics as an emerging contaminant class that forensic workflows have not yet been designed to detect or counter.

The researchers argue that the problem warrants immediate action and call for suitable mitigation strategies to strengthen the routine forensic DNA workflow. Practical responses could take several forms. Laboratories might incorporate purification steps that separate plastic particles from DNA before quantification, adopt quantification chemistries less susceptible to fluorescence interference, or add validation studies that characterize how common polymers—polystyrene, polyethylene, polypropylene, polyethylene terephthalate—affect each step from extraction to interpretation. Evidence-handling protocols could also be revisited, since plastic packaging is ubiquitous in forensic storage. The study stops short of prescribing specific remedies, but its message is clear: until mitigation exists, microplastic contamination is an unmeasured variable in casework, capable of silently shrinking DNA estimates by an order of magnitude and erasing genetic markers without any obvious warning sign to the analyst.

There is also a broader scientific payoff in the paper’s mechanistic approach. By combining docking predictions, infrared spectroscopy, quantitative PCR, and full STR profiling, the team built a coherent causal chain from molecular binding to profile degradation—a model that can now be applied to other polymers and other contaminants. The same framework previously illuminated how metals sabotage PCR, and it could guide the design of inhibitors-resistant enzyme formulations or buffer additives that shield DNA from polymer surfaces. For a field whose credibility rests on reproducibility, understanding why and how a contaminant distorts results is the first step toward neutralizing it. As microplastics continue to accumulate in bodies, waterways, and dust, the intersection of environmental pollution and forensic genetics is no longer hypothetical. This study provides the first detailed mechanistic account of how one of the world’s most common plastics collides with DNA evidence, and it suggests that crime laboratories worldwide may need to add a new item to their contamination checklist—one measured in microns.

Subject of Research: Mechanistic interaction between polystyrene microplastics and DNA and its impact on forensic DNA profiling

Article Title: Understanding the mechanistic interaction between DNA and polystyrene microplastic and the effect of microplastic on forensic DNA analysis

Article References: Yadav, N., Tehsin, S., Tanpure, D., Sahoo, S., Dash, A. A., Priyadarshini, K., Priyadarshini, P., & Dash, H. R. (2026). Understanding the mechanistic interaction between DNA and polystyrene microplastic and the effect of microplastic on forensic DNA analysis. International Journal of Legal Medicine. https://doi.org/10.1007/s00414-026-04017-3

Image Credits: AI Generated

DOI: 10.1007/s00414-026-04017-3

Keywords: microplastics, polystyrene, forensic DNA analysis, DNA profiling, STR markers, PCR inhibition, Taq DNA polymerase, ATR-FTIR, DNA quantification, low-template DNA, contamination, International Journal of Legal Medicine