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

The research team, led by Vanessa DeClercq and Morgan G. I. Langille of Dalhousie University’s Faculty of Medicine, designed their study specifically to confront one of the most persistent controversies in microbiome science: whether bacteria genuinely reside within tumours and circulate in the bloodstream of cancer patients, or whether the DNA sequences detected in such samples are artefacts of laboratory contamination and the extraordinary sensitivity of modern sequencing technology. To do this, they applied an unusually comprehensive battery of molecular techniques to every sample, including full-length 16S rRNA gene amplicon sequencing, nested short-read 16S amplicon sequencing, metagenomic shotgun sequencing, and digital PCR for absolute quantification of bacterial DNA. Crucially, every sample was processed in duplicate, providing technical replicates against which the reliability of each measurement could be judged.

The results were striking in their asymmetry. When the researchers attempted full-length 16S gene sequencing on their lung tumour, adjacent lung tissue, and blood samples, the technique failed to generate usable data for nearly all of these specimens. This was not a subtle signal-to-noise problem but a fundamental inability of the method to amplify meaningful bacterial genetic material from samples that contained, in effect, almost nothing to amplify. In contrast, saliva samples and positive control specimens, which harbour rich and genuine microbial communities, yielded abundant, high-quality sequence data with strong reproducibility between replicates, confirming that the laboratory pipeline itself was functioning correctly.

A second strategy, nested short-read 16S sequencing, did manage to produce sequence data from the low biomass samples, but what it produced was far from reassuring. The tumour, adjacent tissue, and blood specimens contained very few bacterial taxa, and even those few varied dramatically between technical replicates of the same sample. When the researchers compared the taxonomic composition of these samples with their negative controls, which track DNA introduced during sample collection and laboratory processing, the low biomass specimens proved compositionally indistinguishable from the controls. In other words, there was no reliable way to tell a genuine tumour-associated bacterial community from background contamination picked up along the way.

Digital PCR provided the quantitative backbone for these observations. Unlike standard sequencing, which describes the relative proportions of different bacteria but says little about how much DNA is actually present, digital PCR counts target molecules directly, delivering an absolute measurement of bacterial biomass. The measurements confirmed what the sequencing results implied: lung tumour, adjacent tissue, and blood samples contained extremely low quantities of bacterial DNA, comparable to the levels found in negative controls. Saliva samples, by contrast, carried orders of magnitude more bacterial DNA. This quantitative gulf between genuinely microbe-rich samples and the near-sterile tumour and blood specimens goes to the heart of the technical challenge, because at such low biomass, even trace amounts of contaminating DNA from reagents, laboratory environments, or collection procedures can dominate the apparent microbial profile.

Metagenomic shotgun sequencing, which reads DNA across the whole genome rather than targeting a single gene, told a consistent story. In the lung tumour, adjacent tissue, and blood samples, this approach detected very few taxa, and, importantly, there was minimal overlap between the taxa identified by metagenomic sequencing and those identified by 16S sequencing from the same specimens. If the detected bacteria reflected real communities resident in the tumours, one would expect at least reasonable agreement between independent methods probing the same DNA. Saliva and positive control samples, in contrast, showed substantial overlap of detected genera across methods, exactly what one would expect when a genuine, abundant microbial community is being measured. The discordance in the low biomass samples is a hallmark of noise rather than signal.

These findings matter because the idea of a tumour microbiome has moved rapidly from curiosity to potential clinical application. Several high-profile studies have claimed that distinctive bacterial profiles can be found in tumours and circulating blood, and that these profiles might serve as biomarkers for early detection, prognosis, or treatment selection in cancers including lung cancer. If bacterial signatures could be read reliably from a blood sample, the logic goes, clinicians might one day supplement or even replace invasive biopsies with a simple liquid biopsy. But the new study demonstrates that, at least for lung cancer, the technical foundations of such ambitions remain shaky. The bacterial signals in tumour and blood samples were both weak, meaning barely above background, and inconsistent, meaning they failed to replicate even within the same sample processed twice.

The study’s methodological rigour is itself a lesson for the field. Technical replicates, in which the same sample is independently extracted, prepared, and sequenced, provide a direct test of measurement precision. The researchers found that while high biomass samples like saliva produced highly concordant replicates, the low biomass tumour, tissue, and blood specimens yielded wildly divergent replicate profiles, a clear indicator that the apparent diversity was driven by stochastic contamination rather than stable biological communities. The authors argue that this kind of replicate testing, combined with alternative sequencing strategies and absolute quantification of bacterial DNA, should become standard practice before any microbiome finding from low biomass samples is accepted as biologically meaningful.

The contrast between the different sample types in the study also offers a measure of reassurance about the underlying methods. Saliva proved to be highly diverse, strongly reproducible across replicates, and concordant across sequencing platforms, while positive control samples behaved as expected throughout. This means the researchers’ negative findings cannot be dismissed as a failure of their equipment or protocols. Instead, the problem appears to be intrinsic to the samples themselves: the lung tumours, adjacent lung tissue, and blood of these patients contained so little bacterial DNA that no current methodology could reliably distinguish any true signal from the noise of collection and processing environments. Whether lung tumours truly harbour sparse bacterial communities or none at all remains an open question that this study suggests may be extraordinarily difficult to answer.

For patients and clinicians hoping for microbiome-based diagnostics in lung cancer, the message is one of tempered expectations rather than closed doors. The authors emphasise that their work provides important insights into site-specific microbiomes from lung cancer patients and into the formidable challenges of assessing the tumour microbiome, and they call on the research community to adopt more rigorous validation standards before clinical claims are built on fragile data. As the field grapples with reproducibility concerns that have shadowed tumour microbiome research in recent years, this study stands as a model of the kind of scrutiny required: multiple sequencing approaches, technical replicates, careful controls, and absolute quantification, all applied to the same specimens. Only through such disciplined methods, the researchers conclude, can the field separate genuine biology from artefact and determine whether the dream of reading cancer’s microbial signature is grounded in reality or destined to dissolve at the boundaries of detection.

Subject of Research: Microbiome profiling of lung tumour and blood samples from lung cancer patients using replicates and multiple sequencing methods

Article Title: Technical replicates and multiple sequencing approaches reveal weak and inconsistent microbiome signals in lung tumour and blood samples from patients with lung cancer

Article References: DeClercq, V., Comeau, A. M., Kwawukume, A., Murphy, R., Parmar, N. R., Quinn, D. P., Wright, R., Wallace, A., & Langille, M. G. I. (2026). Technical replicates and multiple sequencing approaches reveal weak and inconsistent microbiome signals in lung tumour and blood samples from patients with lung cancer. Microbiome. https://doi.org/10.1186/s40168-026-02529-z

Image Credits: AI Generated

DOI: 10.1186/s40168-026-02529-z

Keywords: tumour microbiome, lung cancer, 16S rRNA sequencing, metagenomics, digital PCR, low biomass samples, contamination, technical replicates, bacterial biomarkers, microbiome reproducibility, non-small cell lung cancer, liquid biopsy

Reppe is located in the Kolfe Keraniyo Sub-city of Addis Ababa, where an open dumpsite established in 1964 has become surrounded by expanding residential communities. The site now receives ash from the nearby waste-to-energy plant, creating a direct connection between incineration residues and a long-used disposal area that lacks the engineered barriers found in a modern sanitary landfill. In such settings, rainfall can pass through waste and ash, producing leachate that dissolves or carries contaminants into surrounding soils and potentially toward groundwater. To investigate that pathway, the researchers collected three bottom-ash samples and three fly-ash samples from the plant’s ash-handling system, along with six surface-soil samples from a transect extending from the ash deposition zone toward the nearest residential area. The soil was sampled at depths of 0 to 15 centimetres, the biologically active surface layer most relevant to contact, dust and other exposure routes. Sampling took place during February and March 2024, the dry season, when rain-driven dilution was less likely to obscure contamination patterns.

In the laboratory, the team processed half-gram portions using United States Environmental Protection Agency Method 3050B, an acid-digestion procedure designed to release metals from soil and solid material before instrumental measurement. Chromium, copper, lead and zinc were measured with flame atomic absorption spectrophotometry; cadmium was measured with graphite-furnace atomic absorption, which is more sensitive at low concentrations; and mercury was analysed using a cold-vapour or hydride-generation approach. Each sample was analysed in triplicate. Quality-control procedures included certified reference materials, procedural blanks, daily calibration and replicate testing. Recoveries from the reference materials ranged from 92 to 105 per cent, while relative standard deviations were below 5 per cent. These checks indicate that the analytical procedures were precise for the samples tested, although the study’s conclusions remain limited by the small number of samples and the absence of a local uncontaminated reference soil. Instead, background values used in several calculations came from average upper-continental-crust concentrations, which may overestimate or underestimate enrichment at a particular Ethiopian site.

The most striking results came from the ash. The study reports mercury concentrations reaching 2,630 micrograms per litre and cadmium concentrations reaching 1,530 milligrams per litre in ash samples, with values varying substantially between locations and ash types. The reported mercury maximum was thousands of times higher than the comparison soil limit cited in the study, while the cadmium maximum was hundreds of times above the World Health Organization guideline used by the researchers. Because mercury and cadmium are toxic at relatively low concentrations and can be mobile under suitable chemical conditions, their presence in loosely managed ash is especially important. The study’s contamination-factor analysis identified mercury as the dominant contaminant, with ash values ranging from 12.9 to 65.8 times the chosen background. Cadmium showed moderate to severe enrichment, particularly in fly ash, whereas chromium, copper, lead and zinc generally displayed much lower contamination factors relative to the background used. The authors describe the resulting ash profile as mercury-dominated, followed by cadmium, with the other metals contributing less to enrichment.

The distinction between bottom ash and fly ash helps explain why combustion residues can concentrate particular contaminants. Bottom ash is the heavier material that remains in the furnace, while fly ash consists of finer particles carried with combustion gases and captured by pollution-control equipment. During incineration, volatile elements such as mercury and cadmium can enter the gas phase and later condense onto fine particles as the gases cool. Those particles may therefore carry a disproportionate share of certain metals. Statistical results from the Reppe ash samples support this interpretation. Principal-component analysis found that two components explained 94.5 per cent of the total variation. The first, accounting for 70.5 per cent, carried strong loadings for lead, cadmium and copper, a grouping the researchers associate with anthropogenic combustion sources such as mixed municipal waste, batteries and electronic materials. The second explained 24 per cent and was linked mainly to chromium and mercury, suggesting a combination of geochemical background and combustion-related behaviour. A strong positive correlation between lead and cadmium, reported as r = 0.91, further indicates that these elements may share a common source in the ash.

The risk calculations translate those concentrations into a broader ecological warning. The study’s total ecological-risk index for every ash sample fell between 1,086 and 3,000, well above the threshold of 600 classified as very high risk in the assessment framework. Mercury contributed more than 80 per cent of the total toxicity-unit values in the ash samples, reflecting both its measured concentration and its high toxic-response factor. Some bottom-ash samples had summed toxicity units above eight, while fly-ash values ranged from 2.93 to 4.88; the authors interpret these results as evidence that the material should be handled as hazardous waste rather than placed in an uncontained dump. The numbers are screening and assessment metrics, not direct measurements of human illness or exposure. They indicate the potential for ecological harm if contaminants are released, inhaled as dust, ingested or transported into water, but they do not by themselves establish the health risk to a particular resident. That distinction matters, especially because the study did not conduct biomonitoring, groundwater testing or epidemiological assessment.

Soils along the leachate-affected transect contained lower metal concentrations than the ash, yet mercury remained the dominant concern. Reported mercury values in the soil samples ranged from 205 to 1,015 micrograms per litre, and contamination factors ranged from 5.1 to 25.4 times the selected background. Three soil samples had ecological-risk indices at or above 600, placing them in the study’s very-high-risk category, while the full range for soils was 255 to 1,065. Cadmium was generally less enriched according to the contamination-factor analysis, and chromium, copper, lead and zinc were often near the chosen background values. However, correlations among chromium, copper and lead suggested that localized waste disposal or metal-bearing refuse had influenced parts of the transect. Mercury behaved differently: its inverse relationship with some of those metals and positive association with zinc were consistent with separate combustion and atmospheric-deposition pathways. The findings therefore do not describe a uniform plume. They show a heterogeneous site where some contaminants remain close to the ash source, while mercury may be redistributed through volatilization, condensation, leachate movement and re-emission.

Source-apportionment results estimated that anthropogenic inputs accounted for 58 per cent of the metal signal in ash and 38 per cent in leachate-impacted soil, with the remainder assigned to geogenic or mixed sources. Those percentages are model-based estimates rather than direct measurements of individual waste streams, and they depend on the background assumptions and the small dataset. Still, they reinforce the central message: the contamination cannot be explained solely by the natural composition of local soil. The authors recommend that ash, particularly fly ash exceeding hazardous-waste thresholds, be stabilized and disposed of in engineered facilities equipped with leachate collection rather than placed in the open dumpsite. They also call for groundwater monitoring, restricted access to high-risk areas, remediation of contamination hotspots and stronger national standards for waste-to-energy residues. Separating batteries, electronic waste and mercury-containing products before combustion could reduce the metals entering the ash. The study sampled a plant operating at less than half capacity, so contamination could differ with full operation or changes in the waste feedstock. Even with those limitations, the results offer a baseline for Addis Ababa and a broader warning: converting waste into energy does not eliminate hazardous elements, and the safety of the system depends on how its ash is contained after combustion.

The study’s dry-season design provides a snapshot of conditions when rainfall was unlikely to dilute surface contamination, but it cannot establish how concentrations change during wet periods. Seasonal sampling would help determine whether intensified runoff mobilizes metals beyond the sampled transect or instead redistributes them within the dump. Likewise, the six soil samples were selected purposively along visible leachate pathways, making them useful for identifying hotspots but unsuitable for estimating contamination across the entire dumpsite. Additional samples from uncontaminated soils, different depths and groundwater would improve comparisons and clarify whether metals are retained near the surface or migrating downward.

The reported measurements also require careful interpretation because the study expresses some ash and soil results in mass-per-volume units, whereas ash and soil are solid matrices. Direct comparison with soil guidelines therefore depends on the extraction and reporting basis used. Risk indices are valuable for prioritizing investigation, but they combine measured concentrations with toxicity factors and reference values; they are not substitutes for exposure measurements. Follow-up work could pair chemical testing with leachability experiments, dust monitoring and bioavailability analyses. Such evidence would show which fraction of the total metal burden can actually move into water, air or living organisms, helping regulators design controls proportionate to the site’s most plausible exposure pathways.

Subject of Research: Heavy-metal contamination in waste-to-energy ash and leachate-impacted soils

Article Title: Heavy metal contamination in thermal power plant ashes and leachate-impacted soils at Reppe dumpsite in Addis Ababa, Ethiopia

Article References: Tamene, M., Admassu, T., Alemayehu, T., & Mekonen, S. (2026). Heavy metal contamination in thermal power plant ashes and leachate-impacted soils at Reppe dumpsite in Addis Ababa, Ethiopia. Discover Soil, 3(1), Article 145. https://doi.org/10.1007/s44378-026-00291-0

Image Credits: AI Generated

DOI: 10.1007/s44378-026-00291-0

Keywords: heavy metals, mercury, cadmium, waste-to-energy, fly ash, leachate, soil contamination, ecological risk, Addis Ababa, Heavy, metal, contamination