Understanding the mechanistic interaction between DNA and polystyrene microplastic and the effect of microplastic on forensic DNA analysis.

Microplastics contamination in the forensic biological samples and their possible detrimental effect on forensic DNA profiling is least explored. In-silico prediction showed more favourable interaction of polystyrene with Taq DNA polymerase (-4.57 kcal/mol) and the mtDNA HVI region (-1.98 kcal/mol). It showed a higher interaction with D8S1179 (-1.95 kcal/mol), followed by D13S317 (-1.93 kcal/mol), D21S11 (-1.89 kcal/mol), and D2S1338 (-1.53 kcal/mol) STR markers. ATR-FTIR analysis revealed the involvement of deoxyribose C-O stretching peak (1066 cm⁻¹ to 1047 cm⁻¹), phosphate asymmetric stretch (1242 cm⁻¹ to 1260 cm⁻¹), and purine ring C-N stretching (671 cm⁻¹ to 737 cm⁻¹) during the interaction of polystyrene with CT-DNA. 0.5 ng and 1.0 ng of control DNA were estimated as 0.027 ng and 0.046 ng respectively, in presence of 25 to 100 µg/ml polystyrene by RT-PCR. Treated sample IPC Ct value (27.72) did vary significantly compared to the control samples (27.83), suggesting fluorescence interference of polystyrene contributed to underestimation of DNA quantity. Spiking of 25 µg/ml of polystyrene adversely affected the amplification of D10S1248, TH01 and D12S391 markers. Peak height imbalance of the QS markers (0.44) suggested a significant PCR inhibition by 100 µg/ml of polystyrene MPs. All the tested concentrations of the MPs showed a significant detrimental effect on the quality of the DNA profiles. Such compromised profiles might complicate the analysis of LT-DNA samples and mixed profiles. Thus, the microplastics contamination in the forensic biological samples warrants immediate action and suitable mitigation strategies should be developed to increase the robustness of the routine forensic DNA workflow.