Detection of Terbufos (Organophosphate) Intoxication in Necrophagous Larvae Using Biospectroscopy (ATR-FTIR) with
Jéssica Teixeira Jales1,2, Taciano de Moura Barbosa3, Hellyda Katharine Tomaz de Andrade Silva4
1Forensic Genetics Lab, Forensic Expert at the Scientific Police of Rio Grande Do Norte (PCI-RN), Natal, Rio Grande Do Norte, Brazil. jessica_jales@hotmail.com.
Abstract:
Entomotoxicology studies the effect and detection of different xenobiotics in scavenger insects, aiding in the correct estimation of the interval and cause of death. Terbufos (organophosphate) stands out in the forensic field for its association with intoxication cases. However, the methodologies for its detection remain laborious, expensive, and destructive for crime clues, with the need for simpler, accessible, and conservative tools for detection of this compound in the entomological evidence. Thus, this study aims to evaluate (i) Attenuated Total Reflection-Fourier Transform Infrared (ATR-FTIR) as a tool to differentiate larvae collected from negative control carcasses and those treated with terbufos and (ii) the overall sensitivity and specificity of the technique for identifying terbufos exposure in forensic contexts, discussing its applicability in real cases of organophosphate poisoning. For this, Lucilia eximia (Diptera: Calliphoridae) larvae (n = 120; 30/group), collected from rat carcasses previously treated with 5 (T1), 10 (T2), or 20 (T3) mg/kg of terbufos, as well as from untreated control carcasses (negative control-NC), were used for spectra collection and standardization of classification model. For data analysis, differentiation, and classification, unsupervised (PCA) and supervised (PCA-LDA, GA-LDA, and SPA-LDA) analysis algorithms were used. The PCA showed a tendency of differentiation between the analyzed groups. However, only with the supervised analysis algorithms, spectra from the negative control, T1, T2, and T3 groups were differentiated. The PCA-LDA and SPA-LDA algorithms specially differentiated the T3, T2, and NC groups, reaching an average 85% sensitivity and 90% specificity, while the GA-LDA showed 100% sensitivity and specificity, being the model of choice for analyzing this dataset. The main variables listed for sample differentiation were in the regions of protein phosphorylation, phosphate stretch, and protein content. Thus, this study showed that the ATR-FTIR coupled with multivariate analysis algorithms can efficiently differentiate larvae collected from carcasses non-intoxicated or intoxicated with different doses of terbufos, representing a viable, fast and efficient screening alternative for entomotoxicology.
