Abstract
In this study, we present entomotoxicological data on the accumulation of cadmium and thallium in a forensically important blowfly, Lucilia sericata, and evaluate the reliability and utility of such information as toxicological evidence for poisoning as a cause of death. We observed that Cd and Tl content in different growing stages of L. sericata (larvae, puparial cases, and adults) was increasing with increasing metal concentration in the feeding substrate, namely metal-enriched liver. However, patterns of accumulation differed between the two metals investigated, showing a linear relationship for Cd and a saturable pattern for Tl. For cadmium, the highest bioaccumulation factor (BAF) was found in the larval stage (in the range of 0.20–0.25), while for thallium, puparial cases accumulated more metal than the other stages tested (BAF in the range of 0.24–0.42). Thallium was also observed to have a negative effect on larval growth, resulting in lower weight and smaller puparial size. With this study, we update the information on the bioaccumulation of cadmium in forensically important blowflies and provide the first report on the bioaccumulation of thallium as well as its developmental impact in blowflies. Specifically, our results suggest that analysis of puparial cases could yield useful information for entomotoxicological investigations. The content of Cd and Tl in larvae, puparial cases, and adults of L. sericata was determined by inductively coupled plasma mass spectrometry (ICP-MS). The validation parameters of the method such as sensitivity, detection limits, quantification limits, precision, and accuracy were evaluated. The method detection limit (MDL) for all types of samples was in the range of 1.6–3.4 ng g−1 for Cd and 0.034–0.15 ng g−1 for Tl, and the accuracy of the method was confirmed by a high recovery of metals from certified reference materials (91.3% for Cd and 94.3% for Tl).
Highlights
Forensic entomology is commonly associated with death investigations, in which its main application is in determination of the minimum postmortem interval
We demonstrate that larvae, adults, and empty puparial cases of L. sericata found on decomposing human remains, can be used as an alternative material for the detection of Cd and Tl present in the body at the time of death
Of the three developmental stages analyzed, the highest average content of Cd was found in larvae, whereas for Tl, the highest bioaccumulation factor was observed for puparial cases
Summary
Forensic entomology is commonly associated with death investigations, in which its main application is in determination of the minimum postmortem interval (minPMI) This is accomplished by estimating the time of insect colonization, based on knowledge of the rate of development of pioneer colonizers and on the succession of different insect species during the decomposition of animal/human remains (Greenberg, 1991; Campobasso et al, 2004; Bugelli et al, 2017a). Of the many species that may be present on or in a dead body, blowflies (Diptera: Calliphoridae) are usually the first to appear on the crime scene, and they may provide crucial information—such as the cause of death— months or even years after body decomposition (Wang et al, 2008; Byrd and Castner, 2010; Braga et al, 2013) This approach was first used in 1980, when phenobarbital was detected in fly larvae collected from a skeletonized body. There have been some critiques of the use of entomotoxicology in forensic science (Gaudry et al, 2001; Tracqui et al, 2004), many studies have shown that insects can provide reliable evidence in toxicological analysis during criminal investigations (Silva et al, 2017; Chophi et al, 2019)
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