Students' foundational understanding of chemical reaction in the forensic science bachelor's degree program at the National Autonomous University of Mexico

OBJECTIVE

To compare the understanding of the concept of chemical reaction-as operationalized by Bloom's taxonomy of cognitive levels-of students in forensic science bachelor's degree with that achieved by students majoring in chemistry, as a prerequisite for future professional collaboration and communication.

MATERIALS AND METHODS

Using previously validated and published tests developed to assess students' knowledge, comprehension, and application of the concept of chemical reaction, we explored how conceptual understanding developed in students enrolled in (a) a forensic science degree program in a Mexican public university and in (b) chemistry undergraduate programs offered by the same university, and whether both groups achieved comparable attainment levels.

FINDINGS AND IMPLICATIONS

Despite receiving considerably less chemical instruction, forensic science students achieved comparable levels of conceptual understanding of chemical reaction to those exhibited by chemistry students. This finding is encouraging because it might mean that future forensic scientists could graduate with a solid foundation of chemical knowledge. More research, particularly on the learning of other key concepts, will be needed to verify these initial findings.

Effect of Malathion on the Development of Megaselia scalaris (Loew, 1866) (Diptera: Phoridae), a Forensically Important Fly

Malathion is a widely used organophosphorus pesticide; it is also a molecule of forensic interest due to its moderate to high toxicity in nontarget organisms, humans included. This compound is present in some fatal intoxications, accidental or intentional; its presence in the tissues on which the cadaveric entomofauna feeds may affect its growth rate and life cycle duration leading to an error in the estimation of the minimum postmortem interval (PMImin). Since the toxic effect of malathion on the cadaveric entomofauna could affect the estimation of the PMImin, the aim of this work was to study the toxic effect of malathion on the growth and development of the scuttle fly, Megaselia scalaris, a fly of forensic interest which plays an important role in forensics cases related to human remains found indoors or in concealed environments. The study was complemented with some morphological observations; no morphological changes were observed in the larvae, nor the adult flies exposed to malathion. Malathion affects the viability of the egg and pupa, it also reduces the larval growth rate and increases the duration of the larval stage; therefore, the estimation of the PMImin, with this species when malathion is present in tissues, could be affected.

Standardization of a Culture Medium for Megaselia scalaris (Diptera: Phoridae) for Entomotoxicological Studies

One of the problems faced by entomotoxicological studies is the large variability of experimental set-ups and the absence of harmonized protocols to compare the data and results obtained by different research groups. Among the wide range of influencing factors on the development and growth of insects, food substrates are remarkably relevant. This article proposes a standardized growth medium to be employed in future entomotoxicological studies on the scuttle fly Megaselia scalaris (Loew, 1866), (Diptera: Phoridae). This species plays an important role in forensic cases related to the decomposition of human remains found indoors and/or in concealed environments, because of their small size and ability to enter these locations at an earlier time than many other insects. Because of these traits, it can be used for the estimation of the minimum postmortem interval (mPMI). We achieved the formulation of a medium that overcomes two traditional disadvantages of culture media used to raise necrophagous Diptera, the unknown media composition and different growth rates from those reared in tissue. The proposed medium is a known composition formulation, free of xenobiotics, in which M. scalaris shows growth rates and development times similar to those obtained when it is reared in tissue. This new diet might be used in future studies to test the effect of substances of forensic interest (prescription or illicit drugs, poisons, etc.) on the larval development time, helping to adjust the estimation of mPMI based on the presence of such substances. Additionally, the formulation revealed some interesting data about nutritional requirements of this species.