Diatoms, known as Bacillariophyta (previously Bacillariophyceae), are single-celled, photosynthetic organisms. The unique feature about these organisms is a structure called a frustule, which comprises two silica cell walls known as Theca. These thecae form a sandwich-like structure of two halves that fit together. Based on the frustule structure, these organisms are sub-classified into the orders Centrales and Pennales. The Centrales are radially symmetric, while the Pennales have bilateral symmetry [5].

Classification of Bacillariophyta relies on several factors. The size of these organisms can range from 2 to 200µm. Along with high variation due to size difference, the silica cell wall of Bacillariophyta is heavily decorated with a plethora of structures such as spines, ridges, elevations, pores, and ribs, which simplifies the process of identifying genera and species [13].

Diatoms exhibit notable significance across multiple disciplines. In the realm of environmental studies, Diatoms establish a clear, identifiable association between their community’s composition and the physicochemical parameters of the environment in which they are formed. [5], While in the field of forensic science, diatoms can deliver crucial aid in the investigation of cases involving deaths due to drowning.

Since the outer structure of Bacillariophyta is made up of silicon dioxide, their decomposition is a very arduous and time-consuming process. As a result, their presence in decomposed bodies is a common occurrence. However, since these organisms are independent and photosynthetic, their presence in a body cannot be ruled out as a natural occurrence. The presence of a diatom species in a drowned dead body and at the site of recovery can be considered as evidence corroborating death due to drowning. Research conducted on drowning cases has revealed that diatoms present in the water body penetrate the alveolar system and bloodstream of the victim due to breathing in water. This in turn causes the diatoms, specifically of pennate order, to perforate the soft tissues and diffuse into the organs of the victim such as lungs, kidneys, and in some cases brain and bone marrow. Forensic science laboratories all across the globe are often tasked with detecting diatoms in organs of drowned victims such as the femur, bone marrow, liver, and lungs Establishing a correlation between the species of Bacillariophyta extracted from tissue samples and the species found at the site of recovery is a crucial step in the investigation of drowning cases as it can confirm the site of drowning. Cases of Antemortem drowning are confirmed through the detection of diatoms in the bone marrow [17].

The principle behind the investigative test for diatoms is based on the fact that microalgal species diffuse through the soft tissues of the victim due to active respiration while struggling. These microalgae, along with the inhaled water, are then distributed throughout the body via systemic circulation to various organs. Thus, one can infer that the determination of the manner of death is significantly aided by quantitative and qualitative analysis of diatoms. It is observed that in cases of antemortem drowning, the diatom count exceeds in body organs as a result of struggle, while in post-mortem drowning, the count remains negligible. Reference samples of the suspected water bodies where drowning took place are often required to compare the diatoms observed from a drowning case. Thus, a systematic record of various species of Bacillariophyta can be prepared through mapping of the relevant water bodies present in that region. This systematic record can significantly aid in the investigation of drowning cases [10].

On a national scale, drowning accidents have left a significant impact on the statistics as observed by the concerned agencies. According to a survey conducted by the National Crime Records Bureau, published in their 2022 report on Accidental Deaths and Suicides, it was observed that 7,00,688 reports were filed under accidents due to other causes, among which 4,22,444 people died and 4,28,435 were reported injured. Among these, 9.1% of cases were due to drowning-related incidents. Drowning was reported as the cause of 38,503 deaths, an increase of 5.1% from the previous year’s statistic of 36,362 reported deaths. Among reported deaths in Madhya Pradesh alone, the largest statistic for reported deaths (5,427 out of 38,503) was filed under drowning accidents [2].

Moving towards the focus of this study, in the Indore region alone, multiple cases of drowning incidents, both accidental and homicidal, have been reported in the past. There have been reports of accidental drowning in Bilavali Lake [18], Regional Park [11], and multiple reports of accidental drownings in Sirpur tanks [19], [8], [4], [15]. Incidents like these highlight the significance of Diatom-based study as a crucial tool for forensic analysis.

The prime intention of this study is to map out selected water bodies of the Indore region by recording the variation of diatom population present in them, namely, Bilawali Lake, Gulawat Lake, Regional Park Lake, Sirpur Upper Tank, and Sirpur Lower Tank for diatomological mapping. On an interdisciplinary level, mapping out water bodies in this manner periodically can aid in continuous observation of diatom flora concerning changes in the physiochemical parameters of the concerned water body due to pollution or other environmental factors, while also keeping relevance to the contemporary fields of significance such as forensic science and environmental studies. Concerning forensic relevance, in cases involving malicious intent, or cases where the victim is relocated due to external factors such as human activity, an attempt to hide evidence, or by natural factors like flowing water or animal activity, this systematic record of diatom helps to characterize the exact place of drowning.

The geographical location of the Indore District lies in the western part of Madhya Pradesh state between Latitude 22.719568 and Longitude 75.857727 [20]. Despite being a populated city, Indore exhibits a variety of wildlife, abundant in flora and fauna, which depends on various waterbodies within and around the city. These places naturally evolve into tourist attractions and, consequently, become susceptible to drowning accidents. Among these, five random locations were selected for this study: Bilawali Lake, Gulavat Lake, Regional Park, Sirpur Lower Tank, and Sirpur Upper Tank.

Analysis of micrographs prepared for the study of the diatom population across five chosen sites revealed distinct patterns of variation, which were captured through the utilization of both qualitative and quantitative approaches. Identification of genera for different diatoms and the variation in distribution across five sites were confirmed statistically. The micrographs from five locations and their subsequent statistical analysis are as follows:

The findings of this study indicate a periodic, detailed analysis of the diatom genera, which can significantly aid in forensic and environmental endeavors. This study provides a significantly more comprehensive cataloging of diatom species than prior attempts, with enhanced imaging facilitating more accurate identification and documentation [13]. Since these water bodies are also proven tourist hotspots and have historically been involved in drowning incidents, by systematically surveying these locations, this research addresses critical gaps in forensic limnology [2],[4],[8],[11],[14],[17],[18]. At a local level, a location-specific database of observed genera can serve as a significant forensic tool in the arsenal of investigators in determining drowning sites. A species-specific study of these locations, focusing on the factors responsible for such variations, can also aid in the identification of possible pollutants. Since these water bodies are hotspots for significant tourist activity and have reported cases of drowning incidents, this comprehensive approach establishes a valuable forensic reference framework, both as a forensic tool and an environmental indicator.