The global trend towards utilizing local resources has highlighted the need for research into readily available natural materials. Freshwater sapropel, a common lake sediment, presents such an opportunity. This study aims to systematically investigate the medical properties of Latvian sapropel, paving the way for its scientifically-based application in balneology and the development of new pharmaceutical products. Sapropel, a complex mixture of organic matter, microorganisms, and minerals, has a long history of traditional use for health improvement. However, scientific understanding of its composition, bioactive components, and potential applications remains limited. This research bridges this gap by characterizing Latvian sapropel samples from various locations, assessing their suitability for pharmaceutical use, and considering the relevant legislation and environmental impacts associated with its extraction and processing. The importance of this research extends to sustainable resource management, promoting economic development through the creation of new, exportable products, and advancing the understanding of sapropel's therapeutic potential.

Existing literature highlights sapropel's diverse applications, including agriculture and cosmetology. Studies have shown its potential for improving soil properties (Bakšienė & Janušienė, 2005; Blečić et al., 2014) and as an ingredient in cosmetic formulations (Strus et al., 2018; Strus, 2015). However, research focusing on its biomedical and biopharmaceutical potential remains scarce. Previous work has examined the accumulation of metals in sapropel (Stankevica et al., 2012; Stankevica et al., 2014), and its biological characteristics (Tretjakova et al., 2015). The study by Schepetkin et al. (2002) focused on medical drugs derived from humus matter, providing a broader context for understanding sapropel's bioactive compounds. While some studies have explored sapropel processing for high added-value products (Obuka et al., 2018; Kļaviņa et al., 2019), a comprehensive assessment specifically targeting pharmaceutical applications is lacking. This research addresses this gap by providing a detailed analysis of sapropel's composition and safety parameters in the context of pharmaceutical regulations.

The research involved a multi-step process, beginning with the selection of five Latvian lakes based on factors such as sapropel deposit depth, hydrological regime, agricultural history, and potential industrial waste exposure. One hundred and five sapropel samples were collected during winter, from three different depths at multiple points in each lake. The methodology encompassed detailed characterization of the sapropel, including organoleptic analysis (color, texture, smell), determination of dry matter content, and classification into organic, silica-containing, carbonate, or mixed types. Active components were extracted using an alkaline method. Subsequent analysis included measuring total organic carbon (TOC), humic acid (HA), and fulvic acid (FA) concentrations using spectrometry. The pH level was determined using distilled water. Organic matter and carbonate content were assessed using the loss-on-ignition (LOI) method. Trace metal (Pb, Cd, Ni, Co, Cu, Sb, Cr) and pesticide (DDE/DDT) concentrations were determined using electrothermal atomic absorption spectrometry and ELISA, respectively. Total phenolic content (TPC), total antioxidant status (TAS), and DPPH radical scavenging activity were measured using established methods. Finally, microbiological analysis was conducted by the Institute of Food safety, Animal Health and Environment "BIOR", using standard ISO 4833-1:2013 for colony-forming unit (CFU) counts and species identification. The sampling and analysis procedures followed established guidelines (LVS EN 1997-2 AC:2014 L), ensuring data quality and reproducibility.

The study revealed variations in sapropel characteristics across the sampled lakes and depths. Organoleptic properties varied from greenish-yellow to almost black, correlating with silica and organic matter content, respectively. The pH levels ranged from 7 to 8, indicating a high mineral content. Trace metal analysis showed the presence of Pb, Cd, Co, Ni, and Cu in all samples, but concentrations remained below maximum acceptable levels according to SCCS guidelines. Some samples exhibited detectable levels of DDT and DDE, although concentrations were below the limit of quantification in most cases. Antioxidant activity, linked to HA and FA concentrations, varied significantly between lakes, with Audzelu, Mazais Kivdalovas, and Zeilu lakes showing the highest levels. Microbiological analysis revealed a range of bacterial species, some with potential antimicrobial properties and others considered opportunistic pathogens. CFU/g counts were significantly higher than permissible limits for cosmetic or medical applications in all samples. This indicates the need for sterilization or addition of preservatives before use.

The findings demonstrate the potential of Latvian sapropel as a source of bioactive compounds for pharmaceutical applications. The presence of antioxidants and various minerals indicates potential benefits for skin health and other therapeutic uses. However, the microbiological analysis highlights the need for rigorous quality control to eliminate potential pathogens before utilization in pharmaceutical products. The presence of trace metals and pesticides emphasizes the importance of careful selection of sampling locations to minimize contamination risks. Future research should focus on developing effective sterilization or preservation methods to meet regulatory standards while maintaining the sapropel's bioactive components. Further investigation into the specific bioactive molecules present in sapropel and their mechanisms of action is also needed to fully realize its pharmaceutical potential. The legal framework governing sapropel extraction and use must be carefully considered to ensure both sustainable resource management and adherence to environmental protection regulations. This research contributes significantly to the development of new, locally-sourced pharmaceutical products and services, promoting economic growth while considering environmental sustainability.

This study demonstrates the potential of Latvian freshwater sapropel for pharmaceutical applications, identifying its richness in bioactive compounds and minerals, but also highlighting the need for rigorous quality control measures to eliminate potential pathogens and contaminants. Future research should focus on optimization of extraction methods, development of sterilization protocols, and detailed characterization of specific bioactive molecules. These findings offer a strong foundation for the development of new pharmaceuticals derived from this readily available natural resource. Further research is also needed to fully explore the potential health benefits and to ensure safe and sustainable utilization of sapropel.

The study is limited by the relatively small number of lakes sampled and the specific time of year the samples were collected. Further research should include a wider range of lakes and sampling across different seasons to establish a more comprehensive understanding of sapropel variability. Additionally, the analysis focused on a specific set of parameters, and future studies might explore other potential bioactive compounds and their associated activities. Finally, this research focuses on the potential of sapropel for pharmaceutical use, further economic and ecological studies are necessary for wider application and industrial development.