Assessment of sapropel use for pharmaceutical products according to legislation, pollution parameters, and concentration of biologically active substances

Sapropel, a complex organic sediment from lakes, has long been used in medicine, balneotherapy, and cosmetology for benefits such as wrinkle prevention, reduction of swelling, improved skin structure, and support of lymphatic and circulatory systems. Its bioactivity is largely attributed to humic and fulvic acids and other bioactive components with antioxidant and antibacterial properties. Despite its broad traditional use, standardized extraction and quality criteria remain limited. This study addresses the need to evaluate Latvian freshwater sapropel for pharmaceutical and topical applications by characterizing pollution parameters (heavy metals and pesticides), concentrations of biologically active substances (humic/fulvic acids, phenolics), antioxidant capacity, pH, physical characteristics, and microbiological flora, while also considering the applicable legislative framework for sustainable extraction and safe use.

Prior research and traditional practices highlight sapropel’s therapeutic use in balneology and dermatology, with reports of antibacterial and antioxidant effects linked to humic substances. Much of the existing literature has emphasized sapropel’s applications in agriculture and cosmetology rather than standardized medical or pharmaceutical use. Historical and contemporary sources document the role of therapeutic muds, while studies on humic/fulvic acids describe their high molecular heterogeneity and potential as antioxidants. Regulatory guidance, especially in cosmetics, sets microbiological limits and safety expectations for products derived from natural materials. This backdrop underscores the need for systematic quality standards, pollutant monitoring (e.g., heavy metals, legacy pesticides like DDT/DDE), and validated extraction methods to support medical-grade sapropel products.

- Site selection: Used the Latvian lake database and official geological surveys; criteria included sapropel deposit depth and thickness, lake hydrology, agricultural history near lakes, potential exposure to industrial waste, access, and absence of risks to subsurface utilities. Five Latgale district lakes were selected: Audzelu, Dunakla, Ivusku, Zeilu, and Mazais Kivdalova. Sampling occurred in winter using an over-ice platform for stability. - Sampling design: Thickness of sapropel layers and suitable sediment depths were determined at each lake and multiple points within lakes. Appropriate sapropel layers were generally 2.0–9.0 m below the sediment surface (observed range 0.9–11.4 m); layers shallower than 1.5 m were excluded. Samples were collected at 3 depths per extraction point across 1–11 points per lake (target 21 samples per lake). Each sample was georeferenced with extraction depth. - Collection and storage: Sapropel was collected with a stainless-steel semi-cylindrical chamber (1000×75 mm) with cone cap and shutter. Sediments were transferred to closed plastic containers, refrigerated, and stored at 4 °C protected from light and oxygen. - Extraction of active components: An alkaline extraction method was used to obtain sapropel extracts. - Physicochemical characterization: • pH measured in distilled water at a 1:2.5 sample:water ratio. • Total organic carbon (TOC), humic acid (HA), and fulvic acid (FA) concentrations measured spectrometrically. • Loss-on-ignition (LOI): dried samples heated 4 h at 550 °C and 2 h at 900 °C to estimate organic matter and carbonate content. • Trace metals (Pb, Cd, Ni, Co, Cu, Sb, Cr) quantified by electrothermal atomic absorption spectrometry with Zeeman background correction after microwave digestion with nitric acid and hydrogen peroxide; dilutions to 20 mL with Milli-Q water. - Antioxidant and phenolic assays (performed on extracts; FA carbon fraction assessed up to 700 mg/L): • Total phenolic content (TPC) by Folin–Ciocalteu method with gallic acid standards; absorbance at 765 nm; six replicates; results as mg GA equivalents per gram of plant material analogously applied to extracts. • Total antioxidant status (TAS) using Randox kit on RX Daytona analyzer. • DPPH radical scavenging assay with absorbance at 515 nm; IC50 (mg·mL⁻1) calculated; Trolox standard curve to express results as TE mmol·L⁻1. - Pesticides: DDE/DDT determined by ELISA. - Microbiology: Conducted by BIOR following ISO 4833-1:2013 (30 °C pour plate) with results in CFU/g; species isolated and identified; additional relevant ISO standards cited for cosmetic product microbiological criteria. - Organoleptic/lithological assessment: Visual appearance, color, texture, homogeneity, odor (e.g., H₂S), impurities (sand, gravel), and classification (organic, silica-containing, carbonate, mixed).

- Deposits and organoleptics: Suitable sapropel layers were typically 2.0–9.0 m below the sediment surface (observed 0.9–11.4 m), with jelly-like, homogeneous texture that becomes denser with depth. Colors ranged from greenish-yellow (higher silica) to almost black (higher organic matter, lower mineral content). Most Latvian samples represented mixed-type sapropel of planktonic/plant origin, sometimes associated with peat. - pH and bioactive components: pH ~7–8 across lakes, indicating relatively high mineral content. Humic and fulvic acids and TOC varied by lake (selected values from Table 3): • Zeilu: pH 7.8; TOC 126.4; HA 160.2; FA 74.3; TPC 77.2. • Mazais Kivdalova: pH 7.3; TOC 129.1; HA 167.8; FA 72.9; TPC 103.6. • Ivusku: pH 8.0; TOC 106.5; HA 113.1; FA 76.5; TPC 70.3. • Dunakla: pH 8.0; TOC 104.3; HA 138.4; FA 44.5; TPC 62.4. • Audzelu: pH 7.1; TOC 125.4; HA 161.8; FA 70.0; TPC 118.5. Antioxidant activity depended on FA carbon fraction concentration (assessed up to 700 mg/L FA-C). AO levels were higher in extracts from Audzelu, Mazais Kivdalova, and Zeilu; Dunakla showed notably lower AO and FA; Ivusku exhibited low AO despite relatively high FA. - Heavy metals: Pb, Cd, Co, Ni, and Cu were present in all samples, but none exceeded SCCS guideline tolerances for cosmetics (Pb 20 ppm, Cd 5 ppm, Ni 200 ppm, Co 70 ppm, Cr(III) 100 ppm, Sb 100 ppm). Example concentrations (mg/kg, Table 3): • Pb: 2.60–5.84; Cd: 0.1–0.2; Ni: 3.1–25.2; Co: 1.7–8.2; Cu: 3.9–13.3; Cr: 9.1–52.4; Sb: 0.3–0.4. Elevated Pb/Cd in upper layers indicate anthropogenic influence; some Ni increases likely natural; overall low mobility and ecological risk noted. - Pesticides: DDE/DDT detected variably across depths; surface waters generally had lower concentrations than sapropel. Highest levels appeared in Mazais Kivdalova and Zeilu (all depths) and Audzelu site 2, but values were below the limit of quantification (QL). Latvian EQS for surface waters: DDT 0.025 µg/L (annual average), p,p′-DDT 0.01 µg/L. - Microbiology: High microbial loads in raw sapropel exceeded cosmetic product limits by orders of magnitude. CFU/g (Table 3): Zeilu 2.65×10^5; Mazais Kivdalova 2.0×10^5; Ivusku 1.1×10^5; Dunakla 2.3×10^7; Audzelu 2.1×10^7. Dominant species included: Zeilu (Serratia fonticola, Pseudomonas veronii, P. chlororaphis), Mazais Kivdalova (P. veronii), Ivusku (Paenibacillus amylolyticus, Aeromonas bestiarum), Dunakla (Aeromonas sobria, Pseudomonas marginalis, Brevundimonas diminuta), Audzelu (Acinetobacter johnsonii). Some isolates are opportunistic pathogens (e.g., Serratia fonticola, Aeromonas sobria), indicating need for sterilization and strict microbiological control. - Compliance and quality criteria: Proposed standardization factors include organoleptics, heavy metals, pesticides, microbiology, and pH. Legislative review outlines permitting and environmental safeguards for extraction in Latvia.

The study demonstrates that Latvian freshwater sapropel contains appreciable humic and fulvic acids, phenolics, and antioxidant capacity, supporting its potential as a raw material for pharmaceutical and topical products. Heavy metal concentrations in sediments were well below SCCS limits for cosmetic ingredients, and pesticide residues (DDT/DDE) were at or below quantification, suggesting manageable contaminant profiles with appropriate monitoring. However, raw sapropel exhibits high microbial loads and occasional opportunistic species, necessitating sterilization or preservation and compliance with stringent microbiological standards for end products. Variability in composition and antioxidant activity among lakes underscores the need for site-specific characterization and standardized extraction to ensure consistent quality. The legislative framework in Latvia provides mechanisms to minimize environmental impacts and ensure sustainable extraction. Collectively, these findings address the central aim: to evaluate sapropel’s suitability for medical and cosmetic use and to define criteria and processes for safe, standardized, and environmentally responsible utilization.

- Latvian freshwater sapropel is a suitable raw material for obtaining extracts with bioactive humic substances and antioxidants, supporting development of pharmaceutical/cosmetic products and services. - Appropriate sapropel layers are generally found 2.0–9.0 m below the sediment surface (observed 0.9–11.4 m); layers shallower than 1.5 m are not fully developed. - Heavy metals (Pb, Cd, Co, Ni, Cu, Cr, Sb) did not exceed SCCS acceptable levels; DDT/DDE were detected at low levels, below quantification. - Antioxidant levels and HA/FA concentrations vary markedly by lake; higher AO was observed in extracts from Audzelu, Mazais Kivdalova, and Zeilu. - Although no active pathogens were identified, CFU/g in raw sapropel exceeded cosmetic limits, requiring sterilization/preservation and routine microbiological monitoring before medical/cosmetic application. - Guidelines for sapropel extraction and quality assessment were developed, aligning with Latvian environmental legislation to support sustainable industrial use. - Future work should refine standardization across sites, expand microbiological characterization, optimize extraction and sterilization protocols, and assess product safety/efficacy in clinical contexts.

- Geographic scope limited to five lakes in the Latgale district of Latvia; results may not generalize to other regions or lake types. - Sampling was conducted in winter; potential seasonal variations in composition, microbiology, and pollutant levels were not assessed. - Pesticide findings (DDT/DDE) were often below the limit of quantification, limiting precise concentration estimates. - Antioxidant assays were evaluated on extracts with a fixed fulvic acid carbon fraction (up to 700 mg/L), which may not represent other concentration ranges or extraction conditions. - Microbiological diversity was only partially characterized (nine species reported); broader microbial and pathogen profiling was not exhaustive.