Influence of Solvent Polarity on Extraction Yield and Toxicity of Aquatic and Semi-Aquatic Plants

The exploration of aquatic and semi-aquatic plants as a sustainable reservoir of bioactive secondary metabolites represents a vital frontier in natural product chemistry, particularly for applications in aquaculture management and eco-friendly pharmacology. This study systematically investigated the influence of solvent polarity on the extraction efficiency and toxicological profiles of fifteen selected aquatic and semi-aquatic plant species collected from the Khulna region of Bangladesh. The extraction of bioactive compounds is significantly influenced by the polarity of the solvent used, which dictates both yield and biological activity. A serial exhaustive extraction methodology was employed utilizing a polarity gradient of five solvents: hexane, ethyl acetate, ethanol, methanol, and water. Toxicological assessments were conducted using the Brine Shrimp Lethality Test (BSLT) and the Zebrafish (Danio rerio) Larvae Acute Toxicity Assay. The results indicated that ethyl acetate and methanol were the most efficient solvents for the majority of species, consistent with findings that polar solvents maximize phenolic and flavonoid yield. Colocasia esculenta achieved the highest overall yield of approximately 26% in ethyl acetate. A statistically significant correlation (p < 0.05) was observed between solvent polarity and extract toxicity. While hexane and ethyl acetate extracts were largely non-toxic (LC₅₀ > 1000 µg/mL), polar organic extracts (ethanol and methanol) frequently demonstrated moderate to high toxicity, particularly for Polygonum hydropiper and Bacopa monnieri. Notably, Limnophila indica exhibited high lethality (97% mortality) exclusively in aqueous extracts against zebrafish larvae, highlighting the presence of water-soluble toxins often overlooked in invertebrate screenings. This study advocates for the use of ethyl acetate to balance high yield with safety and underscores the necessity of vertebrate models in toxicological profiling.

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