Screening of Dittrichia viscosa (L.) Greuter metabolites as potential natural biocides for cultural heritage applications

Biodeterioration driven by phototrophic microorganisms represents a persistent challenge in cultural heritage conservation. In this study, metabolites from Dittrichia viscosa (L.) Greuter was extracted, purified, and evaluated for their biocidal potential using Raphidocelis subcapitata as a standardized model microalga commonly employed in ecotoxicological screening. Four sesquiterpenoids—tomentosin, 11α,13-dihydrotomentosin, inuviscolide, and α-costic acid—were isolated and structurally characterized by NMR and GC–MS. Among them, tomentosin and inuviscolide exhibited significant growth-inhibitory effects, with tomentosin showing a clear dose-dependent response (IC₅₀ ≈ 5–6 mg L⁻¹). Although the test organism is not a typical stone colonizer, these results provide a preliminary assessment of the phytotoxic activity of D. viscosa metabolites and support their further evaluation against biodeteriogenic microorganisms and heritage-relevant substrates.