Natural indigo toxicity for aquatic and terrestrial organisms

• Published in: Ecotoxicology and environmental safety 2025-01, Vol.290, p.117606, Article 117606
• Main Authors: Oliveira de Farias, Natália, Siviero Guilherme Pires, Marta, de Jesus Moreira, Bruna, dos Santos, Amanda, Freeman, Harold Stanley, Toukola, Peppi, Fernandes de Albuquerque, Anjaina, Räisänen, Riikka, de Aragão Umbuzeiro, Gisela
• Format: Article
• Language: English
• Subjects: Chemical characterization; Enchytraeus crypticus; Leuco dye; Natural indigo; Parhyale hawaiensis
• ISSN: 0147-6513; 1090-2414; 1090-2414
• DOI: 10.1016/j.ecoenv.2024.117606

Indigo is a widely used colorant available from natural and synthetic origin. It is practically insoluble in water. Indigo can reach aquatic sediments through wastewater discharges from dyeing processes, terrestrial compartments from the treatment sludges used as biosolids and dyed textiles disposed in landfills. The aim of this work was to chemically characterize a commercial natural indigo dye from Isatis tinctoria (woad) and, evaluate its toxicity using a sediment organism (Parhyale hawaiensis) in an acute test (96 h) and the soil dwelling invertebrate Enchytraeus crypticus in a chronic assay (21 days). These organisms are model organisms and representative of the environmental compartments where dye’s destination is expected. Also, the toxicity of natural indigo was evaluated under the conditions in which it is applied to textiles. Specifically, water column invertebrate Daphnia similis was used to test indigo in its leuco form along with the salts used for its generation. The composition of the test sample was 91 % indigo, 4 % indirubin and 5 % of other components including flavonoids. The sample was toxic to P. hawaienis (LC50 309 g kg−1) and inhibited the reproduction of E. crypticus at concentrations 5.06 and 7.59 g kg−1 in dry soil. The leuco form of indigo was acutely toxic to Daphnia similis at concentrations 0.2 and 1 g L−1. The data of this study can be used to guide other indigo toxicity studies and provide information that can be used in preliminary risk assessment evaluations of environmental compartments, such as aquatic sediments and indigo contaminated soils. •Natural indigo was toxic to amphipod Parhyale hawaiensis with a LC50 of 309 g kg−1.•Natural indigo decreased reproduction of the soil invertebrate Enchytraeus crypticus.•Ecotoxicological effects may be related to the physical effects of indigo particles.•Leuco form of indigo was toxic to Daphnia similis due to salt level and decrease pH.