Natural indigo toxicity for aquatic and terrestrial organisms

Area of Science:

• Environmental toxicology
• Ecotoxicology
• Dye chemistry

Background:

• Indigo dye, a common colorant, enters ecosystems via wastewater and landfill disposal.
• Its insolubility poses challenges for environmental fate and toxicity assessment.
• Natural indigo from Isatis tinctoria was chemically characterized and its ecotoxicity evaluated.

Purpose of the Study:

• To chemically characterize natural indigo dye.
• To assess the toxicity of indigo to key environmental organisms.
• To provide data for preliminary environmental risk assessments.

Main Methods:

• Chemical characterization of commercial natural indigo.
• Acute toxicity testing on sediment organism Parhyale hawaiensis (96h).
• Chronic toxicity testing on soil invertebrate Enchytraeus crypticus (21 days).
• Toxicity testing of leuco-indigo and associated salts on Daphnia similis.

Main Results:

• Natural indigo (91% indigo, 4% indirubin, 5% other) showed toxicity to P. hawaiensis (LC50 309 μg/kg).
• Indigo inhibited E. crypticus reproduction at 5.06-7.59 μg/kg (dry soil).
• Leuco-indigo was acutely toxic to Daphnia similis at 0.2-1 μg/L.

Conclusions:

• Natural indigo dye exhibits significant toxicity to aquatic and soil invertebrates.
• Results inform risk assessment for indigo in sediments and soils.
• Further studies can build upon these findings for comprehensive environmental safety evaluations.