Quantitative Detection of Hexavalent Chromium in Aquatic Environments Using Digital Image Colorimetry and the Green Chemistry Approach

Hexavalent chromium, Cr(VI), is a highly toxic heavy metal that poses serious threats to human health and the environment, necessitating efficient and sustainable detection methods. In this research, a green analytical approach was developed using digital image colorimetry (DIC) combined with black mulberry (Morus nigra L.) aqueous extract as a natural complexing agent for Cr(VI) detection in water samples. The interaction between Cr(VI) and the anthocyanin pigments in the extract induced a distinct color change from red to purple, enabling qualitative and quantitative analyses. The maximum absorbance wavelength of the Cr(VI)–mulberry extract complex was observed at 570 nm, with a high coefficient of determination (R2 = 0.9982) for UV–vis spectrophotometry and 0.9981 for DIC, confirming a strong linear correlation. The method exhibited a limit of detection (LoD) of 0.0410 ppm and a limit of quantification (LoQ) of 0.138 ppm, comparable to UV–vis. Analysis of four environmental samples revealed that two samples with Cr(VI) contamination exceeded regulatory limits, measured at 0.283 and 0.951 ppm, respectively, highlighting the need for ongoing monitoring. The developed DIC method is cost effective, is reagent efficient, and aligns with green chemistry principles by minimizing hazardous chemicals, reducing waste, and supporting sustainable analytical practices for heavy metal detection.