Ecotoxicological Effects of Synthetic Food Dyes on <scp> <i>Daphnia magna</i> </scp> and <scp> <i>Lemna minor</i> </scp>

Synthetic food dyes are widely used in Ghana, yet their ecological effects on freshwater ecosystems remain understudied. This study investigated the acute toxicity of five commonly used synthetic food dyes (tartrazine, allura red, sunset yellow, carmoisine, and green S) on two bioindicators, Daphnia magna and Lemna minor, following OECD 202 (2006) and OECD TG 221 protocols. The physicochemical analysis suggested that synthetic dyes, even in dilute form, can alter water chemistry. Although the electrical conductivity (EC), salinity, and total dissolved solids (TDS) values for sunset yellow were relatively low (8.12 mS/cm, 7.50 psu, and 2.98 g/L, respectively), tartrazine, carmoisine, and green S recorded high levels of EC, TDS, and salinity. Levels of Cd and Hg in all the dyes were below the detection limit (<0.001 mg/L). Carmoisine, however, recorded 0.003 mg/L for Cd. Levels of Cr, Pb, Fe, and Mn were above the limits for food dyes (≤0.002, ≤0.043, and ≤0.006 mg/L), raising environmental concern. The EC₅₀ showed that allura red is the most toxic, and tartrazine is the least toxic. IC₅₀ showed that green S is the most toxic and sunset yellow is the least toxic. All the dyes showed potential toxicity, and when released into the environment without treatment, they will have adverse effects on the aquatic environment. Bioaccumulation potential revealed that Pb, Mn, As, and Hg were accumulated in daphnia, whereas Cr, Cd, and Fe were not due to their low solubility, ionic competition, and strict cleansing mechanisms by daphnia. These findings emphasize the ecological risks of unregulated dye pollution in Ghanaian waters and highlight the importance of region-specific ecotoxicological data to guide environmental policies, regulations, and sustainable wastewater management practices.