Untreated Hair Dye Effluents Enter the Environment: Are They a Threat to Human Health?

The effluents generated during the process of hair dyeing exhibit a complex composition, comprising chemical compounds with varying toxicity levels. While the adverse impact of hair dyes on human health is acknowledged, there is a notable absence of studies addressing the toxicity associated with effluents produced during these activities. The primary objective of this study was to assess two effluents emanating from beauty salons after brown hair dyeing: one resulting from hair washing with water, shampoo, and conditioner, referred to as the complete effluent (CE), and the other from washing the dyed hair solely with water, excluding surfactants, referred to as the dye effluent (DE). In vitro bioassays were conducted with the human hepatoma cell line (HepG2/C3A). Cytotoxicity was evaluated through 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and Trypan Blue tests, while genotoxicity and mutagenicity were assessed by comet assay and cytokinesis-block micronucleus test, respectively. The cells were exposed for 4 h to various dilutions of the two sampled effluents [100.0% (1); 50.0% (2); 25.0% (3); 12.5% (4); 6.25% (5); 3.125% (6)]. Cytotoxicity was induced by CE-1, DE-1, DE-2, and DE-3 dilutions as indicated by both assays, whereas CE-2 dilution exhibited cytotoxicity solely through the MTT assay. These findings suggest impaired cell membrane integrity, permeability, and mitochondrial activity. Nontoxic dilutions (4, 5, and 6) were viable for the comet assay and micronucleus test, revealing genotoxicity without mutagenic potential. Consequently, residual concentrations of effluents were found to induce nonlethal and reparable primary DNA damage. Moreover, the effluents decreased the cytokinesis-block proliferation index and the cell replication index, indicating interference and arrestment in the cell cycle. These outcomes highlight the potential threat posed by residual concentrations of hair DEs to environmental quality and human health, emphasizing the imperative need for pre-disposal treatments in salon settings.