**2. Negative impacts of textile dyes on human and animal health**

Textile industry effluents are considered the most polluting compounds both by the volume generated and discarded and by their toxicity [9]. Wastewater from the textile industry is estimated to contain between 10 and 200 mg L−1 of dyes, as well as other organic chemicals, inorganic compounds, and additives. Even after the treatment of such effluents, about 90% of the dyes are still dumped in water bodies without undergoing chemical changes [1]. The biodegradation of such dyes is hampered by their xenobiotic nature, aromatic structure, high thermal resistance, and photostability [4].

In recent studies, Gita et al. [9] have observed that the toxicity of dyes is generally low for mammals and aquatic organisms, however, secondary products formed by biodegradation, especially aromatic amines from anaerobic dye reduction, can be harmful. In addition, these authors found that the concomitant presence of dyes and other pollutants in textile wastewater, such as heavy metals, can have a synergistic effect, causing considerable damage to the aquatic environment.

The main concern about the discharge of dyes is the presence of genotoxic, mutagenic, teratogenic, and carcinogenic effects, observed in animal studies [9]. Carcinogenicity is related to the formation of ions that bind to DNA and RNA, causing mutations and leading to the formation of tumors. In this sense, benzidine and 2-naphthylamine dyes are associated with a high incidence of bladder cancer [10]. Azure-B dye is capable of interspersing in the helical structure of the DNA and may have cytotoxic effects since it is an inhibitor of monoamine oxidase A (MAO-A), an enzyme that acts on the central nervous system and is important to human behavior [10]. Sudan 1 dye, widely used in the textile industry, although illegal in many European countries and the US, is also used in foods, such as paprika. Such dye, when present in the body of humans and animals, is transformed by the action of enzymes in carcinogenic aromatic amines [10]. Furthermore, human exposure to dyes can still generate skin and lung irritations, headaches, congenital malformation, and nausea [11].

Triphenylmethane dyes are phytotoxic to agricultural plantations, cytotoxic to mammals, and generate tumors in several fish species [10]. The violet crystal dye is also a powerful carcinogen, capable of inducing tumors in fish, such as hepatocellular carcinoma and reticular cell sarcoma in several organs [10].

Some of the main environmental problems related to the disposal of synthetic dyes are—*i*. contamination of surface water, which leads to decreased penetration of light,

with damage to photosynthesis and consequent oxygen deficiency; *ii*. accumulation of nonbiodegradable organic dyes along with the food chain; *iii*. Soil and water contamination, and *iv*. inhibition of growth and development of various crops of agricultural interest [4].

In the literature, a correlation is described between the increase in the concentration of dyes and the decrease in the growth of microalgae, reaching the total suppression of their growth [9]. In that study, different concentrations of three dyes were used to evaluate the specific growth rate of green algae *Chlorella vulgaris* exposed to dyes. Such findings are important because the inhibition of microalgae growth causes disturbances in the trophic transfer of energy and nutrients in aquatic environments [4].

Aquatic macrophytes are used as natural ecological markers to quantify the phytotoxicity of textile dyes when exposed to effluents that contain those since there is a change in all their parameters [4]. In the presence of two textile dyes, *Lemna giba*, an aquatic macrophyte, had its growth rate and photosynthetic pigment content decreased. The authors of the study concluded that this species can be used as a bioindicator of polluting dyes [12]. High concentrations of dyes are reported to decrease vital elements, such as P, Mg, Ca, S, and Ca in plants of *Eichhornia crassipes* and *Salvinia natans*, which also presented damaged roots, chlorosis, and necrosis in leaves [13].

Among thousands of dyes studied, found in effluents, more than 100 have the potential to form carcinogenic amines. However, these potentially toxic dyes are still marketed and used, especially in small textile factories. In several places around the world, the demands of export and cheap labor sustain the existence of factories with a small-scale activity that clandestinely releases toxic dyes into water bodies [10].
