Problems of Dye in the Environment:
- Depending on exposure time and dye concentration, dyes can have acute and/or chronic effects on exposed organisms.
- The presence of very small quantities of dyes in water (less then 1 ppm) is highly visible due to their brilliance.
- The greatest environmental concern with dyes is their absorption and reflection of sunlight entering the water. Light absorption diminishes photosynthetic activity of algae and seriously influence on the food chain.
- Dyes can remain in the environment for an extended period of time, because of high thermal and photo stability. For instance, the half-life of hydrolysed Reactive Blue 19 is about 46 years at pH 7 and 25 °C.
- Many dyes and their breakdown products are carcinogenic, mutagenicand/or toxic to life. Dyes are mostly introduced into the environment through industrial effluents.
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Fig: Dyes cause a lot of problems in the environment |
The degradation product of dyes could be carcinogenic. The formation of Decoloration of Textile Wastewaters 177 carcinogenic aromatic amine o-tolidine from the dye Direct Blue 14 by skin bacteria has been established.
Textile dyes can cause allergies such as contact dermatitis and respiratory diseases, allergic reaction in eyes, skin irritation, and irritation to mucous membrane and the upper respiratory tract. Reactive dyes form covalent bonds with cellulose, woollen and PA fibres. It is assumed that in the same way reactive dyes can bond with –NH2 and –SH group of proteins in living organisms. A lot of investigations of respiratory diseases in workers dealing with reactive dyes have been made. Certain reactive dyes have caused respiratory sensitisation of workers occupationally exposed to them.
Public perception of water quality is greatly influenced by the colour. So, the removal of colour from wastewater is often more important than the removal of the soluble colourless organic substances. Removal of the dyes from the textile wastewater is often very costly, but a stringent environmental legislation has stimulated the textile sector in developing wastewater treatment plants.