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sexta-feira, 13 de julho de 2012

Clothing Leaches Little Titanium Dioxide During Washing

Wastewater: Discharges from laundry are minimal compared to other sources of TiO2 in the environment, scientists find

Photograph of a washing machine.
No Leaching

When titanium dioxide is 
embedded in clothing, 
only small amounts 
of wash off.
Credit: Shutterstock

Textile manufacturers add titanium dioxide to some clothing to brighten it and to prevent the color-fading effects of ultraviolet light. But environmental scientists worry about how much of the compound leaches from laundry’s wash cycle into wastewater and eventually into the environment. Now a study reports that very little titanium dioxide washes out of clothing(Environ. Sci. Technol., DOI: 10.1021/es301633b).
Scientists have scant data on TiO2’s toxicity in the environment. But previous studies have shown that it makes its way into wastewater via food, cosmetics, and other sources. No one had looked at washing machine effluent as a potential source.
So Bernd Nowack of the Swiss Federal Laboratories for Materials Science and Technology and his colleagues put six textiles composed of varying amounts polyester, polyamide, cotton, and other materials through the laundry. They then used elemental analysis to measure the amount of TiO2 in the soapy wash water and rinses.
Five of the textiles leached between 0.01 and 0.06% of their total TiO2 during the first cycle, producing effluent concentrations of less than 0.7 mg/L, barely exceeding detection limits. Four of those textiles continued to leach barely detectable amounts during additional washings. The low leaching for those four textiles is likely due to their TiO2 being incorporated directly into the fabric, Nowack says.
However, the sixth textile, a polyester-wool mix, had a surface coating of TiO2, which Nowack thinks is a rare method of adding the chemical to clothing. That textile lost about 20% of its TiO2 over the course of 10 washings, leading to a concentration of 4.7 mg/L in the washing fluids and 0.64 mg/L in the rinse water. A textile composed of cellulose, cotton, and elastane, which lost very little of its embedded TiO2 in the first wash, also leached 20% of its TiO2 over 10 washes, but Nowack can’t explain why.
Based on their data, the team estimated that the concentration of TiO2 in wastewater from textiles is between 1 and 15 µg/L. Previous studies have estimated wastewater levels of the chemical from food and cosmetics to be on the order of hundreds of micrograms per liter. “Overall, we conclude that textiles don’t comprise an important source of TiO2 to wastewater compared to other sources like food and sunscreen,” Nowack says.