Study evaluates engineered nanoparticles in wastewater

Have you ever wondered what happens to sunscreen after it swirls down the drain with your soap? Probably not, but it is a question that makes Prof. Chin-Pao Huang curious.

Sunscreen contains titanium dioxide, an engineered nanoparticle (ENP) that improves the product's performance, reducing your sunburn risk while outdoors. But if titanium dioxide doesn't dissolve, where does it go once you wash it off?

Huang, Donald C. Phillips Professor of Civil and Environmental Engineering at the University of Delaware, is principal investigator (PI) of a new grant exploring whether ENP are present in ground wastewater. Murray Johnston, professor in the Department of Chemistry and Biochemistry, serves as co-PI on the project.

By definition, nanomaterials are materials 1-100 nanometers in length - one thousand times smaller than a human hair. ENP are synthetic materials created in a laboratory. Invisible to the naked eye, they possess unique properties that are increasingly used in cosmetics, pharmaceuticals, electronics and appliances.
The same properties that make ENP attractive, however, also have drawbacks. According to Huang, increased nanomaterial use will ultimately result in their escape into the environment, namely the atmosphere, soil and water. Municipal and industrial wastewater is expected to be the major transport route for ENP due to the way these ENP are being used by consumers.

"There is a lot we don't know yet about the ENP lifecycle, including how nanomaterials present in our environment affect organisms, water and the ecosystem," says Huang. Their small size makes detecting and isolating ENP technically challenging, he adds.

Funded by a three year $599,000 STAR grant from the U.S. Environmental Protection Agency (EPA), Huang's group is focusing on the fate, transport and behavior of four main engineered nanomaterials:

• Titanium dioxide (found in sunblock and food additives);
• Zinc oxide (found in cosmetics and food);
• Carbon nanotubes (increasingly used in medicines and printer ink); and
• Silver (used in refrigerators and disinfecting products).

"Knowing what happens to the particles will allow scientists to focus on making them safer for the environment," explains Huang.

The UD research team is using a new experimental technique to collect and characterize wastewater and sludge samples from four major municipal wastewater treatment plants in Philadelphia, Baltimore, Washington, D.C., and Wilmington. The technique involves using electrically assisted tangential flow (EATF) membrane filtration and electrospray aerosol analysis (EAA), coupled with a nano aerosol mass spectrometer (NAMS), to trace and quantify which nanomaterials remain in the system and where they end up.

The results will assist wastewater process design engineers in developing new treatment processes to eliminate solids such as titanium dioxide from wastewater and prevent it from leeching into the environment where its effects, as yet, are unknown. It will also help public and private sector decision makers in revising wastewater treatment quality standards.

"This is the only research study worldwide being carried out at such a large and comprehensive scale," says Huang. He believes a concerted effort is needed not just locally, but globally as well. To that end, Huang plans to initiate similar research programs with scientists from partner institutions in Taiwan, Korea and China.
Research will be conducted in the Aquatic Environmental Engineering Laboratory in UD's Department of Civil and Environmental Engineering and the Aerosol Chemistry Laboratory in the Department of Chemistry and Biochemistry.

About the researchers

Chin-Pao Huang is one of the most highly respected aquatic chemists worldwide. He has more than 40 years of research experience in aquatic chemistry and physical-chemical processes for water and wastewater treatment. His expertise includes transport of heavy metals in municipal wastewater treatment plants, speciation of lead in groundwater and interactions between nanoparticles and aquatic organisms.
Murray Johnston's career includes more than 20 years of research experience as a leader in the development and use of aerosol mass spectrometry to study the source and transformation of particulate matter. His current work emphasizes the detection and characterization of nanoparticles in ambient air, especially the urban environment.

Source: Nanowerk