My Research at Tsinghua University

May 26th, 2011 by

Perhaps a few readers will be interested in the research that I have been doing over the past few years at Tsinghua University, located in Beijing, China. Tsinghua University is considered to be one of the best universities in China, also sometimes known as the MIT of China. I have been doing research in the Persistent Organic Pollutants Research Group of the School of Environment for the past two years.

Old gate of Tsinghua University, Beijing China, established in 1911

School of Environment, Tsinghua University

Persistent Organic Pollutants (POPs) are chemical contaminants which exhibit persistent, bioaccumulative, and toxic properties in the environment. They also have long distance transport potential and therefore have been found to exist in remote areas, such as the Arctic, where they accumulate in the fat, blood and inner organs of animals such as polar bears. The Stockholm Convention on POPs was signed in 2001 and put into effect in 2004, as an international accord to reduce and eliminate the use and production of designated POPs. The original convention took place in 2001 as a response to a call from the United Nations Environment Programme (UNEP) to take action on POPs, and included a list of the “Dirty Dozen” chemicals, which were designated as the “worst offender” chemicals. In 2009, a second set of 9 chemicals were added as the “new POPs”. China is a party to the Stockholm Convention, and thus has shown commitment to eliminating the production and use of the listed POPs.

Molecular structure of PFOS, one of the "new POPs" as designated by the Stockholm Convention for its persistent, bioaccumulative, and toxic properties

My research focused on one of the “new POPs”, called perfluorooctanesulphonate (PFOS), which is a fully fluorinated eight carbon chain with a sulfonic acid head. Because this chemical is both oleophobic and hydrophobic (exclusion of both non-polar oils and polar water), it was historically used as a surfactant and coating for many products, including fabrics and carpeting. The most common product utilizing PFOS was produced by 3M, and called Scotchgard™. In addition, it is commonly used as a processing aid in industries including metal plating, and paper treatment, and as a key ingredient in aqueous fire-fighting foams (used to combat fires fueled by highly flammable gases or liquids).

In 2000, 3M, then the largest producer of the parent compound Perfluorooctane sulfonyl fluoride (POSF), announced the discontinuation of all its PFOS-related products because of the chemical’s toxicity to humans and the environment. Shortly thereafter, most other countries followed suit and banned the production of the chemicals. However, because of a lack of appropriate substitutes and technical transfer, China continues to be the only country still reported to be producing POSF and utilizing PFOS, despite its entrance into the Stockholm Convention.

Relatively speaking, China has only produced a small amount of POSF compared to 3M, however, there the true effects of this contaminant are still not determined because of incomplete emissions inventory, which is typically needed to be able to assess a contaminant’s effect in a certain region. Mostly, there is no existing, complete centralized record of exactly which industries are still utilizing PFOS. The first part of my research was to determine the key areas in China for which more investigation investment would be likely to contribute the most emission of PFOS into the environment. I designed a emissions inventory methodology specific to the contamination patterns of PFOS in the Chinese environment that grouped lifetime product releases into wastewater treatment plant effluents, while determining key industries for further investigation. Wastewater treatment effluent concentrations were determined to exhibit a correlation with more easily-obtainable geo-referenced data, such as population density and city GDP. This way, an estimate of PFOS emission can be extrapolated without having to test every city’s wastewater effluents.

A schematic for the emissions scenario I designed for back calculating source load from environmental concentrations

While designing the emissions inventory methodology, I found that China-specific industrial data and emissions factors are greatly lacking, but that environmental monitoring concentrations are much more available for a wide range of areas within China. Therefore, utilizing these environmental concentrations, I developed a unique multimedia fugacity model to estimate source load in a given area, given PFOS’ physical-chemical properties and the hydrological conditions of the modeled area. I completed a case study example and successfully proved my model’s stability for a segment of the Huangpu River in Shanghai.

In addition, also using the available environmental monitoring concentrations, I also carried the first national probabilistic risk assessment for PFOS in China. Probabilistic risk assessment is different from deterministic risk assessments, which have been performed in the past, in that it is able to incorporate spatial and temporal variability. Based on toxicity data reported in the literature, I also derived a predicted no effect concentration range (PNEC) by which to evaluate the conservativeness of previously reported PNEC values.

Me, at the 100th Anniversary Celebration of Tsinghua University at the Great Hall of the People, Beijing, China

Me and Yang Liwei, first Chinese taikonaut in space at the 100th year anniversary of Tsinghua University at the Great Hall of the People, Beijing, China

I enjoyed my two years at Tsinghua University. Aside from my research, I participated in many of my research group’s and school activities. This year was the 100th Anniversary of the founding of the university, and I was chosen as a representative of the School of Environment to attend the celebration at the Great Hall of the People, where President Hu Jintao (alumus of Tsinghua University Hydraulic Engineering) spoke, along with the presidents of Tsinghua University, Peking Univeristy, Yale University and student and faculty representatives. This year was also the first year that The Department of Environmental Science and Engineering became the School of Environment, an event that represents the growing importance of environmental issues in China and the country’s commitment to training the country’s best and brightest to help solve some of China’s most pressing environmental challenges.

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