Environmental impact research has allowed us to better understand the consequences of utilizing certain chemicals in manufacturing and other industrial processes. In the past, however, contamination to precious water supplies and healthy ecosystems has occurred through the frequent use of compounds that were not understood to be hazardous until later. For example, many U.S. Navy bases employed a group of industrial chemicals called polychlorinated biphenyls (PCBs) for wire coating and other uses. PCBs were preferred because they were non-flammable, which provided an advantage over other plastics that could more easily catch fire. Years later, it was discovered that PCBs pose a grave risk to the environment, and in the 1970s they were banned from further use or production in the United States. Unfortunately, PCBs are persistent because they do not degrade, and they are retained in organic matter in soil. Some of them are characterized by significant toxicity, which can lead to adverse effects and death in fish and wildlife. In addition, organisms exposed to PCBs, including fish, are often caught and consumed by the human population. This is problematic because PCBs are toxic to humans and can cause cancer.
Environmentalists and scientists alike have long been interested in ways to detect the fraction of a contaminant that can move into organisms, including humans. If this bioavailable fraction could be estimated accurately, a better understanding of the risk and approaches for cleanup could be developed in order to prevent further damage by harmful chemicals. More specifically, an important question remains — what is the best way to detect the imminent danger to the surrounding environment presented by insoluble contaminants, such as PCBs? When entering a water source, much of these chemicals sink to the bottom and collect in sediments. This interstitial space —the space in between individual pieces of sediment — however, is comprised of water and accounts for the exchange between the rock and soil, as well as the surrounding water and organisms. It is when PCBs or other contaminants are able to seep into the interstitial water that poses the greatest threat to aquatic life in the area, exposing nearby organic matter to the harmful chemicals through this exchange of water. It is possible to measure the mass of contamination found at the base of harbors and rivers trapped by soil, but organisms don't necessarily encounter the same risks that measurements on the sediments alone would reveal. Accounting for all of the contaminant in the sediment could be misleading because some of the contaminant is sheltered from the organisms below the surface.
It is still difficult to answer the lingering question, "what is actually going to cause risk?" Difficulty arises in that within a 100-gram sample of soil, only 10 to 40 milliliters of water may exist. To detect these contaminants — which are not very soluble — researchers would need at least 10 times that amount of water to accurately measure the concentration. Alternatively, to discover how much contaminant is contained within the sediment porewaters, the passive sampling method has been adopted. In passive sampling, samples are collected by inserting sorbents. — absorbent materials capable of soaking up contaminant within the sediment — and concentrating the contaminant sufficiently to allow it to be detected by routine measurements. Until now, sorbents have been primarily used to assess the situation, not to evaluate the performance of cleanup of the contamination.
Dr. Danny Reible, Donovan Maddox Distinguished Engineering Chair and professor of civil, environmental, and construction engineering at Texas Tech, has been awarded a $450,000 grant from Geomorphis Information Systems. The grant will allow him to investigate the effectiveness of sorbents — particularly activated carbon — in absorbing contamination in order to control and reduce exposure to organisms. During this three-year project, Reible will investigate the PCB contamination at Hunter's Point Naval Shipyard, a facility of a Naval Base in San Francisco, California. Songjing Yan, a chemical engineering Ph.D. student, Dr. Magdalena Rakowska, and post-doctoral fellow, will work with Reible. Activated carbon will be used to absorb PCB contamination, while passive sampling technology utilizing a different sorbent will then assess the change in contaminant concentration as a result of the carbon.
This project will consist of several key goals. First, baseline monitoring will be conducted in which the concentration of contaminants will be measured before the insertion of the sorbent. Second, several pounds of activated carbon will be placed in every square yard of the area under investigation. The activated carbon will then absorb the contamination contained within sediment. If the technology works as suggested, the amount of contamination retrieved by the carbon will be enough to reduce the actual risk to nearby organisms. Next, periodic measurements will be taken to discover the change in concentration in the water contained in sediment as a result. These measurements will be done by utilizing passive sampling, using a 30-micron layer of another organic sorbent on a glass capillary half a millimeter in thickness that is placed into the soil. Lastly, analysis of the change in concentration, and therefore risk to the environment, will be determined based on the resulting data.
Reible's research will track the performance of a new technology in the field originally suggested by Dr. Richard Luthy at Stanford University. Reducing contaminant availability, in which the goal is decreasing the contaminant that is available for exposure and risk instead of removing the contaminant completely, could in the future be the main way of treating sites such as the naval shipyard. The new method could eventually be adopted in a variety of locations in order to prevent further damage by many different contaminants, replacing older methods that involved incomplete removal of the contaminant or severe destruction of healthy ecosystems in order to rid them of PCBs. Instead of removing PCBs entirely, this approach will reduce risk by preventing much of the contamination from reaching organisms. Reible will also further develop techniques for measuring contaminants via passive sampling techniques in order to assess risk and evaluate performance in order to better focus the limited dollars available for remediation of contaminated sites.