Remediation of soils contaminated with toxic organic compounds.

Decontamination or removal of soil that is contaminated with toxic organic compounds can be very costly, as illustrated by the values in Figure 1. In numerous situations, cleanup activities do not take place because the cost of clean-up may exceed the value of the property or dramatically decrease the willingness of the property owner to initiate remediation. Therefore, inexpensive, but effective, remedial methods are needed because the number of U.S. sites that are contaminated by toxic organic chemicals, toxic inorganic chemicals, or a mixture of the two is quite large. In addition to the nearly 1300 locations on the National Priorities List ("Superfund") and subject to RCRA (Resource Conservation and Recovery Act) there are a much larger number of sites of smaller size that may pose a threat to adjacent populations. For example, Brown, et al. estimated that 75,000 to 100,000 or more of below-ground petroleum storage tanks were leaking. Glass, et al. (1995) estimated that, in the US alone, about 37,000 candidate sites for Superfund, 80,000 sites for RCRA, 1.5 million leaking underground storage tanks, and about 25,000 Department of Defense sites in need of remediation exist. Similar situations exist in developed countries of Europe and in less developed nations. In the U.S., sale of contaminated property is difficult or impossible, a situation which may lead to abandonment by the owner and lost opportunities to redevelop contaminated, but potentially very valuable, urban sites into productive uses. Long-term use of property for military operations has also resulted in contamination with organic solvents, petroleum hydrocarbons, and explosives. Wilson and Clarke (1994) estimated that remediation costs for NPL and RCRA sites alone could be as much as $750 billion, or an amount equal to the U.S. military budget for about 15 years. The cost estimate for European sites (including the European Union) is between $300 and $400 billion. At these costs, it is unlikely that more than a small fraction of the most critical sites will ever be remediated. One solution to the high cost of clean-up it to switch from expensive remedial methods to alternative methods that are significantly less expensive. On average, bioremediation is among the lowest cost methods for detoxification of soils contaminated with organic compounds (Figure 1) and composting is intermediate in cost among bioremediation technologies (Figure 2). When comparing the total budget for cleanup of a large site, the savings associated with use of bioremediation instead of chemical or physical based technologies give bioremediation an overwhelming monetary advantage (Table 1).