The deliberate release of genetically engineered microorganisms (GEMs) into the environment is a promising approach to the amelioration of environmental problems such as pollution and pest control.
GEMs may find their way into the aquatic environment, (oceans, streams, groundwaters, lakes, wastewaters, and sludges) either by direct release into that environment or, after uses on land, via surface runoff and soil seepage into groundwaters, streams, lakes, and estuaries. Since experience with the deliberate release of GEMs is very limited, it is necessary to develop approaches for risk assessment of the potential adverse effects that could be caused by the introduction of a large number of novel microorganisms into the aquatic environment. The accepted approach to risk assessment (hazard identification, exposure, and dose-response assessment, leading to risk characterization) has been used to develop models for risk assessment of the deliberate release of GEMs into the aquatic environment. The new concept introduced in this risk assessment is that of “critical mass,” defined as the number of GEMs applied at a specific site that would result in replacement of endogenous microorganisms. This “critical mass” would depend both on the properties of GEMs and on the number and properties of endogenous microorganisms at the site of GEMs application. An experimental assessment of critical mass may be possible by using aquatic microcosms corresponding to the aquatic environment into which GEMs would be released.
The Ambient Water Quality Criteria that were promulgated by the U.S. Environmental Protection Agency (EPA) in 1980 included water concentration levels which, for many pollutants, were so low as to be unmeasurable by standard analytical methods. Criteria for controlling toxics in municipal sludge would likely pose similar problems of sampling and analysis. Risk assessment methodologies recently developed by the U.S. EPA provide criteria derivation procedures for each of the following sludge management practices: land application (including distribution and marketing), landfilling, incineration, and ocean disposal. These methodologies recommend that numerical limits on toxicant concentrations in sludge, or on rates of toxicant disposal, should be used to minimize risk to human health and the environment. Implementation of these numerical criteria would require refinement of sampling and analytical techniques for sludges, and various types of field validation studies would be needed to ensure that the criteria are appropriately protective.
The U.S. Environmental Protection Agency (EPA) is developing comprehensive technical regulations under the Clean Water Act Section 405(d) on the reuse and disposal of municipal wastewater sludge. The reuse and disposal options are land application (including distribution and marketing), landfilling, incineration, and ocean disposal. This paper identifies the key questions to be addressed by EPA and the tasks and major steps to pursue in answering these key questions.
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