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.