Future Directions and Needs

Estimates of cleanup costs for hazardous waste sites pla-netwide are of the order of US$ 1 x 1012. These massive costs to clean up national defense and industrial facilities are effectively unsustainable and largely being deferred to later generations, especially at sites such as Chernobyl in the Ukraine. Waste disposal requirements of the twentieth century were usually followed, but these practices were rarely based on environmental and other resource sustainability. In the future, any development and further use of xenobiotic compounds for better living must be accompanied by the development of sustainable biotechnologies or other approaches to sustainably manage any wastes. Classical plant breeding and agroeconomic practices may be used to develop some sustainable waste management practices. But more likely the inventiveness of humankind in chemistry for better living will not be limited to xenobiotic compounds analogous to primary and secondary metabolites.

This concern is especially acute for the nascent development of nanotechnologies. These micron-scale particles are conceived to have almost unlimited applications based on the development of macromolecules that have intense concentrations of activities or energy that secondary metabolites, natural macromolecules, and microorganisms do not currently possess. Thus any development of applications of nanosize particles should be preceded by environmental fate and transport investigations and the ecological engineering of sustainable biotechnologies to manage any risks of uncontrolled environmental releases.

The ecological engineering of the cleanup of existing unsustainable releases of hazardous wastes is also very much needed to reduce the impact of the original manufacturing and disposal decisions. For example, the cleanup costs in the US may be reduced on the order of US$ 1 x 109 using phytoremediation, but additional optimization of applications is necessary and fundamental research is necessary to provide additional methods of cleanup. To achieve these and even greater cost savings, research investments on the order of 10% of the savings (US$ 1 x 108) are normally justified. Current research investments for phytoremediation in the US seem to be on the order of US$ 1 x 106yr~\ a difference that may explain why some twentieth-century waste management costs are being deferred to future generations.

The development of phytoremediation applications is particularly vulnerable to shortfalls in fundamental research. For the field of phytoremediation to continue to grow at a very rapid pace compared to bioremediation and other innovative cleanup technologies, significant investments are required in fundamental investigations of plant enzymatic activities, genetics, proteomics, and primary and secondary metabolites. The US EPA Contaminated Sites Program and the US Strategic Research and Development Program were vital in initiating the field in the early 1990s. If not for the European Cooperation in the Field of Scientific and Technical Research (COST, http://lbewww.epfl.ch/ COST837/) to guide research, applications of phytoreme-diation may have already stalled despite recent limited programs to support applications research from the US National Science Foundation, EPA, Strategic Research and Development Program, and Office of Naval Research.

Compared to microbes and mammals, much less of plant proteomes seem to have been explored for enzymatic activities useful in waste management, pharmaceutical and nutraceuticals development, and other societal needs. Yet over the history of modern scientifically based medicine and the much longer application of traditional medicine, many plant activities have been found to be useful. For the approximately 10 000 plant proteins known, less than 1% have been investigated for waste treatment applications. In addition, only a few classes of compounds have been tested for transformation by plant and microbial enzymes.

Investigation ofthese enzymes for various applications is of the highest priority. Development of microarrays of enzyme activities, DNA, and chemical compounds can significantly decrease screening time. When screening for phytoremediation plants, other arrays could be useful to simultaneously screen for new pharmaceuticals, nutra-ceuticals, and other products.

Future applied research should continue to investigate plants and microorganisms that are associated with unique and unusual poisons and other natural toxins. Uniquely evolved plants and microorganisms near metal outcroppings, in deserts, in cold regions, and in other rigorous environments, or evolved in secluded regions like Australia, should continue to be investigated. However, better comprehensive plant proteomes cross-referenced to pollutants must be developed to guide this important research, as was done in the development of pesticides and herbicides during the green revolution.

Understanding genetic and proteomic diversity is vital to better engineer ecosystems rationally in place of plant monocultures and simple ecosystems of highly controlled plants and microorganisms. Furthermore, current simplified design procedures for wetlands, grasslands, crops, and plantations are rarely if ever based on optimized engineering protocols and infrequently make use of sustainable ecological engineering design. Thus many phytoremediation applications, while more cost effective than most other alternatives, still may not be sustainable if excess fertilization, irrigation, and soil augmentation are used to apply monocultures and imported plant species. Ecological engineering needs to be introduced to phytor-emediation, starting with a comprehensive reorganization of applications and research to date in terms of basic ecological engineering concepts. Without ecological engineering optimization, the costs of increased eutrophi-cation and decreased water quality, water shortages, and poor soil may be unsustainable in the face of growing populations of humans planetwide.

Next in priority is that classical breeding techniques need to be explored to select optimal plants to use in phytoremediation. So far the little experience in plant breeding seems to have come from characterizing metals accumulating plants.

Finally, metabolic and genetic engineering research must be pursued further to sustainably manage xenobiotic and heavy metal pollutants. Highly evolved, large, immobile plants that dynamically self-engineer provide the best opportunity to control and apply microbial, animal, and plant genes in complex cleanups using transgenic organisms.

So far, transgenic plants are feasible for some phytor-emediation applications but have not been shown to be fully necessary and useful.

So much more is necessary to define potential roles of thousands of plant enzymes, define how all of the approximately 200 000 secondary metabolites are metabolized, and optimize and engineer the necessary transgenic plants. Thus de novo development of new genes does not seem to need to be a current waste management priority. First, the reliability of libraries of pathogenic gene sequences is not known well enough so to be sure that the genetically engineered organism can be used in the environment. Second, the release in the environment of a de novo gene may not have been adequately assessed in terms of risk.

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