Specificity, ecological principles

Environmental toxicology is based on the premise that the amount of chemical reaching an active site in, or on the surface of, an organism determines whether a compound will exert a specific beneficial or adverse effect or pose an ecological or health risk. This basic toxicological principle is embodied in the expression attributed to Paracelsus that it is "the dose that makes the poison."... 

In most cases, evaluations of ecological impacts are site-specific and, as a consequence, are not considered when establishing a generally applicable waste classification system. These impacts normally are addressed in disposal site selection, design, and operation, and they may be used in establishing waste acceptance criteria for the site. To the extent that ecological impacts can be evaluated generi-cally, NCRP believes that the principles and framework for risk-based waste classification presented in this Report are sufficiently flexible to take them into account. 

Evidence from recent studies in ecology suggest that functional redundancy exists within some natural communities, but the relative contribution of different species to specific functions is far from equal, and the disappearance of certain species (i.e., dominants and keystone species) can have disproportionately large effects on overall system function and the occurrence of other species. For this reason, the precautionary principle advises that species loss be considered at least as a cause of incremental damage. Landscape-level models offer the possibility to improve our interpretation of local phenomena (e.g., species disappearance) in a wider spatial context. 

Because olfactory receptors can detect a wide array of structural types (in principle, any), the evolution of pheromones has been influenced primarily by ecological factors. First, certain types of chemical compounds can travel great distances and convey information in complex environments, including those that lack light. These compounds can be adapted, through evolution, to the medium within which the animal functions (e.g., water or air). Second, other types of chemicals are sufficiently stable that they can convey information for extended periods terrestrial species benefit most from these. Third, complex structures and/or mixtures of smaller structures can be information-rich and highly specific (i.e., immune to eavesdropping by other species because of the selective nature of olfactory receptors). Finally, products that are readily and naturally produced by... 

Terrestrial wildlife movements are such that site-specific tools are more efficiently used to refine exposure estimate. In this case, site-specific exposure estimates are used and compared with safe thresholds for toxicity, termed toxicity reference values (TRVs). Toxicity reference values for wildlife have been developed for energetic compounds. This chapter presents a brief overview of the processes used to establish these tools for ERA for explosives and related soil contaminants that are frequently of potential ecological concern at the affected military sites. This chapter also provides recommendations for use of these values in the ERA process. Investigations addressing the importance and extent of habitat disturbance as a component of the ERA process on explosives-contaminated ranges are reviewed in Chapter 11. General bioaccumulation principles and applications of the bioaccumulation factor and bioconcentration factor (BAF and BCF, respectively) concepts that are often employed in the ERA process to determine bioaccumulation potential of MC for terrestrial receptors are reviewed in Chapter 10. 

Basic and applied research efforts show that the oxidative transformation of renewable feedstocks represents a promising approach for the production of high-value chemicals under environmentally acceptable conditions. Many laboratory-scale processes are carried out under mild conditions, and the employment of molecular oxygen ensures ecological and economic advantages. In these processes, a crucial role is played by the catalytic step that requires a specific selectivity toward the desired product. In principle, either enzymatic catalysis or chemical catalysis can be effectively employed in a given process and, in some cases, the performance of the different processes is quite similar as presented in the following sections. 

The modem industrialized world would be inconceivable without catalysts. There is no other technical principle which combines economic and ecological values as closely as catalysis. The development of chemical products iu advanced, industrialized societies will only be technically, economically and ecologically possible by means of specific catalysts. Examples include the specific production of stereochemicaUy pme pharmaceuticals, the constraction of tailored polymer materials, the reduction of pollutants from manufacturing plants and combustions systems (e.g. power stations, motor vehicles). Another major topic for the 21 century, the production, storage, and conversion of energy, will also be promoted by catalysts [4]. 

Risk may arise from any chemicals released into the environment, intentionally or by accident, during manufacture, use or dissipation of the products. The expected concentration time profile for chemicals at specific locations in the various environmental media - water, air, soil and biota - may result in hazards to humans and the environment. Hence, ecological risk assessment must evaluate the probability whether the exposure level of potential contaminants may exceed effective (i.e. toxic) concentrations in the environmental compartment of concern. The basic principle is the comparison of the environmental and the toxic concentrations of the contaminants ... 

---