Chemical paradigm

The definite establishment of the chemical paradigm was the ciystallization of urease by Sumner in 1926, and further enzymes (tiypsin etc.) by Northrap and Kunitz in 1930/31. In every known case the pure enzyme turned out to be a protein (Sumner and Myrback, 1950). 

Buchner s findings marked a new—chemical—paradigm leading research and theory on enzymes. The activity in scientific research increased significantly due to the new guidance (Table 1.2). Technical development also got a new, scientific basis on which to proceed in a rational way. 

The different approaches to management of stochastic risks for radionuclides and hazardous chemicals are referred to in this Report as the radiation and chemical paradigms (EPA, 1992a). The following discussion of the two paradigms for management of stochastic risks is adapted from previous papers (Kocher, 1999 Kocher and Hoffman, 1991). 

Chemical Paradigm for Risk Management of Stochastic Responses... 

The chemical paradigm for management of stochastic risks is applied to control of exposures to stochastic chemicals under authority of several environmental laws. The chemical paradigm also applies to control of radiation exposures when these exposures are regulated under authority of any laws other than AEA. 

The chemical paradigm also differs from the radiation paradigm in that there are no standards that apply to all controlled sources of exposure and all hazardous substances combined, as in radiation protection standards. Regulations for hazardous chemicals generally apply only to specific release pathways (eg., the atmosphere) or... 

Fig. 3.12. The chemical paradigm for management of stochastic risks (Kocher, 1999).

The chemical paradigm for risk management also is used in regulating exposures to hazardous chemicals that cause deterministic effects and exhibit a threshold in the dose-response relationship. For these substances, RfDs, which are often used to define acceptable exposures, represent negligible doses, because RfDs usually are well below assumed thresholds for deterministic responses in humans and action to reduce doses below RfDs generally is not required. This interpretation is supported by cases where doses above an RfD are allowed when achieving RfD is not feasible. A particular example... 

In contrast, acceptable in the chemical paradigm usually means negligible because further reductions in risk usually need not be considered even if they would be cost-effective, and unacceptable ... 

Table 3.5—Differences in interpretations of acceptable and unacceptable risks in radiation and chemical paradigms for management of stochastic risks. ...

Description of Risk Interpretation in Radiation Paradigm 1 Interpretation in Chemical Paradigm ... 

A proper reconciliation of the radiation and chemical paradigms for risk management is important to the development of a comprehensive and risk-based hazardous waste classification system. In particular, the proposed waste classification system developed in Sections 6.2 and 6.3 of this Report is based fundamentally on the concept that an acceptable risk generally can be substantially greater than a negligible risk. This distinction is used to define different classes of waste that pose an increasing hazard. 

Shilov s catalytic process using a mixture of Pt(II) and Pt(IV) salts for the conversion of methane into methanol and methyl chloride in aqueous solution makes a chemical paradigm for alkane functionalization. One of the new approaches finds oxidative functionalization of methane is catalyzed by a (bipyrimidine)platinum(II) complex in concentrated sulfuric acid at 100 In... 

The Continuous Stirred Tank Reactor (CSTR) has provided a chemical paradigm for nonlinear complex dynamics for almost a century. Advances in this regard are reviewed with special emphasis on polymerization. 

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