Hazard Assessment Risk Model,

The Defense Priority Model (DPM) is designed to provide an estimate of the relative potential risk to human health and the environment from sites containing hazardous materials. The DPM evolved from a model called the Hazard Assessment Risk Model (HARM) developed by Oak Ridge National Laboratory from 1984-1986 for the Air Force. The automation of DPM was done first in KES(r) and then in Arity Prolog(r) for use on an IBM-PC/AT class machine. The computerized model has already become more sophisticated than the paper model and as development continues, it is possible to take advantage of additional expert system features. This paper is designed as a case study of DPM development and presents the reasons for the choice of expert system environment and its evolution, the current scope of the model, and planned additions that will increase the functionality of model in the future. The methodology used to evaluate this expert system is also described. 

A large number of research and review papers have been published in recent years on the integration of data on physicochemical properties, in vitro derived toxicity data, and physiologically based kinetics and dynamics as a modeling tool in hazard and risk assessment [72-85]. 

On July 18, 2000, the Agency released HWIR-waste exemption levels for 36 chemicals that were developed using a risk model known as the Multimedia, Multi-pathway and Multi-receptor Risk Assessment (3MRA) Model.17 The May 16, 2001, HWIR-waste rule revised and retained the hazardous waste mixture and derived-from rules as previously discussed in this module. In addition, the rule finalized provisions that conditionally exempt mixed waste (waste that is both radioactive and hazardous), if the mixed waste meets certain conditions in the rule.5... 

As it has been shown in this chapter knowing the concentrations of chemicals in the environment is a key aspect in order to carry out meaningful hazard and risk assessment studies. Predicting concentrations of chemicals can serve as a quick and robust way to produce an acceptable screening level assessment however if further precision is desired, the complexity of real environmental scenarios can make it a cumbersome and unaffordable task. Models improvement requires not only refining their computation algorithms but also and more important, implementing new inputs and processes in order to better describe real scenarios. 

Table 3 describes the main parts of an environmental risk assessment (ERA) that are based on the two major elements characterisation of exposure and characterisation of effects [27, 51]. ERA uses a combination of exposure and effects data as a basis for assessing the likelihood and severity of adverse effects (risks) and feeds this into the decision-making process for managing risks. The process of assessing risk ranges from the simple calculation of hazard ratios to complex utilisation of probabilistic methods based on models and/or measured data sets. Setting of thresholds such as EQS and quality norms (QN) [27] relies primarily on... 

In the past, risk assessment consisted largely of computer-based models written to start from hazard assessment assays, such as chronic toxicity assays on rodents, encompass the necessary extrapolations between species and between high and low doses, and then produce a numerical assessment of the risk to human health. Although the hazard assessment tests and the toxic end points are different, an analogous situation exists in environmental risk assessment. A matter of considerable importance, now getting some belated attention, is the integration of human health and environmental risk assessments. 

Bartell SM, Gardner RM, O Neill RV. 1988. An integrated fates and effects model for estimation of risks in aquatic systems. In Adams WJ, Chapman GA, Landis WG, editors. Aquatic toxicology and hazard assessment. Volume ASTM STP 971. Philadelphia (PA) American Society for Testing and Materials, p 261-274. 

Mackay, D., Hubbarde, J., and Webster, E., The role of QSARs and fate models in chemical hazard and risk assessment, QSAR Combinatorial Chem., 22, 106-112, 2003. 

ISO 16312-1 2006 Guidance for assessing the validity of physical fire models for obtaining fire effluent toxicity data for fire hazard and risk assessment—Part 1 Criteria. 

It would appear to be worthwhile to support efforts to develop risk assessment approaches along the lines I have discussed rather than join a consensus saying that it cannot be done, or in supporting selecting mathematical models which arbitrarily define hazards and risks. 

A similar application of ecotoxicological data is hazard assessment. Unlike risk assessment, hazard assessment is nonprobabilistic and relies upon indices rather than probabilities. One such index is the hazard quotient , which is the ratio of the expected environmental concentration (based upon field surveys or simulation models) divided by a benchmark concentration. The benchmark concentration is derived from some measure of toxicity such as the LC50 or no-observed-effect level. Hazard assessments are often conducted at different levels or tiers of increasing complexity and specificity if a chemical is identified as potentially hazardous by tier (the least complex and specific test), a decision is made to take action or, if more information is needed, to proceed to tier 2 tests. After tier 2 tests, a decision is made whether to take action or proceed to tier 3 tests, and so on. This process is repeated until it is decided that there is enough information to determine whether or not there is significant ecological hazard. If there is, then regulatory action is taken. 

There has been a question about which method is more appropriate for the analysis of toxicity data. In order to make a selection it is important to understand that toxicity data is used for hazard or risk assessment. Curve-fitting and regression modeling has clear advantages. 

Agencies like the EPA commonly employ default assumptions in exposure, hazard assessment, and risk assessment assumptions. In most of these matters, the amount of available evidence is far less than that available for hormesis. Furthermore, our collective information confirms that among the available toxicological models, the hormetic one is the most predominant. 

---