Risk assessment process, hazardous wastes

The process of risk assessment for hazardous waste sites is still under development, and so necessarily is the development of regulations that build on risk assessment, but the commitment to utilize risk assessment appears firm. 

PBPK models improve the pharmacokinetic extrapolation aspects of the risk assessment process, which seeks to identify the maximal (i.e., safe) levels for human exposure to chemical substances (Andersen and Krishnan 1994). PBPK models provide a scientifically sound means to predict the target tissue dose of chemicals in humans who are exposed to environmental levels (for example, levels that might occur at hazardous waste sites) based upon the results of studies where doses were higher or were administered in different species. Figure 2-4 shows a conceptualized representation of a PBPK model. 

Fig. 3.4. Depiction of probabilistic exposure and risk assessment process for hazardous waste disposal (Garrick and Kaplan, 1995).

Dose-Response Relationships. The primary objective of this study is to set forth the foundations of a risk-based waste classification system that applies to hazardous chemicals and radionuclides. Most aspects of the risk assessment process that provide the basis for establishing this system are conceptually the same for chemicals and radionuclides, although the specific data (e.g., solubilities) may differ. One important exception is the assumed relationship of the probability of a response to a unit dose of a substance that causes stochastic effects, which is called the dose-response relationship There are important conceptual differences in the way this relationship has been defined and used for hazardous chemicals and radionuclides, and these differences could pose a major impediment to development of a risk-based waste classification system that applies to both types of substances on a consistent basis. These differences are elucidated in the following section. 

In general, calculation of the risk or dose from waste disposal in the numerator of the risk index in Equation 6.2 or 6.3 involves the risk assessment process discussed in Section 3.1.5.1. As summarized in Section 6.1.3, NCRP recommends that generic scenarios for exposure of hypothetical inadvertent intruders at waste disposal sites should be used in calculating risk or dose for purposes of waste classification. Implementation of models describing exposure scenarios for inadvertent intruders at waste disposal sites and their associated exposure pathways generally results in estimates of risk or dose per unit concentration of hazardous substances in waste. These results then are combined with the assumptions about allowable risk discussed in the previous section to obtain limits on concentrations of hazardous substances in exempt or low-hazard waste. 

In March 1982 the American Chemical Society sponsored a symposium on risk assessments of hazardous chemical waste sites, and the chapters of this volume are the final versions of the papers that were presented and discussed at this symposium. The first chapters present the problem the history of the development of Superfund legislation and the arguments about the most appropriate approaches to risk assessments, specific cases of hazardous waste problems in Louisiana, the problems of Love Canal and their bearing on risk assessment, and the impacts on human health that can result from hazardous waste sites. The next broad topic of the symposium was the central problem of methodology of risk assessment. The practical problems that confront the field teams who examine specific chemical waste sites are what to monitor, how to monitor, and how to have reasonable assurance of the reliability of the results of monitoring. A final chapter considers a problem of central importance to the Superfund effort how to incorporate risk assessment into the regulatory process. 

A hazard is anything that will produce an adverse effect on human health and the environment. In environmental risk assessment, the hazard component generally refers to toxicity. Exposure is the quantitative or qualitative assessment of contact to the skin or orifices of the body by a chemical. Traditional pollution prevention techniques focus on reducing waste as much as possible however, risk assessment methods used in pollution prevention can help quantify the degree of environmental impact for individual chemicals. This approach provides a powerful tool that enables engineers to better design processes and products by focusing on the most beneficial methods to minimize all aspects of risk. 

Scientists and engineers involved in hazardous waste risk assessment often have an innate appreciation of the risks associated with hazardous wastes. However, the pubhc, especially those who live near a hazardous waste site or facility, require information regarding the risk assessment process, its uncertainties, and the value judgments that have been made. This information is conveyed through risk communication, an integral part of the risk assessment process. 

The chemical risk-assessment process begins by identifying chemicals of concern, potential pathways of exposure, and at-risk populations. Consider, for example, a Superfund hazardous chemical waste site, a pesticide manufacturing facility that operated from 1950 to 1970, when it went out of business, and was subsequently razed. Its 20 years of operation were characterized by sloppy waste disposal practices and numerous complaints from nearby residents to local authorities. The site was reported to the U.S. Environmental Protection Agency (ERA) in 1983, and a preliminary site investigation was conducted pursuant to the federal Comprehensive Environmental Response, Compensation and Liability Act of 1980 (CERCLA, or... 

ENVIRONMENTAL SAMPLING FOR HAZARDOUS WASTES Table I. The Process of Environmental Risk Assessment... 

The SFA requires the definition of respective substances, a comprehensive analysis of the system (i.e. boundaries), and it is always limited in its extent due to process properties and data availability. Within this chapter the implementation of SFA for tracing hazardous substances in international informal e-waste treatment has been proved to be a useful method. To assess the hazardous consequences and potential risks of the selected chemicals to humans and the environment caused by informal recycling activities in those regions, different models exist, from which four have been chosen according to their specific focus and various pros and cons. 

The EPA makes decisions about clean-up of abandoned hazardous waste sites under the so-called Superfund law. Risk assessment outcomes are one guide to the decision process. The agency has declared that, for carcinogenic contaminants, clean-up must reach lifetime risks somewhere in the range of one in 10 000 to one-in-one million most decisions seem to aim at risks of one in 100 000 or lower. Hazard index values for non-carcinogens are not expected to exceed one. Costs and technical feasibility figure heavily in these decisions. 

Assessment of a company s waste minimization needs includes examining the content of and volume of hazardous waste streams it generates, and the processes or operations that generate them. The object of this step is to prioritize the needs of the company, based on environmental risk, liability, and economic criteria. 

Estimates of risks to human health resulting from disposal of hazardous wastes will nearly always be calculated values based on models. Even if health effects were to occur in the future, they are likely to be unobservable in the background of similar effects from all causes. Therefore, mathematical predictions of risks are required. In general, risk assessment is the process by which toxicology data... 

From the perspective of the chemist, DQA can be broken down into seven steps shown in Figure 5.3. Similar to the DQO process, the steps may undergo several iterations before the final statement is formulated depending the purpose of data collection, some of these steps may be modified or even omitted. For example, a DQA conducted for hazardous waste disposal data will not be nearly as extensive as the one for a risk assessment project. 

But at the same time the regulation drafters are faced with the still more difficult job of doing a risk evaluation. That is, they must recommend public policy decisions as to the acceptable levels of risks for a variety of hazardous waste activities, e.g., acceptable minimums for the efficiency of destruction of hazardous wastes by incineration. In principle, this process may be not unlike the decisions made by a banker about a potential loan, or an insurance underwriter in setting the rate for an insurance policy a risk assessment is made, and an appropriate safety margin is factored into the interest rate or the policy premium to arrive at an acceptable level of risk for the individual case (but based on experience and projections for a large number of cases). 

---