Assessing Risks from Chemicals

The European system for regulating synthetic chemicals, described in Chapter 5, is predominantly risk-based . This means that restrictions on the manufacture or use of chemicals must be justified by reference to evidence that there is a risk of the chemical causing a specified type of harm. REACH (Registration, Evaluation, Authorization and restriction of Chemicals) does not define the term risk , but the directive on risk assessment of new substances defined it as the incidence and severity of the adverse effects likely to occur [...] due to actual or predicted exposure to a substance (Article 2 of Directive 93/67/EEC). In the first part of this chapter I look at how risks from chemicals are assessed. What does chemicals risk assessment in practice aim to achieve Can it provide the reliable evidence needed for agreement by all parties on whether or not a chemical poses a risk My answer to this second question is no there are multiple uncertainties in chemicals risk assessment which lead to protracted debates as to whether a chemical poses a risk or not. 

In the second part of this chapter I discuss attributes of chemicals that contribute to their riskiness. In Chapter 101 address how such assessments of riskiness could be used in regulation. 

The hardest part of engineering risk assessment has turned out to be the prediction of the modes of failure. Serious accidents at nuclear installations, such as those at Three Mile Island or at Chernobyl, have been caused by modes of failure that had not been analysed at all. For example, the report of the Presidents Commission on the Accident at Three Mile Island (Presidents Commission, 1979, p9) highlighted that the concentration of the assessment process on more obvious large break scenarios meant that the eventual mode of failure, which was a result of a chain of a number of more minor events, was not even considered. Despite the use of significant resources in the design process, the risk assessment had been unable to characterize the complex system adequately, a system that was totally human-made and defined. In particular, the risk assessment process had not been able to identify modes of failure caused by humans involved in the operations of the reactor behaving in unexpected ways. 

Chemicals risk assessment attempts to characterize the system — of a chemical in the environment or in the human body — and then estimate the risk of the chemical causing harm. A key question is whether the system can be adequately characterized to reliably estimate the probability of harm, or even to identify what harm the chemical may cause. Just as engineering systems have caused harm because they failed in ways that were not predicted, the most serious hazards of synthetic chemicals have often been unexpected, and not considered in risk assessments. 

Chemicals risk assessment generally consists of three stages (1) hazard assessment, (2) exposure assessment and (3) risk characterization. However, REACH divides the first stage into four human health hazard assessment, physicochemical hazard assessment, environmental hazard assessment, and persistent, bioaccumulative 

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US-EPA s Risk Assessment Guidehnes set forth recommended principles and procedures to guide US-EPA scientists in assessing the risks from chemicals or other agents in the environment. They also inform US-EPA decision-makers and the public about these procedures. 

The Interdepartmental Group on Health Risks from Chemicals (IGHRC) in the United Kingdom has published a document entitled Uncertainty Factors Their Use in Human Health Risk Assessment by UK Government (IGHRC 2003). The document intended to lay out the principles used in the United Kingdom. 

IGHRC. 2003. The Interdepartmental Group on Health Risks from Chemicals. Uncertainty factors Their use in human health risk assessment by UK Government. Leicester Institute for Environment and Health, University of Leicester, http //www.silsoe.cranfield.ac.uk/ieh/pdf/cr9.pdf... 

The European Commission s Joint Research Centre (on behalf of DG S ANCO) has started a project known as European Information System on Risks from Chemicals Released from Consumer Products/Articles (EIS-ChemRisks) (EU 2004), which is designed as a network to collect exposure data, exposure factors, exposure models, and health-related data. The overall objective is to develop tools and reference data to enable harmonized exposure assessment procedures in the EU. A toolbox has been designed to collect exposure information from four reference systems to systematically support exposure assessors in the EU ... 

These four stages are identical to the four steps of the risk assessment process set out in a key 1983 US publication on risk assessment (NRC, 1983), demonstrating the influence of the US approach on Europe. It is recognized, however, that this model is not always appropriate, with ozone depletion being quoted as an effect for which stages 2 and 3 do not apply. In these cases regulators have to assess risks on a case-by-case basis and give a full description and justification of their assessments in their report to the Commission. In Chapter 7 I discuss how risk from chemicals are assessed in practice. 

In the next chapter I will look at how risks from chemicals are assessed. Do the current methods of assessment succeed in estimating risks as the probability of harm I suggest that rather than trying to estimate risks we should assess how risky a chemical is. 

Blair et al. (1998) performed a retrospective cohort mortality study of 14 457 workers employed for at least one year between 1952 and 1956 at an aircraft maintenance facility in the United States. Among this cohort were 6737 workers who had been exposed to carbon tetrachloride (Stewart et al., 1991). The methods used for this study are described in greater detail in the monograph on dichloromethane. An extensive exposure assessment was performed to classify exposure to trichloroethylene quantitatively and to classify exposure (ever/never) to other chemicals qualitatively (Stewart et al., 1991). Risks from chemicals other than trichloroethylene w ere examined in a Poisson regression analysis of cancer incidence data. Among women, exposure to carbon tetrachloride was associated with an increased risk of non-Hodgkin lymphoma (relative risk (RR), 3.3 95% CI,... 

The immediate future in risk assessment will focus on the difficult but necessary task of integrating experimental data from all levels into the risk assessment process. A continuing challenge to toxicologists engaged in hazard or risk assessment is that of risk from chemical mixtures. Neither human beings nor ecosystems are exposed to chemicals one at a time, yet logic dictates that the initial assessment of toxicity start with individual chemicals. The resolution of this problem will require considerable work at all levels, in vivo and in vitro, into the implications of chemical interactions for the expression to toxicity, particularly chronic toxicity. 

The principle of Paracelsus that the dose makes the poison is paramount. It means that all chemicals, from whatever source, human manufacture or natural, are potentially toxic at some dose. This is a fundamental concept which underlies toxicology and is crucial to the assessment of risk from chemicals and their safe use. The coroUary to this principle is that aU chemicals are potentially safe at some, perhaps extremely low, dose and therefore most can be used safely. The relationship between the dose and toxic effects of chemicals wiU be discussed later (see pp. 36-9, 298-301). 

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