Risk assessment tiered

This chapter has outlined the general principles of the use of extrapolation in criteria setting and risk assessment. Extrapolation is used in the setting of criteria, where only effects are considered, as well as in risk assessments, where both effects and exposures are considered. In formulating approaches to criteria setting and risk assessment, tiers are often used to simplify the process. In keeping with the... 

In human risk assessment, tier 4 approaches would require PBPK modeling, BRN models, or other highly specific approaches. In ecological risk assessment, emphasis can be put on modes of action in relation to subgroups of exposed species (e.g., insecticidal action and focus on impacts on insects). This type of approach was proposed some years ago (Posthuma et al. 2002), and has been applied in the evaluation of pesticide risks (De Zwart 2005 Henning-de Jong et al. 2008). 

Research is needed on developing the triggers to move from one hazard tier to the next and on risk assessment methods. 

Interest has been expressed in the possibility of using biomarker assays as a part of risk assessment for regulatory purposes, and some workers have suggested tiered testing procedures that follow this approach (see, for example, Handy et al. 2003). It is to be hoped that regulatory schemes, such as that of REACH (see European Union 2003), will be sufficiently flexible to incorporate new assays and testing strategies as the science advances. 

It is advisable, then, in a tiered approach to concentrate first on crops and activities (scenarios) that are considered to be relevant with respect to the expected level of exposure and to exclude those not relevant. Second, whether or not the toxicological properties of the product may lead to general restrictions on re-entry should be investigated. If both the likelihood of reentry and the hazard due to the toxicity of the compound cannot generally be neglected, a risk assessment over several steps should be carried out. The assessment may be based on surrogate data and "worst-case" assumptions at first and then refined, if necessary. One possible approach to a tiered evaluation procedure is presented in Figure 1. 

If the classification and labeling of the product according to Tier II indicate that body protection is necessary, the following specific instructions, points 2 and 3, should be included on the label, unless the risk assessment according to Tiers III through V indicates otherwise. Point 2 ... 

Maund SJ, Hamer MJ, Warinton JS et al (1998) Aquatic ecotoxicology of the pyrethroid insecticide /amMa-cyhalothrin considerations for higher-tier aquatic risk assessment. Pestic Sci 54 408-417... 

Environmental risk assessment examines the potential adverse effects to ecosystems from exposure of the aquatic, terrestrial and air components. Initial assessment normally focuses on the aquatic compartment, including effects on microorganisms in waste water treatment plants. This first tier risk assessment can be extended to cover the sediment part of the aquatic compartment and the soil compartment. At higher tonnage levels, effects relevant to the food chain are evaluated, i.e., secondary poisoning. Diderich in Chapter 8 of (73) discusses the principles of EU environmental risk assessment. 

Fig. 2 Scheme of the tiered approach of the European Medicines Evaluation Agency (EMEA) for environmental risk assessment... 

It is concluded that the TTC concept for systemic toxicity is suitable as a starting point for a tiered testing and risk assessment strategy within REACH. However, it is also underlined that the... 

Tiers are widely used to help improve the efficiency of the risk assessment process. They generally start with a simplified assessment to screen out scenarios with obviously high or low risks. 

Data used to describe variation are ideally representative of some population of risk assessment interest. Representativeness was a focus of an earlier workshop on selection of distributions (USEPA 1998). The role of problem formulation is emphasized. In case of representativeness issues, some adjustment of the data may be possible, perhaps based on a mechanistic or statistical model. Statistical random-effects models may be useful in situations where the model includes distributions among as well as within populations. However, simple approaches may be adequate, depending on the assessment tier, such as an attempt to characterize quantitatively the consequences of assuming the data to be representative. 

Giddings JM, Anderson TA, Hall LW, Kendall RJ, Richards RP, Solomon KR, Williams WM. 2000. Aquatic ecological risk assessment of atrazine a tiered, probabilistic approach. Novartis 709-00. Greensboro (NC) Novartis Crop Protection. 

A tiered approach is also used for calculating estimated residues in animal commodities (meat, milk, and eggs), and higher-tier calculations can have a significant impact in decreasing estimates of dietary exposure and risk. The Tier III assessment for atrazine and simazine (Tables 27.3 and 27.4) is based on calculations of the estimated theoretical residue in animal commodities, whereas the Tier I assessments use tolerance values. These theoretical residues are often referred to as secondary residues. Calculations for estimating secondary residues in animal commodities are performed by constructing livestock (beef, dairy, and poultry) diets comprised of treated feed items to obtain a... 

Parkhurst, B.R., W. Warren-Hicks, R.D. Cardwell, J. Volison, T. Etchison, J.B. Butcher, and S.M. Covington (1996). Aquatic ecological risk assessment A multi-tiered approach to risk assessment, 91-AER-l. Alexandria, VA Water Environment Research Foundation. 

Table 7.15. Tier 1 ecological risk assessment of POPs to pelagic organisms in Hong Kong in 2000-2004...

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