Risk Characterisation Ratios

The exposure assessment (left hand side of Figure 1) and the effects assessment (right hand side of Figure 1) taken together lead to a risk assessment that determines the likelihood and severity of adverse effects in the exposed population (human, animal or the environment). This is conducted by comparing the Risk Characterisation Ratios (RCR) such as Predicted Environmental Concentration (PEC)/Predicted No Effect Concentration (PNEC) - PEC/PNEC for the various ecosystems to be protected or the margin of safety (MOS) for exposed human populations. 

Guidance to date supports the risk assessment principles for general chemical substances already published by the Commission (1996). Consequently, the risk characterisation simply involves a quantitative comparison of the outcome of the hazard/effects assessment with the exposure assessment. For human risk this involves the calculation of the TER (Toxicity Exposure Ratio) and comparing it with the MOS (Margin Of Safety). For environmental risk the PEC/PNEC ratio (Predicted Environmental Concentration versus the Predicted No-Effect Concentration) for the various environmental compartments. 

As shown in the risk assessment figure, the decision making takes place at the risk characterisation step, where the results of the environmental distribution, the calculated concentration, and the ecotoxicological data, the effect concentration, come together. The most common way is to divide the predicted environmental concentration by the effect concentration in the acute or chronic situation, called the PEC-PNEC-ratio. In the European Union the toxicological concentration is divided by the predicted environmental concentration revealing the TER the toxicity-exposure-ratio. 

In a quantitative human health risk characterisation, the exposure data for relevant use situations is compared to the pivotal NO(A)EL to determine either that the derived Margin of Safety (MOS) is exceeded or that the ratio of the level of exposure/AOEL does not exceed 1. If this is the case, the risk characterisation of the biocidal product should be acceptable. 

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... 

---