PNEC Predicted no-effect

Alternative Methods PNEC Predicted no effect concentration... 

MEC measured environmental concentrations ( ig L ), PNEC predicted no effect concentration, REEmec literature reference for the MEC value, REEnmc literature reference for the PNEC value... 

Figure 5.3 Three alternative options to assess the risk of mixtures 1) mixtures can be tested in the field or the laboratory, particularly completely unknown mixtures 2) if toxicity data on (sufficient) similar mixtures are available, the mixture can be evaluated using a reference value, for example, in a PEC/PNEC ratio and 3) mixtures of which the components are known can be evaluated using component-based approaches (mixture algorithms). PEC = Predicted Environmental Concentration, PNEC = Predicted No Effect Concentration.

Figure 5.12 The principle of tiering in risk assessment simple questions can be answered by simple methods that yield conservative answers, and more complex questions require more sophisticated methods, more data, and more accurate risk predictions. PEC = Predicted Environmental Concentration, PNEC = Predicted No Effect Concentration, HI = Hazard Index, CA = Concentration Addition, RA = Response Addition, TEF = Toxicity Equivalency Factor, RPF = Relative Potency Factor, MOA = Mode of Action, PBPK = Physiologically Based Pharmacokinetic, BRN = Biochemical Reaction Network.

PNEC Predicted no-effect concentration or level. The maximum level (dose or concentration) that, on the basis of current knowledge, is likely to be tolerated by an organism or ecosystem without producing any adverse effect. 

From the hazard characteristics of the surfactants, like NOEC the PNEC (Predicted No Effect Concentration) can be deduced. 

A knowledge of chronic and sub-acute toxic effects is the basis of a risk-assessment procedure which is closer to natural conditions. It is decisive to know what concentration of surfactant causes no observable effects any more. For the quantitative description of a chronic exposure situation, the NOEC value is used. By the eventual use of additional safety factors a so-called PNEC (predicted no effect concentration) value can be derived. The latter describes a situation where in the environment no deleterious effects should be expected any more. Aquatic toxicity and biological degradation are closely connected with each other insofar as a... 

Risk assessment can be summarized in the following two relationships and using the terminology PEC (predicted environmental concentration) and PNEC (predicted no-effect concentration) ... 

For the ecological assessment, risk analysis was based on the traditional PEC/ PNEC ratio (Hazard Quotient) where PEC is the predicted environmental concentration (resulting from chemical analysis) and PNEC the predicted no-effect concentration. Ecological assessment for aquatic species was based on rainbow trout or fathead minnow while terrestrial assessment was based on small rodents like mice rats and rabbits. Exposures associated with HQ<1 were considered negligible. 

The objective is to predict the concentration of the substance below which adverse effects in a particular environmental compartment are not expected to occur, i.e., the predicted no effect concentration (PNEC). However, in some cases, it may not be possible to establish a PNEC, and a qualitative estimation has to be made instead. An assessment factor is applied to... 

The method compares the predicted environmental concentrations (PECs), as indices of exposure, with predicted no effect concentrations (PNECs), as indices of... 

In general, only valid studies were used to derive predicted no effect concentrations (PNECs). Because in some cases only a few valid data were available, studies valid with restrictions have been used based on expert judgement. Invalid or non-assignable studies have not been used. In instances of volatile compounds, valid studies were generally those using closed, flow-through systems, preferably with analytical measurements. 

The assessment of whether a substance presents a risk to the receiving environmental compartment is based on a comparison of the measured or predicted environmental concentration (PEC) of the chemical of concern with the predicted no effect concentration (PNEC) to organisms in the ecosystem. This is briefly discussed in Chapter 7.4. Studies carried out so far, e.g. by Vandepitte and Feijtel [91], show that the risk of anionic surfactants such as LAS, AE and AES for the aquatic environment is low, since the PECs are always lower than the maximum permissible concentrations. 

Effects assessment, by, as in the case of risk assessment for chemicals and pesticides, determining a set of marker organisms (including algae, zebrafish, insect larvae, benthic worm, water flea, etc.) that represent ecosystem components and food networks and are used to indicate acute and chronic effects. This step is also used to define the predicted no-effect concentrations (PNECs). 

The environmental risk assessment approach most commonly adopted consists of estimation of the risk quotient (RQ) (as suggested by Hernando et al. [103]), which is defined as the ratio between the environmental concentration (measured or predicted, respectively MEC and PEC) and the predicted no-effect concentration (PNEC), and can be used to collocate compounds in one of three risk bands RQ < 0.1, minimal risk to aquatic organisms 0.1 < RQ < 1, median risk and RQ > 1, high risk [103—105]. In their risk assessment calculations, [106], further to [107], estimated PNEC values at 1,000 times lower than the most sensitive species assayed, so as to take into account the effect on other, potentially more sensitive, aquatic species to those used in toxicity studies. 

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. 

REACH uses the terms derived no-effects level (DNEL) for hazards to human health and predicted no-effect concentration (PNEC) for hazards to the environment. 

Table 8.4 Predicted environmental concentrations (PECs), predicted no-effect concentrations (PNECs), and risk quotients (RQs) for nano-Ag, nano-Ti02, and CNTs in the environmental compartments air, water, and soil calculated in a realistic (RE) and a worst-case (HE) scenario.

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