Migration Worst case

It is assumed that the moisture content of the soil has been determined to be approximately 50% under worst-case conditions. Using this information and the results from vendor tests, it has been determined that a minimum dose of one part solidification reagent to two parts soil is required for the migration control of lead. Testing has shown that the optimum solidification reagent mixture would comprise ca. 50% fly ash and ca. 50% kiln dust. Thus, ca. 7000 t (6364 T) each of fly ash and cement kiln dust would be required. The reagents would be added in situ with a backhoe. As one area of the soil is fixed, the equipment could be moved onto the fixed soil to blend the next section. It may be anticipated that the soil volume would expand by ca. 20% as a result of the fixation process. This additional volume would be used to achieve the required slope for the cap. An RCRA soil/clay cap placed over the solidified material is necessary to prevent infiltration and additional hydraulic stress on the fixed soil. It is estimated that the fixation would reduce lead migration by 40% and that the fixed soil may pass the U.S. EPA levels for lead. 

A second possibility consists of experimentally determining the SST limits from measurements at the worst-case conditions (n measurements with standard deviation 9,12,13 gg-p limit is defined as the lower or upper limit of the one-sided 95% confidence interval around the worst-case average result. For example, for resolution, the lower limit will be considered, while for migration time it would be the upper. The confidence intervals are defined as in Equations (16) and (17), when considering the lower or the upper limit, respectively. 

In order to use the migration equations, especially the generally accepted equation (7-51), values for the partition coefficient K of the migrant between P and L and the diffusion coefficient DP of the migrant in P are needed. For migrants with a high solubility in the foodstuff or simulant, the value K = 1 can be used and a worst case estimation is obtained in this way. 

Indirect migration assessment by compositional analysis of plastics Assessment by worst-case assumptions of total mass transfer... 

Reynier A, Dole P and Feigenbaum A, 1999, Prediction of worst case migration presentation of a rigorous methodology. Food Additiv. Contam. 16 (4), 137-152. 

FDA also concluded that establishing a 0.5 pg/kg dietary concentration as the threshold of regulation is appropriate because it corresponds to a migration level that is above the measurement limit for many of the analytical methods used to quantify migrants from food-contact materials. Thus, decisions are usually made based on dietary concentrations that result from measurable migration into food or food-simulating solvents rather than on worst-case estimates of dietary concentration based on the detection limits of the methods used in the analysis. 

Mass balance estimation of worst case styrene migration... 

Interpretation of result The calculated migration values here are realistic since results calculated using Eq. (14-4) cannot be larger than the mass balance result (Example 14-1). The calculated amount of styrene is still above the assumed sensory threshold limit of 0.1 mg/kg in the product for the worst case in step 4 but is equal to the estimation using the experimental diffusion coefficient in step 5. 

In the following Dp-values calculated with the refined Eq. (15-3) and partition coefficients KpF assumed to equal 1 are used for estimating worst case migration rates for additives from polyolefins with Eq. (7-51). These estimated values are compared with experimentally obtained migration values carried out under well defined conditions for several additives from HDPE and different PP-types (Table 15-3a) into olive oil (O Brian et al., 1999 and 2000). The results are summarized in Table 15-3b. 

Restrictions for the residual amount of a component instead of a specific migration limit are set by the legislator in cases where specific migration of a component is difficult to obtain (for example, because the component is very volatile) or impossible to determine directly (for example, if the component is very reactive and would react with the food simulant). There are two ways to determine the residual content, by worst-case calculation or by analytical determination. The generic approach is shown in Eig. 5.3. 

In order to use eqn 8.21 in practical cases the availability of data for two fundamental constants is needed (i) the partition coefficient, Kpp, of the migrating compound between the polymer P and the foodstuff or simulating liquid F and (ii) the diffusion coefficient. Dp, of the migrant in P. So far upper limits for migration amounts are needed from regulatory standpoints, predictions of worst case scenarios can start with the assumption of good solubility of the migrant in F and consequently A pp = 1 can be used. Much... 

For borderline cases where recoveries are outside of the analytical tolerance, at say 50-70%, it is arguable whether correction of the concentrations found in the migration test for the recovery is justified. But it can be viewed to be a worst case and so in principle it is recommended. Losses may also occur due to insolubility of the substance in the food simulant or adsorption onto glass/metal surfaces and this should be investigated by rinsing the cell with a suitable solvent. 

When applying the conventional food contact ratio the worst-case migration potential did not exceed the SML for any of the substances derived from plastics nor did the calculated worst-case exposure exceed the ADI/TDI or other exposure restriction value in any products. However, when the actual food contact ratio was applied the ADI/TDI or other exposure restriction value of several substances could theoretically be exceeded. The worst-case calculations assume that intimate contact is made with the entire surface of the packaging. This is not the case for the majority of snack foods that are solids or semi-solids and so the actual area of contact made will be less than the total area available for contact (e.g. crisps). The levels of those migrants (diisobutyl phthalate, dicyclohexyl phthalate, dibutyl sebacate, diphenyl 2-ethylhexyl phosphate and 2-ethyl-1-hexanol) that had the potential to exceed the assigned restrictions, assuming 100% migration, were determined in foods. Of the five substances tested for, only one, dicyclohexyl phthalate, was detected in one of the foodstuffs (tortilla corn chips), at a concentration of 0.60 ppm. 

Relatively high levels for the worst-case migration potential for styrene were also calculated (the SML for styrene is currently under review) and the concentration of styrene in the appropriate foodstuffs was determined. Low levels of styrene were measured but in all cases were less than 5 ppb. Thus despite the high contact temperatures between the foodstuff and the packaging, the relatively high packaging area mass of food ratio and the presence of fat on the food surface, the migration levels observed were low. 

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