Total Diet Study
In Total Diet Studies (TDS), substance occurrence data is obtained from measuring food products as consumed. TDS offers a more direct measure of substance concentrations compared to traditional monitoring and surveillance programs that are concerned with contamination of raw agricultural commodities. In a TDS, food selection is based on national consumption data in such a way that 90 to 95% of the usual diet is represented by the samples. Selected foods are collected, prepared as consumed and related foods are pooled prior to analysis. The compositions these TDS food samples are described by the TDS food sample compositions data module.
In MCRA, TDS concentration data can also be used in dietary exposure assessments, using it as an alternative type of concentration data where the modelled foods are not the raw primary commodities (RACs), but these are TDS food compositions. To link the concentration data to the consumed foods, the TDS food sample composition information is used in the food conversion algorithm in a manner analogous to the use of food recipes describing the composition of a composite food. The main difference is that the translation proportion is always 100% (default). Take, as an example, a TDS food FruitMix that is composed of apple, orange and pear, then a consumed food (food-as-eaten) apple-pie is converted to apple, wheat and butter (in some specific proportions) and subsequently, apple is converted to modelled food FruitMix (100%). Not necessarily all foods as consumed are represented in a TDS food sample. In addition to the TDS food sample compositions, there may be additional foods that are not officially part of a TDS food, but which can be extrapolated to a TDS food sample. Through the use of food extrapolations (read across translations), these foods may be directly linked to a TDS food sample, e.g., by specifying that pineapple is translated to FruitMix, pineapple or foods containing pineapple will also be matched to a FruitMix concentration.
Because TDS samples only contain one single, average measurement, TDS occurrence data can currently only be used for only applicable for chronic exposures assessments. However, when variability information is available for the raw primary foods in the TDS food samples (e.g., from monitoring), this information may be used to approximate the variance of TDS samples.
For more information about Total Diet Studies, visit the TDS-Exposure website http://www.tds-exposure.eu.
TDS reduction to limit scenario analysis
The outcome of a MCRA risk assessment may be that some foods dominate the right upper tail of the exposure distribution. A scenario analysis answers the question to what extent the risk of foods with a high exposure would have been diminished by an intervention or by taking any precautions. To be able to do so, some information is needed about the concentration distributions of the raw agricultural commodities (RACs) that make up the TDS food sample. The decision to intervene or not can be based on comparison between the p95 percentile point of the concentration distribution and a concentration limit value that associated with a high risk.
For p95 ≤ limit, most concentration values are below the value that is considered as a potential risk, so there is no urgency to take any precautions.
When the opposite is true, i.c. p95 > limit, there may be an argument to intervene for this specific food.
In MCRA, limits and p95’s are supplied by the concentration distributions module. In the MCRA interface, a scenario analysis can be checked and the scroll down list allows to select the foods that should be included in the scenario analysis. For the selected foods, concentration reduction factors are computed based on the p95 percentile and the limit value:
These reduction factors (computed for the RACs) are applied to the simulated concentrations on the level of the TDS composite foods of which the conversion paths contain the RACs included in the scenario analysis.
Here, \(c_{\mathit{TDS}}\) is the concentration value of the TDS food.