Total Diet Study¶
In Total Diet Studies (TDS), dietary exposure is based on whole diets as consumed. TDS offers a more realistic measure of exposure compared to traditional monitoring and surveillance programs, that is concerned with contamination of raw agricultural commodities. In a Total Diet Study, food selection is based on national consumption data in such a way that 90 to 95% of the usual diet is represented. Selected foods are collected, prepared as consumed and related foods are pooled prior to analysis. The composition of a TDS food sample is used in the conversion algorithm in an analogous manner as recipees describing the composition of a composite food (table for FoodTranslations). The main difference is that the translation proportion is always 100% (default). Take TDS food FruitMix which is composed of apple, orange and pear (table for TDSFoodSampleCompositions), then food-as-eaten apple-pie is converted to apple, wheat and butter and subsequently, apple to food-as-measured FruitMix (100%). Not necessarily all foods as consumed are represented in 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 (table for FoodExtrapolations, 100%), pineapple or foods containing pineapple as ingredient enter the exposure assessment. The default translation proportion is 100%. The TDS approach for assessing risks are associated with chronic exposures only, in a single compound context or cumulative exposure assessment. In MCRA, Total Diet Studies are implemented in the chronic risk assessment module. For more information about Total Diet Studies, visit the TDS-Exposure website http://www.tds-exposure.eu.
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 variability of the concentration distribution of the raw agricultural commodities that make up the TDS food sample. These distributions may be characterised by a mean and a dispersion factor, the standard deviation or, preferably, a percentile point e.g. p95. Monitoring samples may be used for this purpose. In addition, for each subsample food an upper concentration limit is needed. This value is interpreted as the concentration that is considered a high risk. The decision to intervene or not is based on the comparison between this upper limit and p95.
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 in table for ConcentrationDistributions. In the MCRA interface, a scenario analysis is checked (optionally) and in the scroll down menu only foods are shown with p95 > limit. Selected foods enter the risk assessment with a reduced concentration value:
where \(c_{TDS}\) is the concentration value of the TDS food with reductionfactor = p95 / limit.
Read across versus TDS compositions¶
After the conversion from food-as-eaten to food-as-measured, part of the foods or their ingredients are not linked to a TDS food. These are so-called failed foodconversions. All other foods or ingredients enter the risk assessment and contribute to the exposure distribution. The total exposure can be traced back to foods that enter the risk assessment through read across translations or through TDS compositions. In the FruitMix example, the total exposure for FruitMix is split into a part due to the consumption of apple, orange and pear, the remaining part relates to the consumption of pineapple. The first part is summarized as exposure due to all TDS sample compositions, the second as foodextrapolation.
For uncertainty see appendix