Skip to 0 minutes and 1 second The branch of medicines that is concerned with how things cause disease is epidemiology. In epidemiology we’re trying to understand associations between particular types of exposure. For example, microorganisms such as bacteria and viruses or chemicals such as mycotoxins and health effects and diseases. When dealing with food contaminants, there are two main methods used for measuring exposure - food-based exposure assessment and biomarkers. Food-based exposure assessment is where we measure how much food you eat and how much toxin is in it. This is the conventional method, and the one that most authorities use to assess exposure.
Skip to 0 minutes and 48 seconds The process of the food-based exposure method is to take a sample of the food and measuring the level of the contaminants in the food and then trying to work out how much of that food - and hence the chemical - is being eaten. This method of measurement can be difficult, as different people eat different amounts. It is especially difficult if the contaminant is not evenly spread throughout the food in question or if there are several different foods containing the chemical. When considering how much people are exposed to a contaminant such as aflatoxin, the probable daily intake (PDI) is used to estimate exposure.
Skip to 1 minute and 29 seconds This is a calculation based on how much contamination is present in the food, how much of the food is consumed by the average individual, and expressed as the amount per kilogramme body weight. However, this estimate is affected by uneven contamination levels of the food. For example, how the toxin may be concentrated in particular units of food rather than being evenly distributed. The difficulties inherent in measuring intake of food. It is especially difficult if there is more than one source of the toxin. Another way to carry out the analysis of how much chemical has been consumed is to take a biological sample, then use it to measure the presence of the chemical or its metabolites in the sample.
Skip to 2 minutes and 18 seconds Blood, urine, saliva, and hair can all be used for biological collection for analysis. These biological markers of exposure, or biomarkers, have the advantage that you are measuring how much is present in the individual without having to estimate how much of the contaminated food they have eaten. Therefore, a biomarker is a measure of internal dose of how much of our body is exposed to these toxins. This is a more accurate marker of biological effect, as it measures what and how much is in the body. According to WHO, a biomarker is a chemical, physical, or biological parameter that can be used to measure interaction between a biological system and the environmental agent.
Skip to 3 minutes and 6 seconds We previously saw how benzo(a)pyrene is metabolised in the body to form DNA adducts. Aflatoxin, which contaminates crops in warm, humid climates, is also metabolised in the body to form DNA adducts. This figure shows that alfatoxin also produces metabolites that are excreted in urine and protein adducts in the blood, although it is the DNA adducts that give rise to mutations as part of the process by which liver cancer occurs. The other metabolites and the protein adducts can be used as biomarkers of exposure because they also show that a person has been exposed to aflatoxin. Consequently, DNA adducts, protein adducts, and the metabolites have all been used to assess human exposure to aflatoxin.
Skip to 3 minutes and 54 seconds In the aflatoxin case study later in this topic, more information will be given on how DNA and protein adducts have been used to understand the association between aflatoxin and liver cancer and between aflatoxin and other health effects. Biomarkers used to measure exposure needs to be carefully validated. For example, what is the relationship between the biomarker measured in the urine or blood and the amount of contaminants that was ingested? This can be worked out through animal studies to understand the metabolism of the contaminant. The method used to measure the biomarker is critical as well, as this must be as accurate and reproducible as possible and be sufficiently sensitive to measure low levels of exposure often found in human studies.
Skip to 4 minutes and 44 seconds It is also good if the method is affordable and can measure a large number of samples in a short time.
Biomarkers and exposure measurement
If we want to understand how food contaminants may affect human health, we need to be able to both measure:
- the amount of the contaminant to which people are being exposed
- and assess the effects of that exposure on health
This video will look at ways of measuring human exposure to food contamination through the use of biomarkers.