W5 : Chemical contaminants

Question 1

What are the 6 different types of chemical contaminants that can be found in food, from farm to fork?

Answer 1

1) Natural chemical contaminants (mycotoxins in peanuts / cereal grains ; phytotoxins in plants)

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2) Pesticide residues

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3) Environmental contaminants

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4) Process contaminants

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5) packaging contaminants

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6) illegal substances

Question 2

Envrionmental contaminants can be further categorised into what 2 categories?
Give an example of each

Answer 2

1) Organic contaminants
- Antibiotic usage
- Dioxin accumulation in fish, where dioxins are released into waste water from industrial processes

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2) Inorganic contaminants
- Mecury in fish
- Cadmium in spices
- Lead in cereal grains / rice

Question 3

What are process contaminants?

Answer 3

Undesirable chemicals formed in foods as a result of chemical reactions between natural components in food, or between food additives.

Question 4

Acrylamide is a process contaminant. How is it formed, what are the prdocuts that are usually associated with it and what are some mitigation strategies?

Answer 4

Through Maillard reaction of amino acid (asparagine) and reducing sugars. Usually associated with starchy products (potato, cream crackers etc)
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Mitigation strategies:
1. Reduce temperature during frying
2. Reduce reactant conc –> e.g. if deep frying potato, can genetically modify potato to reduce asp content so less acrylamide formed
3. Reduce frying time

Acrylamide -> causing browning of crackers

Question 5

Benzene is a process contaminant. What type of products is it usually found in and how does it form?

Answer 5

Usually found in beverages.
- It is formed in low levels due to reaction between additives, ascorbic acid (Vit C) + benzoate salts

Question 6

How do packaging contaminants cause contamination in food?

Answer 6

It is when chemicals in food packaging leach into food, especially exposure to :
1. High temp
2. Long durations
3. Food to material contact ratio is high

Question 7

What are some examples of packaging contaminants?

Answer 7

1. Plasticisers -> to make plastic packaging more flexible and mouldable. Commonly used in PVC, such as plastic cups/containers

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2.Lead and cadmium present in ceramic glasses.

Question 8

What is the general name for illegal substances found in food?

Answer 8

Adulterants

Question 9

What is an adulterant?

Answer 9

A substance deliberately added to a product but not listed as an ingredient, or a substance that ends up in a product by accident when it is made

Question 10

_____ is an adulterant added to milk to artificially boost protein content.

Answer 10

Melamine

Question 11

What is an example of an illegal substance / adulterant that may unintentionally end up in a product, and how does it arise?

Answer 11

Methanol in alcoholic drinks.
- Due to unclean containers during fermentation
- Contamination of microbes during fermentation

Question 12

Methanol is an adulterant that can be accidentally introduced during fermentation.

Is methanol also deliberately added? If yes, when is it usually added and why?

Answer 12

Methanol is deliberately added at the end of processing, where drinks are mixed with low grade industry ethanol (containing 5% methanol) to artificially boost alcohol content, so can sell at a higher price point.

Question 13

What is the Margin of Exposure (MOE)?

Answer 13

The Margin of Exposure (MOE) is a risk assessment tool used to evaluate the level of concern for a chemical contaminant that has no established safe threshold (e.g., genotoxic carcinogens). It compares the estimated human exposure to a reference point (BMDL) derived from toxicological studies.

Question 15

For genotoxic carcinogents, a margin of exposure (MOE) of ____ presents a low public health concern.

Answer 15

10,000

Question 16

What is a benchmark dose? What is meant by BMD10?

Answer 16

A dose (conc) of a carcinogen corresponding to a specified change in effect over background.
- BMD10 : the dose that will give rise to a 10% of the effect level

Question 17

Wat is the bench mark dose lower confidence limit (BMDL)? What does BMDL10 mean?

Answer 17

• The lower confidence limit (95%) of a point on the dose-repsnse curve that characterizes the adverse effect, to account for the uncertainity in data
• BMDL10 : the dose that gives rise to 10% of the effect level, factoring uncertainties such as population sensitivity
• The BMDL is a more conservative estimate of BMD that will give rise to a specified response level.

Question 18

What is the “response” / “adverse effect” level that is being measured in the MOE curve?

Answer 18

A measurable outcome researchers use to observe and quantify the dose-response relationship.
- For example, if want to measure development of cancer, can use more quantifiable measures such as biomarkers (formation of DNA adducts from carcinogen + DNA)

Question 19

Since the BMDL is a conservative measure of BMD, it is safe enough to treat it as a safety reference value. (i.e. if i eat below 0.15 mg/kg body weight/week, it means that i definitely won’t develop cancer)

Answer 19

False. For genotoxic carcinogens, there is typically no “safe threshold” because even small amounts below the BMDL can theoretically increase the risk of cancer.

Question 20

State the equation of margin of exposure.

Answer 20

Reference value (such as BMDL) / Estimated dietary exposure

Question 21

What is a tool that can be used to measure the estimated dietary exposure to a contaminant?

Answer 21

Total diet survey (TDS)

Question 23

Describe how a total diet survey works.

Answer 23

1) The carcinogen is identified in foods that are of higher risk (have higher concentration of carcinogens). For example, acrylamide in french fries commonly consumed in SG.
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2) Dietary surveys are conducted to gather information on how much of these foods are consumed by different population groups (e.g., children, adults, elderly).
Example: In Singapore, consumption patterns for French fries might be higher among teenagers and younger adults.

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3) Representative samples of the identified foods are collected from various sources to reflect the typical diet of the population. (e.g. sampling fries from McDonalds / burger king)

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4) Samples are tested for carcinogen levels using analytical techniques like HPLC, GC-MS, or ELISA to measure the concentration of the contaminant in the food.

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5) Dietary exposure is calculated

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6) Derive MOE by comparison with BMDL.

Question 24

A low**er Margin of Exposure means a ____ health risk.

Answer 24

Higher
- because lower margin of exposure means you are exposed to the carcinogen less before you develop the adverse effect / response.

Question 25

What is the difference between NOAEL and MOE in terms of units?

Answer 25

NOAEL : expressed as daily intake values

MOE : expressed as weekly / monthly values

Question 26

What substances are NOAEL/ADI and MOE used for respectively and why?

Answer 26

1. NOAEL : for chemical additives, where their consumption patterns are controlled and predictable (due to regulation). Daily exposure is consistent and measurable, making lifetime exposure estimates (e.g., Acceptable Daily Intake, ADI) based on NOAEL appropriate.

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MOE : used for chemical contamiants which are involuntary and irregularly consumed, and have cumulative effects and lead to chronic issues. Thus, MOE provides a flexible, comparative measure of risk, focusing on long-term exposure rather than fixed daily thresholds.

Question 27

What is the ALARA principle in risk management?

Answer 27

“As low as reasonably achievable”.
- It is a is a guiding concept in managing exposure to hazards, particularly those with no established safe threshold