QUESTION 1.1 (10 marks)
Natural vs Synthetic Chemicals: A Critical Discussion
Many people believe that natural chemicals are safer than synthetic ones simply
because they come from nature. However, this is not always true. The idea that natural
is safe and man-made is dangerous is a myth. Whether a chemical is natural or
synthetic does not determine how harmful it is. What really matters is how toxic the
substance is, the dose taken and how it affects the body.
For example, aflatoxins are natural chemicals produced by a fungus that can grow on
peanuts and grains. These toxins are natural, but they are also among the most
powerful cancer-causing substances known. Another example is the poison in deadly
nightshade which contains toxic alkaloids that can kill a person. Arsenic is a naturally
occurring chemical found in the Earth’s crust but it can poison water and cause cancer.
These examples show that nature also produces very dangerous chemicals.
Many synthetic chemicals are used in medicines, food, and cleaning products to
improve our quality of life. These chemicals go through testing and safety checks before
being sold to the public. For example, paracetamol is a synthetic drug used to relieve
pain and fever. When used correctly, it is very safe. But even natural substances, like
herbal medicines, can be dangerous if not taken properly or if they interact with other
drugs.
Toxicology, the study of poisons, teaches us that “the dose makes the poison.” This
means that any chemical natural or synthetic can be harmful if you are exposed to too
much of it. Even water, which is essential for life, can be deadly if too much is
consumed too quickly. Oxygen can be toxic at high pressures.
People may trust natural products more because they associate them with health and
the environment. Advertising and product labels often use the word “natural” to make
items seem safer or more appealing. However, this is a marketing strategy and not
based on scientific evidence. We should not judge the safety of a substance based only
on where it comes from.
It is important to rely on scientific research and testing rather than assumptions. Both
natural and synthetic chemicals must be studied to understand how they behave in the
human body and the environment. Proper risk assessments should be done for all
chemicals, regardless of their source.
In conclusion, the idea that natural chemicals are always safer is not supported by
toxicological evidence. What really matters is how much of the chemical you are
exposed to, how it enters your body, and how toxic it is—not whether it is natural or
synthetic. Therefore, we should approach all chemicals with careful analysis and not be
misled by common myths or marketing messages.
QUESTION 1.2 (15 marks)
Why Chemical Exposure Risk Perception Can Be Problematic in the Workplace
The article by Khadan, Koohpaei, and Tabar (2017) focuses on how workers in the
chemical industry understand and respond to chemical risks. It shows that people’s
perceptions of chemical dangers are not always accurate. This is a serious problem
because if workers do not fully understand the risks, they might not protect themselves
properly, which could lead to accidents or health problems.
One main reason for poor risk perception is lack of knowledge and training. Many
workers do not have enough education or information about the chemicals they work
with. If someone does not understand how dangerous a chemical is, they might not use
protective equipment or follow safety rules. The article found that better training helps
workers to better understand risks and act safely.
Another issue is familiarity. If someone works with chemicals every day and nothing bad
happens, they may begin to think that the chemicals are not dangerous. This feeling of
safety is false and dangerous. The article explains that people who are used to seeing
or handling chemicals may underestimate the risks, especially if they have not seen
anyone get hurt. The attitudes of workers and the workplace culture also affect risk
perception. If the workplace does not take safety seriously, or if managers do not
encourage safe behavior, workers may feel that safety is not important. The article says
that when managers do not support or enforce safety practices, workers are less likely
to follow them.
Another problem is poor communication. If employers do not clearly explain the risks or
how to handle chemicals safely, workers may get confused or make mistakes. The
article emphasizes that regular and clear communication is important for improving risk
perception. The economic situation of workers can also play a role. Some workers may
ignore safety rules because they are afraid of losing their jobs or because they want to
finish tasks quickly. The article found that financial pressures and job insecurity can
make workers less likely to report safety problems or take time to follow safety
procedures.
Lastly, the availability of personal protective equipment (PPE) is important. If workers do
not have the right gear, or if the gear is uncomfortable, they may not use it. The study
found that when PPE is not provided or not comfortable, workers avoid using it even
when they know the risks. In conclusion, the article by Khadan et al. (2017) shows that
risk perception is affected by knowledge, training, workplace culture, communication,
economic pressure, and availability of safety equipment. All of these factors can lead to
unsafe behavior. Therefore, companies should focus on education, safety culture, and
good communication to make sure workers understand and respond to chemical risks in
the right way.
QUESTION 2 [25]
2.1 ADME of Terbufos and Its Toxicity (15 marks)
Terbufos is an organophosphate pesticide used in agriculture to control pests. Although
it is restricted for professional use, illegal sale in informal areas has led to tragic
poisonings in South Africa. Understanding how terbufos behaves in the body helps
explain why it is so dangerous. This is where the ADME process standing for
Absorption, Distribution, Metabolism, and Excretion takes place.
Absorption:
Terbufos can enter the human body through several routes by eating contaminated
food, breathing it in, or through the skin. In the recent cases, children were poisoned
after eating snacks sold at spaza shops that were contaminated with terbufos. Because
it is fat-soluble, terbufos is absorbed easily, especially through the digestive system.
Even a small amount can be harmful, especially in children whose bodies are more
sensitive.
Distribution:
Once terbufos enters the body, it quickly travels through the bloodstream to various
organs, including the brain, liver, lungs, and kidneys. It crosses cell membranes easily
due to its chemical structure. This wide distribution makes it more dangerous, as it can
affect both the nervous system and vital organs. Children are at higher risk because
their organs are still developing, and their body weight is low, so the concentration of
poison per kilogram is higher.
Metabolism:
In the liver, terbufos is broken down (metabolised) into even more toxic compounds.
One of its main metabolites, terbufos sulfone, binds to and blocks enzymes called
acetylcholinesterase (AChE). These enzymes are crucial for breaking down a brain
chemical called acetylcholine, which is involved in muscle control. When AChE is
blocked, acetylcholine builds up in the body, causing muscles to twitch, breathing to
become difficult, and the heart to beat irregularly. In severe cases, it can lead to death
from respiratory failure. This is why terbufos is considered extremely toxic.
Excretion:
Terbufos and its by-products are eventually removed from the body through urine and
faeces. However, this process takes time, and if a large dose was taken in, the body
may not be able to get rid of it quickly enough. The longer the poison stays in the body,
the more damage it causes, especially to the brain and nervous system.
In conclusion, terbufos is highly toxic due to its ability to be absorbed easily, spread to
many organs, change into more dangerous forms in the body, and stay in the system
long enough to cause severe harm. The illegal sale of such a substance in communities
is a serious public health risk. It affects not just individuals, but entire families and
communities, especially children who are most vulnerable.
2.2 Health Risks of Prolonged Sitting at Work (10 marks)
Prolonged sitting in the workplace has become a serious health issue, especially with
the rise of desk jobs and computer work. Sitting for long periods every day may seem
harmless, but it actually increases the risk of many health problems.
First, sitting too long slows down blood circulation, especially in the legs. This can lead
to swollen ankles, blood clots, and even heart problems. It also reduces the movement
of blood sugar into muscles, which can increase the risk of type 2 diabetes.
Second, sitting for extended hours reduces the amount of calories burned. This makes it
easier to gain weight, which can lead to obesity, another risk factor for heart disease,
diabetes, and high blood pressure.
Third, poor posture from sitting at a desk can lead to back and neck pain. Over time,
this can become chronic and affect a person’s ability to work comfortably.
Fourth, there is evidence that sitting too long is linked to mental health issues such as
anxiety and depression. Lack of movement can affect brain function and mood,
especially if a person is sitting alone for most of the day.
One may think that exercising after work is enough to undo the damage of sitting all
day, but this is not true. Research shows that regular exercise does not completely
cancel out the harm caused by sitting for too many hours in a row. For example, going
to the gym for 30 minutes after sitting for 8 hours does not erase the strain that the body
has already experienced during the day.
The key is to break up sitting time throughout the day. Standing up every 30 minutes,
taking short walks, stretching, or using a standing desk can help reduce health risks.
Moving often helps the body maintain normal blood sugar, improves circulation, and
reduces strain on muscles and joints.
In conclusion, prolonged sitting is more dangerous than it appears. It can lead to serious
physical and mental health problems. While exercise is still important, it cannot undo the
effects of sitting for long hours without breaks. Employers and workers should take
steps to reduce sitting time and make movement a part of the daily work routine.
QUESTION 3
3.1 Explain the difference between local and systemic effects of toxic chemicals
in the workplace
In the workplace, toxic chemicals can affect the human body in two main ways: locally
and systemically. Local effects happen at the exact point where the chemical first
touches the body. For example, if a worker accidentally spills a corrosive chemical on
their skin, they may experience a burn, rash, or irritation only at that spot. Similarly, if a
worker inhales fumes from a chemical without a mask, their nose, throat, or lungs might
be irritated. These are all local effects because the damage is limited to the area where
contact occurred and the chemical has not spread to other parts of the body.
Systemic effects occur when the chemical enters the body—through the skin, lungs,
mouth, or eyes—and then travels through the bloodstream to other internal organs.
Once in the blood, the toxic substance can affect areas far from the entry point, such as
the brain, liver, kidneys, or heart. For example, a pesticide that enters through the skin
might damage the nervous system or kidneys without showing signs at the entry point.
These effects are often more dangerous and harder to detect because they can affect
vital body systems, and symptoms may only appear after a delay.
Understanding the difference between local and systemic effects is important in
occupational health. Some chemicals may cause both types of effects. Workers
exposed to these chemicals may feel fine at first but suffer from long-term health
problems if the substance spreads internally. Therefore, it is essential that employers
identify which chemicals in the workplace are capable of causing local or systemic
harm, so they can put proper safety measures in place to protect workers from both
kinds of exposure.
3.2 How terbufos can cause local and systemic effects, and four measures to
prevent exposure (Well-discussed)
Terbufos is a toxic organophosphate pesticide that is very dangerous to human health.
It can cause both local and systemic effects depending on how someone is exposed. If
terbufos touches the skin or eyes, it can cause local effects like redness, irritation, or
chemical burns. Inhaling the fumes may irritate the throat or lungs. These effects
happen at the point of contact and can be painful or uncomfortable. However, the real
danger is its systemic toxicity. Once terbufos enters the body—whether through the
skin, mouth, or lungs—it quickly moves into the bloodstream. There, it interferes with
nerve signals by blocking an enzyme called acetylcholinesterase. This can cause
serious health problems like difficulty breathing, muscle twitching, confusion, vomiting,
and even death if not treated in time.
To protect workers from these risks, the following four prevention measures should be
implemented:
1. Use of Personal Protective Equipment (PPE): Workers must be provided with
appropriate PPE such as gloves, masks, goggles, and full protective clothing.
This prevents direct contact with terbufos and reduces the risk of inhaling harmful
fumes. Employers should ensure PPE is worn correctly and consistently.
2. Training and Awareness Programs: Workers need proper training on the dangers
of terbufos and how to handle it safely. This includes learning how to read
chemical labels, store pesticides correctly, and act quickly in case of exposure. A
well-informed worker is more likely to avoid risky behavior.
3. Safe Handling and Storage: Terbufos should be kept in secure, clearly labelled
containers away from food and drinking water. Storage areas should be locked
and only accessible to trained personnel. This prevents accidental exposure,
especially in informal areas like spaza shops.
4. Health Monitoring and Medical Surveillance: Regular health check-ups and
biological monitoring can help detect early signs of pesticide poisoning in
workers. Early detection can prevent serious health effects and ensures prompt
treatment if exposure occurs.
QUESTION 4
4.1 Differentiate between the dose-response relationship and dose-effect
relationship
In toxicology, the terms dose-response and dose-effect sound similar but have different
meanings. The dose-response relationship refers to how the strength or intensity of a
response changes with different amounts of exposure to a chemical. For example, if
someone is exposed to a low dose of a substance, they may have no symptoms, but at
a higher dose, they may become very sick. This helps scientists understand how much
of a substance is harmful and where the safe exposure limit is. On the other hand, the
dose-effect relationship looks at whether a specific health effect appears at a certain
dose. It focuses more on the type of effect whether the chemical causes a headache,
skin rash, or death not just how strong the reaction is. In simple terms, dose-effect is
about what kind of health issue occurs, and dose-response is about how the severity of
the issue increases as the dose increases. Both concepts are important in setting safety
standards in workplaces and protecting people from harmful exposures.
4.2 Explain the concept “the dose makes the poison” to an employee concerned
about arsenic in rice (9 marks)
If an employee is worried about arsenic in brown or white rice, the best way to help
them understand is to explain the concept of “the dose makes the poison.” This means
that any substance—even something harmless like water—can be dangerous if taken in
very large amounts. With arsenic, it’s important to understand that it is a naturally
occurring element found in soil and water, and small amounts can enter rice as it grows.
Brown rice tends to have more arsenic than white rice because the outer layers are not
removed. However, in the amounts normally found in rice, arsenic is not harmful for
healthy people who eat a balanced diet. The body can handle low doses without getting
sick. Problems only arise when a person is exposed to high doses over a long time. You
can explain to the employee that eating rice in moderate amounts, along with other
healthy foods, is safe. Just like with sugar or salt, the key is not to overeat it. So, there is
no need to panic or stop eating rice—just make sure it is part of a well-balanced meal
plan. In short, the poison is in the dose, not the food itself.
4.3 Discuss “the dose makes the poison” in relation to arsenic and explain target
organ toxicity with examples (10 marks)
The idea that “the dose makes the poison” means that how much of a chemical a
person is exposed to determines whether it will cause harm. This concept is especially
important when discussing arsenic, a naturally occurring toxic element that can be
found in food and water. At very low doses, such as those commonly found in rice or
drinking water in some areas, arsenic may not cause immediate harm. But at higher
doses or with long-term exposure, it becomes poisonous. The human body can usually
deal with small amounts, but repeated exposure can lead to serious health problems.
One of the key things to understand with toxic substances like arsenic is target organ
toxicity. This means that certain organs in the body are more likely to be affected by the
toxin than others. In the case of arsenic, long-term exposure can damage several
important organs. For example, the skin may develop dark patches, rough spots, or
even skin cancer. The liver and kidneys, which help to process and remove toxins from
the body, can also be harmed by ongoing exposure. In some cases, arsenic may lead to
lung cancer, especially if it is inhaled through contaminated dust. The nervous system
can be affected too, causing symptoms like numbness, confusion, or weakness.
In conclusion, arsenic is a good example of how a naturally occurring substance can be
harmless at low levels but toxic at high doses. Understanding both the dose and which
organs are affected is essential for managing health risks related to chemical exposure.
REFERENCING
Casarett, L.J., Doull, J., Klaassen, C.D. (2013). Casarett & Doull’s Toxicology: The
Basic Science of Poisons (8th ed.). McGraw-Hill Education.
Gold, L.S., Slone, T.H., & Ames, B.N. (1997). Misconceptions about the Causes of
Cancer. FASEB Journal, 11(13), 1041–1047.
National Research Council. (2006). Toxicity Testing for Assessment of
Environmental Agents: Interim Report. The National Academies Press.
Health Canada. (2018). Toxic Substances and Health. Government of Canada.
World Health Organization (WHO). (2020). Chemical Safety and Human Health.
WHO Fact Sheets.
European Food Safety Authority (EFSA). (2015). Scientific Opinion on the Risks for
Public Health Related to the Presence of Aflatoxins in Food. EFSA Journal, 13(3), 4002.
International Agency for Research on Cancer (IARC). (2012). Arsenic, Metals,
Fibres, and Dusts. IARC Monographs on the Evaluation of Carcinogenic Risks to
Humans, Volume 100C.
BfR (Federal Institute for Risk Assessment, Germany). (2020). Natural Does Not
Equal Harmless.
Halliwell, B., & Gutteridge, J.M.C. (2015). Free Radicals in Biology and Medicine (5th
ed.). Oxford University Press.
National Institute for Occupational Safety and Health (NIOSH). (2022). Toxicology
Overview. CDC/NIOSH Publications.
Trewavas, A. (2004). A Critical Assessment of Organic Farming-and-Food Assertions
with Particular Respect to the UK and the Potential Environmental Benefits of No-Till
Agriculture. Crop Protection, 23(9), 757–781.
American Council on Science and Health. (2015). Natural vs. Synthetic Chemicals:
Myths and Facts. ACSH Reports.
Gallo, M.A., & Doull, J. (1991). History and Scope of Toxicology. In: Amdur, M.O.,
Doull, J., & Klaassen, C.D. (Eds.), Casarett and Doull’s Toxicology (4th ed.). Pergamon
Press.
Calabrese, E.J., & Baldwin, L.A. (2003). Hormesis: The Dose-Response Revolution.
Annual Review of Pharmacology and Toxicology, 43, 175–197.
Healthline. (2021). Natural Doesn’t Always Mean Safe. Retrieved from
www.healthline.com