Week 4: Environmental Health Hazards

In this week lesson, we get to learn about Environmental Health Hazards in detail. There are three types of hazards: Chemical Hazards; Microbial Hazards; Physical and other Hazards. We also learn about the definition of NOEC and LC50.

NOEC (no observed effect concentration) means the test concentration immediately below the lowest tested concentration with statistically significant adverse effect. The NOEC has no statistically significant adverse effect compared to the control.” (GHS Glossary)

LC50: “LC stands for “Lethal Concentration”. LC values usually refer to the concentration of a chemical in air but in environmental studies it can also mean the concentration of a chemical in water.

According to the OECD (Organisation for Economic Cooperation and Development) Guidelines for the Testing of Chemicals, a traditional experiment involves groups of animals exposed to a concentration (or series of concentrations) for a set period of time (usually 4 hours). The animals are clinically observed for up to 14 days.

The concentrations of the chemical in air that kills 50% of the test animals during the observation period is the LC50 value. Other durations of exposure (versus the traditional 4 hours) may apply depending on specific laws.” (Canadian Centre for Occupational Health and Safety)

*LD50: “LD stands for “Lethal Dose”. LD50 is the amount of a material, given all at once, which causes the death of 50% (one half) of a group of test animals. The LD50 is one way to measure the short-term poisoning potential (acute toxicity) of a material.

Toxicologists can use many kinds of animals but most often testing is done with rats and mice. It is usually expressed as the amount of chemical administered (e.g., milligrams) per 100 grams (for smaller animals) or per kilogram (for bigger test subjects) of the body weight of the test animal. The LD50 can be found for any route of entry or administration but dermal (applied to the skin) and oral (given by mouth) administration methods are the most common.” (Canadian Centre for Occupational Health and Safety)

  1. Chemical Hazards.

As you know, from the previous posts, there are three ways of exposures:

  • Oral: expose to chemical contaminants through drinking water or food.

For example, in Vietnamese food, people usually use “fish sauce” as in ingredient. Our group did a research on this and here is what we found:


During this research, I found out so many things. It surprised me that the food we consume daily could contain so many chemicals, both good and bad for our health.

  • Dermal: expose to chemical contaminants through your skin or basically everything you touch.

You can be expose to chemical hazards easily through dermal in a way you least imagine. Chemical hazards appear in your daily life through various form: in a cosmetic you use, in the clothes you wear, in the detergent you use for washing/cleaning things, ect.

  • Inhalation: expose to chemical contaminants through breathing.

You would be surprised to see how polluted the air you breath in is, whether it’s indoor or outdoor.

In fact, you can see it in the Air quality index. This page show you the current air quality in every country in the world at the current time, which is really convenient.

To know how good the air in your city is, you can compare the statistic with this table

AQI Air Pollution
Health Implications
0–50 Excellent No health implications.
51–100 Good Few hypersensitive individuals should reduce outdoor exercise.
101–150 Lightly Polluted Slight irritations may occur, individuals with breathing or heart problems should reduce outdoor exercise.
151–200 Moderately Polluted Slight irritations may occur, individuals with breathing or heart problems should reduce outdoor exercise.
201–300 Heavily Polluted Healthy people will be noticeably affected. People with breathing or heart problems will experience reduced endurance in activities. These individuals and elders should remain indoors and restrict activities.
300+ Severely Polluted Healthy people will experience reduced endurance in activities. There may be strong irritations and symptoms and may trigger other illnesses. Elders and the sick should remain indoors and avoid exercise. Healthy individuals should avoid outdoor activities.
Concentration, micrograms per kubic meter air, µg/m3
Index classification SO2 NO2 PM10 PM2.5 O3 CO TRS
good below 20 below 40 below 20 below 10 below 60 below 4000 below 5
satisfactroy 20-80 40-70 20-50 10-25 60-100 4000-8000 5-10
fair 80-250 70-150 50-100 25-50 100-140 8000-20000 10-20
poor 250-350 150-200 100-200 50-75 140-180 20000-30000 20-50
very poor above 350 above 200 above 200 above 75 above 180 above 30000 above 50

2. Microbiological Hazards

There are 6 types of Micro-Organisms:

  • Bacteria
  • Viruses
  • Protists (animal and plant like)
  • Algae
  • Fungi (yeasts and molds)
  • Prions

These micro-organisms are practically everywhere around you. You can also be exposed to it through oral, dermal and inhalation.

For further reading, you can try these pages:





3. Physical and Other Hazards

Beside chemical and biological, you can also be exposed to physical hazards such as dust, noise, vibration, radiation, temperature, moisture, ect.

Further information can be found here:

https://www.ccohs.ca/topics/hazards/physical/ (personally, I think this page has a lot of useful information, maybe you can find something you need here XD )


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