Chapter 8: Environmental Health Toxicology

Environmental toxicology, also known as entox, is a multidisciplinary field of science concerned with the study of the harmful effects of various chemical, biological and physical agents on living organisms.

Rise of Synthetic Chemicals
There has been widespread synthetic chemical production since WWII. People were largely unaware of the health risks of many toxicants. The potent insecticide DDT was sprayed widely in public areas, even on people.

Types of toxicants
- Carcinogens: cause cancer
- Mutagens: cause mutations in DNA
- Teratogens: cause birth defects
- Allergens: cause unnecessary immune response
- Neurotoxins: damage nervous system
- Endocrine disruptors: interfere with hormones.

Toxicology is the branch of science concerned with the nature, effects, and detection of poisons.

Dangerous chemicals are divided into two broad categories: 
• Toxic - Poisonous 
 Can be general or very specific. Often harmful even in dilute concentrations.

 • Hazardous - Dangerous 
Flammable, explosive, irritant, acid, corrosive.

Toxic Chemicals

Allergens - Substances that activate the immune system. 
• Antigens - Allergens that are recognized as foreign by white blood cells and stimulate the production of specific antibodies. 
• Other allergens act indirectly by binding to other materials so they become antigenic. 
• Sick Building Syndrome 

 Endocrine Disrupters disrupt normal hormone functions. 
• Thyroxine 
• Insulin 
• Adrenalin 
• Endorphins 

 Neurotoxins - Metabolic poisons that specifically attack nerve cells. 
• Different types act in different ways. 
• Heavy Metals kill nerve cells. 
• Anesthetics and Chlorinated Hydrocarbons disrupt nerve cell membranes. 
• Organophosphates and Carbamates inhibit signal transmission between nerve cells.

Mutagens - Agents that damage or alter genetic material. 
• Radiation 

Teratogens - Specifically cause abnormalities during embryonic growth and development. • Alcohol - Fetal Alcohol Syndrome 

Carcinogens - Substances that cause cancer. 
• Cigarette smoke 


Exposure and susceptibility

• Airborne toxins generally cause more ill health than any other exposure (lining of lungs easily absorbs toxins)
• Largest toxin exposure reported in industrial settings.
• Condition of organism and timing of exposure also have strong influences on toxicity.

Exposure routes 

• Ingestion – chemicals can enter the body by eating or drinking
• Inhalation – chemicals can be breathed into the lungs
• Absorption - chemicals can enter the body by moving through the skin

Factor affecting toxicity

• Not all people are equal.  Sensitivity to a toxicant can vary with sex, age, weight, and so forth.
• The more sensitive is actually babies.older people and poor health

Types of exposure

• Acute – usually a single exposure for less than 24 hours (immediate health problem)
• Sub-acute – exposure for one month or less
• Sub-chronic – exposure for one to three months
•  Chronic – exposure for more than three months (very difficult to assess specific health effects due to other factors)

Mixture of toxicants 

• Substances may interact when combined together
• Mixes of toxicants may cause effects greater than the sum of their individual effects. These are called synergistic effects.
• A challenging problem for toxicology: There is no way to test all possible combinations! (And the environment contains complex mixtures of many toxicants.)

Mechanisms for minimizing toxic effects

Every material can be poisonous under certain conditions.

 • Most chemicals have a safe threshold under which their effects are insignificant.

Metabolic Degradation
• The liver is the primary site of detoxification of both natural and introduced poisons.

Excretion and repair

Effects of waste products and environmental toxins reduced by eliminating via excretion. 
• Breathing 
• Kidneys (Urine)

Tissues and organs often have mechanisms for damage repair.
 • Any irritating agent can be potentially carcinogenic

Types of effects

• Local effects – damage at the site where a chemical first comes into contact with the body; examples are redness, burning and irritation of the skins
•  Systemic effects – adverse effects associated with generalized distribution of the chemical throughout the body by bloodstream to internal organ.
• Target organ effects – some chemical may confine their effects to specific organ; the most common organs affected by such chemicals are liver, lungs, heart, kidneys, brain and nervous system, and the reproductive system`

REFERENCES:

* based on my lecturer's notes sir Mohd Jamalil bin Mustafa

*https://en.wikipedia.org/wiki/Environmental_toxicology