Harmful Substances Spread and Concentrate in the Environment


Chemicals know no boundaries! They Transport Through Air, Soil & Water

Transport in Air



The 3 stages of transport of substances in air are:

  1. Release of the chemical (source) Dispersion – of the chemical in the atmosphere (the chemicals scatter in various directions
  2. Deposition of the chemical in soil or water
  3. Direction and distance of airborne chemicals are determined by :
    • pollutant’s properties
    • wind speed
    • direction of wind
    • ocean currents
    • precipitation
    • snow

Transport in Groundwater

Spaces between soil contains air and water, chemicals in water moves to the water table.


Water table:

The top of the groundwater zone.

It then travels down to the groundwater (the next zone) where there is no air spaces.

Groundwater moves in all directions (sideways, up, down) and can move very slowly (1m per year) or very quickly (1m per day)

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The tiny spaces between soil grains, if these are tightly packed, the groundwater containing the chemical moves slowly


Soil is one with interconnected pores (pores that are connected) which allows the quick movement of groundwater

Transport in Surface Water



  • Substances enter surface water from air, groundwater, runoff, outflow from sewers and sewage treatment plants
  • If the substance does not easily dissolve, it attaches to solids and will not travel very far and become more concentrated in the area

Transport on Soil

Water carrying substances can do 4 things:

  1. evaporate
  2. soak into the soil and be taken up by plants
  3. run onto streets or streams
  4. soak through the soil and move downward dissolving substances as it goes, carrying them along (this liquid is called leachate)
  • Composition of the soil affects the rate of the leachate’s movement, for example, clay prevents leachate’s movement
  • Soils with a lot of organic material slows the movement of chemicals if they are absorbed by the organic material

Transport of Hydrocarbons in Soil


  • Hydrocarbons are caused by vehicles and industry
  • Hydrocarbons are carried by water in the soil
  • Those that do not dissolve coat grains of soil and fills up the pores in the soil, thus, concentration increases and also cleanup is difficult
  • Hydrocarbons are toxic to plants and animals (humans too!)

Changing the Concentration of Harmful Chemicals in the Environment

The concentration of pollutants can be changed using different techniques:

o   Dispersion, dilution, biodegradation, phytoremediation and photolysis


The scattering of a substance away from its source


Reduces the concentration of a pollutant by mixing the polluting substance with large quantities of air or water

 Dispersion and dilution may not meet government standards in leaving an area clean enough.




The breakdown of materials by organisms such as earthworms, and micro-organisms like bacteria, fungi, algae and protozoa.

Organisms need their own specific conditions to grow and reproduce:

Aerobic biodegradation:

Means that an organisms needs oxygen for the process

Anaerobic biodegradation: 

Requires no oxygen for the process

Factors Affecting Biodegradation

Temperature, soil moisture, pH, oxygen supply and nutrient availability



A technique that can be used to reduce the concentration of harmful chemicals in soil and groundwater by the planting of plants that absorb or accumulate (build up) large amounts of chemicals from the soil.

  • The plants are allowed to grow absorbing the chemicals, then are harvested and burned or composted.
  • These chemicals include metals, hydrocarbons, solvents, pesticides, radioactive materials, explosives and landfill leachate.


The breakdown of compounds by sunlight.

  • For example, photodegradable plastic, it is made up of chemicals that when they react with sunlight, they turn the plastic into a fine powder.

Hazardous Chemicals Affect Living Things


Is the increase in concentration of a chemical or element as it moves up the food chain.

For example, if algae are infected with mercury, insects eat many algae, each obtaining amounts of mercury; fish eat many of the infected insects therefore obtaining even more amounts of mercury; and this continues up the food chain.


How hazardous chemicals affect living things is also seen in the Case Study:

The Exxon Valdez Oil Spill.

Hazardous Household Chemicals

  • Hazardous household chemicals includes:
    • household cleaners
    • paint and paint products
    • personal hygiene products
    • pesticides and fertilizers
    • pet-care products
    • automotive fluids
  • An average household has between 12L and 40L of hazardous products
  • These products can cause burns, heart, kidney and lung ailments, cancer, death.

Government Regulations

Designed to protect consumers and reduce risks in transporting, storing, using and disposing of hazardous materials.

Workplace Hazardous Materials

Information System (WHMIS) :

Provides information on hazardous materials using symbols.

Material Safety Data Sheets (MSDs): 

  • Detailed information sheets about hazardous products, provided by the manufacturer; includes:
  • description (its composition, physical appearance and chemical characteristics)
  • precautions
  • health effects
  • first aid treatment
  • spill procedures
  • disposal advice


  • There are different labels for different purposes:
  • Ex. transport, use in the workplace, supply and disposal

New Product Regulations

  • To place a new product in the market, companies must provide information including
    • Intended use
    • physical and chemical properties
    • active ingredients
    • Instructions for use/safety precautions
    • Health effects
    • Environmental effects
    • Toxicity to humans
    • First aid instructions in case of poisoning

Storage and transportation of Hazardous Chemicals




  • Is relevant to prevent accidents and injury
  • Some examples include:
    • Leave in original containers
    • Make sure they have secure lids
    • Place in storage areas where they cannot fall over and spill
    • Store in cool, dry, ventilated places away from heat

Transportation of Consumer Goods

  • Hazardous materials should be placed in the trunk
  • Containers should stand upright and should not be able to move
  • Never mix chemicals together in one container
  • Should be left in original container when being disposed of

Disposal of Hazardous Chemicals

  • Never down the drain or into soil
  • Sewage treatment plants and septic tanks cannot remove these chemicals
  • Can contaminate drinking water, soil and air, and harm organisms if disposed of improperly

Hazardous Waste Collection Sites

  • These sites are used to dispose of hazardous wastes like paints and fertilizers
  • Materials not recyclable are labelled and sent to incineration plants