This article describes the various sources of hazardous substances in our environment and the pathways through which they exist. Recall that hazardous substances are those materials that pose a significant threat, both now and in the future, to human health and the environment when improperly managed.
Substances considered hazardous are those that are ignitable, corrosive, reactive, toxic, or all of these. Substances designated as “hazardous‟ are generated by a wide range of industries of varying sizes.
The term hazardous and toxic substances are often used interchangeably to refer to a substance that can be poisonous or can cause health effects.
For toxic substances in the environment to exert adverse effects on humans, they must deposit on and/or penetrate through a body surface and reach target sites where they can alter the normal functions and/or structures.
The critical pathways and target sites can vary greatly from substance to substance and, for a given substance, can vary with its chemical and physical form. Understanding the sources and pathways of these hazardous substances will help in determining the risk of harmful environmental and health effect from the substances.
Sources of Hazardous Substances
Having identified some of the hazardous and toxic substances in the preceding unit, we now look at where these substances come from. We are going to discuss it using two main identified sources: Natural and Synthetic (Anthropogenic) with more emphasis on the synthetic sources.
Read Also : Classification of Hazardous Substances
1. Natural Sources of Hazardous Substances
These refer to those substances that occur in nature (i.e. not produced by human activities). They may exist as minerals, metals or gases in different media of the earth surfaces. Their exposure in a dose in a particular area can pose significant hazard to lives and the environment.
Examples include what happens when an erupting volcano spews out huge quantities of rocks, ash, chlorine, sulfur dioxide, and other chemicals.
Other natural chemicals can pollute too, but sometimes human actions allow natural substances to reach dangerous levels as in the following illustrations:
1. Radon is a naturally radioactive chemical, a gas that arises from transformations occurring in underlying rocks and soil around the world as natural radioactive uranium decays. But, levels of radon in outside air are low. It is when radon seeps up into and concentrates in human structures that problems may arise.
2. Arsenic and Asbestos are naturally occurring chemicals that exist in rocks and soil; when there is high concentration, it may dissolve into water sources, thereby making them toxic to life.
2. Synthetic (Anthropogenic) Sources of Hazardous Substances
These are substances created by human activities. In recent times, due to increase in innovations, technological advancement and better quality of life, the number of synthetic substances on the environment has increased tremendously.
The produced hazardous substances are mostly used in households, industries, workplaces and agricultural development. A brief description of some of the hazardous substances and where they are mostly found are explained below:
Household hazardous substances: Majority of the materials used on daily basis at different households, to a large extent, can be classified as being hazardous. They range from paints, electrical and electronics equipment, water storage and treatment materials, lightings, adhesives, solvents etc.
For example, paints are among the main sources of lead in the households; most adhesives, solvents, batteries contain zinc, manganese, mercury, copper, lead, cadmium, nickel, acids, arsenic compounds, copper etc.
When their concentration exceeds the permissible healthy limit, exposure to these substances may have negative effects on humans and the environment.
Industrial hazardous sources: Industries and all manufacturing facilities use and release certain hazardous substances into the environment. These releases into the environment may either be routine or accidental.
Examples include: all industries that release fumes into the atmosphere through combustion; motor vehicles including cars, buses, airplanes, ships and off- road vehicles; chemical and petroleum refineries; manufacturing facilities; plant generating electric power by burning coal, oil, or natural gas; mining; constructions; military operations; pharmaceuticals; health; food, etc. On a day- to- day basis, humans produce and interact with hazardous substances.
Agricultural sources: Most supplements and chemicals used in growing crops and raising animals contain varying concentration of hazardous chemicals. They include agro-chemicals, such as pesticides, herbicides, fertilizers and others.
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