Download Environmental Hazards

SYNERGY DHENKANAL
Environmental Risk
Environmental
risk due to various environmental
hazards is an important
topic for
environmental engineers to recognise and understand in order to protect human society and
ecosystems from harms or damages at local, regional or global scales. For example, to deal with
contaminated soil and ground water at a brown field, risk and exposure assessment help engineers
choose an optimal solution to either treat the hazard (e.g., to remove the contaminants from the soil
and water) or reduce the exposure (e.g., to cover up the land with a barrier).
Hazards
A hazard is a threat to life, health, property, or ecosystems, i.e., it involves something that
could potentially be harmful. Therefore, when a dormant hazard comes to fruition, it will cause physical
damage or destruction, loss of life, or drastic change to the environment, and result in an incident,
accident, emergency event, or disaster. Hazards may be broadly classified into two groups:
Man-made hazards (also called anthropogenic hazards): created by humans
due to human
intent, negligence, or error, such as crime, terrorism, war (sociological hazards), industrial hazards,
power outage, hazardous materials (technological hazards), etc.
Natural hazards: caused by a natural
process with a negative effect on people or the
environment, such as volcanoes, floods, earthquakes, etc. Many natural and man-made hazards are
interrelated (e.g. earthquakes may cause tsunamis which in turn damage nuclear power plants to
release radioactive waste).
Environmental Hazards
Environmental hazards include hazardous material pollution and natural
hazards.
Hazardous Wastes
SYNERGY DHENKANAL
Hazardous wastes are classified into several categories such as explosive, flammable, irritant,
carcinogenic, corrosive, etc. Nowadays, landfill of hazardous wastes is banned in the EU and
incineration should be used to dispose them. Assessment of waste sources is quite a difficult task as
waste producers do not always retain inventories of their waste streams because hazardous waste is a
liability and a cost burden. Therefore, waste assessment is a highly expensive exercise requiring time,
patient, training and money. Among various effects of hazardous wastes, toxicity is of direct concern
by the public. Environmental toxicology is an interdisciplinary science field dealing with the effects of
chemicals
on
living
organisms.
SYNERGY DHENKANAL
Toxic effects are divided into two types: carcinogenic and noncarcinogenic. A carcinogen promotes or
induces tumours with uncontrolled abnormal growth and division of cells. Noncarcinogenic
matters cause toxicological responses without carcinogenic effects, such as organ damage, neurological
damage, learning difficulties, etc. A common method of expressing toxicity is the median lethal
dose (LD50),
which is the dose causing the death of 50 percent of a test organism population. The median lethal
dose
is represented as the mass of chemical dose per body mass of the test organism using the unit of
mg/ kg. Stating it this way allows the relative toxicity of different substances to be compared and
normalised for the variation in the size of the animals exposed (although toxicity does not always
scale simply with body mass). It should be noted that LD50 measures acute toxicity only (as opposed
to chronic toxicity
at lower doses). The species-specific nature of toxicity presents a shortcoming in extrapolating
animal
test results to humans. When animal studies are used to determine standards for human exposure,
a philosophy of ‘safe than sorry’ is adopted to apply a significant safety factor to set a conservative
level by several orders of magnitude (the safety factor is usually between 10 to 1000).
Natural Hazards
Natural hazards can be further divided into geological hazards and hydrometeorological
hazards.
Geological hazard examples include
1. earthquake: a result of sudden release of energy in the Earth’s crust that creates seismic waves.
Earthquakes are caused mostly by ruptures of geological faults, but also by other events such
as volcanic activities, landslides, mine blasts, and nuclear tests. At the Earth’s surface,
earthquakes manifest themselves by shaking and sometimes displacement of the ground.
When the epicenter of a large earthquake is located offshore, the seabed may be displaced
sufficiently to cause a tsunami. Major earthquakes can cause losses of human lives and
huge damages to buildings as illustrated by Figure 5.1;
SYNERGY DHENKANAL
Damaged building by the Great Sichuan Earthquake, China, 2008