The term green chemistry
is defined as: The invention, design and application
of chemical products and processes to reduce or
to eliminate the use and generation of hazardous
While this short definition appears straightforward,
it marks a significant departure from the manner
in which environmental issues have been considered
or ignored in the upfront design of the molecules
and molecular transformations that are at the
heart of the chemical enterprise.
Looking at the definition of green chemistry,
the first thing one sees is the concept of invention
and design. By requiring that the impacts of chemical
products and chemical processes are included as
design criteria, the definition of green chemistry
inextricably links hazard considerations to performance
Another aspect of the definition of green chemistry
is found in the phrase “use and generation”.
Rather than focusing only on those undesirable
substances that might be inadvertently produced
in a process, green chemistry also includes all
substances that are part of the process.
Therefore, green chemistry is a tool not only
for minimizing the negative impact of those procedures
aimed at optimizing efficiency, although clearly
both impact minimization and process optimization
are legitimate and complementary objectives of
Green chemistry, however, also recognizes that
there are significant consequences to the use
of hazardous substances, ranging from regulatory,
handling and transport, and liability issues,
to name a few. To limit the definition to deal
with waste only, would be to address only part
of the problem.
is applicable to all aspects of the product life
cycle as well.
Finally, the definition of green chemistry includes
the term “hazardous”. It is important
to note that green chemistry is a way of dealing
with risk reduction and pollution prevention by
addressing the intrinsic hazards of the substances
rather than those circumstances and conditions
of their use that might increase their risk.
Why is it important for green chemistry to adopt
a hazard-based approach?
To understand this, we have to revisit the concept
of risk. Risk, in its most fundamental terms,
is the product of hazard and exposure:
Risk = Hazard X
A substance manifesting
some quantifiable hazard, together with a quantifiable
exposure to that hazard, will allow us to calculate
the risk associated with that substance. Virtually
all common approaches to risk reduction focus
on reducing exposure to hazardous substances.
Regulations often require increases in control
technologies and treatment technology, and in
personal protective equipment such as respirators,
gloves, etc., in order to reduce risk by restricting
By achieving risk reduction through hazard reduction,
green chemistry addresses concerns about the cost
and potential for failure of exposure controls.
Regardless of the type of exposure control, ranging
from engineering controls through personal protective
gear, there is always going to be an upfront capital
cost; to what degree this cost can be recouped
will be situation-specific, but it will always
be there. In contrast, there is no additional
upfront capital cost necessarily associated with
While some green chemistry options may require
capital investment, others may actually lower
total cost of operations from the outset. This
result is frequently the case in some of the easiest
ways of implementing green chemistry technologies.
Exposure controls, because they rely on either
equipment or human activity to accomplish their
goals, are capable of failing.
Respirators can rupture, air scrubbers can break
down, and so forth. When failure occurs, risk
is maximized because the resultant exposure is
to a constant hazard. Green chemistry, in contrast,
does not rely on equipment, human activity, or
circumstances of use but, instead, changes the
intrinsic hazard properties of the chemical products
and transformations. Consequently, green chemistry
is not as vulnerable to failure, as are the traditional
approaches to hazard control.
The definition of green chemistry also illustrates
another important point about the use of the term
“hazard”. This term is not restricted
to physical hazards such as explosiveness, flammability,
and corrosibility, but certainly also includes
acute and chronic toxicity, carcinogenicity, and
Furthermore, for the purposes of this definition,
hazards must include global threats such as global
warming, stratospheric ozone depletion, resource
depletion and bioaccumulation, and persistent
chemicals. To include this broad perspective is
both philosophically and pragmatically consistent.
It would certainly be unreasonable to address
only some subset of hazards while ignoring or
not addressing others. But more importantly, intrinsically
hazardous properties constitute those issues that
can be addressed through the proper design or
redesign of chemistry and chemicals.
Use of alternative feedstocks
The use of feedstocks that are both renewable rather than depleting and less toxic to human health and the environment.
Use of innocuous reagents
The use of reagents that are inherently less hazardous and are catalytic whenever feasible.
Employing natural processes
Use of biosynthesis, biocatalysis, and biotech-based chemical transformations for efficiency and selectivity.
Use of alternative solvents
The design and utilization of solvents that have reduced potential for detriment to the environment and serve as alternatives to currently used volatile organic solvents, chlorinated solvents, and solvents that damage the natural environment.
Design of safer chemicals
Use of molecular structure design and consideration of the principles of toxicity and mechanism of action to minimize the intrinsic toxicity of the product while maintaining its efficacy of function.
Developing alternative reaction conditions
The design of reaction conditions that increase the selectivity of the product and allow for dematerialization of the product separation process.
Minimizing energy consumption
The design of chemical transformations that reduce the required energy input in terms of both mechanical and thermal inputs and the associated environmental impacts of excessive energy usage