Figure 5.6 Spheres or layers of
influence in a system. The system
consists of interdependencies
among each layer.
Adapted from: B. R. Allenby and T. E.
Graedel, Industrial Ecology , Prentice
Hall, Upper Saddle River, NJ, 1995.
( e.g., “car” mentality: dispersed communities,
business, large parking facilities)
•Built (e.g., roadways)
•Supply (e.g., fuel)
•Maintenance (e.g., repair)
10 − 2 , and volatile chemicals are at or above 4. The values
are limitless because they are a ratio of concentration in air and water.
10 − 4 and 4
Solubility : the potential of the chemical to enter water. Very soluble chemi-
cals are on the order of 10,000 ppm and nonsoluble entities have a solubility
of less than 0.1 ppm.
Bioconcentration : the tendency/potential of the chemical to be taken up by
biological entities (algae, fish, animals, humans, etc.). A low potential is
defined as 250 (unitless) or less, while a high potential is found at 1000 or
Atmospheric oxidation (half-life, days): helps to define the fate of the chemical
once it enters the atmosphere. A short half-life is desirable, as the chemical
will have little time to cause adverse effects. A rapid half-life would be on
the order of 2 hours or less. A slow half-life is between 1 and 10 days; longer
than 10 days is a persistent chemical.
Biodegradation : the ability of the environment to break down the chemical.
A short biodegradation time is ideal so that the chemical does not persist.
There are two sectors of biodegradation; one is dimensionless and one has
units of time. A biodegradation factor on the order of hours is very quick,
whereas a factor on the order of years is long.