Submodule 11A, Toxic Chemicals from the Environment.
Chapter 17, Applications: Environmental Toxicology and Pollution
Air Pollution
Primary air pollutants enter the atmosphere directly, while secondary air pollutants are formed in the atmosphere, usually when primary air pollutants mix with solar radiation or other substances in the atmosphere.
Particulates.
We discussed the major process of particulate toxicity in model on respiratory
toxicology and asbestos.
We should note that some substances are not terribly toxic, but simply irritate
the URT, which leads to watery eyes, runny nose, coughing. If these irritations
are chronic, pathological changes may take place. Also, the depth in the lungs
to which particles travel is a function of aerodynamic diameter. Unlike asbestos,
most particulates are "roundish" and their aerodynamic diameter is
approximately their mean diameter.
Gases or Vapors
Carbon monoxide (discussed earlier)
Sulfur dioxide and nitrogen dioxide (read Page 308, 309)
Ozone, aldehydes, and PAN (read top of Page 310)
Formaldehyde (we discussed earlier)
Indoor Air Quality (IAQ )
A detailed chemical analysis of the air we breath will indicate traces of many
chemicals, including some of those we have studied which are known to be toxic,
such as benzene and formaldehyde. At what concentrations do these chemicals
lead to toxic effects? What are the effects of mixtures? By now you know there
are no easy answers to these questions. Here I need to mention that most serious
IAQ complaints are generated in the workplace. Besides the trace chemicals,
there are many HVAC (heating ventilating and air condition) issues, i.e., too
hot, too humid, chemical smells, cooking smells, cigarette smoke, etc. In addition,
there are workplace
stresses, i.e., job demands, interpersonal conflicts, and employment security
issues. These are often wrapped up with labor-management disputes and disagreements,
and sometimes lawyers. All these make it difficult to be very scientific about
just one variable, the effects of a chemical. (Besides chemicals, there are
microorganisms and their toxins to be considered.) Here's a nice site with information
on IAQ and handling
IAQ problems, see especially Section 4, the rest is optional reading. Note
especially that many symptoms of workplace stress, presumably absent any IAQ
issues, are often similar to the IAQ issues that are investigated. Other than
that, a careful evaluation of which particular chemicals are involved is the
first step to applying any scientific toxicology principles.
Water Pollution
Skim this section, there is little toxicology we have not covered already.
Toxic Wastes.
Skim this section, there is little of direct interest.
Bio-What!!
Here are some terms that are often confused: Bioconcentration versus bioaccumulation.
The term bioconcentration is commonly used to describe chemicals that
have higher concentrations in plants or animals than in the surrounding medium,
generally water. So if the concentration of PCB is 1 ppm in the water and 10
ppm in the fish, we say PCB is bioconcentrated. Bioaccumulation is related
to the persistence of a contaminant in the environment. Bioaccumulation has
two meanings, as I use the word. First, within an organism, it means the chemical
is not excreted or metabolized. DDT, for example, is not quickly altered in
the body. So if an individual is exposed to DDT each day, the amount in the
body increases. Within an ecosystem, the term bioaccumulation refers to this
same persistence, but now this bioaccumulation continues up the food chain.
That is, contaminated organisms lower in the food chain are ingested by animals
further up the chain, who cannot metabolize or excrete it either, and so it
bioaccumulates in them. Eventually the tissue concentration may be much higher
towards the top of the food chain. This use of term bioaccumulation is sometimes
referred to a biomagnification.