Lists and Factors
Let's cruise through some lists of chemicals and their regulatory levels. First, we'll do occupational. Remember the difference between an occupational exposure and an environmental exposure. Occupational exposures are to an adult worker, assumed healthy, for 8 hours per workday for a 30 or 40 year work career. Environmental exposures are to people of all ages and health statuses, for 24 hours per day, 365 days per year for a lifetime. Although it does not fit too well in a course on scientific toxicology, you should realize that people are getting paid while they are being exposed at work, while for environmental exposures the receptor is generally not paid. This has little to do with P450 isozymes, but a lot to do with peoples perception of the harm. Also, while what you read in the newspaper most often deals with environmental exposures to environmental chemicals, my guess is that on a mass of contaminants absorbed-basis, there are more total contaminants absorbed by workers in the workplace than all environmental exposure put together. (I can't prove that.)
Occupational
OSHA
The OSHA regulations specify certain limits, Permissible Exposure Levels
("PEL's") that must not be exceeded. Most of these are expressed as
"8-hour time-weighted averages." There are special limits for some
chemicals, "short term exposure limits" and "ceiling limits."
Check out the definitions of "exposure limits" on this web site:
MSDS - An Explanation of Common Terms. The most common exposure route in
industry is inhalation and most PEL's refer to the permissible air concentration.
For gases and vapors this may be expressed in mg/m^3 or ppm. For particles it
is generally expressed as mg/m^3, except for asbestos which is expressed in
fibers per cc. The absorption of substances through the skin is harder to quantify,
but if the "skin" designation is used, the skin should not be exposed
at all. The OSHA PEL's are found in 29 CFR 1910, in an appendix which is also
known as Subpart Z - Toxic and Hazardous Substances. 1910.1000 - Air contaminants,
has some definitions, 1910.1000 TABLE Z-1 - TABLE
Z-1 Limits for Air Contaminants. For historical and legal reasons, a few
air contaminants are listed in 1910.1000 TABLE Z-2 - TABLE
Z-2 , note these are especially "important" contaminants. Be sure
to check out hydrogen sulfide in that table. A third Z table, 1910.1000 TABLE
Z-3 - TABLE
Z-3 Mineral Dusts , is short but complex. Silica, that is silicone dioxide,
the chief ingredient in sand, is very toxic, but only if the grains are small
enough to be inhaled into the pulmonary regions. Also, some silica crystal structures
are much more toxic than others. Some contaminants are controlled by special
regulations. Scroll to the bottom of this page, OSHA
Regulations. You'll see the Z tables and below them, from 1910.1001 to 1910.1052,
substances that are individually controlled. These chemicals usually have special
requirements besides the PELs, such as medical monitoring. What is the number
of the regulation(s) that controls 1910.1013 - beta-Propiolactone? (Open the
file, you will see that it refers to another, nearby, regulation).
When OSHA promulgates a new regulation on air contaminants, it is not uncommon that OSHA is sued twice. Once by a labor organization that says the new regulations are not sufficiently protective of worker health, and once by an industry group that says the regulations have no scientific basis and are economically unjustified. It can take up to 10 years for OSHA to develop a new regulation. OSHA is allowed to accept some worker ill health, as long as it is economically impractical to avoid. A one in 10,000 mortality is sometimes quoted as OSHA's limit of "acceptable" harm, but I have never seen OSHA say that.
NIOSH
NIOSH promulgates Recommended Exposure Levels (RELs). These are not the law;
they are recommendations. RELs are often considered to be "conservative,"
that is, overly protective of worker heath. You can find the RELs in the NIOSH
Pocket Guide (you can find the PEL's there too.)
ACGIH
The American Conference of Governmental Industrial Hygienists is an organization
devoted to worker safety. In order to be a voting member of the ACGIH, you must
be an employee of a government or academic institution, i.e., voting members
can't be an employee of industry or a consultant. The ACGIH promulgates TLVs,
which we have mentioned. Since they sell the booklet, they don't put it on the
web. You can find the TLV of individual substances from their MSDS sheets. Besides
a list of air contaminants, similar to OSHA's Z Tables, ACGIH also presents
Biological Exposure Indices, and other workplace standards. They don't do much
with ionizing radiation, though, but refer you to International Commission on
Radiological Protection (ICRP) for details.
The TLV's are the standard of choice for practicing industrial hygienists. Many
TLVs are the same as PELs, but some are not. For practice in the US, if the
PEL is lower, then that must be used. If the TLV is lower, or outside of the
US, the TLV is preferred. Since the TLVs are given great weight by industrial
hygienists, they are not changed lightly. ACGIH has a procedure for announcing
intended changes, and holding hearings and gathering information before changes
are finalized.
Environmental
Hazardous Wastes
Because the definition of "hazard" and "waste" are difficult,
note how broad the definitions in 12A are, the RCRA regulations are specific
and have lists. Briefly waste may be either "characteristic" or "listed."
One of the characteristics is "toxicity." But in that case, toxicity
is very narrowly defined. It refers to the leachate that might seep from a landfill
containing the waste. So a test called a TCLP is used to determine how much
of a solid contaminant will leach (at least under the conditions of the test)
into a fluid (a weak acid). The toxicity list is then described as the concentration
of contaminant in this fluid. Here is the toxicity
list from RCRA. You'll recognize the usual list of suspects. (If you don't remember "round up all the usual suspects." See https://www.youtube.com/watch?v=NRKGblpzhZQ ) Remember the
numbers on this list are not a safe dose or allowance in the water or air, they
are just a definition of the results of this leaching test. Check out the allowable
levels of selenium. RCRA also has 4 lists of "listed wastes." The
"F" or "K" lists are generally complex mixtures and the
exact chemical composition is hard to get at. You could look at a few of these
to get an idea, but its not required:
K list; F
list. The U and P lists are of chemicals. They are mostly pure chemicals,
but presumably have been converted to waste somehow and now must be disposed.
That is, the toxicity of a U listed or P listed waste could be assumed to be
that of the named chemical. So note these P
and U list. The "U" or "P" is in the left hand column.
The P wastes are more dangerous than the U wastes. (Note that some hazardous
waste is listed because of hazardous characteristics other than toxicity, for
example reactivity)
Clean Water Act
Hazardous Chemicals under CWA
(just scan the list) are those that cause imminent or substantial danger and
therefore require "best available technology" to avoid discharge.
Now the discharge of these pollutants is not forbidden, just that the EPA had
the duty to look at them and might not grant a permit based on their presence.
Beyond that, for a new source, there are many requirements, such as the discharge
should not float to the top and form a scum layer, or settle to the bottom,
and so on. The concentration permitted in the receiving waters will depend on
the use of that water. A lower concentration for bathing waters than for industrial
waters.
Clean Air Act
There are two main branches of the Clean Air Act. The National Ambient Air
Quality Standards and the National Emission Standards for Hazardous Air
Pollutants.
The National Ambient Air Quality Standards
Monitors six pollutants: Sulfur oxides, particulates, carbon monoxide, lead,
and the smog components, ozone and nitrogen oxides. The National Emission Standards
for Hazardous Air Pollutants or “Air Toxics” originally regulated
only 7 air toxics: beryllium, mercury, vinyl chloride, asbestos, benzene, radio
nuclides, and arsenic.
The 1990 Amendments to the CAA now regulate 189 hazardous
air pollutants “that may reasonably be anticipated to cause adverse
effects to human health or adverse environmental effects." But again, the
discharge of these is not forbidden. For example, in order to be a "major
source" an industry must discharge 10 tons of any one of these, or 25 tons
aggregate of several of these. Discharge of these is required to meet Maximum
Available Control Technology (MACT).
Safe Drinking Water
The SDWA has lists with numbers
an engineer can work with, rather than vague descriptions.[See the MCL and MCLG for some substances.] Because this is a
list with great economic consequences, it affects all public water supplies,
it also has the potential to affect human health. These numbers are indeed a
"dose" in toxicology terms. And they are intended to represent the
upper limit on the contaminants that might be ingested in a lifetime. But how
scientific are they? Take the Maximum Contaminant Level (MCL) for arsenic. The
old MCL was 50 ug/L, but that was changed to 10 ug/L in 2006. That was a
political issue a while back, when the EPA attempted to promulgate the 10 ug/L. Look at the executive
summary of the National Academy of Science (NAS) document. Arsenic
in Drinking Water (1999). You can only read one page (Go to the dropdown menue on the left) at a time from this
site, but its better then buying the book. However, the report was not written by the NAS, it was written by the NRC. You'll need to read these for homework.
Note that the NAS report is about as scientific as practical. Arsenic is common
and much epidemiology is possible. There is lots of laboratory data. What does
it say? Whatever it says, that is about the maximum amount of information a
regulator could expect. Now how was it applied?