Historical Use of Chlorinated Solvents and Their Stabilizing Compounds - Environmental Investigation and Remediation - page 41

• Marketing literature by the major solvent producers

• Patents

• Industrial literature from technical journals and trade magazines

• Toxicology studies that analyzed and identii ed the complete range of toxic substances

present in solvents

MSDSs may not disclose all additives, indicating that formulations are proprietary, that quantities
are less than 1%, or that components are either nontoxic or nonvolatile. Disclosure rules varied through
time, and different states required disclosure of different information. For example, California's
Proposition 65 rule requires listing reproductive toxins. Worker health and safety rules and transporta-
tion regulations require disclosure of some regulated compounds in the solvent formulation.
Product fact sheets and consumer guidance from the major solvent producers provide a rich
resource for understanding the nature of solvent use, demands for stabilization, and the operator's
challenge for maintaining solvent stability. The literature from Dow Chemical, available online, is
particularly informative; however, with a few exceptions, the solvent marketing literature does not
disclose the ingredients of solvent-stabilizer formulations. The approximate proportion of a given
solvent formulation including its stabilizers can be inferred by contrasting the density of virgin,
unstabilized solvent with that of a stabilized formulation, because stabilizers are in general substan-
tially less dense than chlorinated solvents and most are less dense than water.
Hundreds of patents have been issued for stabilizing chlorinated solvents in the major industrial
countries. The i rst patent for stabilizing a solvent was issued in 1914 to Walter Snelling of Pittsburgh,
Pennsylvania, for stabilizing carbon tetrachloride i re extinguishers against corrosion of brass con-
tainers. Snelling used aliphatic hydrocarbons such as ethylene and acetylene (ethyne) compounds
added at 0.5-3% to combine with “free chlorine” to inhibit corrosion.
Patents for stabilizing chlorinated solvents and new “designer solvents” continue to be issued
today. The listing of a stabilizer formulation in a patent does not prove that it was deployed for com-
mercial use; many patented formulations were never brought to market. In demonstrating how a
particular new formulation presents an improvement over the prior art, some patents present the
composition of degreasing grades of solvents in use at the time, determined by laboratory analysis.
This information can be used to piece together the history of typical solvent formulations by the
classes of compounds used to achieve stabilization of solvents against attack by acids, metals, and
ultraviolet light. In some instances, patents list the specii c compounds and the quantities of stabiliz-
ers of the leading formulations at the time the patent was issued. Patents also reveal the relative
proportions of stabilizer compounds that work together to prevent reactions with the solvent. Some
stabilizers work synergistically with other stabilizer compounds, and the patent literature reveals
the stoichiometric relationships between them.
The industrial literature—including that from institutions promulgating specii cations and perfor-
mance standards for solvent use in military and industrial applications—is another source of infor-
mation on identity and quantities of stabilizers in chlorinated solvents. Promulgation of air-quality
regulations pursuant to the Clean Air Act led to an industry-wide effort to minimize solvent losses in
vapor degreasing operations. Similarly, the land ban on disposal of liquid waste solvent led to
increased attention to maximizing solvent recovery through recycling operations. The literature on
solvent recycling includes information on replenishment of solvent stabilizers lost during distillation
or other solvent-recovery processes and thereby reveals typical stabilizer formulations in the 1980s.
Studies on the toxicity of the major chlorinated solvents distinguished between the toxicity of
pure solvents and that of technical grade solvents. A few solvent stabilizers are considerably more
toxic than the solvents they stabilize. A number of articles on toxicology reveal the composition of
the solvents assayed; some endeavor to separate the toxic effects of epoxide stabilizers from those
of the chlorinated aliphatic solvents.
Tables 1.21 through 1.24 present a compilation of the documented presence of stabilizers in different
solvent formulations obtained from cited sources, as identii ed at the beginning of this section. The