Handbook of Solvents - George Wypych - ChemTech - Ventech!

20.9 Toxicity of environmental solvent exposure for brain, lung and heart 1409
of the mean, each tests confidence intervals were developed that included 95% of values,
excluded as abnormal approximately 5% of unexposed subjects on each test that defined abnormal
precisely. For these tests they were values outside the mean plus 1.5 x standard deviations
(sd) that defined normal. The next concern what was the best summary for each
subject. The number of abnormalities was best adjusting balance and vision above other
tests and given grip strength, blink reflex and color discrimination 0.5 for right and left sides
of the body.
The attributes of plausible association leading to attribution of effect include temporal
order, strength of association, exposure intensity and duration, specificity, consistency of
findings and coherence and plausibility. 1 As noted earlier the fact of exposure or suspected
exposure may be the only certainty about exposure so its plausibility is important based on
chemical properties, experiments and studies of workers. Consistency with results of occupational
exposures and animal experiments is helpful. Koch’s 4 postulates developed to
judge causation of infectious agents (1, organism present in every case; 2, grown in pure
culture; 3, produces the disease when inoculated and 4, recovery and growth in pure culture)
are usually inapplicable. This reality is discomforting to some interpreters of the new observations.
The next section reviews the neurobehavioral affects of solvents found in the environment
in the order of importance. 2,4 We begin with trichloroethylene (TCE) and related short
chain chlorinated agents. 22 Next are ring compounds toluene including related xylene and
styrene with comments on creosols or phenols. The chlorinated ring compounds follow:
dichlorophenol and polychlorinated biphenyls and their highly neurotoxic derivatives, the
dibenzofurans. Other straight chain solvents leading off with n-hexane move through white
solvent (paint thinner) and solvent mixtures.
Before studies of effects of TCE on many brain functions came the measurement of
blink reflex latency in 22 people exposed at home to solvents rich in TCE at Woburn, MA.
They showed significant delay of blink but no other functions were measured. 16 In France
about this time workers exposed to TCE had similar delays of blink. 24 Earlier experimental
exposure of 12 subjects to TCE at 1,000 parts per million (ppm) for 2 hours in a chamber
had produced rapid flickering eye movements when following figures on a rotating drum
(optokinetic nystagmus), a lowered fusion limit. 22 Thus TCE induced dysfunction of several
cranial nerves VI (with III, IV) and V and VII. Nystagmus normalized after a washout and
recovery time. Blink is the easier and quicker measurement. 16
A community within Tucson, AZ of over 10,000 people who depended on well-water
for drinking and bathing had developed many complaints and had excesses of birth defects
and cancers that associated with TCE in their water. The source was metal cleaning that included
stripping off protective plastic coatings, from demothballing aircraft stored on the
desert with TCE. This had dumped vast quantities of TCE on the porous, desert floor that
drained into the shallow Santa Cruz River aquifer. Testing of 544 people from this water exposure
zone showed increased blink reflex latency, impaired balance, slowed simple and
choice reaction times, reduced recall, poor color discrimination, and impaired problem
solving in making designs with blocks, digit symbol substitution and Culture Fair (consisting
of 4 subtests: selection of designs for serial order, for difference, for pattern completion
and refining defined relationships). 25,26 Also peg placement in a slotted board and trail making
A (connecting 25 numbers in ascending sequence and B connecting numbers alternating
with letters). 27 TCE concentrations at the well heads and distribution pipes to homes were