8
Continuing
research has demonstrated that the ocular effects reported from DMSO treatment
of dogs, rabbits,
guinea pigs and swine are species-specific and not reproducible in primates,
including humans. Even though
ocular toxicity, specifically lenticular refractive changes, have been reported
in some animal studies with
dogs, rabbits and swine (Rubin and Barnett, 1967; Smith et al. 1969)
(3)
and
in guinea pigs (Rengstarff et al.,
1972)
(4)
, it
was subsequently demonstrated that the ocular effect was species-specific
and was not reproduci-
ble in
primates, including humans (Smith et al., 1969)
(3)
(de
la Torre et al. 1981)
(5)
. Furthermore,
full ophthal-
mologic
examinations revealed no DMSO-related lenticular changes in any of 84 patients
treated three times
daily for three months with topical 70% DMSO, topical 2% DMSO or 0.85% normal
saline (maximum theoretical
dosage of 2.6 g DMSO/kg/day), which is comparable to dosages used in the animal
studies (Shirley et al.,
1988)
(6)
.
Human and Animal Metabolism
DMSO is metabolized in humans by oxidation to dimethyl sulfone, DMSO
2
or
by reduction to dimethyl sulfide,
DMS.
DMSO and DMSO
2
are
excreted in the urine and feces. DMS is eliminated through the breath and
skin
with a characteristic "garlic" or "oyster-like" odor.
Human excretion of orally administered DMSO is com-
plete within 120 hours, with urinary excretion being the primary pathway.
The rate of renal clearance has
been shown to be similar for chronic and singly administered doses regardless
of dose concentration. No resid-
ual accumulation of DMSO has been reported in humans or lower animals who
have received DMSO treatment
for protracted periods of time, regardless of route of dose administration.
Metabolite
Toxicity
The metabolites of DMSO are DMSO
2
, which
naturally occurs at low levels in human urine (PDR, 1994)
(8)
,
and DMS,
which naturally occurs in plants, the atmosphere, and lakes and oceans (Pearson
et al., 1981)
(9)
. Both
of these
metabolites are readily excreted from the body. Based on their widespread
natural occurrence and
ready degradation and/or excretion, the production of these metabolites from
the proposed use of DMSO on food
producing plants is not expected to pose any toxicological concern.
Inhalation
Fishman and coworkers at the Naval Medical Center
(10)
performed
many toxicological measurements on
the exposure
of rats to DMSO vapors. The following single and repeated exposures were made:
DMSO
Concentration
Length
of Exposure
1600
milligrams per cubic meter
4 hours
2900
milligrams per cubic meter
24
hours
2000
milligrams per cubic meter
40
hours
200
milligrams per cubic meter
210
hours
(7 hrs/day, 5 days/week for 30 exposures