Dichlorvos (DDVP) Risk Characterization Document - California ...

levels not verified, too few pregnant rabbits, high mortality, exposure for only part of organogenesis).
A NOEL could not be determined for this study.
Inhalation - Rabbit
Two experiments were conducted in the Tunstall Laboratory with rabbits exposed to DDVP by
inhalation. In the first experiment, female Dutch rabbits (19-20/group) were exposed to DDVP (>97%
purity) from day 1 of mating to gestation day 28 (Thorpe et al., 1971b). The DDVP nominal air
concentrations were 0, 0.25, 1.25, or 6.25 ug/L for 23 hours per day (equivalent to 0, 0.13, 0.65, or
3.25 mg/kg-day). Cholinesterase activities of the plasma, erythrocyte, and brain were measured at
the end of the experiment. Severe toxicity and mortality were observed after the 6th day of exposure
in the 6.25 ug/L group. Cholinergic signs observed included anorexia, lethargy, muscular tremors,
mucous nasal discharges, and diarrhea. Severely affected rabbits were prone with heads turned to
one side. Sixteen of 20 does died or were killed because of intoxication. There were no observations
reported for earlier time periods. Plasma, erythrocyte, and brain ChE activities were significantly (p @
0.05) inhibited to 65, 32, and 44%, respectively, of control values for the 1.25 ug/L group; and 27, 7,
and 15%, respectively, of control values for the 6.25 ug/L group. The NOELs were 0.25 ug/L (0.13
mg/kg-day) for ChE inhibition and 1.25 ug/L (0.65 mg/kg-day) for cholinergic signs and death. No
developmental toxicity was reported.
In the second experiment, Dutch rabbits (20/group) were exposed to DDVP (0, 2, and 4 ug/L,
equivalent to 0, 1.0, and 2.0 mg/kg-day) by inhalation using the same protocol (Thorpe et al., 1971b).
One doe in the 2 ug/L group died after 2-3 days of exposure. Six does of the 4 ug/L died or were
killed because of intoxication with signs as noted in the first study. Five of the six does in the 4 ug/L
group were affected in the week when the DDVP concentration reached as high as 6.6 ug/L due to a
blockage of the chamber filter. There was apparent increase in late gestational fetal death in the 4
ug/L group. The NOEL was less than 2 ug/L (1.0 mg/kg-day) based on mortality in the 2 ug/L group.
Both of the experiments were considered unacceptable to DPR according to FIFRA guidelines
(inadequate number of fetuses, inadequate examination).
New Zealand rabbits (number of rabbits used not specified) were exposed to DDVP (96% purity, at a
nominal concentration of 4 ug/L) for 7 hours per day from gestation days 6 to 18 (Schwetz et al.,
1979b). Even though the MTD was supposedly used, no maternal or fetal toxicity was observed. This
study was considered unacceptable to DPR according to FIFRA guidelines (MTD not reached). A
NOEL could not be determined for this study.
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