toxicological profile for malathion - Agency for Toxic Substances and ...

MALATHION 77
3. HEALTH EFFECTS
serum IgG or IgM levels; however, malathion (11.5 mg/kg/day) significantly attenuated the normal
increase in IgG level that occurs after administration of the antigens tetanus toxoid and ovalbumin. The
IgM fraction after antigen stimulation was not affected. Antibody titers against tetanus toxoid and
ovalbumin were significantly decreased in high-dose rats throughout the study and in the mid-dose rats
after 22 weeks. The MMI response in ovalbumin immunized rats was significantly decreased in mid- and
high-dose rats in a time-related manner. Rats exposed to malathion and immunized with ovalbumin or
tetanus toxoid showed a significant decrease in LMI response especially with the high dose and at longer
times with the mid-level dose. Mild lymphoid depletion of the spleen was described in another
intermediate-duration study in rats treated with 130 mg malathion/kg/day for 6 weeks, whereas marked
depletion occurred at 390 mg/kg/day (Piramanayagam and Manohar 2002).
Male Hissar mice received malathion (approximately 4.2, 10.5, or 21 mg/kg/day) in the diet for 3–
12-weeks (Banerjee et al. 1998). Mice exposed to 10.5 mg/kg/day malathion for 12 weeks and
immunized with SRBC showed a significant decrease in relative spleen weight. There was no significant
change in thymus weight. Malathion did not significantly alter levels of IgG or IgM. Exposure to
21 mg/kg/day for 3 weeks did not alter primary antibody titer against SRBC, but significantly decreased
the secondary antibody titer against SRBC throughout the experiment. Serum antibody titer to ovalbumin
was also decreased in high-dose mice after 8 weeks of exposure to malathion. Exposure to the high-dose
for 3 weeks caused a reduction in the PFC response only after secondary immunization, but exposure to
10.5 or 21 mg/kg/day for more than 6 weeks caused a dose-related decrease in PFC response after both
primary and secondary immunization. Exposure to malathion (mid- and high-dose) produced a marked
decrease in the MMI response to ovalbumin and tetanus toxoid immunization. In male New Zealand
rabbits treated by gavage with 0.5 or 2.5 mg/kg/day malathion for 21 days, there was no significant effect
on serum IgG or IgM levels. High-dose rabbits showed a significant decrease in antibody titer to
ovalbumin after 7 and 11 weeks of primary immunization (5 and 9 weeks after secondary immunization,
or 3 and 7 weeks after tertiary immunization) with the antigen. No effect was seen with the low-dose.
Rabbits exposed to malathion for 15 weeks and immunized with ovalbumin or tetanus toxoid showed a
significant decrease in LMI response after 7 weeks of antigen.
The effects of a commercial malathion formulation (50% malathion) on the immune system of female
SJL/J mice was investigated by Johnson et al. (2002). The mice were gavaged with 0, 0.018, 7.2, or
180 mg of malathion/kg on alternate days for 28 days. Malathion did not stimulate cholinergic activity as
monitored by the lack of significant change in brain acetylcholinesterase activity. The only significant
effect observed was a significant enhancement of the primary IgM response to SRBCs when the response