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

MALATHION 141
3. HEALTH EFFECTS
acetylcholinesterase, about 25% regeneration occurs in the first 7–10 days, and is regenerated by the liver
in about 2 weeks (Abou-Donia 1995). After severe poisoning, plasma cholinesterase activity remains
depressed for up to 30 days, which corresponds to the time that it takes the liver to synthesize new
enzymes. Although a more sensitive indicator of exposure to organophosphates than RBC
acetylcholinesterase, plasma cholinesterase is less specific since the levels may also be suppressed due to
genetic factors and to a variety of conditions and diseases (Zimmerman and Henry 1984; Tafuri and
Roberts 1987). The rate of decrease of RBC acetylcholinesterase correlates better with appearance of
symptoms than the absolute value reached after exposure (Maroni et al. 2000). Reduction of RBC
acetylcholinesterase after severe exposure lasts up to 100 days reflecting the time of production of new
cells. RBC acetylcholinesterase levels are representative of acetylcholinesterase levels in the nervous
system, and, therefore, may be a more accurate biomarker of the neurological effects of chronic low level
exposure of humans to malathion (Midtling et al. 1985). Tafuri and Roberts (1987) proposed a
classification of organophosphate poisoning as follows. Clinical signs and symptoms of intoxication may
occur when plasma cholinesterase levels drop to below 50% of the normal value. Mild poisoning, with
the patient still ambulatory, may occur when plasma cholinesterase levels are 20–50% of normal;
moderate poisoning with inability to walk with levels 10–20% of normal; and severe poisoning with
respiratory distress and unconsciousness with plasma cholinesterase levels