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

MALATHION 106
3.4.1.1 Inhalation Exposure
3. HEALTH EFFECTS
While inhalation of malathion vapor or spray mist is well anticipated to be an efficient route of absorption
of malathion, especially in occupational applications, no specific studies were located in the literature on
absorption of malathion through inhalational exposure.
3.4.1.2 Oral Exposure
The many case reports of malathion intoxication following accidental or intentional ingestion (see
Section 3.2.2, Oral Exposure) of the pesticide provide ample evidence that malathion is well absorbed
through the gastrointestinal tract in humans. Also, a controlled study with volunteers who received
malathion in capsules provides direct evidence of absorption, as ingestion of malathion induced a
decrease in both plasma and RBC cholinesterase activity levels (Moeller and Rider 1962).
In mice, rapid absorption of oral doses of malathion was shown by its decrease from the gastrointestinal
tract. 14 C-Succinyl malathion gavaged at 1 mg/kg to fasted female ICR mice was rapidly absorbed (20%
in 1 minute, 28% in 5 minutes, 40% in 15 minutes, 45% in 30 minutes, and 89% in 60 minutes) (Ahdaya
et al. 1981). The half-time of absorption was 34 minutes. Ligation of the pylorus to measure stomach
absorption resulted in absorption of 20% in 1 hour, indicating that most absorption occurred in the
intestine (Ahdaya and Guthrie 1982).
As described in the section on elimination, ingested malathion is rapidly eliminated, mainly into urine,
further indicating rapid absorption of ingested doses.
3.4.1.3 Dermal Exposure
There is extensive information on dermal absorption of malathion in humans and animals. The dermal
route constitutes a major route of exposure during and following malathion application to fields and
following aerial spraying for pest control and residential use. Dermal absorption occurs as a result of high
capacity of the skin and the affinity of the plasma proteins for malathion (Menczel et al. 1983).