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

MALATHION 207
6. POTENTIAL FOR HUMAN EXPOSURE
backyard vegetables treated with malathion may also be exposed to higher levels of the chemical relative
to the general population.
In an assessment of exposure to malathion and malaoxon in areas of southern California that had received
aerial applications of malathion for public health purposes estimates of the various exposures were made
for both average and high-end exposure scenarios. In general, estimated exposures to malathion residues
increased with the extent of outdoor activity and with higher levels of consumption of backyard
vegetables (Marty et al. 1994). The most important routes of exposure for adults were dermal exposure
and ingestion exposure from consumption of contaminated, unwashed backyard vegetables, with
respective estimated doses of 1–246 and 30–80 µg/kg/day (Marty et al. 1994).
It has been reported that malathion was oxidized to malaoxon following its release in 1990 in the Los
Angeles Basin of California for control of the Mediterranean fruit fly; concentrations of malaoxon in air
were greater than those of parent malathion (Wolfe and Sieber 1993). Because malathion is less toxic in
the parent (thiono) form than in its oxon form, exposure to malathion residues are potentially more
harmful in situations that favor the formation of the degradate malaoxon. Such a case may occur when a
dust formulation is utilized on plant or tree leaves, which allows for the formation of a catalytic surface
where oxidation to malaoxon may take place, particularly in the presence of a high level of atmospheric
oxidant such as ozone and in times of low humidity; these conditions are thought to be favorable to the
buildup of the oxon (Wolfe and Sieber 1993). These data indicate that the restricted entry intervals that
do not account for such cases may lead to higher potential exposures to workers who enter a field with
such conditions too early after spraying.
6.8 ADEQUACY OF THE DATABASE
Section 104(i)(5) of CERCLA, as amended, directs the Administrator of ATSDR (in consultation with the
Administrator of EPA and agencies and programs of the Public Health Service) to assess whether
adequate information on the health effects of malathion is available. Where adequate information is not
available, ATSDR, in conjunction with the National Toxicology Program (NTP), is required to assure the
initiation of a program of research designed to determine the health effects (and techniques for developing
methods to determine such health effects) of malathion.
The following categories of possible data needs have been identified by a joint team of scientists from
ATSDR, NTP, and EPA. They are defined as substance-specific informational needs that if met would