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

MALATHION 182
6. POTENTIAL FOR HUMAN EXPOSURE
Following repeated aerial applications of malathion, at a target rate of 23.8 mg/m 2 , to urban/residential
areas (1,500 km 2 ) of southern California between August 1989 and July 1990 to eradicate medflies, the
CDFA Environmental Monitoring Branch measured the mass deposition, air concentrations, and selected
water concentrations of malathion and its primary oxidation product, malaoxon (Bradman et al. 1994).
Mass deposition of malathion ranged from 1,100 to 2,413 µg/ft 2 ; mass deposition of malaoxon ranged
from 2.9 to 6.0 µg/ft 2 (Brown et al. 1993b). Based on measured values of mass deposition, daily
malathion and malaoxon residue levels in soil were estimated for a single application. Based on a mixing
depth of 1 cm, soil concentrations of the parent and its oxon degradate were estimated as 1.4 and
0.01 µg/g, respectively; based on a mixing depth of 0.1 cm, the corresponding estimated concentrations in
soil were 14.1 and 0.10 µg/g (Bradman et al. 1994).
Malathion may also be released to the soils by improper handling of pesticide formulations during
processing or handling, including from spills or the usage of poor storage and containment practices. In a
study of 49 randomly chosen agrichemical facilities located throughout Illinois, malathion was detected in
soil samples at 6 of the 18 sites that handled the compound (Krapac et al. 1995). Malathion was detected
in 11 of the soil samples from the six sites, at a mean concentration of 125 µg/kg (ppm) and at a
concentration range of 31–690 µg/kg; the common range of detections was 22–100 µg/kg.
Malathion has been detected in soil at 11 of the 1,623 current or former NPL sites where malathion has
been identified in some environmental medium (HazDat 2003). Malathion has been detected in sediment
at 4 of the 1,623 current or former NPL sites where malathion has been identified in some environmental
medium (HazDat 2003).
The most recent TRI data indicate that 11 sites in the United States processed malathion in 2000 (TRI00
2002); no releases to soil were reported for that year (Table 6-1). The TRI data should be used with
caution because only certain types of facilities are required to report. This is not an exhaustive list.
6.3 ENVIRONMENTAL FATE
The malathion released to the atmosphere can be transported back to surface water and soil by wet
deposition (Harman-Fetcho et al. 2000; McConnell et al. 1998). Malathion that is released to the
atmosphere can also be transformed by indirect photolysis to its oxygen analog, malaoxon, by oxidation
with photochemically produced hydroxyl radicals (Howard 1991).