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

MALATHION 194
6. POTENTIAL FOR HUMAN EXPOSURE
increased to a maximum of 61.6 ng/m 3 within 24 hours of spraying, and was 3.3 ng/m 3 within 96–
120 hours of spraying (Brown et al. 1993b). The mean concentration of malaoxon in the air was
5.4 ng/m 3 during the spraying, was a maximum of 48.1 ng/m 3 within 24–48 hours of spraying, and was
4.5 ng/m 3 within 96–120 hours of spraying (Brown et al. 1993b).
6.4.2 Water
Several studies have been conducted to determine the presence and concentration of malathion in runoff
waters as well as in surface waters of various river basins in agricultural areas of the United States.
Malathion was not detected (detection limit of 35 ng/L) in storm water runoff (from rice fields and fruit
orchards) within the Sacramento River Basin, California, following a storm event in January 1994
(Domagalski 1996). In a study of pesticides in the streams of an agricultural and an urban area of
Colorado, conducted from April 1993 to April 1994, 25 water samples were collected each from the
Lonetree Creek Basin near Greely, Colorado (an agricultural land-use area), and the Cherry Creek Basin
(urban area) near Denver, Colorado; 2 of the samples in the agricultural area and 7 of the samples in the
urban area were collected during storm runoff events (Kimbrough and Litke 1996). Malathion was not
detected (detection limit of 0.014 µg/L) in the water samples from the agricultural area, but was present in
approximately 30% of the samples from the urban area, at a maximum concentration of 0.16 µg/L;
statistical analysis of the data indicated that concentrations of malathion were significantly higher in the
storm runoff event samples than in the nonstorm samples.
In a study of pesticide fluxes in nine surface water bodies of the Mississippi River Basin, the
concentrations of 26 pesticides, including malathion, were monitored between May 1991 and March 1992
at nine sites, including three sites on the Mississippi River and six sites located near the mouths of major
tributaries of the Mississippi (Larson et al. 1995). Malathion was detected (detection limit of 0.005 µg/L)
at only two of the eight sites for which data were reported. In the White River Basin, the malathion flux
as percentage of the total agricultural usage of malathion (0.98 metric tonnes or 980 kg) in the river basin
was 0.12% (1.18 kg); in the Missouri River Basin, the malathion flux was