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

MALATHION 195
6. POTENTIAL FOR HUMAN EXPOSURE
Carolina, was detected (detection limit of 0.5 ng/L) in the subsurface water at a maximum mean
concentration of 32 ng/L, with a range in individual samples of below the limit of detection to 47 ng/L.
In the surface microlayer (top #1 mm) samples, malathion was detected at a maximum mean
concentration of 32 ng/L, with a range in individual samples of below the limit of detection to 57 ng/L.
Monitoring studies have been conducted to determine the presence of numerous pesticides, including
malathion, in groundwater in the United States. In a review of pesticides in groundwater monitoring data
in the literature, Ritter (1990) reported that malathion occurrence in groundwater from normal agricultural
use was reported in the literature for only one state. In a database of pesticides in groundwater that was
compiled by EPA from data available for 1971–1991, results indicated that malathion was detected in a
total of 12 wells in three states (California, Mississippi, and Virginia) at concentrations ranging from
0.007 to 6.17 µg/L; monitoring data were reported for a total of 3,252 wells (EPA 1992). Forty-one landuse
studies were conducted in 1993–1995 at a total of 1,034 agricultural and urban sites representing
20 major hydrologic basins throughout the United States to assess the occurrence of 46 pesticides,
including malathion, in shallow groundwater for the National Water-Quality Assessment (NAWQA)
program; 31 of the studies were in agricultural areas and 10 were in urban areas (Kolpin et al. 1998).
Malathion was detected (detection limit of 0.005 µg/L) at 0.2% of all sites, with detection frequencies of
0.4% for sites where corn and alfalfa growth accounted for >20% of the crops grown there, and 1.7% for
sites where orchards or vineyards accounted for >50% of the crops (Kolpin et al. 1998).
6.4.3 Sediment and Soil
To estimate soil concentrations following an aerial application 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 for the eradication of medflies, mass deposition data for malathion and its primary oxidation
product, malaoxon, were obtained from the CDFA Environmental Monitoring Branch (Bradman et al.
1994). Based on measured values of mass deposition, daily malathion and malaoxon residue levels in soil
were estimated for a single application using two sample mixing depths. Based on a mixing depth of
1 cm, soil concentrations of the parent and its 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).
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