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

MALATHION 209
6. POTENTIAL FOR HUMAN EXPOSURE
reverse osmosis (EPA 1982). Another method of disposal that has been suggested for malathion is
combustion in molten potassium chloride. The destruction of malathion is 99% and the products of
combustion can be used as a fertilizer (United Nations IRPTC 1985).
Environmental Fate. There is a lack of data on the degradation (fate and persistence) of malathion
in soil under both aerobic and anaerobic acidic conditions, as well as on the degradation of malathion on
dry surface soils where hydrolysis is less likely to occur. Further studies with malathion are needed to
assess these particular situations. Monitoring data for pesticide disposal and other hazardous waste sites
are also lacking and would be useful in determining the prevalence of malathion residues at these sites.
As very little definitive information was found in the literature on the transformation and degradation of
malathion in air, additional studies are needed on this topic, including on the transformation of the parent
to malaoxon through photolysis and on the subsequent degradation of malaoxon. Several researchers
have suggested the possibility of the volatilization of malathion from nonnatural surfaces, such as metals,
plastic playground equipment, cement, and paved areas, based on mass deposition study data (Bradman et
al. 1994; Brown et al. 1993b). More information is needed on the potential volatilization of malathion
from nonnatural surfaces such as pavements and playground equipment. Additionally, information is
needed on the potential for photodegradation of malathion and malaoxon on such surfaces in order to
characterize the fate of malathion in the environment when it is used over widespread areas for public
health purposes. Information on the physical properties and the fate and persistence of the malathion
degradate malaoxon (which is also present in malathion as an impurity) would be particularly useful in
assessing the human health risks from malathion use, as the oxon is considered to be more toxic than the
parent compound (EPA 2000a).
Bioavailability from Environmental Media. Malathion can be absorbed following inhalation or
dermal contact with contaminated media, and by ingestion of contaminated water or food, particularly of
unwashed backyard vegetables (Bradman et al. 1994; Brown et al. 1993b; Durham and Wolfe 1962; EPA
2000a; Kutz et al. 1992; MacIntosh et al. 1999a; Whitmore et al. 1994). Dermal contact with malathion
present in soil or on treated crops and ingestion of malathion present on backyard vegetables or soil
particles are exposure routes that may be of concern. No information was found in the available literature
on the bioavailability of malathion following ingestion of soil or dermal contact with contaminated media;
such data are needed to determine potential exposures to humans.
Food Chain Bioaccumulation. The majority of the data available on the bioaccumulation of
malathion suggest that, while malathion may be bioconcentrated, it is rapidly metabolized or depurated