The Movement of Pesticides in Soils
PERRY L. McCARTY, Associate Professor
PAULH. KING, Graduate Student
Sanitary Engineering Department
Stanford University
Stanford, California
INTRODUCTION
The increasingly widespread use of synthetic organic pesticides in agricultural
practice has raised considerable concern as to their potential for harmful contamination of both surface and groundwater resources. In order to evaluate possible effects on water quality from this source it is necessary to determine the principal
factors which govern the movement of pesticides in agricultural soils. The investigation described in this paper was undertaken in order to determine the type of
information required for a satisfactory prediction of this movement.
PREVIOUS STUDIES
Since the development of organic pesticides many investigators have studied
the tendency of these chemicals to move by leaching through the soil. Considerable data has been collected, but unfortunately most of the available information
stems from use of relatively insensitive bio-assay type analysis. Many cases where
no movement is reported are subject to considerable question, for in most reports
the authors do not give a lower limit of detectability for the analytical procedure
employed. The advent of gas chromatography and with it the ability to detect
pesticide concentrations in the low parts per billion range has made it practical to
study pesticide movement in soils on a laboratory scale. Nonetheless, the majority of the work which has been reported concerns the relatively soluble organic
herbicides and little attention has been given to the chlorinated hydrocarbon or
the organic phosphorus insecticides. Much of this work is included in the general
literature reviews concerning the behavior of pesticides in soils which have been
published by Bailey and White (1), the United States Public Health Service (2) and
the Commonwealth Bureau of Soils (3).
The extent of movement of organic phosphorus insecticides has been related
to their water solubility by Reynolds and Metcalf (4). Getzin and Chapman (5)
studied the leaching of radioactive phosdrin and concluded that the organic matter
content of the soil was primarily responsible for binding organic phosphorus insecticides against the leaching action of water. Lichtenstein and his co-workers (6,7)
have studied the movement and persistence of a number of insecticides under
leaching and non-leaching conditions. Parathion, DDT, and lindane all exhibited
some mobility and retention was considerably less in sand than in muck soils. Bowman, et al, (8) in a more comprehensive study of the chlorinated hydrocarbon insecticides reported on the behavior of eleven members of this group in eight types
of soils showing the extent of volatilization, degradation, elution with a non-
polar solvent, and leaching of the pesticides by water.
GENERAL CONSIDERATIONS
In defining the type of information required to satisfactorily predict the move-
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