Page 223 - Partition & Adsorption of Organic Contaminants in Environmental Systems

Partition and Adsorption of Organic Contaminants in Environmental Systems. Cary T. Chiou
Copyright ¶ 2002 John Wiley & Sons, Inc.
ISBN: 0-471-23325-0

8 Contaminant Uptake by Plants

from Soil and Water

8.1 INTRODUCTION

The contamination of soils or water by pesticides and other substances leads
to the subsequent contamination of plants grown in these soils. Many
soil-incorporated pesticides are known to translocate into plants and crops
following their applications. Although scientists began investigating plant
uptake as early as the early 1950s, soon after insecticides were introduced for
agricultural purposes, there has been only moderate progress in this area of
research because of the complexity of the contaminant soil-to-plant transport
process. Some key parameters affecting the system include the levels of
contaminants in soil (or water), the contaminant physicochemical properties,
the particular plant species, the soil type that sustains the plant, and the time
of plant exposure. Because of insufficient understanding of the contaminant
sorption to soils in earlier years (1950s through 1970s),the crucial link between
contaminant levels in soils and plants could not be forged at that time. Even
in a number of later simpler studies on plant uptake from water, the published
work investigated only relatively simple systems, such as small, young plants
or excised plant parts, in controlled laboratory systems usually not sufficiently
representative of natural settings. As the plant-uptake process has yet to be
further characterized with extensive data, we are especially interested in a
simple physical model to guide future investigations. Knowledge of contami-
nant uptake by plants is of vital interest not only because it will improve our
understanding and alleviation of the crop-contamination problem but also
because it may provide us with a means to effectively bioremediate contami-
nated soil and groundwater sites by appropriate plantings. Some critical plant-
uptake data and the proposed model concepts are presented in this chapter.
Plant uptake of contaminants is considered to occur by a passive and/or an
active process, depending on the contaminant and plant type (Shone and
Wood, 1974; Briggs et al., 1982). Passive transport proceeds in the direction of
decreasing chemical potential, the same process that is primarily responsible
for bioconcentration of nonionic compounds by fish; it also appears to be the
primary process for plant uptake of these compounds. Active transport, on
the other hand, takes place against the chemical potential gradient, requiring
the expenditure of energy; it applies to certain plant nutrients and possibly to
some other inorganic and organic ions. The passive plant uptake of contami-
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