Page 238 - Partition & Adsorption of Organic Contaminants in Environmental Systems

CONTAMINANT LEVELS IN AQUATIC PLANTS AND SEDIMENTS 229

TABLE 8.4. Concentrations of Aldrin, Dieldrin, Heptachlor, and Heptachlor
Epoxide in Carrington Silt Loam and Crops in Field Plots after a Growing Season
Concentrations in Soil and Crops (ppm)
Heptachlor
Soil/Crop Aldrin Dieldrin Heptachlor Epoxide
Soil 3.1 1.8 4.2 0.78
Radishes 0.05 0.13 Trace 0.12
Beets Trace 0.17 0.03 0.12
Potatoes (whole) 0.11 0.31 0.29 0.49
Potatoes (peels) 0.63 1.82 3.03 2.35
Potatoes (pulp) Trace 0.16 Trace 0.24
Onions Trace 0.05 NA a NA
Carrots 0.36 0.55 1.34 NA
Lettuce 0.03 0.17 Trace 0.05

Source: Data from Lichtenstein (1960).
a
NA, data not available.

An interesting observation by Lichtenstein (1960) is that the contaminant
concentrations in the peels (skin) of potatoes are considerably higher than
those in either whole potatoes or their pulps (Table 8.4). Although the mass-
diffusion effect would make the concentrations higher in the peels than in the
pulps, it is not clear without the relevant lipid data whether this disparity
is caused solely by the mass diffusion or in addition by the lipid-content
difference. A similar but more pronounced disparity was later reported by
Lichtenstein et al. (1965) for the uptake of dieldrin from soil by carrots and
by Mattina et al. (2000) for the uptake of chlordane by carrots, potatoes, and
beets. The exact cause of this phenomenon is yet to be uncovered.

8.8 CONTAMINANT LEVELS IN
AQUATIC PLANTS AND SEDIMENTS

Contaminant levels in underwater plants of a polluted aquatic system should
approach more closely the equilibrium values with their in situ bed sediments
because of the enhanced plant uptake through roots and bulk-water diffusion.
In other words, the a pt values in Eq. (8.6) should be greater for underwater
plants than for land-grown plants, if other parameters (e.g., plant composition
and exposure time) are comparable. For relatively water-insoluble compounds
such as DDT, PCBs, and some PAHs, where the contaminant levels in sedi-
ments and plants are controlled primarily by contaminant partition into SOM
and plant lipids, respectively, Eq. (8.6) may be reduced to
C pt a ( C som K som ) lip (8.12)
f K lip
pt