Contaminant Fate and Transport - Urban Watersheds: Geology, Contamination, and Sustainable Development - page 303

On land and in sediments, other heavy metals such as barium, cadmium, chromium, lead,
copper, and zinc can accumulate in plant matter if they are present at sufficient concentra-
tions in soil within the root zone of plants (Nedunuri et al. 1998). Removal of contaminants
from near-surface soil is not uncommon and sometimes the preferred alternative. Suitable
locations for removal include closed landfill sites requiring a vegetative cap to minimize
erosion potential, or sites where contamination is shallow, relatively static, and has become
a chronic problem (Singer et al. 2003). Phytoremediation — the removal of contamination
using plants—has been applied to other contaminants including organic compounds, but
with limited success.

8.4.6 Other Contaminants

The remaining contaminants encountered in urban areas span a wide variety of organic
and inorganic compounds. Their fate and transport is briefly discussed here.

8.4.6.1 Pesticides and Herbicides

Pesticides and herbicides are released into the environment for specific purposes and are
most commonly detected in near-surface soils and surface water rather than groundwater
(USGS 2006b). The highest concentrations of pesticides exist in the nation's streams and
sediments within urban areas where they have been detected in 83% of streams and 70%
of sediments (USGS 2006b). Figure 8.22 breaks down the pesticides detected in streams
and bed sediments by land use. While the total tonnage of pesticide and herbicide use in

Streams with concentrations greater than
aquatic-life benchmarks for water and bed sediment

Agricultural areas

57%

Stream water

31%

Bed sediment

Urban areas

Stream water 83%

Bed sediment

70%

Undeveloped areas

Stream water 13%

Bed sediment

8.4%

Mixed land uses

Stream water

42%

Bed sediment

36%

0 50 75 100

Percentage of stream sites with one or more pesticide
compounds exceeding an aquatic-life benchmark

25

FIGURE 8.22
Pesticide detections in streams and sediments in the United States. (From United States Geological Survey
(USGS), Pesticides in the nation's streams and groundwater, 1992-2001—A summary, USGS Fact Sheet 2006-
3028, Washington, DC, 2006b.)