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Phytoremediation of Organics
White and Kottler (2002) used citric acid to augment the remediation of
weathered DDT/DDE (DDT metabolite) with four species of plants including
clover, hairy vetch, mustard, and ryegrass. Uptake of DDE was significantly
increased while the region around the roots was depleted in concentration.
Other surfactants and organic acids have been used to enhance the release
of POPs. This is commonly characterized as chemically augmented phytoremediation. In order to improve the phytoremediation potential of plants and
microbes, one may try using surface-active compounds including synthetic or
biosurfactants (Agnello et al., 2014; An et al., 2011; Ramamurthy & Memarian,
2012); several different organic acids (Agnello et al., 2014; Gonzalez et al.,
2010); and nanoparticles (Pillai & Kottekottil, 2016; Rani et al., 2017).
Herbicides, fungicides, and insecticides produced and used in recent years
tend to have less residual action and decreased environmental stability
than highly chlorinated POPs. Nevertheless, their remediation/detoxification is still necessary to avoid toxic effects on nontarget organisms during
accidental exposure, and from field run-off during sudden rains, as they are
typically applied at concentrations that are >100 × toxic levels (e.g., Fairchild
et al., 1998; Plhalova et al., 2012).
Loffredo et al. (2020) found Cannabis sativa L. seedlings to be very effective in
removing the systemic fungicide metalaxyl-M from water. Residual compounds
accumulated in the hemp tissues over 7days were much lower than the amounts
removed from the medium, suggesting efficient metabolization. When hemp
was allowed to germinate and grow in columns filled with soil contaminated
with metalaxyl-M and the herbicide, metribuzin, it showed a noticeable remediation capacity. The authors used this study to suggest that hemp is a promising
candidate for phytoremediation of wastewater and soil from pesticides.
3.3 Landfills and Containment
Containment of contaminants is an issue at landfills where waste is deposited
and managed. In order to control contaminant movement within landfills,
trees are often planted on the down gradient side to remove contaminated
leachate from the site. This concept has also been used at the edges of fields
to capture agricultural chemicals with a riparian strip to prevent them
from entering a creek or river. There are significant savings when vegetation is used for pump-and-treat applications (Negri et al. in McCutcheon &
Schnoor, 2003). The organic contaminants may be biodegraded or transpired
and destroyed in the atmosphere. Trees that have the ability to reach the
water table and have value when harvested are generally recommended for
these applications. Trees have been used to some extent directly on landfill covers, but native plants, including shrubs and forbs, are recommended
(USEPA, 2015). Deep-rooted grasses may also be effective. Grasses have been