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Phytotechnology with Biomass Production
to note that as shown by Nartey & Zhao (2014) different kinds of biochar prepared in different ways from different starting materials may have different
effects.
Among pesticides, there is a large class of obsolete pesticides (insecticides)
containing significant amounts of chlorination, resulting in persistence.
Examples include aldrin/dieldrin/endrin, lindane (α-hexachlorocyclohexane),
chlordane, chlordecone (Kepone), DDT, heptachlor, toxaphene, and others. Many of these are banned in many countries, but residues and waste/
abandoned sites are still present (Agbeve et al., 2013; Tarla et al., 2020).
Weathered DDT is still found in many locations, and portions of Africa continue to use it for control of malaria-bearing mosquitos (Tarla et al., 2020).
Many other pesticides are present in agricultural/horticultural soils and in
plants harvested from such soils. For instance, Agbeve et al. (2013) found
β-HCH, δ-HCH, γ-HCH, heptachlor, aldrin, γ-chlordane, α-endosulfan,
p.p′-DDE (2,2’-p,p’dichlorodiphenyl-1,1-dichloroethene), dieldrin, endrin,
β-endosulfan, p.p′-DDD (2,2’-p,p’dichlorodiphenyl-1,1-dichloroethane, p.p′DDT, and methoxychlor in roots of Cryptolepis sanguinolenta, a traditional
antimalarial herb of Ghana, in both dry and rainy season’s growth. Roots
were thoroughly washed before analysis, which may have reduced the pesticide load, though perhaps not completely, as sorption is quite strong on root
surfaces. The detected levels were below regulatory limits except for some
samples with high aldrin/dieldrin. It is not known whether the various pesticides were long-term residues, or from banned products still being used.
Tarla et al. (2020) discuss some of the problems with waste pesticide disposal.
There is potential for phytoremediation of DDT because it is taken up by some
vascular plants (Lunney et al., 2004) particularly some species of the Cucurbitaceae
family. Zucchini, a popular edible vegetable, accumulates large amounts from
contaminated soil. It also accumulates aldrin, dieldrin, and endrin, such that
it may be used to remove these residues from agricultural lands long contaminated with high levels, above current regulatory limits (Otani et al., 2007).
However, very few species take up these compounds (only 2 of 15 families tested
by Otani et al. (2007)), limiting ability to clean up many sites.
Paul et al. (2015) conducted a field investigation at three DDT‐contaminated
areas in PPNP in Canada. Cucurbita pepo (pumpkin) and three native grass species, Schizachyrium scoparium, Panicum virgatum, and Sporobolus cryptandrus, were
grown at three different sites in PPNP having low (291ng g −1 ), moderate (5083ng
g −1 ), and high (10,192ng g −1 ) soil DDT contamination levels. A threshold soil
DDT concentration was identified at ∼5000ng g −1 where the DDT uptake into
C. pepo was maximized, resulting in plant shoot and root DDT concentrations of
16,600 and 45,000ng g −1 , respectively. Two of the native grass species (P. virgatum
and S. scoparium) were identified as potential phytoextractors, with higher shoot
extraction capabilities than that of the known phytoextractor C. pepo when optimal planting density was taken into account. Hexachlorocyclohexane, a common persistent contaminant (Agbeve et al., 2013; Tarla et al., 2020), has been
remediated using plants also (Becerra-Castro et al., 2013).