Page 208 - Plant-Based Remediation Processes

200 M. Griga and M. Bjelkova ´

Table 11.1 Yield of above-ground biomass and fibre of important fibre crops
Common name of Biomass yield Fibre yield
1
1
Plant species plant/product (tonne ha ) (tonne ha )
Linum usitatissimum Flax 6.5–7.5 1.1–1.5
Linseed 2–5 0.2–0.5
Cannabis sativa Hemp 8–15 1.5–1.9
Hibiscus cannabinus Kenaf 5–12 0.4–1.3
Gossypium hirsutum Cotton 1–3.4 0.3–1.1
Corchorus olitorius Jute 30–35 1.4–4
Boehmeria nivea White ramie 1.7–2 0.3–0.5
Asclepias syriaca Common milkweed 12.3 1.4
Agave sisalana Sisal 5,000 Plants 2.8–5
Musa textilis Banana/abaca – 5
Cocos nucifera Coconut/coir 1,000 nuts 0.1
Crotalaria juncea Sunhemp 7–10 0.6–0.8

Fibre crops may represent a good compromise between the lower HMs accumu-
lation potential and the possibility of industrial (non-food) processing of
contaminated biomass. Fibre crops are world-wide distributed group of plant
species belonging taxonomically to various plant families. The common denomi-
nator is their use of above-ground biomass (Table 11.1) for mainly industrial (non-
food) or energy purposes. They include approximately 2,000 species—annual and
perennial—belonging to monocotyledonous as well as dicotyledonous plants.
About 20 species have got an economical (some of them local) importance.
Majority of fibre species is grown in tropical and subtropical zones. Cellulose, a
natural polymer with high strength and stiffness per weight, is the building material
of long fibrous cells, which can be found in the stems, the leaves or the fruits/seeds
of fibre plants. Thus, based on the fibrous cells localisation within the plant we can
recognise bast fibre species (e.g. flax, hemp, jute, kenaf, ramie and sida), leaf fibre
species (sisal, banana and palm) and fruit/seed fibre species (cotton, coconut, kapok
and luffa) (Brouwer 2000). World acreage and production of the most important
fibre crop commodities are illustrated in Table 11.2. During last 20 years, the fibre
crops have been also considered as potential candidates for phytoremediation,
particularly for phytoextraction of heavy metals from contaminated soils (Griga
et al. 2003a, b; Linger et al. 2002). Within fibre crops of temperate and subtropic
zone, the flax/linseed and hemp represent economically the most important species
and also the majority of heavy metal-related data were obtained and published in
these two fibre crops. As the main portion of HM-data in flax and hemp have been
published in national scientific literature, this review tries to summarise all this
available literature in order to bring a complex view of recent knowledge of flax and
hemp phytoremediation potential and also to critically assess original expectations
versus real situation of recent days.