Recent advances in phytoremediation of arsenic-contaminated soils - In-Situ Remediation of Arsenic-Contaminated Sites - page 80

4.4.4 Pretreatment of arsenic-contaminated irrigating water
In South and Southeast Asia, extensive irrigation with arsenic-contaminated groundwater accounts
predominantly for the elevated arsenic in paddy soils. Besides the above strategies to minimize
arsenic contamination in soil-rice system, it is equally important to take proper measures to
scavenge arsenic from irrigation water. Arsenic phytofiltration, an emerging technology, has
been tested in both laboratory- and pilot-scale experiments using arsenic hyperaccumulators such
as P. vittata . With initial As(V) concentration ranging from 20 to 200 gL − 1 , both P. vittata and

another arsenic hyperaccumulator P. cretica exhibited high removal efficiency to reduce arsenic
to below the drinking water limit of 10

µ

gL − 1 within 24 h (Huang et al ., 2004). Furthermore,
rapid arsenic removal has also been observed by repeatedly using the same batch of P. vittata
after a short recovery (12-36 h), indicating the high sustainability of this technology. While in
the presence of 1.6 mg L − 1

µ

gL − 1 , a short term (60 min) arsenic
influx into P. cretica roots was decreased by 88% as a result of the strong anion competition
for root uptake (Huang et al ., 2004). However, for the well-established P. vittata (6-7 month
old), P treatment (1.2 and 2.4 mg L − 1 ) exerted little effect on arsenic depletion, with arsenic in
the contaminated groundwater decreased from initial 130 µ gL − 1

P with initial arsenic of 200 µ

to less than 10 µ gL − 1 in 2 d

(Natarajan et al ., 2009).
In a pilot scale phytofiltration system, arsenic concentration in the outflow was invariably less
than 2 µ gL − 1 through 84 d demonstration with initial arsenic between 6.6 and 14 µ gL − 1 and
flow rate between 255 and 1900 L d − 1 . Besides, arsenic removal efficiency was unaffected by day
length, light intensity and humidity (Elless et al ., 2005), demonstrating the high reliability of this
technology. Therefore, to reduce arsenic buildup in agriculture soils, phytofiltration is potentially
useful for arsenic depletion from irrigation water in the regions where prevalent arsenic contam-
ination occurs in water supply. However, phytofiltration with P. vittata is limited to subtropical
and tropical regions and more suitable for small-scale water treatment considering the increased
cost of fern maintenance in cold areas and huge space need for large-scale treatment system.

4.5 CONCLUSIONS

Arsenic phytoextraction with hyperaccumulators such as P. vittata has a potential for soil reme-
diation with low to moderate arsenic contamination. Arsenic phytoextraction technologies based
on greenhouse and field studies mainly include candidate plant screening, fertilizing, rhizosphere
manipulation, growth timing, and harvest method, which provide essential basis for larger scale
application of this technology. Proper measures need to be taken to diminish fern invasive risks
particularly in eco-fragile regions and to achieve safe disposal of arsenic-rich biomass.
Arsenic phytostabilization with indigenous tolerant species with low translocation capacity is
advantageous for heavily contaminated sites with high levels of arsenic and other toxic metals.
Amendments such as iron oxides, phosphate, organic matter, N-fixation legume and mycorrhizal
inoculation are important for plant survival in hostile environment and serve as core strategies to
facilitate the success of phytostabilization.
To alleviate arsenic contamination in soil-rice system, a range of agronomic strategies and
biotechnologies from water management and Si and Fe fertilization to pretreatment of irrigation
water provide effective phytoexclusion measures to remediate arsenic-contaminated agriculture
soils and reduce arsenic uptake by rice.

ACKNOWLEDGEMENT

This project is supported by the Construct Program of the Key Discipline in Hunan Province,
China, Hunan Provincial Natural Science Foundation of China (No.13JJ4044), and program for
excellent talents in Hunan Normal University (No.ET12405).