Agriculture Reference
In-Depth Information
(WHC) by adding deionized water, and harvested after growing for 35 days. After
pretreatment, the Cd concentrations in the tissues were determined.
The Cd concentrations in initial seedlings of five plants were not detectable (Cd < 0.38 mg
kg
-1
). After growing in the artificially Cd-contaminated soils for 35 days, five tested plants
can significantly accumulate much higher Cd concentrations in their shoots relative to Cd-
CK. Among the five plants, Impatiens grown in the Cd-20 treatment had the highest shoot
Cd concentration near 100±11 mg kg
-1
, which was more than the threshold of a Cd
hyperaccumulator (100 mg kg
-l
) reported (Baker et al., 2000). French marigold grown in Cd-
10 and Cd-20 treatments accumulated 44.9±0.7 and 66.3±6.5 mg kg
-l
in their shoots and no
toxic symptoms were observed in the appearance during pot experiment. Chen & Lee (1997)
reported that Star cluster, Scarlet sage, and Impatiens can accumulate 44, 12, and 42 mg kg
-1
,
respectively, in their leaves when
in-situ
growing in a Cd-contaminated site (Tatan village)
in northern Taiwan. For another
in-situ
experiment carried out in Chungfu village in
northern Taiwan, the final Cd concentration in their leaves was 247 mg kg
-1
in French
marigold, 52 mg kg
-1
in Garden verbena, 12 mg kg
-1
in Impatiens, and 11 mg kg
-1
in Scarlet
sage, respectively. French marigold and Impatiens used in this study accumulated higher
Cd concentration in their shoots compared with the result of previous study possibly
resulted from the higher phytoavailability of Cd in artificially Cd-contaminated soils.
Besides the accumulated concentration, bioconcentration factor (BCF = shoot HM
concentration/soil HM concentration) and translocation factor (TF = shoot HM
concentration/root HM concentration) were two indexes most used to evaluate the
accumulating capacity of HMs by plants. For a Cd hyperaccumulator (Baker et al., 2000;
Mattina et al., 2003), the BCF and TF should more than one besides the high concentration
accumulated (100 mg kg
-1
) (Sun et al., 2009). Experimental result of this study showed that
the BCF values of French marigold, Impatiens, Garden verbena, and Scarlet sage were all
more than one and ranged from 1.75 to 5.68 (Table 1). However, Impatiens was the only one
that its TF was in the levels of 1.01-1.66. According to the standards summarized by Sun et
al. (2009) for a Cd hyperaccumulator, Impatiens was a potential Cd hyperaccumulator when
growing in the artificially Cd-contaminated soils. The pot experimental result was against
with the in-situ selection experiment, possible resulted from the special variation and
interaction of HMs in the field.
The total removal of Cd by plants determines the duration needed in decontamination.
Although root of plants accumulated higher concentration of Cd in compartment with
shoot, the total removal of Cd by shoot was larger because of its larger biomass (Fig. 1).
Among the five tested plants, the shoots of French marigold and Impatiens removed 380-510
and 790-820 g Cd plant
-1
from Cd-10 and Cd-20. One can calculate the period needed for
phytoremediation in an ideal situation, i.e. if the removal of plants of each harvest is a
constant and the phytoavailability of Cd will not change with time, etc. It will take
approximately 4.6-8.0 years for continuous planting (six times year
-1
) French marigold and
Impatiens to decrease the current Cd concentration (Cd-10 and Cd-20) to below the SPCS for
cropping lands (5 mg kg
-1
). The major drawback of phytoremediation is that it always
consumes longer period compared with other techniques. Experimental results show that
planting French marigold and Impatiens in Cd-contaminated soils seems to be a feasible
method to remove Cd from contaminated soil and the period needed for decontamination is
acceptable.
