Agriculture Reference
In-Depth Information
2004; Meers et al., 2005). However, results of most previous studies showed that chemical
agents have negative effect on the growth of Indian mustard, sunflower, or corn and thus
decreased the total removal of HMs by plants (Blaylock et al., 2007; Madrid et al., 2003;
Turgut et al., 2004). After the application of chemical chelating agents, the risk of
groundwater contamination may be increased because the mobility of HMs increased (Jiang
et al., 2003; Lai & Chen, 2004; Lai et al., 2005). For those lands with sandy texture or high
level of groundwater table, chemical agents should be carefully applied to decrease the
health risk of groundwater quality (Lai & Chen, 2006; Wu et al., 2004).
Rice dominates the daily intake of cereals in most Asian countries. In Taiwan, about half of
arable land is used as rice-growing field and two rice varieties including Indica and Japonica
varieties are cultivated, but the latter is the major one (90%) because of taste preferences.
Cadmium (Cd), normally occurs in low concentrations in soils (Wagner, 1993), is a non-
essential element for plants and potentially toxic pollutant all over the world. The toxicity of
Cd to plant growth, phytosynthesis, carbonhydrate metabolism, and enzyme activities is
well documented (Javed & Greger, 2011; Sanita di Toppi & Gabrielli, 1999). Elevated levels
of arsenic (As) in soils may potentially enter food chain (Meharg & Hartley-Whitaker, 2002)
and increase the risk of cancer development (Anderson et al., 2011). According to the
SGWPR Act, the cropping land with total soil Cd concentration (aqua regia soluble)
exceeding 5 mg kg
-1
will be announced as Soil Pollution Control Site (SPCS) and all farming
activities are not allowed. However, many previous field surveys showed Cd-contaminated
rice can still be produced from fields with total soil Cd levels lower than 5 mg kg
-1
. The
Standard for the Tolerance of Cd in rice has been reduced from 0.5 mg kg
-1
to 0.4 mg kg
-1
in
2007. Many studies were also subsidized by governments to assess the food safety of rice
cultivated in Cd-contaminated soil. In this paper, we reviewed some previous researches
regarding the accumulation of Cd and As of different rice varieties. Its safety after growing
in As- or Cd-contaminated soils was also evaluated. For those contaminated lands not
suitable for planting crops, the use of phytoremediation and planting non-edible plants may
be a candidate for solving this problem. Experimental results of phytoremediation were also
illustrated in this paper.
2. Phytoremediation for potted Cd-contaminated soils
The selection of suitable plants is the first and the critical step in conducting a successful
phytoremediation. These plants should grow well and accumulate higher concentration of
HMs in the harvestable parts when growing in HM-contaminated soils. There were
approximately 420 species of plants that can be regarded as hyperaccumulators (Baker et al.,
2000). A pot experiment was conducted to test the accumulation capacity of five garden
flower species, which was regard as a potential hyperaccumulator previously (Chen & Lee,
1997). Seedlings of them were planted in the artificially Cd-contaminated loamy soils to
assess their Cd accumulation when growing in control (Cd-CK) (0.43±0.15 mg kg
-l
), Cd-10
(9.73±0.05 mg kg
-l
), and Cd-20 (17.6±0.8 mg kg
-l
) (Lin et al., 2010). One seedling of Star
cluster (
Pantas lanceolata
Deflers.), French marigold (
Tagetes patula
L.), Impatiens (
Impatiens
walleriana
Hook. f.), Garden verbena (
Verbena bipinnatifida
Nutt.), or Scarlet sage (
Salvia
splendens
Ker-Gawl.) was planted in each pot contained three kilograms of artificially Cd-
contaminated soils. The pot experiment was conducted in a 30/25°C (day/night) phytotron
in three replicates, controlled the soil moisture content at 50-70% water-holding capacity
