Assessment of heavy metal uptake and translocation in Dyera costulata for phytoremediation of cadmium contaminated soil

Abstract

Heavy metal pollution is a widespread global problem causing serious environmental concern. Cadmium, one of the heavy metals, is water soluble and can be transferred from soil to plants and enter into the food chain. It is detrimental to human health because it accumulates in the body and can cause renal tubular dysfunction, pulmonary emphysema and osteoporosis. This heavy metal needs to be cleaned up for a clean and safe environment. An experiment was conducted to evaluate the potential of Dyera costulata as a phytoremediator to absorb cadmium from contaminated soils. Dyera costulata seedlings were planted on six different growth media (soil + different levels of cadmium): Control, 25 ppm Cd, 50 ppm Cd, 75 ppm Cd, 100 ppm Cd and 150 ppm Cd. The highest growth performance mainly height, basal diameter and number of leaves were in the control, 50 ppm Cd and 25 ppm Cd treatments, respectively. The highest accumulation of cadmium (52.9 ppm) was in the 75 ppm Cd treatment. Among the plant parts, leaves showed the highest concentration of cadmium. Dyera costulata showed high translocation factor and low bioconcentration factor values in soil at high cadmium concentrations and was also able to tolerate and accumulate high concentrations of cadmium. The roots of Dyera costulata were found to be suitable for the absorption of cadmium in contaminated soils. This species can be an efficient phytoremediator for soils contaminated with cadmium.

Keywords:

• Cadmium accumulation
• contaminated soil
• Dyera costulata
• phytoremediation

Introduction

Sewage sludge, compost, mining waste, chemical fertilizers and other industrial wastes can be transported to natural vegetation and cultivated crops, causing widespread pollution in vast areas of land that eventually become non-arable and hazardous for both wildlife and human populations (Majid et al. 2011). The accumulation of heavy metals in agricultural lands can remain in the soil for many years (Alloway and Jackson 1991). Large areas of land contaminated with Cd were mainly caused by anthropogenic activities such as mining and mineral processing of metallic ores, waste disposal, phosphate fertilizer application and wastewater irrigation. Cadmium (Cd) is one of the most toxic heavy metals present in the environment (Wagner 1993). It is easily absorbed by roots and translocated to different plant parts and enters the human food chain (Baek et al. 2006, Xiao et al. 2008). High accumulation of Cd generally causes growth inhibition and even plant death (Khan and Khan 1983). Cadmium is of particular concern to human health, because it accumulates in the body with a half-life exceeding 10 years and has been linked with renal tubular dysfunction (Buchet et al. 1990), pulmonary emphysema (Ryan et al. 1982) and possibly osteoporosis (Bhattacharyya et al. 1988).

Cadmium is a non-essential element that possesses high toxicity and is easily accumulated from the environment by organisms (Rahimi and Nejatkhah 2010). Restoration of soils contaminated with potentially toxic metals and metalloids is of major concern (Shelmerdine et al. 2009).

Remediation of polluted soil could be carried out using physico-chemical processes such as ion-exchange, precipitation, reverse osmosis, evaporation and chemical reduction. However, these measures require external man-made resources and are costly (Mangkoedihardjo and Surahmaida 2008). Phytoremediation is a viable, relatively low-cost approach to remove heavy metals from soil and groundwater (Mojiri 2011). Plants have many properties that make them ideally suited to clean polluted soil, water and air, in a process called phytoremediation. Malaysia is considered one of the world's 12 leading mega-biodiversity countries with a high diversity of flora and fauna. There are several natural products such as medicinal plants that can be used as phytoremediators. D. costulata is easy to handle in the nursery, survives well when planted out, and has a good rate of growth. Some works of phytoremediation on polluted soils have been documented but phytoremediation with jelutong (Dyera costulata) has not been reported. The present study was therefore conducted to evaluate the heavy metal accumulation and translocation in jelutong (Dyera costulata) plant parts and to study the growth performance of D. costulata in contaminated soils.

Materials and methods

Site description and planting materials

The experiment was conducted at the glasshouse, Universiti Putra Malaysia, Serdang, Selangor, Malaysia for the period February to May 2010. The temperature in the morning was 26°C, 36 °C at noon and reduced to 30 °C in the evening. The growth media was a mixture of soil with different levels of cadmium, viz.: T₀ (Control, soil), T₁ (Soil + 25 ppm Cd), T₂ (soil + 50 ppm Cd), T₃ (soil + 75 ppm Cd), T₄ (soil + 100 ppm Cd) and T₅ (soil + 150 ppm Cd). A completely randomized design (CRD) was used with four replications. Dyera costulata was the test plant. Jelutong (Dyera costulata) is a large timber tree, preferring primary evergreen lowland or hill forest up to 300 m. It grows to approximately 60 m tall with diameters of 2 m and boles clear and straight for 30 m. It grows in Malaysia, Borneo, Sumatra and southern Thailand (Middleton 2004). It is considered low risk/least concern because this species regenerates readily in logged-over forest, it coppices well and it is extremely resistant to girdling (Anon. 2011).

Healthy seedlings of 3-month old and similar in form plants were selected for this study. After filling the pots (28.2 cm×34.2 cm size) with the growth media (10 kg pot^-1) the seedlings of uniform age and size were transplanted into them (1 seedling pot⁻¹). Weeding and watering were done when necessary to ensure normal growth of the seedlings. Twenty-four plants were used to measure growth parameters including basal diameter, number of leaves and height. Height was measured using a ruler and basal diameter by a caliper. The growth parameters were measured twice a month.

Plant and soil sampling and chemical analysis

Plant samples were collected at harvest and soil samples were collected from each pot before planting and at harvest and kept in standard plastic containers and air-dried before physico-chemical analysis. For analysis of heavy metals, 1.0 g dried plant sample and 20 ml aqua regia solution (mixture of concentrated HNO₃ and HCl in a ratio of 3:1) was acid digested at 80 to 120 °C for 3 hours. After digestion the solution was transferred into a 100 ml beaker ready for analysis using an ICP-MS (Inductively Couple Plasma Mass Spectrometry) method (Sahoo et al. 2009). Particle size distribution was analysed by a pipette gravimetric method. Soil pH and total carbon were determined by using a glass electrode pH meter (Jackson 1973) and loss on ignition method, respectively.

Plant biomass measurement

Plant biomass was measured separately according to leaves, stems and roots and calculated. The loss in weight upon drying is the weight originally present. The moisture content of the sample was calculated using the following equation

1

Determination of bioconcentration factor (BCF) and translocation factor (TF)

The plant's ability to accumulate metals from soils and translocate metals from roots to shoots can be estimated using the bioconcentration factor (BCF) and translocation factor (TF), respectively. BCF and TF factors can be calculated as follows:

2

3

Statistical analysis

Analysis of variance for growth and heavy metals concentrations (in soil and plant parts) were done following the ANOVA test and the mean values were calculated by the DMRT (p=0.05) method (Steel et al. 1996). Comparison using t-test was also done to detect any significant differences between before planting and at harvest.

Results and discussion

Properties of the growth media

The growth media was a sandy clay texture which is suitable for seedling growth and development partly because of the high amount of nutrients and water-holding capacity is also high; however, drainage capacity is poor (Rice 2009). Moreover, clay soils also crack excessively while drying, and if they are very low in organic matter, clay soils may lose their structure and become cloddy and compacted (Aljibury 2011).

The soil pH ranged from 4.30 to 4.74 and 4.59 to 5.06 before planting and at harvest, respectively. pH of the growth media increased at harvest having the highest (5.06) in T2 followed by T1 (4.98). Before planting the highest pH was recorded in the control (4.87) followed by T₁ (4.63) and the minimum was in T₅ (4.05) (Figure 1a). It was observed that pH was higher at harvest compared with before planting and this might be due to absorption of heavy metals (acidic elements) from the contaminated soil. Knight et al. (1997) also found significant increment in soil pH grown with Thlaspi caerulescens on contaminated soils which corroborated the findings of our results. Soil pH affects all the chemical, physical and biological properties of soil (Brady and Weil 2002). Element accumulation in plant depends not only on their absolute content in a soil, but also on soil pH (Lorenz et al. 1994; Golovatyj 2002).

Figure 1.  Change in pH (a), total carbon (b) and cadmium concentrations (c) in the growth media at harvest of Dyera costulata as influenced by different cadmium levels. Growth media indicates soil mixing with different levels of cadmium, i.e. T₀=Control/soil, T₁=Soil + 25 ppm Cd, T₂=soil + 50 ppm Cd, T₃=soil + 75 ppm Cd, T₄ soil + 100 ppm Cd and T₅=soil + 150 ppm Cd. Means±SE are shown in error bar (p = 0.05).

Total carbon was significantly different (p≤ 0.05) between before planting and at harvest (Figure 1b). The total carbon content varied from 0.26 to 0.88% and 0.83 to 1.74% before planting and at harvest, respectively. Carbon content in the growth media was increased at harvest compared with before planting. The maximum increment (0.88%) was found in T₂ followed by T₁ (0.76%) and the minimum (0.57%) was in the control (Figure 1b).

Growth performance

Growth parameters such as height, basal diameter and number of leaves were significantly influenced (p≤0.05) by the different treatments. The control showed the maximum height increment (4.13 cm) followed by T₂ (3.75 cm) and T₃ (3.16 cm). Minimum height increment (2.17 cm) was recorded in T₅ (Figure 2a). The highest height increment in the control might be due to lower concentration of cadmium and did not affect the absorption of other essential elements and physiological activities. The height decrease in T₅ might be due to toxic effects of cadmium and shoot mortality. The highest basal diameter increment (3.12 cm) was observed in T₂ followed by the control (2.44 cm). The lowest basal diameter increment (1.98 cm) was in T₅ (Figure 2b). The number of leaves ranged from 6 to 13. Treatment T₁ produced the highest number of leaves followed by the control (9.75) and T₂ (9.25). The minimum number of leaves (6.25) was recorded in T₅. Plant growth decreased in T₅ where Cd concentration was highest in the growth medium. Liu et al. (2008) showed that height of ornamental plant decreased with increasing Cd concentrations, indicating that Cd restricted its growth.

Figure 2.  Plant height (a), basal diameter (b) and number of leaves (c) of Dyera costulata at different months after planting as influenced by different treatments (increase per month). Growth media indicates soil mixing with different levels of cadmium, i.e. T₀=Control/ soil, T₁=Soil+25 ppm Cd, T₂=soil+50 ppm Cd, T₃=soil+75 ppm Cd, T₄ soil+100 ppm Cd and T₅ =soil+150 ppm Cd. Means±SE are shown in error bar (p=0.05).

Seedlings were planted on February 2010. Height, basal diameter and number of leaves increment increased in March and decreased in April (Figure 1). This decrease might be due to the toxic effects of cadmium 2 months after planting (in April). The maximum increments of height, diameter and leaves were in May (3 months after planting) for all treatments. T₂ showed the highest increment in height (3.75 cm) and diameter (3.12 cm) while T₁ produced the maximum leaves in May (Figure 1). This is because the soil conditions became suitable for plant growth after 3 months.

Plant biomass

Treatment T₁ produced the maximum root biomass (45.8 g) followed by the control (44.4 g) and the minimum was in T₅ (28.3 g) (Table 1). There was no significant difference (p≤0.05) in stem biomass among all treatments. Stem biomass varied from 42.1 to 58.0 g having the highest (58.0 g) in T₁ followed by T₄ (51.4 g) and T₂. The minimum (42.0 g) was observed in the control. Leaf biomass varied from 37.8 to 58.7 g with the highest in the control (58.75 g) followed by T₁ (58.10 g), T₂ (53.69 g) and T₃ (51.34 g). The lowest leaf biomass (37.8 g) was in T₄. The total biomass ranged from 111 g to 162 g, the highest in T₁ followed by the control and the lowest was in T₅ (Table 1). Mangkoedihardjo and Surahmaida (2008) reported significant reduction in plant dry matter due to increased Cd concentration. Similar results were also reported by Arvind (2004) and Tomar et al. (2000) in Cd and Pb contaminated soil with Ceratophyllum demersum and Vigna radiata, respectively.

Table I. Dry biomass of leaves, stems and roots of Dyera costulata at harvest as influenced by different treatments (p = 0.05).

Treatment	Root plant^−1 (g)	Stem plant^−1 (g)	Leaves plant^−1 (g)	Total (g)
T0	44.40	42.00	58.70	145
T1	45.80	58.00	58.10	162
T2	33.70	48.50	53.70	136
T3	38.80	46.30	51.30	136
T4	38.70	51.40	43.70	134
T5	28.30	44.90	37.80	111
SE (±)	2.68	2.30	3.38	6.77
Growth media indicates soil mixing with different levels of cadmium, i.e. T0=Control/soil, T1 =Soil + 25 ppm Cd, T2 =soil + 50 ppm Cd, T3=soil + 75 ppm Cd, T4 soil + 100 ppm Cd and T5 =soil + 150 ppm Cd.

Heavy metal concentration in the growth media

Cadmium (Cd) concentration was significantly variable in the growth media (p ≤ 0.05). Before planting, T₅ showed the highest concentration (144.8 ppm) followed by T₄ (109.5 ppm). The lowest Cd concentration (0.30 ppm) was recorded in the control (Figure 1c). After harvest Cd concentration decreased in all treatments (Figure 1c). Treatment T₃ showed the highest decrease (42.7 ppm) followed by T₂ (40.2 ppm) and the minimum (0.09 ppm) was in the control. Plant growth was affected in high Cd concentration media and this is why the plants failed to absorb more Cd. On the other hand, Cd concentration was very low in the control hence absorption was also low. The concentration of Cd in normal soils ranged between 0.01 ppm to 2.0 ppm and the critical level ranged between 3.0 to 8.0 ppm (Alloway 1995). The concentrations of Cd in the growth media were above the critical level except the control.

Heavy metal concentration in plant parts

Cadmium concentration in plant parts was significantly different among the different treatments (p ≤ 0.05). In the leaves, the highest Cd concentration (52.9 ppm) was found in T₃ followed by T₂ (34.1 ppm). The lowest Cd concentration (0.07 ppm) was in the control. Cd concentrations in the stem ranged from 1.46 to 47.2 ppm having the highest in T₅ (47.2 ppm) followed by T₃ (40.0 ppm) and the lowest (1.46 ppm) was in the control (Table II). Treatment T₃ also showed the highest Cd concentration (44.1 ppm) in the roots which was significantly different (p≤0.05) from the other treatments. T₂ gave the second highest concentration (31.2 ppm) in the roots followed by T₁ (24.45 ppm) and the minimum (1.53 ppm) was also in the control. It was observed that Cd concentration in the leaves was higher than the roots (Table II). However, Cd concentration in each plant part increased with increasing Cd in the growth medium up to a certain level after which increasing Cd in soil decreased its concentration in the plant parts. Liu et al. (2008) also reported that Cd concentration in each plant part increased with increasing Cd in solution.

Table II. Cadmium accumulation in different parts and bioconcentration factor of Dyera costulata as influenced by different treatments (p=0.05).

	Cadmium accumulation in different plant parts
Treatment	Leaf	Stem	Root	Bioconcentration factor (BCF)^a
T0	0.07	1.46	1.53	0.91
T1	13.22	24.16	24.45	1.52
T2	34.12	28.72	31.19	1.21
T3	52.96	39.97	44.08	0.74
T4	8.31	34.68	19.48	0.25
T5	12.92	47.16	14.35	0.11
SE (±)	7.99	6.49	5.94	0.22
Growth media indicates soil mixing with different levels of cadmium, i.e. T0=Control/soil, T1=Soil+25 ppm Cd, T2=soil+50 ppm Cd, T3 =soil+75 ppm Cd, T4 soil+100 ppm Cd and T5=soil+150 ppm Cd.
^aRatio of root and soil metal concentrations.

Bioconcentration factor and translocation factor

Bioconcentration factor ranged 0.11 to 1.52. Treatment T₁ showed significantly higher BCF (1.52) followed by T₂ (1.21) and the minimum (0.11) was in T₅ (Table II). T₁ and T₂ treatments showed higher BCF values (1.52 and 1.21, respectively) but the other treatments showed very low values, having the lowest in T₅ (Table II), which may imply restriction in soil-root transfer at higher Cd concentrations in the soil. Similar results were reported by Yoon et al. (2006). Ho et al. (2008) reported 1.92–3.21 BCF in Pb treated kenaf (Hibiscus cannabinus L.).

Translocation factor (TF) was also significantly influenced by the different levels of cadmium (p≤ 0.05). Translocation factor varied from 1.0 to 4.19 (Figure 3). The highest TF (4.19) was in T₅ which was significantly higher than the other treatments (p≤0.05). T₄ showed the second highest TF which was similar to T₂ and T₃ but different from the remaining treatments. The lowest TF value (1.00) was in the control (Figure 3). Translocation was more prominent in T₅. TF of metal excluder species is < 1 whereas metal accumulator species have TF > 1 (Baker 1981). It was observed that all the treatments exhibited higher TF values (>1). Dyera cotulata has high TF and low BCF in soil at higher cadmium concentrations. Heavy metal tolerance with high TF and low BCF values was suggested for phytoaccumulators in contaminated soils (Yoon et al. 2006) and therefore, Dyera cotulata can be used as a potential phytoremediator for soils contaminated with cadmium.

Figure 3.  Translocation factor of cadmium in Dyera costulata as influenced by different treatments. Growth media indicates soil mixing with different levels of cadmium, i.e. T₀=Control/soil, T₁=Soil + 25 ppm Cd, T₂ =soil + 50 ppm Cd, T₃=soil + 75 ppm Cd, T₄ soil + 100 ppm Cd and T₅=soil + 150 ppm Cd. Means±SE are shown in error bar (p = 0.05).

Acknowledgements

We are thankful to the Ministry of Higher Education Malaysia for the financial support through the Research University Grant Scheme (91784) to Universiti Putra Malaysia.