Uptake of B, Co and Ni by Plants from Oil Contaminated Soil Capped with Peat

Sun Tao , Liu Xiao-jie, Paul Yeung, and Xu Jing-gang

1 College of Resources and Environmental Sciences, Northeast Agricultural University, Harbin 150030, China

2 Heilongjiang Provincial Ecological Meteorological Center, Harbin 150030, China

3 National Soybean Engineering Technology Research Center, Northeast Agricultural University, Harbin 150030, China

4 Canagra Development Ltd., Edmonton, Alberta T6R 2C6, Canada

Abstract: Plant uptake of contaminants provides vital information for the reclamation of large area of contaminated soils. A field experiment was conducted using four plant species growing in four kinds of oil contaminated soils to estimate the uptake of organic and inorganic contaminants by plants from the oil contaminated soils. The experiment showed that the concentrations of some selected elements, such as B, Co and Ni in plants growing in the oil contaminated soils were significantly higher than those in plants growing in the uncontaminated control soil. The accumulation of metals in plants increased with plant biomass; however, the removal of metals by plants from the oil contaminated soils was not practical.

Key words: oil contaminated soil, metal concentration, removal, metal uptake and accumulation

Introduction

Plant can be used to decontaminate materials (Liphadzi and Kirkham, 2006; Nouriet al., 2009; Anwarzebet al., 2015). To date, bioremediation research has focused on the role of microorganisms, but it has been shown that plants may also play an important role in the direct and indirect removal of contaminants(Goniet al., 2014). For example, plants can physically remove contaminants from soil by absorbing or translocating them into plant tissues and metabolic processes may then transform the contaminants within the plants (Josuet al., 2017). While absorbing contaminants, plants concentrate them in their harvestable portions, thereby providing a pathway for their removal (Nouriet al., 2009; Maríaet al.,2015; Svetaet al., 2016; Muhammadet al., 2017). The objectives of this experiment were to use plants to take up metals to clean up oil contaminated soils.

Materials and Methods

Plant materials and field experiment

The experiment involved four kinds of treatments: oil contaminated soils (OCS) alone, OCS capped with a 5 cm peat layer and OCS capped with 10 cm peat layer. The adjoining uncontaminated soil was used as the control (CK). Peat was used as amendment in the crude oil contaminated soils and each treatment was repeated for three times.

The soil used in the experiment was a Chernozem with organic C content 15.4 mg · g-1, water soluble P 35.2 mg · kg-1, water soluble K 142 mg · kg-1, alkaline hydrolyzed N 20.9 mg · kg-1and pH 7.45. The organic C content in peat used in the experiment was 482 g · kg-1and the hydrocarbon content in hydrocarbon contaminated soil was 42.8 g · kg-1.

Four plant species were grown in these treatments:reed canary grass, poplar, willow and cattail. The experimental site was located in Fort McMarray,Alberta, Canada. The plant samples were obtained 80 days after plant transplanting and were separated into leaves, stems and roots, then cleaned, dried and ground through a 0.5 mm screen using a Thomas-Wiley Laboratory Mill (Model 4). The concentrations of selected elements in the ground plant tissues were determined by ICP-MS after acid digestion (Parket al., 2013). The analytical results were reported on a dry weight basis. In addition, the accumulation of the metals in plant tissues were also calculated by multiplying the metal concentration with the biomass of the plant segment. The elements reported here were:B, Co and Ni.

Results

Concentrations of metals in plants

A complete list of the concentrations (µg · g-1) of B,Co and Ni elements in plant tissues for the four plant species growing in field plots is presented in Figs.1-3. In general, the concentrations of the elements in the plant tissues decreased, when the oil contaminated soils were capped with peat. Although the treatment of OCS had the highest concentration of most elements,the element concentrations in the tissues of plants growing OCS were not correspondingly high. The difference in element concentration in the plants among different plant species varied with elements and the plant segments (leaf, stem or root). Generally,the concentrations of most elements were higher in the leaves and roots than in the stems.

Fig. 1 Boron concentration in plant segments (µg · g-1)

Boron, cobalt and nickel concentrations in the tissues of plants growing in the oil contaminated soils were higher than those in the control plants. The concentration of boron in the tissues of the four plants growing in the oil contaminated soils was much greater than that in the plants growing in the control soil(Fig. 1). Boron in the tissues of the four plants growing in OCS was more concentrated than that in the plants growing in the oil contaminated soils capped with peat.Among the treatments, boron concentration in the plants growing in OCS were higher than that in the oil contaminated soils capped with 5 cm peat, which in turn was higher than that of OCS amended with 10 cm peat. The concentration of boron in willow (leaves,stems and roots) was higher than that in poplar, which was higher than that in reed canary grass and cattail. The concentration of boron in leaves was higher than that in roots, which in turn was greater than that in stems.

Fig. 2 Cobalt concentration in plant segments (µg · g-1)

Fig. 3 Nickel concentration in plant segments (µg · g-1)

Cobalt was another element which had much higher concentration in the plants growing in the oil contaminated soils than in the plants growing in the control soil (Fig. 2). Cobalt concentrated more in roots than in leaves. The stems had the lowest concentration of cobalt. This was different from boron. Similar to boron, the cobalt in OCS was higher than in OCS capped with peat.

Nickel concentration in the plants growing in the oil contaminated soils was greater than in the plants growing in the control soil (Fig. 3). The concentrations of nickel in the roots and leaves were higher than in the stems. Nickel concentration in reed canary grass was higher than in other three plant species and there was no signi ficant difference among the latter three.

Accumulation of metals in plants

A complete list of the accumulation (concentration×biomass) of metals in the four plant species growing in the field plots is presented in Table 1. Reed canary grass accumulated more metals than other three plant species probably, because it produced more biomass.Metal accumulation in the plants growing in OCS amended with peat because plants grew better in the oil contaminated soils amended with peat for both sickness.

Table 1 Metal accumulation (µg) of cattail growing in oil contaminated soils

Discussion

Uptake of elements was controlled by either the amount of elements in soils or the rate at which elements were taken up by plants (Liphadzi and Kirkham, 2006; Elizabeth and Mary, 2006). In this experiment, the accumulation of most (but not all)elements correlated positively with the biomass of the plants. Therefore, the selection of suitable plant species which could both survive and produce more biomass in the soil was important for the biological removal of elements from the contaminated soils (Bibinet al., 2007). Neither concentrations nor the total accumulations of elements in the plant tissues were significantly correlated with the total element contents in the soils, which was also consistent with the results from the preliminary greenhouse experiment and the results found by other researchers (Liet al., 2014;Kimet al., 2010; Conesaet al., 2011), indicating that the total contents of elements in the contaminated soils were not indicator of the bioavailability of elements to the plants. The forms or status, the transport or movement of the elements and the bioavailability of the elements for plant uptake in the contaminated soils all need further studies (Carmenet al., 2017; Singh and Agrawal, 2010; Muhammadet al., 2017).

Conclusions

The concentrations of B, Co and Ni in the plants growing in the oil contaminated soils were significantly higher than those in the plants growing in the uncontaminated control soil. The peat could increase the plant growth, but reduced uptake of metals by plants. The accumulation of metals in plants increased with plant biomass; however, the removal of metals by plants from the oil contaminated soils was not practical.