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Potential of Lemna gibba L. and Lemna minor L. for accumulation of Boron from secondary effluents
Ecological Engineering 70 (2014) 332–336
Contents lists available at ScienceDirect
Ecological Engineering journal homepage: www.elsevier.com/locate/ecoleng
Potential of Lemna gibba L. and Lemna minor L. for accumulation of Boron from secondary effluents S¸ule Yüksel Tatar, Erdal Öbek ∗ Department of Environmental Engineering, Faculty of Engineering, Firat University, 23119 Elazig, Turkey
a r t i c l e
i n f o
Article history: Received 21 February 2014 Received in revised form 25 April 2014 Accepted 23 June 2014 Keywords: Effluent Boron Phytoremediation duckweed Accumulation
a b s t r a c t Aquatic plants are quite effective in removal of pollutants which cannot be removed in secondary treatment. Lemna gibba L. and Lemna minor L. among the aquatic plants were investigated for the removal of boron from the secondary waste water. Differences in Boron uptake were seen in the chosen aquatic macrophytes. Although boron is at low concentration in water, the bioaccumulated concentrations in Lemna minor L. and Lemna gibba L. were at high levels of between 140 mg Bg 140 –1and 274 mgB g−1, and 381 mgB g−1 523 mgB g−1 respectively. From these results, it was understood that Lemna gibba L. is more prone to accumulate boron compared to Lemna minor L. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Industrial and domestic wastewater contains different organic and inorganic substances. These waters are treated in conventional waste water treatment systems and discharged into the surface waters such as rivers, lakes and brooks. Existence of the pollutants in discharge water indicates that many pollutants could not be removed in these treatment plants. If the quality of treated water is poor, it will negatively effect all the living in aquatic ecosystem. As a result, more treatment is needed before discharge of waste water into the surface water (Sinha et al., 1996; Weis and Weis, 2004; Brix and Arias, 2005; Chen et al., 2005; Upadhyay et al., 2007). Boron (B) minerals are used widely in many industries such as glass, ceramic, cleaning and whitening agents, agriculture, metallurgy, nuclear and medical industries. B, a metalloid essential for plant growth, is often found at elevated concentrations in wastewater as a result of its use for domestic purposes and in industrial production processes. When present in excessive concentrations in the soil solution, B can be toxic to plants (Yermiyahu et al., 1995). Boron compounds are not removed during the discharge of waste water due to their high solubility and mostly mixes with water into which they are discharged. Surface water contains 0.05–0.1 mgB L−1 naturally whereas boron rich water up to
∗ Corresponding author at: Department of Bioengineering, Faculty of Engineering, Firat University, 23119 Elazig, Turkey. Tel.: +90 4242370000. http://dx.doi.org/10.1016/j.ecoleng.2014.06.033 0925-8574/© 2014 Elsevier B.V. All rights reserved.
0.6 mgB L−1 . At this level, boron toxicity can be expected in boron sensitive aquatic plants (Schobel, 1993). Various techniques such as reverse osmosis, B selective resins, membrane filtration, precipitate-coagulation, ion exchangers and adsorption are used for boron removal from water (Simonnot et al., 2000; Ferreira et al., 2006; Dionisiou et al., 2006; Onderkova et al., 2009). Even if these systems bring wastewater to dischargeable standards, they need expensive investment, higher service and repair cost and use of chemicals (Marin and Oron, 2007). Therefore cheap and effective treatment technologies were investigated. It was reported that phytoremedial techniques could be used to remove the pollutants from domestic, commercial, mining and industrial wastewater as a cheap, environment friendly and alternative technique. It was also reported that various aquatic macrophytes removed organic and inorganic pollutants in wastewater by accumulation (Reddy and DeBusk, 1987; Vajpayee et al., 1995; Sinha et al., 1996; Matagı et al., 1998; Rahmani and Sternberrg, 1999; Körner and Vermaat, 1998; Zayed et al., 1998; Körner et al., 1998; Hasar and Öbek, 2001; Wang et al., 2002; Rai et al., 2002; Axtell et al., 2003; Kamal et al., 2004; Miretzky et al., 2004; Brix and Arias, 2005; Oporto et al., 2006; Upadhyay et al., 2007; S¸as¸maz and Öbek, 2009; Khan et al., 2009; Öbek, 2009; Dordio et al., 2010). Some duckweed species are also known to be good B accumulators (Glandon and McNabb, 1978; Frick, 1985). Phytoremediation treatment system uses three different types of plants: aquatic, emergent and submerged plants. Retention time in these systems is adjusted considering waste removal mechanism and harvesting is performed periodically to keep the plant alive
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Table 1 Physiochemical characteristics of secondary-treated municipal wastewater and natural water. Parameter
Unit
Wastewater
Natural water
Temperature pH EC BOD5 COD NO2 − -N NO3 − -N PO4 3− -P NH4 + -N B
◦
20.3 ± 0.6 7.66 ± 0.10 1.16 ± 0.03 50.0 ± 8.0 100.0 ± 5.0 0.66 ± 0.21 2.6 ± 0.2 >5.00 <0.06 370.0 ± 10.0
18.6 7.0 0.36 3.8 8.1 0.21 2.40 0.19 0.78 1.60
C – mS cm−1 mg L−1 mg L−1 mg L−1 mg L−1 mg L−1 mg L−1 ppb
± ± ± ± ± ± ± ± ± ±
0.5 0.1 0.03 0.2 2.0 0.02 0.01 0.02 0.40 0.01
by Davis (1984) was used as treating material in the secondary clarifier. Lemna gibba L. and Lemna minor L. were delivered from botanical garden of Istanbul University and natural waters in Antalya, respectively in June 2013. The plants were grown in a basin full of natural water, the content of which is given in Table 1, for 1 month in laboratory conditions and then adapted in the four of five conical reactors (upper diameter is 50 cm, lower diameter is 40 cm, height of water column is 12 cm) separately. 200 g of plants was placed in each reactor. Two of the reactors contained Lemna gibba L. and the other two Lemna minor L. Reactors were operated in a continuous regime of about 0.02 L min−1 of effluent waste water. One of the reactors in each group was used for daily analyses of plants and water and the other for plant substitution. In order to keep the amount of plant constant in the analysis reactors of Lemna gibba L. and Lemna minor L., the same amount of plants taken for the analyses was transferred into the analysis reactors from the substitution reactors for 7 days. For the following 7 days, 10 g plant and 50 mL composite influent and effluent water samples were put into the tubes containing 0.1% HNO3 for boron analysis. To determine physicochemical parameters in water, 100 mL water was poured into the tubes and kept at 4 ◦ C till analyses. 2.2. Method
Fig. 1. Map of the study area and flowsheet of the Elazı˘g Municipal Wastewater Treatment Plant.
and fresh (Zimmo, 2003). The studies on the removal capabilities of environmental pollutants of the aquatic plants by accumulation have generally been carried out in laboratory conditions and field studies are quite few compared to the laboratory studies. The objective of this research was to determine the ability of Lemna gibba L. and Lemna minor L. to remove Boron from secondary treated municipal wastewater.
2. Materials and methods 2.1. Materials The wastewater of Elazig City was collected and then treated in the conventional activated sludge process. The effluent from the city treatment facility is discharged into Keban Dam Lake (Fig. 1). Physicochemical characteristics of wastewater in the secondary clarifier and the natural water are shown in Table 1. In this study, a plant systematically identified as Lemna gibba L. and Lemna minor L. according to the procedure in Flora of Turkey
After being dried under atmospheric conditions, the plants were dried in a steam oven at 70 ◦ C for 24 h and then ashed at 250 ◦ C for 24 h. The ashed samples (Lemna gibba L. 1.590 g ash from approximate 2.516 g of dried plant and Lemna minor L. 2.595 g ash from approximate 3.80 g of dried plant) were taken by using hand mortars, labeled and sent to Canada for analysis. The ashed samples were digested in HNO3 for 1 h, followed by 1/1/1 mixture of HCl/HNO3 /H2 O for 1 h (6 ml of mixture for 1 g of ashed sample) at 95 ◦ C. Acid was added to the water samples in the laboratory, and samples were filtrated using 0.45 m pore size filters. All samples were analyzed by using inductively coupled plasma mass spectroscopy (ICP/MS - Perkin-Elmer ELAN 9000) technique at ACME Analytical Laboratories Ltd., Canada (Acmelab, 2007). ACME is currently registered with ISO 9001:2000 accreditation. The operation conditions as recommended by the manufacturers (Elan 9000, 2001) are given in Table 2. Physicochemical analysis of the samples was conducted according to Standard Methods for the Examination of Water and Wastewater (APHA, 1995). 3. Results and discussion The results indicating the parameters before and after the experimental study on a daily basis show that Lemna gibba L. and Lemna minor L. accumulated Boron efficiently from wastewater
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Table 2 Operation conditions for ICP-MS analysis. Inductively coupled plasma Nebulizer Spray chamber RF power (W) Plasma gas flow-rate (L min−1 ) Auxiliary gas flow-rate (L min−1 ) Carrier gas flow-rate (L min−1 ) Sample uptake rate (L min−1 ) Detector mode
PerkinElmer Elan 9000 Crossflow Ryton, double pass 1000 15 1.0 0.9 1.0 Auto
Fig. 2. Boron accumulations by Lemna gibba L. and Lemna minor L.
(Tables 3 and 4). Boron accumulations by Lemna gibba L. were given in Fig. 2. Boron concentration in the effluent of the reactors those planted with Lemna gibba L. and Lemna minor L. changed between 369 g L−1 and 410 g L−1 during the experiments (Tables 3 and 4, and Fig. 2). Amounts of boron absorbed from low boron concentration water by Lemna gibba L. and Lemna minor L. were determined between 131.38% and 180.34%, and 33.17% and 64.93%, respectively. Amounts of boron accumulated changed between 381 mgB g−1 and 523 mgB g−1 for Lemna gibba L. and 140 mgB g−1 and 274 mgB g−1 for Lemna minor L. in our study. Metal accumulation by the aquatic plants changes for each species (Albers and Camardese, 1993; Samecka-Cymerman and Kempers, 1996). There are many studies done on boron uptake capacity of Lemna gibba L. and Lemna minor L. (Frick, 1985; Marin and Oron, 2007; Kropfelova et al., 2009; S¸as¸maz and Öbek, 2009). Frick (1985) reported that
Lemna minor L. which were exposed to various solutions containing 10–200 mg L−1 B accumulated 1168 mgB kg−1 in 7 days. Marin and Oron (2007) found that there was 930–1900 mg kg−1 in dry mass of the plants grown in water reservoirs containing 0.3–10 mgB L−1 for 12 days. S¸as¸maz and Öbek (2009) also reported that boron amount which Lemna gibba L. accumulated in the secondary treatment water was 149 mg L−1 . In the study by Kropfelova et al. (2009), three artificial aquatic fields were watered with domestic waste water containing 76–210 g L−1 boron for 2 years. We determined from the measurements that Lemna gibba L. and Lemna minor L. reactors operated with an efficiency between 28.95% and 11.11% for B removal (Table 5). This loss may be caused by sedimentation, adsorption by clay particles and organic substances, co-precipitation with secondary minerals, cation and anion exchange and complexation (Matagı et al., 1998). Boron is an essential micronutrient for the normal growth of plants (Davis et al., 2002). Boron has a very important function in glucose transfer, cell membrane synthesis, lignifications, formation of cell membrane, carbohydrate and RNA metabolisms, respiration, IAA metabolism, phenol metabolism and structural and functional characteristics of biological membranes (Shaaban, 2010). It is also an effective functional element in anther growth, pollen germination, and pollen tube growth (Nable et al., 1997; Huang et al., 2000). We saw differences in boron concentrations accumulated by Lemna gibba L. and Lemna minor L. in our study. Boron accumulated the most in Lemna gibba L. This indicates greater tendency to boron accumulation than Lemna minor L. (Tables 3 and 4, and fig. 2). Differences in essential nutrient accumulations in plants indicate the differences in metabolism activities and growth rates. This in turn shows the difference in metal removal capacities (Upadhyay et al., 2007). When compared with the initial chemical composition of Lemna minor L., it was seen that total concentration of P increased, Ca% decreased after the sixth day, and both K and Mg% decreased till the sixth day and then increased. On the other hand, an increase in Total P concentration and decrease in the other parameters were recorded till the seventh day (Tables 3 and 4). Ho (2000) states that there is an important correlation between calcium, magnesium and boron. Low concentrations of magnesium and calcium are kept in soil but boron is accumulated in plants. Concentrations of the other elements do not affect boron uptake as much as calcium. Interrelation between boron and calcium is physiological. These two elements show similar structural function in cell membranes. This similarity means that lack of boron and calcium gives similar
Table 3 Chemical composition of Lemna gibba L. grown before and after the treatment. Parameter
Before study
P (%) Ca (%) K (%) Mg (%) B (mg g−1 )
0.26 3.24 2.56 0.47 290
After study 1st day
2nd day
3rd day
4th day
5th day
6th day
7th day
0.46 3.16 2.17 0.48 692
0.67 3.51 2.18 0.50 803
0.67 3.07 1.87 0.45 782
0.77 2.99 1.72 0.44 813
0.68 2.66 1.68 0.39 740
0.76 2.63 1.74 0.41 717
0.76 2.53 1.79 0.41 671
Table 4 Chemical composition of Lemna minor L. grown before and after the treatment. Parameter
P (%) Ca (%) K (%) Mg (%) B (mg g−1 )
Before study
0.11 16.21 1.39 0.49 422
After study 1st day
2nd day
3rd day
4th day
5th day
6th day
7th day
0.21 15.74 1.01 0.40 562
0.30 16.02 0.93 0.40 565
0.40 16.12 0.91 0.40 572
0.49 15.65 0.89 0.41 589
0.53 16.25 0.91 0.42 574
0.61 14.44 1.04 0.44 566
0.83 12.31 1.80 0.58 696
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Table 5 B, Ca, K, Mg and P concentrations in influent and effluent water of planted and unplanted reactors. Parameter
Unit
Influent water
P Ca K Mg B
g L−1 mg L−1 mg L−1 mg L−1 g L−1
3266 79.5 21.9 30.5 370
± ± ± ± ±
100 2 1 1 10
indications. On the other hand there is also an important relation between boron and potassium. If the plant is exposed to excess amount of potassium, it is necessary to give boron to prevent the decrease in the productivity. Phosphorus causes increase in boron accumulation in plants at higher concentrations. One of the reasons for the difference in boron uptake in plants is the difference in the structures of cell membranes. Our study showed that boron accumulation by aquatic plants is the same to the uptake by the plants from the soil and closely related to the relation between boron and Ca, Mg, K and P (Ho, 2000). This uptake was determined to change between 140 mgB g−1 and 274 mgB g−1 in Lemna minor L., and 381 mgB g−1 and 523 mgB g−1 in Lemna gibba L. The results inferred that Lemna gibba L. had a better boron accumulation capacity than Lemna minor L. Sawidis et al. (1995) reported that there were differences in heavy metal concentrations of different type plants growth in the same station. In addition, differences were also seen in different species of the same plant. Boron, which is an important microelement for agriculture and environment, is necessary in low concentrations for plants but harmful in high concentrations with its toxic effect (Minareci and Öztürk, 2012). For some crops, if 0.2 mg L−1 boron in water is essential, 1–2 mg L−1 may be toxic (Ayers and Westcot, 1994). Davis et al. (2002) stated that boron is an important trace element but might have a toxic effect in aquatic plants even in low concentrations. Researchers reported chlorosis, necrosis and death in aquatic macrophiles exposed to B more than 22 mg L−1 . It was determined that excess amount of boron caused phytotoxicity (Gün, 2009; Reid, 2010; Grievea et al., 2010) and teratogenic effect (Naghii and Samman, 1997). In our study no phytotoxicity was seen. Higher boron removal by Lemna gibba L. can be attributed to the high metal and nutrient concentration in the effluent water as stated by Upadhyay et al. (2007). 4. Conclusions In this study, it was determined that use of Lemna gibba L. and Lemna minor L. among phytoremediation plants is a cheap and effective method in the treatment of contaminated water with boron and Lemna gibba L. has a higher boron accumulation capacity than Lemna minor L. Our study showed that boron accumulation by aquatic plants is an effective method and closely related to the relation between boron and Ca, Mg, K and P. The system used in this study could be used in the clarifying of effluent waste water without needing a large area and proper for the continuous treatment regimes. Maximum efficiency could be achieved by 2-day harvesting. Lemna gibba L. could be used in the treatment of secondary waste water with low boron concentration due to higher boron accumulation capacity. In addition it can be recommended as bioindicator for boron as well. References Acmelab (2007) http://www.acmelab.com/cfm/index.cfm Albers, P.H., Camardese, M.B., 1993. Effects of acidification on metal accumulation by aquatic plants and invertebrates. 2. Wetlands, ponds and small lakes. Environ. Toxicol. Chem. 12 (6), 969–976.
Control reactor 3240 78 20 28 365
± ± ± ± ±
40 0.7 0.7 0.3 1
Effluent water (Lemna gibba L.) 2950 72.5 18.1 25.7 280
± ± ± ± ±
60 1 0.2 0.5 10
Effluent water (Lemna minor L.) 3100 76 18.5 27.2 315
± ± ± ± ±
100 0.5 0.2 0.2 5
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Contents lists available at ScienceDirect
Ecological Engineering journal homepage: www.elsevier.com/locate/ecoleng
Potential of Lemna gibba L. and Lemna minor L. for accumulation of Boron from secondary effluents S¸ule Yüksel Tatar, Erdal Öbek ∗ Department of Environmental Engineering, Faculty of Engineering, Firat University, 23119 Elazig, Turkey
a r t i c l e
i n f o
Article history: Received 21 February 2014 Received in revised form 25 April 2014 Accepted 23 June 2014 Keywords: Effluent Boron Phytoremediation duckweed Accumulation
a b s t r a c t Aquatic plants are quite effective in removal of pollutants which cannot be removed in secondary treatment. Lemna gibba L. and Lemna minor L. among the aquatic plants were investigated for the removal of boron from the secondary waste water. Differences in Boron uptake were seen in the chosen aquatic macrophytes. Although boron is at low concentration in water, the bioaccumulated concentrations in Lemna minor L. and Lemna gibba L. were at high levels of between 140 mg Bg 140 –1and 274 mgB g−1, and 381 mgB g−1 523 mgB g−1 respectively. From these results, it was understood that Lemna gibba L. is more prone to accumulate boron compared to Lemna minor L. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Industrial and domestic wastewater contains different organic and inorganic substances. These waters are treated in conventional waste water treatment systems and discharged into the surface waters such as rivers, lakes and brooks. Existence of the pollutants in discharge water indicates that many pollutants could not be removed in these treatment plants. If the quality of treated water is poor, it will negatively effect all the living in aquatic ecosystem. As a result, more treatment is needed before discharge of waste water into the surface water (Sinha et al., 1996; Weis and Weis, 2004; Brix and Arias, 2005; Chen et al., 2005; Upadhyay et al., 2007). Boron (B) minerals are used widely in many industries such as glass, ceramic, cleaning and whitening agents, agriculture, metallurgy, nuclear and medical industries. B, a metalloid essential for plant growth, is often found at elevated concentrations in wastewater as a result of its use for domestic purposes and in industrial production processes. When present in excessive concentrations in the soil solution, B can be toxic to plants (Yermiyahu et al., 1995). Boron compounds are not removed during the discharge of waste water due to their high solubility and mostly mixes with water into which they are discharged. Surface water contains 0.05–0.1 mgB L−1 naturally whereas boron rich water up to
∗ Corresponding author at: Department of Bioengineering, Faculty of Engineering, Firat University, 23119 Elazig, Turkey. Tel.: +90 4242370000. http://dx.doi.org/10.1016/j.ecoleng.2014.06.033 0925-8574/© 2014 Elsevier B.V. All rights reserved.
0.6 mgB L−1 . At this level, boron toxicity can be expected in boron sensitive aquatic plants (Schobel, 1993). Various techniques such as reverse osmosis, B selective resins, membrane filtration, precipitate-coagulation, ion exchangers and adsorption are used for boron removal from water (Simonnot et al., 2000; Ferreira et al., 2006; Dionisiou et al., 2006; Onderkova et al., 2009). Even if these systems bring wastewater to dischargeable standards, they need expensive investment, higher service and repair cost and use of chemicals (Marin and Oron, 2007). Therefore cheap and effective treatment technologies were investigated. It was reported that phytoremedial techniques could be used to remove the pollutants from domestic, commercial, mining and industrial wastewater as a cheap, environment friendly and alternative technique. It was also reported that various aquatic macrophytes removed organic and inorganic pollutants in wastewater by accumulation (Reddy and DeBusk, 1987; Vajpayee et al., 1995; Sinha et al., 1996; Matagı et al., 1998; Rahmani and Sternberrg, 1999; Körner and Vermaat, 1998; Zayed et al., 1998; Körner et al., 1998; Hasar and Öbek, 2001; Wang et al., 2002; Rai et al., 2002; Axtell et al., 2003; Kamal et al., 2004; Miretzky et al., 2004; Brix and Arias, 2005; Oporto et al., 2006; Upadhyay et al., 2007; S¸as¸maz and Öbek, 2009; Khan et al., 2009; Öbek, 2009; Dordio et al., 2010). Some duckweed species are also known to be good B accumulators (Glandon and McNabb, 1978; Frick, 1985). Phytoremediation treatment system uses three different types of plants: aquatic, emergent and submerged plants. Retention time in these systems is adjusted considering waste removal mechanism and harvesting is performed periodically to keep the plant alive
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Table 1 Physiochemical characteristics of secondary-treated municipal wastewater and natural water. Parameter
Unit
Wastewater
Natural water
Temperature pH EC BOD5 COD NO2 − -N NO3 − -N PO4 3− -P NH4 + -N B
◦
20.3 ± 0.6 7.66 ± 0.10 1.16 ± 0.03 50.0 ± 8.0 100.0 ± 5.0 0.66 ± 0.21 2.6 ± 0.2 >5.00 <0.06 370.0 ± 10.0
18.6 7.0 0.36 3.8 8.1 0.21 2.40 0.19 0.78 1.60
C – mS cm−1 mg L−1 mg L−1 mg L−1 mg L−1 mg L−1 mg L−1 ppb
± ± ± ± ± ± ± ± ± ±
0.5 0.1 0.03 0.2 2.0 0.02 0.01 0.02 0.40 0.01
by Davis (1984) was used as treating material in the secondary clarifier. Lemna gibba L. and Lemna minor L. were delivered from botanical garden of Istanbul University and natural waters in Antalya, respectively in June 2013. The plants were grown in a basin full of natural water, the content of which is given in Table 1, for 1 month in laboratory conditions and then adapted in the four of five conical reactors (upper diameter is 50 cm, lower diameter is 40 cm, height of water column is 12 cm) separately. 200 g of plants was placed in each reactor. Two of the reactors contained Lemna gibba L. and the other two Lemna minor L. Reactors were operated in a continuous regime of about 0.02 L min−1 of effluent waste water. One of the reactors in each group was used for daily analyses of plants and water and the other for plant substitution. In order to keep the amount of plant constant in the analysis reactors of Lemna gibba L. and Lemna minor L., the same amount of plants taken for the analyses was transferred into the analysis reactors from the substitution reactors for 7 days. For the following 7 days, 10 g plant and 50 mL composite influent and effluent water samples were put into the tubes containing 0.1% HNO3 for boron analysis. To determine physicochemical parameters in water, 100 mL water was poured into the tubes and kept at 4 ◦ C till analyses. 2.2. Method
Fig. 1. Map of the study area and flowsheet of the Elazı˘g Municipal Wastewater Treatment Plant.
and fresh (Zimmo, 2003). The studies on the removal capabilities of environmental pollutants of the aquatic plants by accumulation have generally been carried out in laboratory conditions and field studies are quite few compared to the laboratory studies. The objective of this research was to determine the ability of Lemna gibba L. and Lemna minor L. to remove Boron from secondary treated municipal wastewater.
2. Materials and methods 2.1. Materials The wastewater of Elazig City was collected and then treated in the conventional activated sludge process. The effluent from the city treatment facility is discharged into Keban Dam Lake (Fig. 1). Physicochemical characteristics of wastewater in the secondary clarifier and the natural water are shown in Table 1. In this study, a plant systematically identified as Lemna gibba L. and Lemna minor L. according to the procedure in Flora of Turkey
After being dried under atmospheric conditions, the plants were dried in a steam oven at 70 ◦ C for 24 h and then ashed at 250 ◦ C for 24 h. The ashed samples (Lemna gibba L. 1.590 g ash from approximate 2.516 g of dried plant and Lemna minor L. 2.595 g ash from approximate 3.80 g of dried plant) were taken by using hand mortars, labeled and sent to Canada for analysis. The ashed samples were digested in HNO3 for 1 h, followed by 1/1/1 mixture of HCl/HNO3 /H2 O for 1 h (6 ml of mixture for 1 g of ashed sample) at 95 ◦ C. Acid was added to the water samples in the laboratory, and samples were filtrated using 0.45 m pore size filters. All samples were analyzed by using inductively coupled plasma mass spectroscopy (ICP/MS - Perkin-Elmer ELAN 9000) technique at ACME Analytical Laboratories Ltd., Canada (Acmelab, 2007). ACME is currently registered with ISO 9001:2000 accreditation. The operation conditions as recommended by the manufacturers (Elan 9000, 2001) are given in Table 2. Physicochemical analysis of the samples was conducted according to Standard Methods for the Examination of Water and Wastewater (APHA, 1995). 3. Results and discussion The results indicating the parameters before and after the experimental study on a daily basis show that Lemna gibba L. and Lemna minor L. accumulated Boron efficiently from wastewater
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Table 2 Operation conditions for ICP-MS analysis. Inductively coupled plasma Nebulizer Spray chamber RF power (W) Plasma gas flow-rate (L min−1 ) Auxiliary gas flow-rate (L min−1 ) Carrier gas flow-rate (L min−1 ) Sample uptake rate (L min−1 ) Detector mode
PerkinElmer Elan 9000 Crossflow Ryton, double pass 1000 15 1.0 0.9 1.0 Auto
Fig. 2. Boron accumulations by Lemna gibba L. and Lemna minor L.
(Tables 3 and 4). Boron accumulations by Lemna gibba L. were given in Fig. 2. Boron concentration in the effluent of the reactors those planted with Lemna gibba L. and Lemna minor L. changed between 369 g L−1 and 410 g L−1 during the experiments (Tables 3 and 4, and Fig. 2). Amounts of boron absorbed from low boron concentration water by Lemna gibba L. and Lemna minor L. were determined between 131.38% and 180.34%, and 33.17% and 64.93%, respectively. Amounts of boron accumulated changed between 381 mgB g−1 and 523 mgB g−1 for Lemna gibba L. and 140 mgB g−1 and 274 mgB g−1 for Lemna minor L. in our study. Metal accumulation by the aquatic plants changes for each species (Albers and Camardese, 1993; Samecka-Cymerman and Kempers, 1996). There are many studies done on boron uptake capacity of Lemna gibba L. and Lemna minor L. (Frick, 1985; Marin and Oron, 2007; Kropfelova et al., 2009; S¸as¸maz and Öbek, 2009). Frick (1985) reported that
Lemna minor L. which were exposed to various solutions containing 10–200 mg L−1 B accumulated 1168 mgB kg−1 in 7 days. Marin and Oron (2007) found that there was 930–1900 mg kg−1 in dry mass of the plants grown in water reservoirs containing 0.3–10 mgB L−1 for 12 days. S¸as¸maz and Öbek (2009) also reported that boron amount which Lemna gibba L. accumulated in the secondary treatment water was 149 mg L−1 . In the study by Kropfelova et al. (2009), three artificial aquatic fields were watered with domestic waste water containing 76–210 g L−1 boron for 2 years. We determined from the measurements that Lemna gibba L. and Lemna minor L. reactors operated with an efficiency between 28.95% and 11.11% for B removal (Table 5). This loss may be caused by sedimentation, adsorption by clay particles and organic substances, co-precipitation with secondary minerals, cation and anion exchange and complexation (Matagı et al., 1998). Boron is an essential micronutrient for the normal growth of plants (Davis et al., 2002). Boron has a very important function in glucose transfer, cell membrane synthesis, lignifications, formation of cell membrane, carbohydrate and RNA metabolisms, respiration, IAA metabolism, phenol metabolism and structural and functional characteristics of biological membranes (Shaaban, 2010). It is also an effective functional element in anther growth, pollen germination, and pollen tube growth (Nable et al., 1997; Huang et al., 2000). We saw differences in boron concentrations accumulated by Lemna gibba L. and Lemna minor L. in our study. Boron accumulated the most in Lemna gibba L. This indicates greater tendency to boron accumulation than Lemna minor L. (Tables 3 and 4, and fig. 2). Differences in essential nutrient accumulations in plants indicate the differences in metabolism activities and growth rates. This in turn shows the difference in metal removal capacities (Upadhyay et al., 2007). When compared with the initial chemical composition of Lemna minor L., it was seen that total concentration of P increased, Ca% decreased after the sixth day, and both K and Mg% decreased till the sixth day and then increased. On the other hand, an increase in Total P concentration and decrease in the other parameters were recorded till the seventh day (Tables 3 and 4). Ho (2000) states that there is an important correlation between calcium, magnesium and boron. Low concentrations of magnesium and calcium are kept in soil but boron is accumulated in plants. Concentrations of the other elements do not affect boron uptake as much as calcium. Interrelation between boron and calcium is physiological. These two elements show similar structural function in cell membranes. This similarity means that lack of boron and calcium gives similar
Table 3 Chemical composition of Lemna gibba L. grown before and after the treatment. Parameter
Before study
P (%) Ca (%) K (%) Mg (%) B (mg g−1 )
0.26 3.24 2.56 0.47 290
After study 1st day
2nd day
3rd day
4th day
5th day
6th day
7th day
0.46 3.16 2.17 0.48 692
0.67 3.51 2.18 0.50 803
0.67 3.07 1.87 0.45 782
0.77 2.99 1.72 0.44 813
0.68 2.66 1.68 0.39 740
0.76 2.63 1.74 0.41 717
0.76 2.53 1.79 0.41 671
Table 4 Chemical composition of Lemna minor L. grown before and after the treatment. Parameter
P (%) Ca (%) K (%) Mg (%) B (mg g−1 )
Before study
0.11 16.21 1.39 0.49 422
After study 1st day
2nd day
3rd day
4th day
5th day
6th day
7th day
0.21 15.74 1.01 0.40 562
0.30 16.02 0.93 0.40 565
0.40 16.12 0.91 0.40 572
0.49 15.65 0.89 0.41 589
0.53 16.25 0.91 0.42 574
0.61 14.44 1.04 0.44 566
0.83 12.31 1.80 0.58 696
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Table 5 B, Ca, K, Mg and P concentrations in influent and effluent water of planted and unplanted reactors. Parameter
Unit
Influent water
P Ca K Mg B
g L−1 mg L−1 mg L−1 mg L−1 g L−1
3266 79.5 21.9 30.5 370
± ± ± ± ±
100 2 1 1 10
indications. On the other hand there is also an important relation between boron and potassium. If the plant is exposed to excess amount of potassium, it is necessary to give boron to prevent the decrease in the productivity. Phosphorus causes increase in boron accumulation in plants at higher concentrations. One of the reasons for the difference in boron uptake in plants is the difference in the structures of cell membranes. Our study showed that boron accumulation by aquatic plants is the same to the uptake by the plants from the soil and closely related to the relation between boron and Ca, Mg, K and P (Ho, 2000). This uptake was determined to change between 140 mgB g−1 and 274 mgB g−1 in Lemna minor L., and 381 mgB g−1 and 523 mgB g−1 in Lemna gibba L. The results inferred that Lemna gibba L. had a better boron accumulation capacity than Lemna minor L. Sawidis et al. (1995) reported that there were differences in heavy metal concentrations of different type plants growth in the same station. In addition, differences were also seen in different species of the same plant. Boron, which is an important microelement for agriculture and environment, is necessary in low concentrations for plants but harmful in high concentrations with its toxic effect (Minareci and Öztürk, 2012). For some crops, if 0.2 mg L−1 boron in water is essential, 1–2 mg L−1 may be toxic (Ayers and Westcot, 1994). Davis et al. (2002) stated that boron is an important trace element but might have a toxic effect in aquatic plants even in low concentrations. Researchers reported chlorosis, necrosis and death in aquatic macrophiles exposed to B more than 22 mg L−1 . It was determined that excess amount of boron caused phytotoxicity (Gün, 2009; Reid, 2010; Grievea et al., 2010) and teratogenic effect (Naghii and Samman, 1997). In our study no phytotoxicity was seen. Higher boron removal by Lemna gibba L. can be attributed to the high metal and nutrient concentration in the effluent water as stated by Upadhyay et al. (2007). 4. Conclusions In this study, it was determined that use of Lemna gibba L. and Lemna minor L. among phytoremediation plants is a cheap and effective method in the treatment of contaminated water with boron and Lemna gibba L. has a higher boron accumulation capacity than Lemna minor L. Our study showed that boron accumulation by aquatic plants is an effective method and closely related to the relation between boron and Ca, Mg, K and P. The system used in this study could be used in the clarifying of effluent waste water without needing a large area and proper for the continuous treatment regimes. Maximum efficiency could be achieved by 2-day harvesting. Lemna gibba L. could be used in the treatment of secondary waste water with low boron concentration due to higher boron accumulation capacity. In addition it can be recommended as bioindicator for boron as well. References Acmelab (2007) http://www.acmelab.com/cfm/index.cfm Albers, P.H., Camardese, M.B., 1993. Effects of acidification on metal accumulation by aquatic plants and invertebrates. 2. Wetlands, ponds and small lakes. Environ. Toxicol. Chem. 12 (6), 969–976.
Control reactor 3240 78 20 28 365
± ± ± ± ±
40 0.7 0.7 0.3 1
Effluent water (Lemna gibba L.) 2950 72.5 18.1 25.7 280
± ± ± ± ±
60 1 0.2 0.5 10
Effluent water (Lemna minor L.) 3100 76 18.5 27.2 315
± ± ± ± ±
100 0.5 0.2 0.2 5
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