Bioaccumulation of Elements in Species Polygonum Amphibium L. in Reservoir ”Gruža“ (Serbia)

Snežana Branković1, Radmila Glišić1, Gorica Đelić1, Marina Topuzović1, Zoran Simić1, Aleksandra Milošković1, Vera Đekić2

 

1 University of Kragujevac, Faculty of Science, Department of Biology and Ecology, Radoja Domanovića 12, 34 000 Kragujevac, Serbia, E-mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it

2 Agriculture Research Institute Serbia, Small Grains Research Center Save Kovačevića 31, 34 000 Kragujevac, Serbia

 

Abstract

In this manuscript we investigated the ability of stem, leaf and whole plant species Polygonum amphibium L. to absorb and accumulate some elements (Fe, Pb, Cd, Cu, Mn, Hg, As). Concentrations of the investigated elements in the sediment and plant material were higher than their concentrations in water, while the content of the studied elements in plant material was lower than their content in the sediment. The results exhibited higher concentrations of Hg and As in the water and the sediment than the maximum allowable concentrations in accordance with the Regulations of the Republic of Serbia. Also, results have shown that the tissue of the stem and leaf of P. amphibium has the potential to bioaccumulate Fe, Cu, Mn, Hg and hyperaccumulation of As from water. Further research should focus on the use of P. amphibium in phytoremediation (using biofiltration) of the tested elements from aqueous environments.

Keywords: metals, P. amphybium, bioaccumulation.

Introduction

 

Biomonitoring of different types of pollutants by using accumulating species is based on the capacity of a specific plant and animal species to accumulate large amounts of certain pollutants even from diluted solutions, without any observable adverse effects. Using this kind of monitoring is widespread in marine and freshwater ecosystems, because it is the only way to evaluate the bioavailability of pollutants that exist in the environment and to establish its presence and content in living organisms in a given environment. This technique enables the measurement of concentrations of trace metals, even though their quantities in ecosystems are lower than the detection limits of conventional techniques. It should also be noted that the concentration of pollutants in organisms is a reflection of past and present pollution, while the concentration of the pollutants in the water or sediment is a picture of the situation at the time of measurement.

Monitoring of macrophyte species, density and distribution of the established populations of aquatic plants provides indicative information on environmental effects on aquatic ecosystems. Macrophytes are particularly good biological indicators in continuous, long-period monitoring. The high concentration of some elements in the plant tissues can be the result of increased concentrations and considerable availability of these elements in the surrounding environment, where macrophytes can be used as a bioindicators. Some species of aquatic macrophytes can be used for removing, degradation or transformation of harmful and dangerous substances present in the aquatic environment.

Aquatic plants are used in water quality studies for monitoring the presence of heavy metals and other pollutants in the water and sediment. Contamination of water and sediment with various pollutants is clearly reflected in their increased concentrations in aquatic plants. Aquatic macrophytes are suitable as biological monitors, with respect to their sedentary nature and ability for selective absorption of certain ions. The term biomonitor implies organisms that accumulate pollutants in their tissues and therefore can be analyzed and used to identify the content and bioavailability of various contaminants in aquatic ecosystems (Markert, 2008).

Certain species of macrophytes can be considered as very good indicators of increased pollutant levels in the aquatic environment. Macrophytes accumulate large quantities of different substances and they are therefore useful indicators of local pollution. Sorption of organic and inorganic compounds by aquatic plants is facilitated by their large surface area in comparison with their volume, as well as great permeability of their cell membranes that are in permanent contact with the surrounding solution. Also, aquatic macrophytes have the ability to accumulate chemical agents, and may contain 10-106 times higher concentrations of heavy metals with respect to their concentration in an aqueous environment.

Since aquatic macrophytes absorb and accumulate large amounts of chemical elements, they play a significant role in biofiltration and bioaccumulation and are therefore important bioindicators. Bioindicators are plant communities, species or certain parts of the plant that can provide information about the quality of the environment (Markert, 2008). Macrophytes have the ability to tolerate high concentrations of metals in water, producing a large biomass and they are easy for sampling, all of which is very advantageous for their use as bio-indicators in the monitoring of aquatic ecosystems.

 

Material and Methods

Description of the investigated location - The Gruža Reservoir (Figure 1) (Position: 43° 42' N, 20° 31' E; Altitude: 238-269 m above sea level) was created by damming the middle part of the Gruža River for the following purposes: providing a water supply for the City of Kragujevac, the surrounding villages and the industry; as a protection against flooding, for retaining the sediment and to increase low flows in the downstream section of the River Gruža during drought events.

 

fig01
Figure 1: The Gruža Reservoir.

 

The samples of raw water, sludge (per 2 L) and plant material of the species Polygonum amphibium L. (whole plant, stem, leaf) were taken at certain locations of the Gruža Reservoir. Identification of plant material was performed in the laboratory of the Institute of Biology and Ecology, Faculty of Science in Kragujevac, with the help of standard plant identification keys: Javorka & Csapody (Javorka and Csapody, 1979) and Flora of the Republic of Serbia (Josifović, 1970-1980).

The identified plant material was washed in distilled water, then dried at room temperature, and after that in a drying oven (Binder/Ed15053), 24 hours at a temperature of 105ºC following which it was prepared for chemical analysis according to the applicable standard procedure for water and aquatic plants (APHA, 1995).

Chemical analyses of the raw water, sludge and plant materials were performed in accordance with standard methods in the Institute of Public Health in Kragujevac, and concentrations of the examined elements (Fe, Pb, Cd, Cu, Mn, Hg, As) were determined by means of an inductively coupled plasma-atomic emission spectrometry (ICP-OES, iCAP 6500) directly from the mother liquor. Each sample was read in triplicate, after which the mean value and standard deviation were calculated. Also, the content ratios of the analyzed elements in the sediment and water were calculated, as well as those in the water, sediment, and plant material (stem, leaf and whole plant). The content of elements in the plant material, water and sludge are expressed in mg/kg dry matter and mg/L.

 

Results

The obtained results showed that the mean values of concentrations of the tested elements in water appeared in this order: As>Fe>Mn=Hg>Cu (Table1). The concentrations of Pb and Cd in water were below the detection limit. The concentrations of the elements in the sediment had a similar descending order (As>Fe>Mn>Hg>Pb>Cu>Cd). The element contents in the investigated species were dependent on the type of organ and the element investigated, and ranged from 0.12 mg/kg of Cd in the leaf up to 7515 mg/kg of As in the tree species examined. In general, concentrations of the elements in the species P. amphibium declined as follows: As>Fe>Mn>Hg>Cu>Pb>Cd.

 

Table 1: The concentration (mean value ± SD) of elements in water, sediment, stem, leaf and whole plant P. amphibium.
tab01

 

fig02
Figure 2: The ratio of element concentrations in water, sediment, stem, leaf and whole plant P. amphibium.

 

Also, the ratio of concentration of elements investigated in the plant material (stem, leaf, and the entire plant) and the sediment was less than 1, and ranged from 0.02 for Pb in the whole plant to 0.68 for As in the tree of species P. amphibium.

 

fig03
Figure 3: The ratio of element concentration in sediment, shoot, leaf and whole plant P. amphibium.

 

Discussion

The results of this study showed that the values of Hg and As in the water and sediment were in excess of the maximum allowable concentration for water and soil (Official Gazette of RS, No. 23/94). The tested water samples contained 6 times more As and 30 times more Hg than the maximum permitted concentrations of the given elements. Also, results showed that the sampled sediment contained 440 times more As and 140 times more Hg than the maximum allowable concentration for these elements. The Gruža Reservoir which is used as a water supply for the City of Kragujevac, has been under heavy pressure from various anthropogenic pollutants for many years. A major motorway passes over this reservoir and arable land, where different scientific farming methods are applied, is located in its vicinity. Indirectly, wastewater from local meat processing plants and mushroom farms reaches the reservoir. Also, the reservoir is directly affected by pollution generated by sports and recreational fishing use and real estated development.

The obtained results showed that species P. amphibium efficiently accumulates Fe, Cu, Mn, Hg and As, which is in accordance with some literature data (Samecka-Cymerman, Kempers 2001; Kumar et al., 2006; Yabanli et al., 2014). Literature data suggest that the normal vs. toxic concentrations of some metals and metalloid As (expressed in mg/kg) for plant species which are given in the following order: 30-300 vs. 400-1000 of Mn, 5-30 vs. 20-100 of Cu; 1.0-1.7 vs. 5-20 for As; 0.05-0.2 vs. 5-30 for Cd; 5-10 vs. 30-300 for Pb (Kabata-Pendias, 2011). Also, toxic concentration of Hg in plants is 1-3 mg/kg (Kabata-Pendias, 2011), while concentrations of Fe in plants is in the range of 5-200 mg/kg (Markert, 2008). The obtained results indicate that the stem and leaf of P. amphibium accumulated more Fe, Cd, Hg and As than the prescribed normal and toxic values. Also, the leaf of the studied species contained more Cu than the above mentioned normal and toxic values.

Hyperaccumulators are plants and/or genotypes that accumulate elements in concentrations of 50-100 higher (depending on the element) than plants with no hyperaccumulation ability (Baker and Brooks, 1989). Hyperaccumulators may contain elements of the above-listed concentrations (by weight on a dry matter basis): Cd and As (100 mg/kg, 0.01%); Co, Cu, Ni, Cr and Pb (1000 mg/kg, 0.1%); Mn, Ni and Zn (10 000 mg/kg, 1%). The obtained results demonstrate that species P. amphibium can be classified as an As hyperaccumulator species, given that the leaf, stem and whole plant contain multiple higher concentrations of this metalloid in relation to the previously mentioned hyperacumulating concentrations.

A concentration factor, which represents the ratio between the concentration of the element in the organism (with respect to the dry matter) and its concentration in water, is used for the evaluation of the ability of the test plant, or of its part, to carry out the accumulation of a specific element (Samecka-Cymerman and Kempers, 2004). The concentration factor in the species P. amphibium ranged from 1707.21 for Cu to 29366.94 for As in the stem of this species. Also, the stem concentration factor of species P. amphibium for all investigated elements was higher than the leaf concentration factor.

Many factors can affect the ability of macrophytes to accumulate certain elements. The floating and submerged macrophytes accumulate elements directly from the water column through the leaves and stems, and thus directly reduce their concentrations in the water. Stems of aquatic macrophytes have the ability to acquire elements directly from the water and to keep them because they are completely immersed in it and have a very thin cuticle. It should be added that the ability of macrophytes to uptake elements through the stems (offsprings) is much greater than that of roots, due to the fact that the aquatic plants generally consist of 80% of the offspring's mass in relation to the total plant mass. It is therefore possible that the primary method of element uptake, when concentrations in the surrounding water are high, is through the stems. Also, the plant cell walls play an important role in the accumulation of elements, because more than half of their absorbed quantityis stored in extracellular spaces of roots, stems and leaves. It is known that the cell walls may contain a functional group, such as a carboxyl (galacturonic acid in the pectins) and hydroxyl (in cellulose), which can strongly bind cations from the aqueous solution by complexing, coordinating, chelating and ion exchange (Keskinkan et al., 2003). All this indicates that aquatic plants can play an essential role in biofiltration of different elements from contaminated water.

Aquatic macrophytes do not a regulated uptake mechanism for nutrients and heavy metals, therefore, their importance in the ecosystem is manifested through the process of chemical bioconcentration and excretion, as well as biofiltration. Also, the increased concentration of nutrients and the accumulation of metals in their tissues can be a result of increased concentrations of these in the aqueous medium (Ravera, 2001). Some of the factors which substantially determine the absorption and accumulation of pollutants in plant tissues are as follows: their concentration in the environment, temperature, pH value, the physico-chemical characteristics of pollutants, solubility, antagonism and synergism of adopted ions, as well as the physiological and biochemical properties of plants (the cell membrane permeability and the plant enzymatic activity during absorption).

The results of this study indicate the existence of contamination in the water and sediments by the investigated elements, especially by Hg and As, as well as that the floating aquatic macrophyte P. amphibium could be applied in bioindication and bioaccumulation, primarily of Fe, Cu, Mn, Hg, and As. Also, taking into account the ecology of species P. amphibium, its possibility to produce relatively large biomass and its ability to hyperaccumulate As, we concluded that it can be submitted for consideration as a potential candidate for phytoremediation of aquatic ecosystems contaminated with this metalloid.

 

Conclusion

This study investigated the concentration of some elements (Fe, Pb, Cd, Cu, Mn, Hg, As) in water and sediment, as well as the ability of species P. amphibium to absorb and accumulate the these elements. The obtained results showed high degrees of water and sediment pollution of metals and the metalloid As. It has shown that the water and the sediment contain concentrations of Hg and As higher than the maximum permissible levels prescribed by the Regulations of Republic of Serbia.

The presented results indicate that the concentrations of the investigated elements in the sediment and plant material were significantly greater than their concentration in water. It has shown that the floating aquatic plants macrophytes P. amphibium demonstrate the ability for absorption of Fe, Cu, Mn, Hg and As from the water, as well as hyperaccumulation of As in leaves and stems.

The results of this study suggest that P. amphibium floating macrophytes could be applied for bioindication and bioaccumulation of Fe, Cu, Mn, Hg, and As. Further research should focus on the use of this species in phytoremediation by biofiltration of As in aquatic ecosystems contaminated with this metalloid.

 

Acknowledgments

This investigation was supported by the Ministry of Science and Tehnological Development of the Republic of Serbia (BTR III 41010). The authors are thankful to colleagues from the Institute of Public Health Division of Hygiene and Medical Ecology in Kragujevac for help in chemical analysis of soil and plant samples.

 

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