Introduction

The rapid increase of the level of pollution in soil and shallow groundwater environment due to various industrial and agricultural activities has become a serious issue in Kuwait. This type of pollution has reduced the efficiency of native groundwater to irrigate crops in Kuwait and affected the health of residents (Aliewi and Al-Khatib 2015; Afzal et al. 2014). Phytoremediation has emerged since the 1980s as an important technology for plant-based soil and groundwater remediation. It is a sustainable and a promising treatment technology for soil and groundwater pollution problems (Dhanwal et al. 2017). Phytoremediation is a treatment technology, which utilizes the abilities of plants and their associated microorganisms to remove and degrade pollutants in soil and groundwater. Some of these pollutants include heavy metals (Mohan et al. 2015; Ahmadpour et al. 2015), organic and inorganic compounds, salts (Gerhardt et al. 2017), and hydrocarbon pollutants (Almansoory et al. 2015). Heavy metals above certain limits can be toxic and negatively affect the natural microbial distribution leading to disorder of important ecological processes (Kim and Owens 2010). Padmavathiamma and Li (2007) reviewed hyper-accumulation metals in plants as a means of phytoremediation treatment. They explained that plants absorb metals from soil, accumulate them in roots, and translocate them to harvestable leaves. Phytoremediation was used to decontaminate coalmine effluents from toxic metals using Salvinia molesta and Pistia stratiotes species from India (Lakra et al. 2017). Doni et al. (2015) also used the technology as a sustainable management strategy for the decontamination of polluted scoured marine sediments different plant species of Vaginatum plants and organic matter (compost). They showed that this treatment is capable of reducing significantly both heavy metals and total petroleum hydrocarbons. Using transgenic plants to enhance phytoremediation capabilities was investigated previously (Singh and Singh 2017) and illustrated to be successful. The Jatropha plant was used to treat organic and inorganic pollutants by phytoremediation (Kamusoko and Jingura 2017). They showed that this technology could enhance the management of water movement, leaching of contaminants, containment, and stabilization. They showed that the plant is able to survive on degraded land and has the ability to facilitate reclamation, uptake, translocation, and cleansing of pollutants. In petroleum industrial countries, the contamination of soil affects the growth of plants. Ma et al. (2018), Klimek et al. (2016), and Ogoko (2014) investigated the potential of two plants to petroleum-tolerant hydrocarbon (TPH) and polycyclic aromatic hydrocarbons (PAHs) in the soil contamination. They concluded that this type of pollution can affect the rate of soluble protein and height of plants.

In the industrial world, lithium pollution can affect the plant growth as reported by Antonkiewicz et al. (2017) who showed that plants from the Solanaceae are resistant to high lithium concentrations in salty soils. They can contain more than 1000 mg Li per kg. Wu et al. (2017) and Mahar et al. (2016) showed that bioremediation of plants and soil fertility to boost up plant growth can be enhanced. Plants are proved to use phytoremediation process for the removal of heavy metals and macro-elements from sewage sludge. Kołodziej et al. (2015) illustrate the use of sewage sludge in bioenergy production through studying the effects of sorghum biomass production. Moreover, phytoremediation is a cost-effective method of treatment as compared to conventional methods (Wan et al. 2016). In many cases, phytoremediation provides a feasible alternative to the traditional and more expensive methods such as “pump and treat.” In general, the cost of using this phytoremediation is one-third to one-fifth the costs of other conventional technologies (Carman and Crossman 2000; Black 1995). Phytoremediation is also known to be more acceptable by the public and the regulators since it is environmentally compatible and esthetically pleasing. Despite its important advantages, phytoremediation has some disadvantages and limitations, which make it undesirable for some environmental applications (Filippis 2015). Phytoremediation can only work at sites that are well suited for plant growth. The existence of contaminants in high concentration could be toxic to the plants and therefore may limit application on some sites or some parts of sites (Raskin and Burt 2000). The depth of contaminants is another obstacle that faces phytoremediation. If a pollutant is located in a deep aquifer, then plant roots cannot reach it. Contaminated aquifers must be within 20 ft of the surface in order for plant roots to be able to treat them. Some aquifers may be too deep or located under an urban area that makes it difficult to plant sufficient number of plants to do this job (Smith 1997). However, deep groundwater contaminants or leachate pond effluent may be treated by pumping and drip irrigation on plantations of trees (Schnoor et al. 1995). Phytoremediation is also limited by the suitability and growth rate of the plants. Choosing the suitable plant species is a key factor in phytoremediation. Some plants are able to degrade only certain contaminants. Also, each plant can tolerate specific types of environments (Filippis 2015). Table 1 illustrates the various kinds of contaminants and the plants used for each one.

Table 1 Examples of plants in phytoremediation (Smith 1997)
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Soil and groundwater quality deterioration in Kuwait is a result of urbanization and industrial activities. The aim of this research is to investigate the potential of reed plants as phytoremediation technology to enhance degradation and mineralization of the pollutants (e.g., heavy metals, N compounds, and salts) in the native shallow groundwater in order to increase irrigation efficiency. This is an important issue for Kuwait, which suffers from shortages of suitable water resources for irrigation and agricultural lands. The reed plants were chosen because they are available and common in the desert of Kuwait.

Study area

The study area is Kuwait in the Middle East. Kuwait suffers from water scarcity, unfertile lands for agriculture, and industrial activities that pollute the existing water and land resources despite the fact that they are scarce.

Data used

The data used in this study are generated from two experiments on reed plants. One experiment is conducted in KISR laboratory and the second one is conducted in the agricultural fields of KISR in Kuwait city.

Methodology

Phytoremediation is a broad class of cleanup techniques which apply many treatment mechanisms. In the context, the treatment mechanism is well explained in Chappell (1998) and Van Deuren et al. (2002), which is summarized in terms of breaking down of organic containments in the soil or groundwater by microbial activity and then absorbed by roots or precipitation within the soil zone. Certain plants, called “hyper-accumulators,” absorb large amounts of heavy metals and concentrate them in the plant roots and leaves.

In this research, a groundwater well was identified within the premises of Kuwait Institute for Scientific Research (KISR) as a source of polluted shallow groundwater to be treated by reed plants for irrigation purposes. The native groundwater of this well was analyzed chemically at KISR laboratories. It was found that the TDS, concentration of salts, nitrates, and fluoride were elevated as presented in Table 2. It was an objective to illustrate that the reed plants are capable of reducing the concentration of heavy metals in KISR’s groundwater. In this methodology, the treatment by the reed plant will be tested through their roots and leaves. The significance of that is to test if the effective volumes around the roots and the leaves yield any difference in the efficiency of reed treatment. As will be seen later the effective contact volume of leaves is 3.5% of that volume of the effective contact volume of roots, so this paper investigates as well the relative efficiency of the roots in reducing the concentration of pollutants in the shallow groundwater of KISR premises.

Table 2 Chemical analysis of the original sample (native groundwater)
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Reed plants were first implanted in the fields of KISR and irrigated with freshwater for about 6 months to allow them to grow up naturally, and then reed plants were irrigated with polluted groundwater from the beach well in two experiments: First, decaying reed leaves were tested in a controlled laboratory setting. Second, reed plant roots were irrigated with polluted groundwater to measure any change in the concentration of the inflow and outflow.

In the first experiment, samples of dry leaves were collected from the reed plants. The leaves were then cleaned with distilled water and left to be dried at room temperature. Dry leaves were crushed roughly and used as such. Then, the reed leaves were forced to be fully sunk in the first 10 cm of the polluted groundwater in the experimental tank to maximize the contact between the reed leaves and the polluted groundwater as shown in Fig. 1. By this, the effective volume for the reed leaf experiment is 0.08 m3. The leaf experiment was conducted at the Water Research Centre because of the controlled environment. The repeat time of the sampling was every 2 weeks in order to detect any changes in the concentration of pollutants.

Fig. 1
figure 1

Basic design of reed leaf experiment in the laboratory (Adobe Photoshop version 13.0.1)

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The methodology of using the roots of the reed plant to treat the polluted irrigating water is illustrated in Fig. 2. In this methodology, a tank of 1 m diameter and 2 m height was used as the basin to conduct the experiment. This basin was filled with native soil for about 1.5 m to grow the reed plant. All these dimensions yield an effective volume of 2.31 m3 as the portion of the field basin for the root experiment. The basin of the root experiment as shown in Fig. 2 was flooded with polluted groundwater from KISR’s well to investigate the treatment efficiency of the roots of the reeds, to detect any change in the concentration of chemicals, metals, and salinity between the native water (Table 2) and the outflow taken from the sampling point shown in Fig. 2. Samples were taken every 2 weeks approximately as a repeat time for chemical analysis to detect gradual changes in pollutants concentration.

Fig. 2
figure 2

Basic design of reed root experiemnt in the field

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The materials and methods used for the determination of the concentration of pollutants were the standard methods (APHA 2015) in the laboratory as follows:

  • Major cations and anions (Na, K, Ca, Mg, Cl, and SO4): Ion chromatograph (ASTM D6919-09 and SMEWW Method No. 4110).

  • Nutrients (NO3, NH4): Discrete analyzer (SMEWW Method No. 4500 G, E, F, and C).

  • Trace metals (Fe, Zn, F, Li, Co, Cu, Al, Cd): ICP-OES (USEPA 200.7)

Results and discussion

Suitability of concentration of ions in irrigation water

Because this research addresses the use of plants to improve irrigation efficiency, the suitability of the concentration of ions in irrigation water for plant growth is first presented as follows:

  • Lithium (Li) is toxic for plants. Lithium sources come mainly from Li industrial activities (Hull et al. 2014) and disposal of Li batteries (Al-Thyabat et al. 2013). Compared to other cations in soil, Li is mobile and may leach into receiving waters, be taken up by plants, or have other biological impacts. Li reduces the plant growth by altering metabolism of nutrients in plants (Shahzad et al. 2016). Therefore, reducing Li will help the growth of plants. It is understood that Li has metabolic functions in salt-tolerant plants (Antonkiewicz et al. 2017). Komorowicz, and Baralkiewicz (2016) and Esetlili et al. (2014) reported arsenic, lithium, and fluoride pollution in many industrial countries such as Poland, Turkey, the USA, and China. Anderson et al. (1988) report that the limits of Li in groundwater and soil should be within 0.5 mg/l and 0.98–1.48 mg/l respectively. However, Li is tolerated by most plants up to 5 mg/l in water. There is no official legal act about lithium concentration in the groundwater and soil of Kuwait but the country almost follows the limits provided by Anderson et al. (1988). In Kuwait, Li is a major concern at solid waste dumping sites, cement factories, sewage sludge from treated wastewater plants, agricultural farms where sewage sludge is used, and lithium batteries dumping sites.

  • Fluoride (F) influences the metabolic effects of plant growth. A water fluoride level of 1.5 mg/l can be toxic to plants (Swarup and Dwivedi 2002). The anthropogenic sources were identified as fertilizers, combusted coal, and industrial waste, with phosphate fertilizer being the most significance source of F− accumulated in the soil.

  • Heavy metals can cause significant reduction in plant growth. The heavy metals that have the most toxic effect are Cd, Cu, Zn, and Cr (Athar and Ahmad 2002). The following limits (Rowe and abdel-Magid 1995) should not be exceeded in irrigating water to reduce toxic effects and to improve irrigation efficiency: Al (5–20 mg/l); Cd (0.01–0.05 mg/l); Cr (0.1–1 mg/l); Co (0.05–5 mg/l); Cu (0.2–5 mg/l); Fe (5–20 mg/l); F (1–1.5 mg/l); Zn (2–10 mg/l); and Li (< 2.5 mg/l) (Ahmadpour et al. 2015).

  • Freshwater can easily be absorbed through the roots without problems but brackish water faces difficulties to do that. Salinity can limit plant access to soil water by increasing the osmotic strength of the soil solution. In Kuwait, hotter weather requires more energy from plants to absorb water. The following limits (Rowe and abdel-Magid 1995) are favorable limits for good-quality water to irrigate with: TDS < 960 mg/l; Cl < 140 mg/l; K < 10 mg/l; Na < 50 mg/l; SO4 < 400 mg/l.

  • NH4 should be in the range 15–30 mg/l and NO3 around 50 to 100 mg/l (Rowe and Abdel-Magid 1995).

Domination of ions in the native groundwater (original sample)

The native groundwater was analyzed chemically using Piper methodology (Fig. 3). The results show that the type of this water is brackish with domination of Na-Cl-SO4 salt ions. That means the salt is dominating this water, which makes it difficult to irrigate with especially the TDS value of 11,675 mg/l is substantially above the limit of 960 mg/l (Rowe and Abdel-Magid 1995).

Fig. 3
figure 3

Piper analysis before treatment and after treatment of the native polluted water using reed plants

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The chemistry of the original water shows that Cl = 4148 mg/l which is > 140 mg/l, SO4 = 2862 mg/l which is > 400 mg/l, Na = 2720 mg/l which is > 50 mg/l, and K = 40.8 mg/l which is > 10 mg/l. It should be noted that using the reed plant is not intended to bring down the concentration of these ions to the limit of their use but the aim is to illustrate that the reed plant can reduce considerably the concentration of these ions to improve irrigation efficiency and productivity. The concentration of NH4 in the original sample is 10.1 mg/l which is less than the limit of 3.5–15 mg/l (Caicedo et al. 2000; Rowe and Abdel-Magid 1995) and for NO3 is 115 mg/l which is less than the limit of 50–100 mg/l. The concentration of Li in the original sample is 0.23 mg/l < 5 mg/l and F is 2.3 mg/l which is greater than the limit of 1.5 mg/l.

Analysis of reducing salts in the polluted native groundwater

High concentration of salts affects plant growth by limiting the uptake of calcium and increasing the adsorption of sodium and potassium, resulting in a disturbance in the cationic balance within the plant. The decaying leaf method and root method were used to investigate the reduction of salts in the native polluted groundwater. Figure 3 shows on Piper diagram that the roots of the reed plants in the experiments used at KISR premises treat better the salts in the polluted shallow groundwater sample as follows:

  • Original sample: alkaline water with SO4/Cl salt domination

  • Leaf treatment: alkaline water with less domination of SO4/Cl salts

  • Root treatment: earth alkaline water with less SO4 salt domination. Not dominated by Cl ions and to be less dominated by SO4 ions as salts, this means that on Piper diagram (Fig. 3) the roots managed to push the water type.

The results of reducing the concentration of salts are presented in Table 3 and some of them are shown in Fig. 4. It should be noticed that a 5% error bar is shown on this figure to illustrate the range of values with this error. Two remarks can be observed from Table 3. The first remark is that the concentration of salt ions (Na and SO4) and TDS increased in the first month because of the effect of evaporation and then reduced because the efficiency of the decaying leaves to reduce the concentration of salts was greater than the effect of evaporation. The second remark is that leaves observed a slight reduction in the concentration of salt ions. However, the reductions in the TDS, SO4, Cl, and K values for the same period in the root experiment were substantial as shown in Fig. 4 for Cl ion. It is believed that the roots have bigger surface area and stronger ability to absorb pollutants by the roots and to precipitate them from the irrigating water within the rhizosphere (phyto-stabilization process). In fact, the volume of 2.31 m3 for the effective portion of the roots compared with 0.08 m3 of the leaf effective portion supports that the roots are more efficient in reducing the concentration of salts in the shallow groundwater of KISR premises.

Table 3 Concentration of salt ions (mg/l) after using reed plants
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Fig. 4
figure 4

Reduction of salt ions by reed plants (SO4 by leaves and Cl by roots)

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Analysis of reducing the concentration of N compounds

Irrigation water high in N can cause quality problems in crops. The existence of NH4 as an example at higher concentrations than 30 mg/l is phytotoxic (Kiraly et al. 2013). When the level of NH4 is lower than 3.5 mg/l, then the plant growth will be toxic to seedlings (Caicedo et al. 2000). The optimal level for NH4 in soil for plant growth is around 25 mg/l. In Kuwaiti irrigation environment, the level of NH4 is around 1 mg/l (Akber et al. 2006) which is less than 3.5 mg/l. But the native groundwater contains 10.1 mg/l of NH4 (Table 2) which is greater than 3.5 and less than 25 mg/l. In Table 4, it is shown that the treatment with reed plant through leaves and roots reduced considerably the 10.1 mg/l of ammonium in 8 and 12 months respectively, illustrating the capabilities of the reed plant to almost remove the ammonium concentration from the irrigation water. It seems that the leaves are quicker than the roots in consuming the inorganic nitrogen (ammonium) as a nutrient (plant proteins). Any level of nitrates greater than 50 mg/l in groundwater (after leaching from agricultural soil) can cause pollution problems and low levels of nitrates in the soil will impact the growth of plants (Hachiya and Sakakibara 2017). In Kuwait, the level of nitrates in the soil of most farms was about investigated thoroughly by Akber et al. (2006) and Shahid and Omar (1999). They found the level of nitrates in the soil of these farms to vary between 5 and 298 mg/l. In general, the organic matter outside Kuwait farms is very low. The level of nitrates in the irrigating water as presented in Table 2 is 115 mg/l. It took the reed leaves and roots about 8 weeks (Table 4) to almost remove the 115 mg/l NO3 ions from the polluted groundwater. This illustrates the capability of the reed plant to remove the nitrates almost completely.

Table 4 Concentration of N compounds (mg/l) after using reed plants
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It is clear that the reed plants have the capacity to almost remove N compounds completely in case of excessive nitrogen content. The reed plants transform the inorganic nitrogen from the irrigating groundwater into plant biomass, thereby removing the constituent from groundwater (Rowe and Abdel-Magid 1995). The plant biomass is normally managed to enrich soil fertility and site productivity. Some biomasses are used as a source of renewable energy. However, N is needed for plant growth; therefore, good fertilizers and irrigation management can help solve these problems (Rowe and Abdel-Magid 1995) especially their concentration in the soil of Kuwait away from the farms is not sufficient. Regardless of the crop, nitrates and ammonium should be credited toward the fertilizer rates in general.

Analysis of reducing the concentration of fluoride and lithium

The experiments carried out in this paper show that the reed plants reduced the concentration of F and Li ions through the absorption process as presented in Table 5 below. Table 5 and Fig. 5 show that the leaves of the reed plant reduced the concentration of F and Li ions by 23% and 48% respectively while the reed roots reduced 90 to 86% of the concentration of F and Li ions respectively. This result agrees with Antonkiewicz et al. (2017) who reported that after applying different Li concentrations within nutrient solution for the maize plant, the highest concentration of Li was found in the roots of maize while the lowest concentration of Li was found in the leaves. This illustrates the capability of the roots of reed plant to effectively absorb lithium as tested by Antonkiewicz et al. (2017). It should be noticed that a 5% error bar is shown on this figure to illustrate the range of values with this error. The bar is not shown on the figure when the concentration of Li is very small (i.e., 0.03 mg/l) producing an insignificant 5% error of this value.

Table 5 Concentration of F and Li (mg/l) after using reed plant
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Fig. 5
figure 5

Reduction of F and Li concentrations by reed plants (F by leaves and Li by roots)

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Analysis of reducing the concentration of heavy metals

The reed leaves reduced Co, Cd, and Fe by almost 100% within a period of about 2.5 months (Table 6). They reduced the concentration of Zn, Al, Cr, and Cu by 76%, 73%, 72%, and 64% respectively. The reed roots reduced Co, Cd, Cr, Zn, and Fe by almost 100% within a period of about 3 months. They reduced the concentration of Al and Cu by 53% and 39% respectively.

Table 6 Concentration of some heavy metals (μg/l) after using reed Plants
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For heavy metals, the reed roots act as “hyper-accumulators” to absorb large amounts of metals (such as Zn, Ni, and Cu) and concentrate them in the plant roots. This is why the reed roots are successful in removing heavy metals from polluted groundwater.

In summary, the results of reduction of the pollutants in Kuwaiti soil/groundwater environment are presented in Table 7.

Table 7 Summary of reduction of specific pollutants by reed plants
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Analysis of statistical significance of the results

The purpose of this statistical analysis is to compare results from two experimental treatments by reed leaves and reed roots to decide if the difference between the two treatments is statistically significant. The parameter that will be used in the comparison of the results is the reduction of the concentration of pollutants. Collected data were from two groups: group A—treatment by reed leaves and group B—treatment by reed roots. The statistical tests will be used to determine whether a difference between means for the leaf and the root treatments is statistically significant. The following hypothesis will be used:

  • Null hypothesis no. 1: there is no difference between the means for the leaf and the root treatments.

  • Alternative hypothesis no. 1: A difference between the means for leaf and the root treatments due to reasons related to the mechanisms of treatment and surface area controls the direct contact between the leaves and roots with the pollutants.

The assessment of the hypotheses will be based on:

  • If P ≤ 0.05, then reject the null hypothesis and accept the alternative hypothesis.

  • If P > 0.05, then accept the null hypothesis and reject the alternative hypothesis.

  1. Step No. 1.

    Testing the significance of the reduction (in %) of the concentrations of salts.

Salt ion

Na

Cl

SO4

K

TDS

Group A: L treatment

5%

5%

14%

4%

3%

Group B: R treatment

70%

66%

78%

74%

66%

Results of step no. 1

figure a

The reduction of salt concentrations by reed leaves is 6.2 ± 4.4% (which is very low) and 70.8 ± 5.2% by reed roots (which is considerable). The independent samples test shows the following results:

figure b

The above result is highly significant with confidence more than 99% level (P value = 0.000) to show that the root treatment has greater capability than leaf treatment in reducing the concentration of salts since the mean difference is 64.6%.

  1. Step No. 2.

    Testing the significance to reduce the concentrations of fluoride and lithium (in %).

F and Li ions

F

Li

Group A: L treatment

23%

86%

Group B: R Treatment

48%

100%

Analysis of the reduction of the concentration of F and Li by leaves is on average 54.5% while it is 74% by roots, which indicates that the roots have a better capability than the leaves to reduce the concentration of these ions.

  1. Step No. 3.

    Testing the significance to reduce the concentrations of heavy metals (in %).

Heavy metal ions

Fe

Zn

Cr

Co

Cu

Al

Cd

Group A: L treatment

98%

76%

72%

100%

64%

73%

100%

Group B: R Treatment

100%

100%

89%

100%

39%

53%

100%

Results of step 3

figure c

The reduction of heavy metal concentrations by reed leaves is 83.29 ± 15.46% while by reed roots 83.0 ± 25.91%. Both leaf and root treatments have the same mean. The independent samples test shows the following results:

figure d

From the t test with (P value = 0.98), the root and leaf treatments could not differ from each other. In other words, the treatment type does not affect on the concentrations of heavy metals.

Conclusions

This research has illustrated with evidence that reed plants are capable of effectively removing contaminants from the polluted shallow groundwater in Kuwait. The reduction percentage of contaminant concentration in Kuwait native and polluted groundwater is presented in Table 6.

In this study, the phytoremediation process was proved to be successful through decaying leaves and roots of the reed plants to reduce the concentrations of contaminants (salts ions, nitrogen compounds, and heavy metals). Table 6 shows that the roots of the reed plants can significantly reduce (Cl, Na, K, and SO4) by about 66–78%. Also, the TDS value was reduced by the roots by 66%. The reed plants were capable of removing the nitrogen compounds (nitrates and ammonium ions) with high percentage of reduction. However, N is needed (within limits) for plant growth; therefore, good fertilizers and irrigation management can help solve these problems. Nitrates should be kept for irrigation purposes in Kuwait in the region of 50 to 90 mg/l. Fluoride ion concentration was reduced by about 86% while the roots removed the concentration of lithium significantly. The concentration of the heavy metals in the native polluted groundwater is below the international standards (Rowe and Abdel-Magid 1995) but this research illustrates that the roots of the reed plants are capable to remove completely Cd, Co, Zn, and Fe. The reduction of the concentrations of the heavy metals (of Al, Cu, and Cr) by the roots of the reed plants was 53%, 39%, and 89% respectively.