Research Article | Open Access
S. Wiafe, R. Buamah, H. M. K. Essandoh, L. Darkwah, "Bioremediation of Soil and Water Contaminated with As, Hg, Cd, and Pb Using Heliconia psittacorum", Journal of Environmental and Public Health, vol. 2019, Article ID 3564727, 7 pages, 2019. https://doi.org/10.1155/2019/3564727
Bioremediation of Soil and Water Contaminated with As, Hg, Cd, and Pb Using Heliconia psittacorum
The activities of illegal mining prevalent in most part of Ghana has immensely contributed to the pollution of heavy metals and metalloids in both water and soils. This has resulted in the contraction of diseases associated with the ingestion of these pollutants. The use of macrophytes has been identified as one of the most cost-effective and efficient means to remediate these pollutants from the environment. This study employed the use of Heliconia psittacorum in remediating soils and water contaminated with Hg, As, Cd, and Pb. Uptake of Hg, As, Cd, and Pb by this aquatic plant species from metal-contaminated water and soil was studied in the batch culture experiment. The plants were irrigated with standard heavy metal simulated solutions. After 20, 40, and 60 days, the plant samples were subjected to heavy metal analysis by mass spectroscopy. The macrophyte was able to remediate all the four selected heavy metals in larger quantities and therefore can be used to remediate polluted water and soil.
The buildup of heavy metals and metalloids arising from anthropogenic activities such as artisanal mining impact the environment negatively, particularly soil and water bodies. These contaminants endanger and threaten the environment and sometimes cause irreparable and irreversible consequences. The remediation of these contaminants employs microorganisms and plants which degrade, detoxify, or sequester toxic chemicals present in natural waters and soils . Phytoremediation is an effective in situ technology which is applicable in the restoration of contaminated soils and waters . Heavy metal(loid)s are widely known to be nonessential elements for plants, and they can cause adverse effects on the plant’s photosynthetic system, chlorophyll synthesis, and antioxidant enzyme production, resulting in various forms of damage to the plants . Phytoremediation applications have been recommended as a cheaper and more effective alternative for the removal and recovery of heavy metals from aqueous solutions .
Several plant species has been tested and proved to be effective to take up heavy metals, translocate them into the shoots, and sequester them in non-metabolic-active tissues in less harmful forms . It is worth noting that most known hyperaccumulator species are selective toward one metal and would not be effective at multimetal mixes . The choice of plant species is an important issue in phytoremediation because they should survive the potential toxic effects of the influent and its variability. Aquatic plant species, including free-floating species such as Eichhornia sp., Lemna sp., Azolla sp., and Salvinia sp., submerged species such as Potamogeton sp. and Myriophyllum sp., or emergent species like Limnocharis flava, Typha sp., Scirpus sp., Spartina sp., Phragmites sp., and Cyperus sp., have shown potential for removing metals from different wastewaters [7–11]. Successful application of phytoremediation, however, depends on the identification of plant species (endemic and particularly indigenous species) with an appropriated suite of characteristics .
This work aimed to evaluate the performance evaluation of H. psittacorum in the remediation of water and soils polluted with Hg, As, Cd, and Pb. The specific objective was to determine the synergistic influences of the aforementioned heavy metal(loid)s on the uptake capacity of the macrophyte.
The ability of macrophyte and the extent to which they can retain these absorbed pollutants without leaching them back into the environment have not been thoroughly studied for the mentioned inorganic pollutants. The synergistic or inhibitory effect of the pollutants to the phytoremediation process is yet to be explored. The capacity of the H. psittacorum to survive various concentration and different concentrations of heavy metal(loid)s is also a grey area that needs to be investigated.
2. Materials and Methods
2.1. Location and Experimental Design
The experiment was carried out over a period up to 60 days in a greenhouse setting located at the Ministry of Food and Agriculture demonstration centre in Sunyani, Ghana (7.3502°N, 2.3430°W), under natural light condition (average radiation 542 μmol·s−1·m−2), photoperiod of 12:18 h, air temperature of 28°C, and 75% relative humidity. The experiment was conducted in February, 2018.
2.2. Batch Culture
Uptake of Hg, As, Cd, and Pb by H. psittacorum in metal-contaminated water and sediments was studied in batch culture experiment. Thirteen rectangular (pots) containers with dimensions; 0.26 m length, 0.14 m width, and 0.24 m depth were filled with 5 kg of garden soil which was used to grow the plants. Six plants were grown in each of the pots. The plants seedlings were obtained from the Horticulture Department of the Kwame Nkrumah University of Science and Technology, Kumasi, Ghana. The seedlings were two weeks old when purchased and were then transplanted into the pots. The plants were irrigated at the base of the soil with solutions containing 5 ppm of As, 5 ppm of Hg, 10 ppm of Cd, and 10 ppm of Pb in a simulated solution with 1 litre of deionised water to mimic the conditions that prevail in typical illegal gold mining catchment:where is the concentration in molarity (moles/liters) of the concentrated solution (heavy metal = 1000), is the volume of the concentrated solution (heavy metal = 10 mL), is the concentration in molarity of the dilute solution (after more solvent has been added), and is the volume of the dilute solution (deionised water = 500 mL).
The water used in the simulated solution had a temperature of 22°C and a pH of 6.8. The irrigation was conducted in a one-off episode (i.e., all through the experimentation period; the heavy metals-laden simulated water was applied only once for three days). In the control experimental batches, deionised water was used for the irrigation all through the experimental phase. The initial soil heavy metal(loid)s concentrations were analysed. After 20 days of cultivation, two out of the six plants in each of the pots were harvested and the quantity of heavy metals removed by the plants determined. This process was repeated after the 40 and 60 days of cultivation. During each harvesting episode, two plants from the control set were also harvested and analysed for heavy metals. The harvested plant samples were put in prelabelled polypropylene transparent bags. The bags were securely tired and placed in another bag which was then sealed with a duct tape. All the samples were stored in an ice chest with ice to maintain a low temperature of 4°C during transportation to the ecological laboratory of University of Ghana for analysis. The heavy metal content of the samples was determined using Atomic absorption spectroscopy. The results were expressed as mg/kg dry weight for plant samples.
The macrophyte was planted in thirteen different pots with the irrigation conducted in singular (Hg, As, Cd, or Pb) and in combination as shown in Table 1. The experiment was conducted in August, 2017.
The efficiency of phytoextraction was quantified by calculating the translocation factor (TF). The translocation factor indicates the efficiency of the plant in translocating the accumulated metal from its roots to shoots. It is calculated as follows:where is concentration of the metal in plant shoots and is concentration of the metal in plant roots .
Table 1 shows the irrigation regime of the experiment. The macrophytes (H. psittacorum) were grown in eleven different pots and irrigation carried out as shown in Table 1. Using Hg as a case study, the macrophytes were grown in separate pots and Hg as a single contaminant was used to irrigate the plant. Hg was then paired in simulated solutions with each of the other three metals (Hg + As, Hg + Cd, and Hg + Pb) and used in irrigating the plants in the other pots. Subsequently, Hg together with all the other three metals (Hg + As + Cd + Pb) were dosed into a simulated solution and used in irrigating the rest of the pots. Similar episode of irrigation regime were used for the other three metals (As, Cd, and Pb).
3.1. Mercury Uptake by Heliconia psittacorum
The levels of Hg uptake by the roots and shoots of the H. psittacorum from the simulated irrigation water were all higher than the levels observed in the control batch (Figure 2). Whilst the levels of uptake of Hg remained constant for the control batch over the entire period of study, both the roots and the shoots of the plant showed a consistent increase in the uptake of Hg with days. The level of uptake of Hg by H. psittacorum was found to be higher in the shoots than in the roots in situations where the irrigation water had Hg combinations/together with the three other metals (Hg + As + Cd + Pb); this consequently resulted in the translocation factor (TF) being more than one. The TF of the macrophyte was less than one in the first twenty days of cultivation when Hg was the only contaminant in solution; however, the TF exceeded one within the period of day 20 to day 60. On average, the uptake of Hg into the biomass of H. psittacorum was 12.33 mg/kg in the sixty days. This implies that given a land area of one square meter (1 m2) with an average level of 100 mg/kg soil of Hg metal, at least nine (9) of the H. psittacorum plant species will be required to remediate almost all the Hg-contaminated soil over a sixty-day period.
The uptake of Hg by H. psittacorum when in solution with either As (Hg + As), Cd (Hg + Cd), and Pb (Hg + Pb) was higher than in the control batch (Figure 3). The presence of the other heavy metals did not have any adverse effect on the absorption of Hg. There was an incremental rate of absorption of Hg when paired with As in solution within the first twenty days (TF > 1); the absorption in the shoots decreased marginally up to day 40 (TF < 1) and thereafter increased up to day 60 (TF > 1). The rate of Hg absorption by the roots of the macrophyte when paired with Cd increased steadily over the period of sixty days. The rate of Hg absorption by the shoots on the other hand declined after day 20 up to day 40. The rate of absorption however increased after day 40 to day 60 (TF > 1).
When paired with Pb, the rate of Hg absorption by both the roots and shoots of H. psittacorum increased steadily over the entire period of 60 days. The rate of absorption in the shoots was higher than the rate of absorption in shoots of the macrophyte (TF > 1).
3.2. Arsenic Uptake by Heliconia psittacorum
With As as the only contaminant in the irrigation solution, the roots of H. psittacorum exhibited a higher As absorption capacity than the shoots in the first forty days. On the other hand, the rate of absorption by the shoots of the macrophyte when As was in solution with Hg, Cd, and Pb (As + Hg + Cd + Pb) was higher than in the roots (TF > 1) over the entire period of 60 days. The use of H. psittacorum in the uptake of As was better when As was in solution with Hg, Cd, and Pb than when As was the only contaminant in solution.
On average, the uptake of As into the biomass of H. psittacorum was 2663.15 mg/kg in sixty days. Given a land area of one square meter (1 m2) with an average level of 10,000 mg/kg of As metal, at least four (4) of the H. psittacorum plant species will be required to remediate almost all the As-contaminated soil over a sixty-day period.
Arsenic analysis on samples taken from pots irrigated with water having the paired contaminant (i.e., As + Pb; As + Cd; As + Hg) gives an uptake level far higher than of that the control batch (Figure 5) for the first forty days. The uptake levels in the roots of the macrophytes exceeded that of the shoots (TF < 1). The levels of uptake by both the roots and the shoots drastically declined after forty day by more than 800 mg/kg. This situation may be attributed to reason that the macrophytes’ may have attained its saturation period after forty days of absorption of the As metal.
Comparing the levels of uptake in the shoots of the macrophyte to the levels in the control batch, it stands to reason that most of the As metals were absorbed from the soil/water into the roots of the macrophyte. As metal did not remain in the roots but most of the absorbed metals were able to be translocated into the shoots of the plant, indicating appreciable translocation rate.
3.3. Cadmium Uptake by Heliconia psittacorum
With regards to Cd absorption, the roots of H. psittacorum showed a higher capacity than the shoots in the first and last twenty days of the experiment when cadmium was either the only contaminant in solution or combined with the other three metals. The levels of Cd uptake was higher when in solution alone than when in solution with the other three metals. On an average, the uptake of Cd into the biomass of H. psittacorum was 68 mg/kg in the sixty days of the experiment. For a land area of one square meter (1 m2) with an average level of 100 mg/kg of Cd metal, at least two (2) of the H. psittacorum plant species will be required to remediate almost all the Cd-contaminated soil over a sixty-day period.
The uptake of Cd when paired with Pb (Cd + Pb); As (Cd + As); and Hg (Cd + Hg) as the contaminants in the irrigation water was appreciably higher than the control batch for the first forty days but experienced a decline afterwards. When Cd was paired with either As (Cd + As) or Hg (Cd + Hg), the translocation factors (TF) of the plant were more than one for the first twenty days. The TF of the plant was less than one over the entire sixty-day period when Cd was paired with Pb in solution. In all three scenarios, the levels of uptake in both the roots and shoots were appreciable for the first forty days and subsequently declined afterwards apparently because the macrophyte had reached its saturation limit.
3.4. Lead Uptake by Heliconia psittacorum
The levels of Pb uptake by the roots and shoots of the plant in the simulated irrigation water were all higher than the levels in the control batch. Whilst the levels of uptake of Pb remained constant for the control batch over the entire period of study, both the roots and the shoots of the plant showed a steady increase in the uptake of Pb with days. This indicates that the H. psittacorum is capable of remediating Pb metal from either soil or water. The performance of H. psittacorum in the uptake of Pb (when Pb was the only contaminant in the simulated irrigating water) had the translocation factor (TF) more than one after the first twenty days. The levels of Pb in the shoots first twenty days were very marginal but afterwards, there were exponential rise up to the fortieth day and subsequent gradual increase up to the sixtieth day.
In the case when Pb was analysed on samples taken from the pots irrigated with water having Hg, Pb, Cd, and As, the translocation factors (TF) were all less than one in the entire period of exposure. On an average, the uptake of Pb into the biomass of H. psittacorum was found to be 1189 mg/kg in sixty days. Given a land area of one square meter (1 m2) with an average level of 10,000 mg/kg of Pb metal, at least nine (9) of the H. psittacorum plant species will be required to remediate almost all the lead-contaminated soil over a sixty-day period.
The uptake of Pb when in paired solution with As resulted in a translocation factor of more than one over the entire period. When Pb was paired with Hg, the translocation factor of the macrophyte was more than one after forty days of absorption. Both the roots and shoots of the macrophyte did not show probable sign of uptake when Pb was in solution with Cd. The uptake of lead by H. psittacorum was inhibited by the presence of cadmium.
The evaluation made with respect to the performance of the macrophyte in the remediation of Hg, As, Cd, and Pb from contaminated water and soil showed that the plant had the capacity to bioaccummulate the contaminant from the environment particularly when the metals existed in a solution individually as the only contaminants or when all the four heavy metals (Hg + As + Cd + Pb) were in a simulated solution.
Generally, the macrophyte was able to absorb the Hg metal into its aerial parts (shoots) better than the roots when Hg was the only contaminant in solution or when Hg was in combination with As, Cd, and Pb (Hg + As + Cd + Pb). The absorption of mercury by root and shoot of H. psittacorum when Hg was in solution with As, Pb, and Cd (Hg + As + Cd + Pb) as contaminants was significant as it showed a difference from day 20 to 40 ( value = 0.00); the rate of absorption from day 40 to 60 was not statistically significant ( value = 0.806). The rate of Hg uptake when it was the only contaminant in solution did not show a significant difference between day 20 and day 40 in the roots of H. psittacorum ( value = 0.989), and there was a significant difference in the level of uptake between the fortieth and sixtieth days ( value = 0.002). In the shoots of the same plant, the levels of absorption were significant within the entire sixty-day period of exposure ( value = 0.000).
Madera-Parra et al.  assessed the accumulation of Hg amongst other heavy metals by Heliconia psittacorum in a constructed wetland, and the results showed a TF of more than one for Hg by Heliconia psittacorum. The results obtained by Madera-Parra et al. validates what has been established by this research.
The rate of absorption of As by the roots of H. psittacorum when Arsenic was in solution with Hg, As, Pb, and Cd as contaminants did not show any significant differences within the entire period of sixty days ( value = 0.879); the rate of absorption by the shoots showed a significant difference within the first forty days ( value = 0.011). The uptake of As in the situation where As was the only contaminant in showed a significant difference in the roots of H. psittacorum for the first forty days ( value = 0.000); there were no significant differences in the rate of As uptake between the fortieth and sixtieth days ( value = 1.00). In the shoots, the levels of absorption were significant within the entire sixty days of exposure ( value < 0.05). Generally, the uptake of As by H. psittacorum performed better when As was in solution with the other three metals.
Aksorn and Visoottiviseth  studying the capacities of various potential macrophytes (Typha spp., Canna spp., Colocasia esculenta, Heliconia psittacorum, and Thalia dealbato) for the absorption of As observed all the five macrophytes had different efficiencies for the absorption of As after 14 and 28 days of harvest. They however concluded that Colocasia esculenta was the best plant for removing arsenic from water for a 28 day exposure period. They also concluded that As accumulation by the emergent plants increased over the exposure period. Arsenic was accumulated mainly in the roots of the plants. The conclusions drawn from Ekkasit and Pornsawan goes to buttress the results obtained from this research.
The rate of absorption of Cd by the roots of H. psittacorum when it was in solution with the rest of the three metals (As + Pb + Hg + Cd) did not show any significant differences within the entire sixty-day period of exposure ( value > 0.05); however, the rate of absorption in the shoots of the same plant showed significant differences within the entire sixty-day period of exposure ( value < 0.05). When Cd was the only contaminant in solution which did not show a significant difference in the roots of H. psittacorum within the entire sixty days of exposure; however, there were significant differences in the level of uptake in the shoots of the same plant over the entire sixty-day period of exposure ( value < 0.05).
Ma  used T. capensis for the biomonitoring of Cd and other heavy metals, on the Bottelary River. His results indicated that the accumulation of Cd was mainly in the roots of T. capensis than the shoots (indicating a TF < 1). The results obtained from this research also shows that most of the Cd metals were accumulated in the roots than in the shoot of both macrophytes except when Cd was in solution with either As, Pb, or Hg.
The performance of H. psittacorum in the uptake of Pb when it was the only contaminant in solution or when in solution with the other three metals (As + Pb + Hg + Cd) resulted in translocation factor of more than one only on the fortieth day of cultivation. The paired combination of Pb with the other metals did not yield high translocation rate. Most of the Pb were absorbed and concentrated in the roots of the macrophytes with few of the Pb translocating into the shoots only on the first twenty days.
The absorption of Pb by roots of H. psittacorum when in solution with the other three metals having (As + Pb + Hg + Cd) did not show any significant differences within the entire period of sixty days ( value > 0.05); however, the rate of absorption by the shoot of the same macrophyte only showed a significant difference within the first forty days ( value = 0.014). When lead was the only contaminant in solution, there was a significant difference in the roots of H. psittacorum for the first forty days ( value = 0.012); however, there were no significant differences in the levels of uptake between the fortieth and sixtieth days ( value = 0.618). In the shoots of the same plant, the levels of absorption were significant within the first forty days ( value = 0.001); however, the levels of absorption in the shoots of the same macrophyte did not show any significant difference ( value = 0.996).
The results of this study give ample information about the uptake of Hg, As, Cd, and Pb by Heliconia psittacorum. In most of the cases, the levels of the heavy metals uptake by the macrophyte in the control batches (without any contaminant) were far less than those with contaminants in the simulated irrigating water. This gives credence to the macrophytes’ ability to absorb heavy metals into its biomass. The performance of H. psittacorum in the uptake of As, Hg, and Cd when each of them was the only contaminant in the simulated irrigating water or when analysed on samples taken from the pots irrigated water having all the four heavy metals as contaminants indicated the translocation factor (TF) to be more than one over the entire period of exposure and also showed an increase in uptake with days. This is an indication of the macrophytes ability to remediate As, Hg, and Cd in water and soil. However, in the situation where either mercury or arsenic was in soil or water with either cadmium or lead, and the TF was less than one. This indicates the inhibition of the mercury or lead by cadmium and lead by H. psittacorum absorption. The performance of H. psittacorum in the remediation of Cd and Pb in single dose also indicated a BF of more than one. The macrophyte is rhizomatous in its propagation, so new shoots keeps springing up from the creeping roots which prevents the absorbed heavy metals from leaching back into the soil/water and also; the rate of absorption is enhanced further from the new shoots which sprung up. The implications of these findings are very essential in the sense that the macrophytes has proven its ability to treat heavy-metal-polluted water and soil. Also, the use of this macrophyte in the treatment of heavy metal polluted water is very cheap and eco-friendly which of course may avert any adverse effect in the treatment of the polluted water/soil. From the foregoing, the performance evaluation of H. psittacorum in the remediation of Hg, As, Cd, and Pb was very good in terms of their abstraction from water and soil.
All the data obtained are primary, and materials used in conducting this research were of high accuracy and are readily available.
Conflicts of Interest
The authors declare that they have no conflicts of interest.
Samuel Wiafe and Richard Buamah carried out the laboratory and field work. Helen Essandoh and Lawrence Darkwah, respectively, conducted the heavy metal analysis and data analysis and the write ups.
This study was funded by the Regional Water and Environmental Sanitation Centre, Kumasi (RWESCK), at the Kwame Nkrumah University of Science and Technology, Kumasi, with funding from the Ghana Government and the World Bank under the Africa Centre’s of Excellence project'. The views expressed in this paper do not reflect those of the World Bank, Ghana Government, and KNUST.
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