Anthropogenic activities have polluted soil and aquatic ecosystems by introducing harmful heavy metals (HMs) such as cadmium, copper, mercury, lead, manganese, nickel, zinc, and others. These HMs lead to serious health conditions in humans like cancer, skin lesions, birth defects, liver and kidney damage, and mental retardation leading to other disabilities. Conventional methods of HM remediation of contaminated soil and water include physical, chemical, biological, and integrated methods. The use of physical and chemical methods, in isolation, has been reduced in practice, owing to their negative impacts, however, work on suitable integrated approaches, and the use of organisms for HM remediation has been in steady progress since past few decades. These approaches have proved to be eco-friendly, cost-effective, and show reduced negative impacts on the environment and biota. However, there is consistent increase in anthropogenic contribution to this problem, so, to keep pace with it, more recently work is in advancement on exploiting the biological system to increase the efficiency of bioremediation, using the latest technologies such as genetic engineering and nanotechnology. This paper provides an overview of the current methods deployed to address this problem, developments made in this field in past few decades, and evokes a research thrust that might lead to novel remediation approaches in the future.

This research aims to study the effect of Mycorrizal fungus and Plant-Growth-Promoting Bacteria (PGPB) on Cadmium (Cd) uptake by one-year-old Eucalyptus Camaldulensis seedlings. The treatments have involved three levels of heavy metal (0, 30, and 60 mg/kg) for Cd, and three bacterial levels (no bacteria (B0), Bacillus (Ba105), and Pseudomonas (Ps36, Ps448)), inoculated with mycorrhizal fungus Glomus mosseae (M1) and non-inoculated with fungus (M0). Results show that absorption of these elements in plant increased as Cd concentration in soil became more. Inoculation by Ps448 bacteria had an incremental effect on Cd uptake by 90%, compared to the non-inoculated (control) samples. Moreover, inoculation of the plants with mycorrhizal fungus increased Cd uptake by 24%, compared to the control. Also, it has been observed that plant resistance to metal stress and plant growth under such conditions ascended in treatments wherein inoculation happened with mycorrhizal fungus and bacteria. The highest Cd heavy metal uptake has been observed in Eucalyptus (shoots and roots), treatment (C2B2M1) with 648.19 micrograms per one seedling in pot. According to the obtained results, Eucalyptus with biological factors (fungi and bacteria) has the ability to clean and purify the contaminated soil with Cd heavy metal.

This research compares the performance of floating systems planted with Vetiveria zizanioides as a hydroponic approach for removing nutrients from two contaminated waters. For this purpose, two pilots with overall net volume of 60 litres were constructed and inoculated by secondary treated domestic wastewater (STDW) and irrigation water obtained from Minab reservoir (IWMR) in batch mode. Regarding the experimental results, the total nitrogen removal efficiency reaches more than 40 and 75%, in two and four days’ detention time, respectively, while these figures are 75 and 85% for phosphorus. The comparative statistical analyses verify that the results reveal significant differences in nitrogen removal, its uptake and the shoots’ dry weight. Conversely, phosphorus removal, its uptake and the roots’ growth are not significantly different. The regression analysis shows that the nitrogen uptake is well correlated with the shoots’ expansion rate as a matter of substrate type. The decay coefficient rates of nitrogen and phosphorus are calculated as 0.43 and 0.52 day-1, respectively. It is then concluded that this system should be used for wastewater treatment rather than for surface water purification. However, it can be recommended as an environmental friendly approach for both, because of the high efficiency in nutrients’ removal and the aeration capability.

Phytoremediation is an eco-friendly method for removal of pollutants, which can be relied upon as a sustainable technology, if implemented under optimum conditions of plant growth. The effectiveness of water hyacinth, a topical weed, for the removal of Zinc (Zn) and Chromium (Cr) ions from aqueous solutions has been presented in this article. The potential of this plant in removing metals by phytoremediation was explored under various environmental factors such as pH, salinity, metal concentrations, available nutrients, and so on. The efficiency of metal removal was observed by varying the different parameters. It was found that the maximum removal of metals occurred at a neutral pH, low amount of salinity, lower metal ion concentrations, and lack of nutrients. The stress induced in a plant by metal absorption was visible from the health and growth pattern of the plants. The stress on water hyacinth due to metals was also assessed, by observing the changes in its chlorophyll and protein content.

Duckweeds are of special interest, as they are naturally growing weeds that have the capacity to tolerate and remove toxic pollutants, including heavy metals from the environment. Studies have revealed that duckweed (Lemna minor) can tolerate and remove heavy metals from aqueous solutions. In the present study, the efficiency of L. minor in the removal of Ni and Cr individually from aqueous solutions was investigated at concentrations of 3.05, 3.98 and 4.9 mg/L for Ni and 1.91, 2.98, and 4.2 mg/L for Cr. Experiments were run for 22 days, after which the metal content in the plant was estimated by atomic absorption spectrophotometer (AAS). The duckweed showed higher percentage of Ni removal than Cr. Specific Growth Rate (SGR) was found to be reduced at high concentrations of both Ni and Cr. Statistical analysis suggested that the growth of the plant was affected by the toxic effect of both Ni and Cr. Bioaccumulation of Ni was higher than Cr in L. minor. The mechanism of removal of both Ni and Cr followed second order kinetics. It is suggested that these duckweeds can remove Ni and Cr from aqueous solution and can also accumulate the same in considerable concentrations, at low initial metal concentrations.

In this study, in the removal of macro (P, S, Na, K, Ca, Mg) and micro (Sb, Ba, Co, Cu, Fe, Pb, Mn, Hg, Mo, Se, Ag, Zn) elements in the effluent of Elazig Wastewater Treatment Plant, the efficiency of Lemna minor L. and Lemna gibba L. has been studied comparatively. For this aim, fronds of these plants have been adapted to the effluent of the treatment plant that feeds pilot scale reactors. The concentrations of elements in fronds harvested during the working period were analyzed by ICP/MS. The analytical results show that Lemna minor L. has a high accumulation potential for P, Sb, Ba, Co, Fe, Pb, Mn, Hg, Ag and Zn while Lemna gibba L. has a high accumulation potential for S, Na, Ca, Mg, Cu, Mo and Se. The results show that Lemna minor L. and Lemna gibba L. can be used as phytoremediators of wastewater.

The current study assesses the effect of fibrous clay minerals’ amendments and arbuscular mycorrhiza incubation on heavy metal uptake and translocation in Eucalyptus grandis and Ailanthus altissima plants. For doing so, Eucalyptus and ailanthus trees have been grown in a soil sample, contaminated with heavy metal iron ore mining and collected from southern Iran. The area under study is arid, with the majority of trees being ailanthus and eucalyptus. Amounts of Cd, Pb, Zn, Cu, and Mn have initially been at toxic levels which declined after cultivation. Fibrous clay minerals have been added to soils as a natural adsorbent to adsorb heavy metals like Pb, Cd, Zn, and Mn. Accumulation of the elements in the roots and shoots has been in the following order: Cu>Zn>Mn>Cd>Pb>Fe. The organ metal concentrations have not statistically translocated from roots to shoots of plants, except for Zn and Cu whose concentrations have been significantly higher in roots. Eucalyptus is well capable of extracting elements from contaminated soils, compared to ailanthus, particularly in case of Cu and Cd. The percentage of mycorrhizal colonization proves to be more in pots with ailanthus plants grown in contaminated soil, suggesting enhanced effect of high metal concentrations on plant infection by G. mosseae. AMF assists soil remediation by enhancing the growth and retention of toxic elements by ailanthus, while no substantial change has been observed between inoculated and non-inoculated eucalyptus plants by AFM, regarding translocation of elements to plants. The possibility of increasing metal accumulation in roots is interesting for phytoremediation purposes, since most high-producing biomass plants, such as eucalyptus, retain heavy metals in roots.

Phytoremediation is an emerging green technology that uses plants and their associated microbes to remediate different environments contaminated with various pollutants. Phytoremediation, as an effective soil remediation technology, has gained popularity in the past ten years both in developed and developing countries. The main goal of the current article is to improve the understanding of phytoremediation of organic pollutants with emphasis on hydrocarbons. To design phytoremediation systems and also enhancement of their efficiency, either in laboratory or in field experiments, there is a serious need for better knowledge of phytoremediation mechanisms and also of factors affecting phytoremediation. In addition to phytoremediation applications, advantages, and limitations, its mechanisms and related new developments have been discussed in this article.

The aim of this study was to compare the selected aquatic plants ability to remove nitrate from wastewater. Excess of these nutrients in water can directly affect human health (methemoglobinaemia) or indirectly through the products of secondary pollution include eutrophication. Negative impact of nutrients excess in surface water often causes the destruction of water ecosystems, and therefore, common substances of these elements must be monitored and managed. Spectrophotometric technique was commonly used for quick and simple analyses of nutrients in waste water. There are calibration curves for each nutrient and for the determination of their concentration. Phytotechnology is one of the biological wastewater treatment methods or processes to eliminate nitrate contaminant from aquatic system. So as to avoid the eutrophic formation of fresh water and to determine the efficiency of nitrate utilization by specific aquatic plants which include Utricularia aurea and Salvinia molesta were collected from a eutrophic lake at Theerthamkara, Kerala. The samples were allowed to grow in nitrate solution for about one month at different concentrations. The optical density (OD) of nitrate solution at 410 nm was measured on alternative days of the experiment by using UV spectrophotometer. After 33 days of treatment periods, the maximum amount of nitrate removed in terms of percentage was found to be 95% by Utricularia aurea and 92% by Salvinia molesta at 100 ppm nitrate concentration. The results revealed that the aquatic plant (carnivorous) based system of phytotechnology was productively removed the nitrate load from the synthetic wastewater containing nitrate.

Heavy metal contaminated soil raises major global environmental and agricultural concern. Recently soil pollution through lead (Pb) and chromium (Cr) becoming serious problem and remediation or utilization of those contaminated soil with potential crops is of the outmost importance. The objectives of present study were to examine the effects of Pb and Cr on three different kenaf and mesta varieties for seed germination, seedling establishment and amount of Pb and Cr uptake by tested varieties in laboratory condition. Three varieties were used for the study namely, HC-95 (kenaf), CPL-72126 (mesta) and Samu-93 (mesta) and the treatments were combination of Pb and Cr chemical at (0,0), (60,60), (80,80), (100,100) and (120,120) mg/L. Increased level of lead and chromium gradually reduced the germination percentage and primary growth parameters compared to control. The shoot and root lengths were affected only little, whereas, the biomass showed a considerable reduction with the increase of Pb and Cr toxicity. Stress tolerance indices showed a gradual and negative response by the plant with the increase of metal concentrations. However, in all the levels of Pb and Cr treatment, the seedlings were capable to tolerate the toxicity and seedlings were established. Bioaccumulation of Cr was higher than that of Pb in all varieties and in all treatments. The interaction of Pb and Cr reduced the toxic effect of both metals to the plants. The findings are helpful for selecting fiber crop varieties for cultivation in contaminated soils or phytoremediation of Pb and Cr from the contaminated soils.