Greetings to all users of the #Hive platform, especially to the friends of the @STEMsocial community, in this entry I will present descriptive content related to phytoremediation as a technique to recover polluted water ecosystems, this due to the serious problem of pollution that crosses water ecosystems, mainly by accumulation of nutrients, heavy metals, and excessive proliferation of aquatic biomass in both natural and artificial wetlands, product of the discharge of contaminated wastewater from domestic, industrial, agricultural and livestock, causing serious problems of socio-economic and environmental.
The incorporation of nutrients and heavy metals into water ecosystems, either through wastewater discharges or through the excess of mineral elements produced by agricultural and livestock activities, has led to a continuous deterioration of surface and groundwater quality on a global scale.
These nutrients and heavy metals have been classified as pollutants because they often enter the water through surface runoff associated with conventional agricultural activities, where considerable amounts of synthetic fertilizers and other agrochemicals are applied, creating chemical and biological imbalances in the aquatic environment.
With regard to livestock production, mainly cattle and buffalo, play an important role in the discharge of mineral elements and heavy metals, which are found in the organic matter generated in these production units and are added to these wetlands causing imbalance and in most cases chemical toxicity.
Contamination of water ecosystems
The pollution of most water bodies is caused by high concentrations of nutrients and heavy metals, which is alarming because of the problems this causes to ecosystems and human health worldwide. It is known that these problems persist because of inefficient treatment of industrial and agricultural water, which constantly contributes to the spread of organic and inorganic pollutants.
Fig. 2 The excessive proliferation of plant species in aquatic ecosystems is due to the presence of high amounts of nutrients. Author: @lupafilotaxia.
Main heavy metal pollutants
Among the heavy metals found in wetlands, we can name aluminum (Al), considered the most abundant metal, this element causes adverse health effects when exposed to high levels (100 mg/m3).
Fig. 3 Aluminum causes adverse effects on aquatic fauna. Author: @lupafilotaxia.
Cadmium (Cd), another metal that enters water bodies through various natural and anthropogenic sources such as fertilization with phosphate and nitrogen products, is also found in manure defecated by animals that have consumed phosphate foods. It has been reported that cadmium has chronic health effects, particularly on the kidneys, bones, and lungs, and causes neurotoxic, teratogenic, and endocrine disrupting effects.
Fig. 4 Cadmium often causes neurotoxic effects. Author: @lupafilotaxia.
Another of the heavy metals present in the wetlands is copper (Cu), it is found in many different forms, such as free ion in dissolved state, or as soluble complexes with organic or inorganic compounds, this metal has great affinity with organic matter, within the main sources of anthropogenic income of copper to the different bodies of water, come from the agricultural activity, through the application of agrochemicals to control phytosanitary problems in crops, in addition to the application of different types of organic waste and discharges of livestock manure.
Fig. 5 Copper has great affinity with organic matter. Author: @lupafilotaxia.
Mercury (Hg) is also released into rivers, lakes and other water sources through anthropogenic processes. In the particular case of Venezuela, the Caroní River basin has been suffering from excessive gold and silver exploitation for more than a decade, with an alarming percentage of informal mining, which does not rigorously contemplate the environmental control standards required by this activity..
Fig. 6 Mercury is often released into water ecosystems through mining activity. Author: @lupafilotaxia.
Another metal present in wetlands is nickel (Ni), whose concentration in aquatic environments has increased considerably, mainly due to mining, the burning of inorganic and organic waste and the discharge of industrial and municipal waste.
Fig. 7 Nickel generally reaches hydraulic ecosystems through industrial and municipal waste discharges. Author: @lupafilotaxia.
Lead (Pb), is also a metal present in water bodies, is known to have entered as a result of oil activity, gasoline and its concentrations of Pb, is the main source of pollution due to the irrational use of industrial processes, combustion of solid waste and agricultural.
Fig. 8 Lead enters water ecosystems as a result of oil activity. Author: @lupafilotaxia.
Techniques used in the decontamination of water ecosystems
It is important to point out, that the increasing concentrations of nutrients and heavy metals, is related to the scarce activities of elimination of these toxic elements, either by oxidation, reduction, chemical precipitation, filtration, electrochemical treatment, evaporation among others, on the one hand these conventional practices have been stopped because of their high operational costs and taking into account that these metals are not biodegradable, has opted to develop new technologies more friendly to the environment, namely:
Bioremediation is the most widely used technique to purify contaminated soil and water bodies, using the metabolic potential of microorganisms, such as bacteria, fungi and yeasts, in order to degrade and transform organic contaminants into simpler compounds that are little or not at all polluting. One of the most common cases is the transformation of hydrocarbons into water and carbon dioxide.
This phytotechnology, takes advantage of the removal capacity of certain aquatic macrophytes to absorb, accumulate, metabolize, mineralize and transform pollutants present not only in the water of rivers, lakes, lagoons, drainage channels, but also decontaminate the soil and air.
Phytoremediation has become the technique par excellence to eliminate heavy metals in contaminated water bodies. On the one hand, it is easy to apply and of low operational cost, it is only necessary to use species of aquatic macrophytes and generate favorable conditions for their proliferation.
Fig. 9 The proliferation of aquatic biomass in fisheries ecosystems. Author: @lupafilotaxia.
Phytoremediation as a method to remove heavy metals in water ecosystems
Some aquatic plant species, such as Eichhornia crassipes and materials of the family Lemnaceae, such as Lemna gibba and Lemna minor, have been evaluated under controlled conditions in order to know their phytoremediation capacity of certain heavy metals, and it has been found that the species L. minor presents more efficient in removing Ni than E. crassipes when it is exposed to low concentrations, which demonstrates that this aquatic macrophytes can be used for the phytoremediation of waters contaminated with this metal.
It has also been evaluated, the effect of photoperiod in the removal of Pb by Lemna gibba and in its growth rate, the results reveal that the photoperiod favors the absorption of Pb in this aquatic species. It has also been determined the phytoremediation capacity as an alternative in the remediation of mercury-contaminated waters, being found a considerable efficiency of this species to remove Hg from the water at 30% Hg. Another important data is that the concentrations of nitrogen and phosphorus present in the vegetative structures of this aquatic macrophyte are not affected by the levels of mercury.
Fig. 10 Aquatic plant species have the ability to transform pollutants present in agricultural drainage channels. Author: @lupafilotaxia.
The aquatic macrophytes, Pistia stratiotes, Lemna spp., Potamogeton pectinatus, Salvinia, Myriophyllum spicatum, Vallisneria spirallis, Hydrilla, Azolla and Phragmites australis, can absorb heavy metals in large quantities, therefore, this phytoremediation capacity is only a biological ability, which can be used to improve water quality through the accumulation of toxic elements in the root systems of these aquatic species.
CONTRIBUTIONS OF THIS PUBLICATION
- This capacity to hyperaccumulate nutrients and heavy metals, make these aquatic plant species, potential organisms for research, especially for the treatment of industrial effluents and wastewater, hence, the biomasses of these aquatic plants are considered as biological resources of great utility phytoremediation, therefore, they can be used for the development of bioabsorbent materials of heavy metals.
BIBLIOGRAPHICAL REFERENCES CONSULTED AND CITED:
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 Bunluesin S., Kruatrachue M., Pokethitiyook P., Upatham S., and Lanza, G. Batch and Continuous Packed Column Studies of Cadmium Biosorption by Hydrilla verticillata Biomass. Journal of Bioscience and Bioengineering. 2007; 103; 6: 509 – 513. Article: Online access
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