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Arsenic - Adsorption and Translocation in Plants

As we know, dangerous arsenic (As) concentrations in natural waters is now a worldwide problem and often referred to as a 20th–21st century calamity. High arsenic concentrations have been reported recently from the USA, China, Chile, Bangladesh, Taiwan, Mexico, Argentina, Poland, Canada, Hungary, Japan, India and Vietnam.

Existing arsenic removal include technologies that have traditionally been used (oxidation, precipitation, coagulation, ion exchange and membrane separation) with far less attention paid to adsorption. Some low-cost adsorbents are as affective including treated slags, carbons developed from agricultural waste (char carbons and coconut husk carbons), biosorbents (immobilized biomass, orange juice residue) and some commercial adsorbents, which include resins, gels, silica, treated silica tested for arsenic removal come out to be superior.

Water hyacinth and duckweed are some of noxious weeds that has attracted worldwide attention due to its fast spread and congested growth, which lead to serious problems in navigation, irrigation, and power generation. On the other hand, when looked from a resource angle, it appears to be a valuable resource with several unique properties such as hyperaccumulation for wastewater treatment or phytoremediation.
Water Hyacinth, Duckweed and Water Lily are among aquatic freshwater plant that has and still being used as animal fodder, bioremediator, wastewater nutrient recovery and even biofuel.

Adsorption is the adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface. This process creates a film of the adsorbate on the surface of the adsorbent. This process differs from absorption, in which a fluid (the absorbate) is dissolved by or permeates a liquid or solid (the absorbent), respectively. Adsorption is a surface-based process while absorption involves the whole volume of the material.

Translocation is a change or transfer of location. In arsenic uptake, arsenic is translocation and accumulation in plant cells.

 

Live Plant as a Bioremediator

The duckweed (Lemna minor) was studied as a pollution monitor for the simultaneous accumulation of arsenic, cadmium, lead and mercury. One particular study found, that more than 70% of arsenic was removed after 15 days while another claims that viable duckweed biomass removed 85-90% of lead with an initial concentration of 5 mg/l. Duckweed is also temperature tolerant with rapid growth and is easy to harvest, it bears high potential for the cost-efficient use in wastewater treatments. The Devils Lake wastewater treatment, located in North Dakota, USA, utilizes these beneficial properties of duckweed and other aquatic plants in the treatment of municipal and industrial wastewater.

Water hyacinth (Eichhornia crassipes) removes arsenic from arsenic-contaminated drinking water. This effect depends on several factors, such as the amount of water hyacinth, amount of arsenic present in the water, duration of exposure, and presence of sunlight and air. On the basis of the present study, the authors suggest that water hyacinth is useful for making arsenic-contaminated drinking water totally arsenic free. Water hyacinth provides a natural means of removing arsenic from drinking water at the household level without monetary cost.

 

Dried Plant as a Bioremediator Experiment

With the characteristic of these hyperaccumulation plant knowledge, Dr. Mai Thanh Truyet suggest using dried plant over live plant which may have the following effects:

  • Reduce adsorption time
  • Increase arsenic quantity adsorbed
  • Arsenic retained in dried plant

  • The following experiments was conducted to confirm his theory:
  • Intitial Experiment
  • Quantity vs. Time Experiment
  • Soak Time Experiment
  • Remediation Prototype 1