Strategies for the Detection and Remediation of Arsenic in Contaminated Waters
Ryan Sitzesa, Sylvana Andreescub, Christina Ispasb
a Department of Civil, Architectural and Environmental Engineering, University of Missouri-Rolla, Rolla, MO
b Department of Chemistry, Clarkson University, Potsdam, NY
Arsenic remains to be a major health concern in northern United States, Bangladesh, India, and China, among other areas. The recent decrease of the maximum allowable concentration of arsenic from 50 to 10 µg/L by the Environmental Protection Agency (EPA) and the maximum suggested level of arsenic to 10 µg/L by the World Health Organization (WHO) has placed an increased demand for more effective treatment technologies and feasible detection methods with lower detection limits.
Conventional treatment technologies include coagulation, adsorption, ion exchange resins, activated alumina, membrane methods such as reverse osmosis and nanofiltration, iron coated sand, and oxidation to less toxic forms, among others, which cannot effectively remove arsenic to the new MCLs set by the EPA and recommended by the WHO. Advanced treatment options to remove trace amounts of arsenic remain costly and are difficult to implement full-scale outside of the lab.
Recent advancements in nanoparticle technology have found that arsenic can be effectively and economically removed under low magnetic fields (~1T) when adsorbed onto iron oxide nanoparticles [6]. The current study investigates whether or not effectiveness of arsenic removal can be enhanced by encapsulating iron oxide nanoparticles with chitosan and alginate based biomaterials. Alginate and chitosan biomaterials have enormous potential as a matrix for metal nanocomposites in environmental applications [9].They are highly biocompatible and exhibit such properties as gel-forming and heavy metal chelation [5]. Alginate and chitosan have the ability to remain stable throughout a wide variety of environmental conditions [14], and have been applied extensively for enzyme immobilization [5],for biosensors [8], drug delivery [1,12], and metal removal [3, 21], among others. Encapsulating magnetic nanoparticles offers many advantages, including reducing direct exposure of potentially toxic nanoparticles to workers or the environment, greater immobilization and manageability of nanoparticles, and potentially enhanced metal removal through added chelation properties and increased surface area for adsorption.
Detection and speciation proves to be one of the greatest challenges in arsenic studies. After speciation with ion chromatography, arsenic can be assayed using inductively coupled plasma mass spectrometry (ICPMS) [10]. However, such an option is very expensive and time consuming for optimization experiments and cannot be feasibly implemented for adsorption studies. Graphite furnace- atomic adsorption spectroscopy (GF-AAS)is a potential alternative [11], but does not exhibit as low of a limit of detection. Other forms of atomic adsorption spectroscopy, such as atomic fluorescence spectroscopy or flameless atomic adsorption coupled with gas-liquid chromatography, is also feasible after hydride generationas a pre-concentration/reduction stepor pre-derivatization/chelation with iodide derivatives [2, 7, 15, 16, 19]. However, hydride generation introduces time-consuming and unneeded complicated steps. Electrochemistry, specifically stripping voltammetry, has been found to be much simpler and very sensitive in the detection of arsenic under diverse conditions [4, 17, 23], and has the ability of indirect speciation in cases where direct speciation is not possible.
Iron Oxide nanoparticles were synthesized according to modified existing methods [13, 18, 20, 22] and encapsulated in a two-step process: dispersion into prepared chitosan and alginate solutions, and cross-linkage with calcium chloride and sodium tripolyphosphate. Magnetic nanoparticles retained magnetic properties after successful encapsulation, as shown in Figure 1, and exhibited rapid arsenic removal. Results indicate that factors such as pH, initial arsenic concentration, types of polymer arrangements, etc. need to be explored further to form statistically sound comparisons and conclusions based on existing treatment technologies. Detection of arsenic was investigated using various types of electrodes, electrolytes, and nanoparticle deposition methods at varying pHs and concentrations for optimization. Figure 2 illustrates a gold-nanoparticle modified glassy-carbon electrode used during the study. Conclusions made from electrochemical optimization highlight the unique challenges and phenomena of the method, as well as discussions of the applicability to arsenic studies.
Figure 1: Encapsulated magnetic nanoparticles before and after being introduced to a magnetic field
Figure 2: gold-nanoparticle modified glassy-carbon electrode
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Environmental Engineering (2007)
Environmental Sustainability REU Program
Advisor: Silvana Andreescu, PhD