Microwave Popcorn Bag
The concern about microwave popcorn bag has increased in the last few years in terms of the waste and their harmful impacts on the environment. A study shows that food packaging accounts for almost two-thirds of the total volume of packaging waste. In addition, the coating materials used in microwave popcorn bags can have negative effects on the environment. Researchers have detected toxic chemicals in the bags, such as perfluorinated compounds (PFCs) and their potential precursors. PFCs are environmentally persistent, bioaccumulative and potentially harmful. Among PFCs, perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) have been reported to be toxic. Perfluorocarboxylic acids (PFCAs) precursors are proved even more toxic than PFCAs themselves. In addition, due to the persistence and mobility properties of PFOA, it has been detected in water, soil, air, and wildlife. To minimize the harmful impacts of PFCs on the environment, people have developed many treatment methods to remove them from aqueous solutions.
Harmful chemicals
Researchers have detected many PFCs in microwave popcorn bags used as coating materials for oil and moisture resistance. The most commonly studied PFCs are PFOA and PFOS. The amount of PFOA in some microwave popcorn bags is determined as high as 300 ug kg . Besides PFOA and PFOS, Moral et al. also determined other perfluorocarboxylic acids (PFCAs) in popcorn packaging, including perfluoroheptanoic (PFHpA), perfluorononanoic (PFNA), perfluorodecanoic (PFDA), perfluoroundecanoic (PFUnA), and perfluorododecanoic (PFDoA) acids.
PFCs are toxic, non-biodegradable and stay in the environment persistently. Accumulation of PFCs in living organism can exert adverse effects in lab animals, aquatic life and human. A study in rats has found that PFOA can induce liver, testes, and pancreatic tumors. The exposure of PFOS to rats may also results in abnormal glucose and lipid homeostasis in the gestational and lactational adulthood. PFCs have been found to inhibit the communication system and the gene transcription in rats. In addition, a study also suggested that PFOA exposure was associated with kidney and testicular cancer in people living near chemical plants. PFOA and PFOS can also cause membranous damage associated with apoptosis and DNA damage in aquatic organisms (particularly in fish) and negative effect on population growth rate of rotifer. However, although the production of PFOA and PFOS was reduced, the production of fluorotelomer-based chemicals applied to food contact papers is still increasing. Some compounds, such as polyfluoroalkyl phosphate surfactants (PAPs) or fluorotelomers (FTOH), have been used in some brands of microwave popcorn bags. Once PFCs are released into the environment, they become contaminants. Evidence shows that water, air, soil, and wildlife have been contaminated by PFCs. For example, PFOA concentrations was up to 0.9 micrograms per liter (µg/L) in some wells in Minnesota between 2004 and 2008, and 0.4 µg/L is the provisional Health Advisory for PFOA in drinking water developed by EPA in 2009.<ref name=":7" /> Besides, Giesy and Kannan detected PFCs in fish, birds, and marine mammals around the world.<ref name=":0" /> People also detected PFOA in the arctic media and biota.<ref name=":1" /><ref name=":2" />
Because of the large amount of production of microwave popcorn bags, they have also become a significant contaminant source (PFCs) to the environment. Due to the disposal of coated paper and manufacturing activities, PFOA has also been detected in wastewater and biosolids.<ref name=":8" /> Soil near disposal sites are contaminated by PFOA as well.<ref name=":3" />
Remediation techniques
Remediation methods
To reduce the destructive impacts of PFCs on the environment, people have developed many technologies to remove PFCs from aqueous solutions, including adsorption, ion exchange, membrane separation, photochemical oxidation, ultrasonication, bioremediation, plasma oxidation, and other techniques.<ref name=":4" /> These technologies require harsh treatment conditions, cause high energy consumption, and cannot be applied in large scale.<ref name=":4" /> Electrochemical oxidation (EO) is a promising technique to remove PFCs from contaminated wastewater. It has many advantages, such as relatively lower energy consumption, milder conditions, and higher removal efficiency.<ref name=":4" />
Electrochemical oxidation mechanism
The EO mechanism and the pathways of both PFCAs and PFSAs are stated below. At the beginning, the carboxyl or sulfonic acid group of PFCs transfer an electron to the anode, and the PFCs radical (C<sub>n</sub>F<sub>2n+1</sub>COO· or C<sub>n</sub>F<sub>2n+1</sub>SO<sub>3</sub>·) are formed. PFCs radicals are unstable, and perfluoroalkyl radicals (C<sub>n</sub>F<sub>2n+1</sub>·) are produced. Then, the C<sub>n</sub>F<sub>2n+1</sub>· radicals react with OH, O<sub>2</sub>, and H<sub>2</sub>O in four possible routes as shown in Cycle A, Cycle B, Cycle C and Cycle D.<ref name=":4" /> The detailed reaction processes are as follows:
C<sub>n</sub>F<sub>2n+1</sub>COO →C<sub>n</sub>F<sub>2n+1</sub>COO⋅+e
C<sub>n</sub>F<sub>2n+1</sub>COO⋅→C<sub>n</sub>F<sub>2n+1</sub>⋅+CO<sub>2</sub>
C<sub>n</sub>F<sub>2n+1</sub>SO<sub>3</sub> →C<sub>n</sub>F<sub>2n+1</sub>SO<sub>3</sub>⋅+e
C<sub>n</sub>F<sub>2n+1</sub>SO<sub>3</sub>⋅+H<sub>2</sub>O→C<sub>n</sub>F<sub>2n+1</sub>⋅+SO<sub>4</sub> +2H
In Cycle A:
C<sub>n</sub>F<sub>2n+1</sub>· + ·OH → C<sub>n</sub>F<sub>2n+1</sub>OH
C<sub>n</sub>F<sub>2n+1</sub>OH + ·OH → C<sub>n</sub>F<sub>2n+1</sub>O· + H<sub>2</sub>O
C<sub>n</sub>F<sub>2n+1</sub>O·→ C<sub>n-1</sub>F<sub>2n-1</sub>· + CF<sub>2</sub>O
In Cycle B:
C<sub>n</sub>F<sub>2n+1</sub>OH → C<sub>n-1</sub>F<sub>2n-1</sub>CFO + HF
C<sub>n-1</sub>F<sub>2n-1</sub>CFO + H<sub>2</sub>O → C<sub>n-1</sub>F<sub>2n-1</sub>COO + HF + H
C<sub>n-1</sub>F<sub>2n-1</sub>CFO +·OH → C<sub>n</sub>F<sub>2n</sub>O<sub>2</sub>H·
C<sub>n</sub>F<sub>2n</sub>O<sub>2</sub>H· → C<sub>n-1</sub>F<sub>2n-1</sub>COO· + HF
In Cycle C:
C<sub>n</sub>F<sub>2n+1</sub>· + O<sub>2</sub> → C<sub>n</sub>F<sub>2n+1</sub>OO·
C<sub>n</sub>F<sub>2n+1</sub>OO· + R<sub>F</sub>COO· → C<sub>n</sub>F<sub>2n+1</sub>O· + R<sub>F</sub>CO· + O<sub>2</sub>
C<sub>n</sub>F<sub>2n+1</sub>O· → C<sub>n-1</sub>F<sub>2n-1</sub>· + CF<sub>2</sub>O
COF<sub>2</sub> + H<sub>2</sub>O → CO<sub>2</sub> + 2HF
In cycle D, volatile fluorinated organic contaminants are released.
EO technique also has some disadvantages, such as high cost and complexity of setting up and operating an electrochemical cell. Due to these disadvantages, EO has not yet been commercialized.<ref name=":4" />
 
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