Difference between revisions of "User:Jhurley/sandbox"

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(Transformation Processes)
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| Physical Description</br>(at room temperature) || Colorless to straw-colored liquid
 
| Physical Description</br>(at room temperature) || Colorless to straw-colored liquid
 
|-
 
|-
| Molecular weight</br>(g/mol) || 147.43
+
| Molecular weight (g/mol) || 147.43
 
|-
 
|-
| Water solubility at 25°C</br>(mg/L)|| 1,750 (slightly soluble)
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| Water solubility at 25°C (mg/L)|| 1,750 (slightly soluble)
 
|-
 
|-
| Melting point</br>(°C)|| -14.7
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| Melting point (°C)|| -14.7
 
|-
 
|-
| Boiling point</br>(°C) || 156.8
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| Boiling point (°C) || 156.8
 
|-
 
|-
| Vapor pressure at 25°C</br>(mm Hg) || 3.10 to 3.69
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| Vapor pressure at 25°C (mm Hg) || 3.10 to 3.69
 
|-
 
|-
 
| Density at 20°C (g/cm<sup>3</sup>) || 1.3889
 
| Density at 20°C (g/cm<sup>3</sup>) || 1.3889
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==Transformation Processes==
 
==Transformation Processes==
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[[File:123TCPFig2.png|thumb|left|Figure 2. Figure 2. Summary of anticipated primary reaction pathways for degradation of TCP. Oxidation, hydrolysis, and hydrogenolysis are represented by the horizontal arrows. Elimination (dehydrochlorination) and reductive elimination are shown with vertical arrows. [O] represents oxygenation (by oxidation or hydrolysis), [H] represents reduction. Gray indicates products that appear to be of lesser significance<ref name="Tratnyek2010"/>.]]
 
Potential TCP degradation pathways include hydrolysis, oxidation, and reduction (Figure 2). These pathways are expected to be similar overall for abiotic and biotic reactions<ref name="Sarathy2010">Sarathy, V., Salter, A.J., Nurmi, J.T., O’Brien Johnson, G., Johnson, R.L., and Tratnyek, P.G., 2010. Degradation of 1, 2, 3-Trichloropropane (TCP): Hydrolysis, Elimination, and Reduction by Iron and Zinc. Environmental Science and Technology, 44(2), pp.787-793.  [https://doi.org/10.1021/es902595j DOI: 10.1021/es902595j]</ref>, but the rates of the reactions (and their resulting significance for remediation) depend on natural and engineered conditions.  
 
Potential TCP degradation pathways include hydrolysis, oxidation, and reduction (Figure 2). These pathways are expected to be similar overall for abiotic and biotic reactions<ref name="Sarathy2010">Sarathy, V., Salter, A.J., Nurmi, J.T., O’Brien Johnson, G., Johnson, R.L., and Tratnyek, P.G., 2010. Degradation of 1, 2, 3-Trichloropropane (TCP): Hydrolysis, Elimination, and Reduction by Iron and Zinc. Environmental Science and Technology, 44(2), pp.787-793.  [https://doi.org/10.1021/es902595j DOI: 10.1021/es902595j]</ref>, but the rates of the reactions (and their resulting significance for remediation) depend on natural and engineered conditions.  
  
 
The rate of hydrolysis of TCP is negligible under typical ambient pH and temperature conditions but is favorable at high pH and/or temperature<ref name="Tratnyek2010"/><ref name="Sarathy2010"/>. For example, ammonia gas can be used to raise soil pH and stimulate alkaline hydrolysis of chlorinated propanes including TCP<ref name="Medina2016">Medina, V.F., Waisner, S.A., Griggs, C.S., Coyle, C., and Maxwell, M., 2016. Laboratory-Scale Demonstration Using Dilute Ammonia Gas-Induced Alkaline Hydrolysis of Soil Contaminants (Chlorinated Propanes and Explosives). US Army Engineer Research and Development Center, Environmental Laboratory (ERDC/EL), Report TR-16-10. [http://hdl.handle.net/11681/20312 Website]&nbsp;&nbsp; [[Media: ERDC_EL_TR_16_10.pdf  | Report.pdf]]</ref>. [[Thermal Conduction Heating (TCH)]] may also produce favorable conditions for TCP hydrolysis<ref name="Tratnyek2010"/><ref name="Sarathy2010"/>.  
 
The rate of hydrolysis of TCP is negligible under typical ambient pH and temperature conditions but is favorable at high pH and/or temperature<ref name="Tratnyek2010"/><ref name="Sarathy2010"/>. For example, ammonia gas can be used to raise soil pH and stimulate alkaline hydrolysis of chlorinated propanes including TCP<ref name="Medina2016">Medina, V.F., Waisner, S.A., Griggs, C.S., Coyle, C., and Maxwell, M., 2016. Laboratory-Scale Demonstration Using Dilute Ammonia Gas-Induced Alkaline Hydrolysis of Soil Contaminants (Chlorinated Propanes and Explosives). US Army Engineer Research and Development Center, Environmental Laboratory (ERDC/EL), Report TR-16-10. [http://hdl.handle.net/11681/20312 Website]&nbsp;&nbsp; [[Media: ERDC_EL_TR_16_10.pdf  | Report.pdf]]</ref>. [[Thermal Conduction Heating (TCH)]] may also produce favorable conditions for TCP hydrolysis<ref name="Tratnyek2010"/><ref name="Sarathy2010"/>.  
  
 +
==Treatment Approaches==
 +
Compared to more frequently encountered CVOCs such as [[Wikipedia: Trichloroethylene | trichloroethene (TCE)]] and [[Wikipedia: Tetrachloroethylene | tetrachloroethene (PCE)]], TCP is relatively recalcitrant<ref name="Merrill2019">Merrill, J.P., Suchomel, E.J., Varadhan, S., Asher, M., Kane, L.Z., Hawley, E.L., and Deeb, R.A., 2019. Development and Validation of Technologies for Remediation of 1,2,3-Trichloropropane in Groundwater. Current Pollution Reports, 5(4), pp. 228–237.  [https://doi.org/10.1007/s40726-019-00122-7 | DOI: 10.1007/s40726-019-00122-7]</ref><ref name="Tratnyek2010"/>. TCP is generally resistant to hydrolysis, bioremediation, oxidation, and reduction under natural conditions<ref name="Tratnyek2010"/>.  The moderate volatility of TCP makes air stripping, air sparging, and soil vapor extraction (SVE) less effective compared to other VOCs<ref name="Merrill2019"/>. Despite these challenges, both ''ex situ'' and ''in situ'' treatment technologies exist. ''Ex situ'' treatment processes are relatively well established and understood but can be cost prohibitive. ''In situ'' treatment methods are comparatively limited and less-well developed, though promising field-scale demonstrations of some ''in situ'' treatment technologies have been conducted.
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===''Ex Situ'' Treatment===
 +
The most common ''ex situ'' treatment technology for groundwater contaminated with TCP is groundwater extraction and treatment<ref name="SaminJanssen2012">Samin, G. and Janssen, D.B., 2012. Transformation and biodegradation of 1,2,3-trichloropropane (TCP). Environmental Science and Pollution Research International, 19(8), pp. 3067-3078. [https://doi.org/10.1007/s11356-012-0859-3 DOI: 10.1007/s11356-012-0859-3]&nbsp;&nbsp; [[Media:  SaminJanssen2012.pdf | Report.pdf]]</ref>. Extraction of TCP is generally effective given its relatively high solubility in water and low degree of partitioning to soil. After extraction, TCP is typically removed by adsorption to granular activated carbon (GAC)<ref name="Merrill2019"/><ref name="CalEPA2017">California Environmental Protection Agency, 2017. Groundwater Information Sheet, 1,2,3-Trichloropropane (TCP). State Water Resources Control Board, Division of Water Quality, Groundwater Ambient Monitoring and Assessment (GAMA) Program, 8 pp. Free download from: [http://www.waterboards.ca.gov/gama/docs/coc_tcp123.pdf California Waterboards]&nbsp;&nbsp; [[Media: CalEPA2017tcp123.pdf | Report.pdf]]</ref>.
 +
 +
TCP contamination in drinking water sources is typically treated using granular activated carbon (GAC)<ref name="Hooker2012">Hooker, E.P., Fulcher, K.G. and Gibb, H.J., 2012. Report to the Hawaii Department of Health, Safe Drinking Water Branch, Regarding the Human Health Risks of 1, 2, 3-Trichloropropane in Tap Water. [https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.269.2485&rep=rep1&type=pdf Free Download]&nbsp;&nbsp; [[Media: Hooker2012.pdf | Report.pdf]]</ref>.
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In California, GAC is considered the best available technology (BAT) for treating TCP, and as of 2017 seven full-scale treatment facilities were using GAC to treat groundwater contaminated with TCP<ref name="CalEPA2017a">California Environmental Protection Agency, 2017.  Initial Statement of Reasons 1,2,3-Trichloropropane Maximum Contaminant Level Regulations. Water Resources Control Board, Title 22, California Code of Regulations (SBDDW-17-001). 36 pp.  [https://www.waterboards.ca.gov/drinking_water/certlic/drinkingwater/documents/123-tcp/sbddw17_001/isor.pdf  Free download]</ref>. Additionally, GAC has been used for over 30 years to treat 60 million gallons per day of TCP-contaminated groundwater in Hawaii<ref name="Babcock2018">Babcock Jr, R.W., Harada, B.K., Lamichhane, K.M., and Tsubota, K.T., 2018. Adsorption of 1, 2, 3-Trichloropropane (TCP) to meet a MCL of 5 ppt. Environmental Pollution, 233, 910-915. [https://doi.org/10.1016/j.envpol.2017.09.085  DOI: 10.1016/j.envpol.2017.09.085]</ref>.
 +
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GAC has a low to moderate adsorption capacity for TCP, which can necessitate larger treatment systems and result in higher treatment costs relative to other organic contaminants<ref name="USEPA2017"/>.  Published Freundlich adsorption isotherm parameters<ref name="SnoeyinkSummers1999">Snoeyink, V.L. and Summers, R.S, 1999. Adsorption of Organic Compounds (Chapter 13), In: Water Quality and Treatment, 5th ed., Letterman, R.D., editor.  McGraw-Hill, New York, NY. ISBN 0-07-001659-3</ref> indicate that less TCP mass is adsorbed per gram of carbon compared to other volatile organic compounds (VOCs), resulting in increased carbon usage rate and treatment cost.  Recent bench-scale studies indicate that subbituminous coal-based GAC and coconut shell-based GAC are the most effective types of GAC for treatment of TCP in groundwater<ref name="Babcock2018"/><ref name="Knappe2017">Knappe, D.R.U., Ingham, R.S., Moreno-Barbosa, J.J., Sun, M., Summers, R.S., and Dougherty, T., 2017. Evaluation of Henry’s Law Constants and Freundlich Adsorption Constants for VOCs. Water Research Foundation Project 4462 Final Report. [https://www.waterrf.org/research/projects/evaluation-henrys-law -constant-and-freundlich-adsorption-constant-vocs  Website]</ref>. To develop more economical and effective treatment approaches, further treatability studies with site groundwater (e.g., rapid small-scale column tests) may be needed.
 +
 +
===''In Situ'' Treatment===
 +
''In situ'' treatment of TCP to concentrations below current regulatory or advisory levels is difficult to achieve in both natural and engineered systems. However, several ''in situ'' treatment technologies have demonstrated promise for TCP remediation, including chemical reduction by zero-valent metals (ZVMs), chemical oxidation with strong oxidizers, and anaerobic bioremediation<ref name="Merrill2019"/><ref name="Tratnyek2010"/>.
 +
 +
===''In Situ'' Chemical Reduction (ISCR)===
 +
Reduction of TCP under conditions relevant to natural attenuation has been observed to be negligible. Achieving significant degradation rates of TCP requires the addition of a chemical reductant to the contaminated zone<ref name="Merrill2019"/><ref name="Tratnyek2010"/>.  Under reducing environmental conditions, some ZVMs have demonstrated the ability to reduce TCP all the way to [[wikipedia:Propene | propene]]. As shown in Figure 2, the desirable pathway for reduction of TCP is the formation of [[Wikipedia: Allyl_chloride | 3-chloro-1-propene (also known as allyl chloride)]] via [[Biodegradation_-_Reductive_Processes#Dihaloelimination | dihaloelimination]], which is then rapidly reduced to propene through [[Wikipedia:Hydrogenolysis |  hydrogenolysis]] <ref name="Merrill2019"/><ref name="Tratnyek2010"/><ref name="Torralba-Sanchez2020">Torralba-Sanchez, T.L., Bylaska, E.J., Salter-Blanc, A.J., Meisenheimer, D.E., Lyon, M.A., and Tratnyek, P.G., 2020. Reduction of 1, 2, 3-trichloropropane (TCP): pathways and mechanisms from computational chemistry calculations. Environmental Science: Processes and Impacts, 22(3), 606-616. [https://doi.org/10.1039/C9EM00557A DOI: 10.1039/C9EM00557A]&nbsp;&nbsp [[Media: Torralba-Sanchez2020.pdf | Open Access Article]]</ref>.  ZVMs including granular zero-valent iron (ZVI), nano ZVI, [[wikipedia: In_situ_chemical_reduction#Bimetallic%20materials | palladized nano ZVI]], and [[wikipedia: In_situ_chemical_reduction#Zero_valent_metals_%28ZVMs%29 | zero-valent zinc (ZVZ)]] have been evaluated by researchers<ref name="Merrill2019"/><ref name="Tratnyek2010"/>.
 +
 +
ZVI is a common reductant used for ISCR and, depending on the form used, has shown variable levels of success for TCP treatment. The Strategic Environmental Research and Development Program (SERDP) Project ER-1457 measured the TCP degradation rates for various forms of ZVI and ZVZ.  Nano-scale ZVI and palladized ZVI increased the TCP reduction rate over that of natural attenuation, but the reaction is not anticipated to be fast enough to be useful in typical remediation applications<ref name="Sarathy2010"/>.
 +
 +
Commercial-grade zerovalent zinc (ZVZ) on the other hand is a strong reductant that reduces TCP relatively quickly under a range of laboratory and field conditions to produce propene without significant accumulation of intermediates<ref name="Sarathy2010"/><ref name="Salter-BlancTratnyek2011">Salter-Blanc, A.J. and Tratnyek, P.G., 2011. Effects of Solution Chemistry on the Dechlorination of 1,2,3-Trichloropropane by Zero-Valent Zinc. Environmental Science and Technology, 45(9), pp 4073–4079. [https://doi.org/10.1021/es104081p DOI: 10.1021/es104081p]&nbsp;&nbsp; [[Media: Salter-BlancTratnyek2011.pdf | Open access article]]</ref><ref name="Salter-Blanc2012">Salter-Blanc, A.J., Suchomel, E.J., Fortuna, J.H., Nurmi, J.T., Walker, C., Krug, T., O'Hara, S., Ruiz, N., Morley, T. and Tratnyek, P.G., 2012. Evaluation of Zerovalent Zinc for Treatment of 1,2,3-Trichloropropane‐Contaminated Groundwater: Laboratory and Field Assessment. Groundwater Monitoring and Remediation, 32(4), pp.42-52. [https://doi.org/10.1111/j.1745-6592.2012.01402.x DOI: 10.1111/j.1745-6592.2012.01402.x]</ref><ref name="Merrill2019"/>. Of the ZVMs tested as part of SERDP Project ER-1457, ZVZ had the fastest degradation rates for TCP<ref name="Tratnyek2010"/>. In bench-scale studies, TCP was reduced by ZVZ to propene with 3-chloro-1-propene as the only detectable chlorinated intermediate, which was short-lived and detected only at trace concentrations<ref name="Torralba-Sanchez2020"/>.
 +
 +
Navy Environmental Sustainability Development to Integration (NESDI) Project 434 conducted bench-scale testing which demonstrated that commercially available ZVZ was effective for treating TCP. Additionally, this project evaluated field-scale ZVZ column treatment of groundwater impacted with TCP at Marine Corps Base Camp Pendleton (MCBCP) in Oceanside, California. This study reported reductions of TCP concentrations by up to 95% which was maintained for at least twelve weeks with influent concentrations ranging from 3.5 to 10 µg/L, without any significant secondary water quality impacts detected<ref name="Salter-Blanc2012"/>.
 +
 +
Following the column study, a 2014 pilot study at MCBCP evaluated direct injection of ZVZ with subsequent monitoring. Direct injection of ZVZ was reportedly effective for TCP treatment, with TCP reductions ranging from 90% to 99% in the injection area. Concentration reduction downgradient of the injection area ranged from 50 to 80%. TCP concentrations have continued to decrease, and reducing conditions have been maintained in the aquifer since injection, demonstrating the long-term efficacy of ZVZ for TCP reduction<ref name="Kane2020"/>.
 +
 +
Potential ''in situ'' applications of ZVZ include direct injection, as demonstrated by the MCBCP pilot study, and permeable reactive barriers (PRBs). Additionally, ZVZ could potentially be deployed in an ''ex situ'' flow-through reactor, but the economic feasibility of this approach would depend in part on the permeability of the aquifer and in part on the cost of the reactor volumes of ZVZ media necessary for complete treatment.
 +
 +
===''In Situ'' Chemical Oxidation (ISCO)===
 +
Chemical oxidation of TCP with mild oxidants such as permanganate or ozone is ineffective. However, stronger oxidants (e.g. activated peroxide and persulfate) can effectively treat TCP, although the rates are slower than observed for most other organic contaminants<ref name="Tratnyek2010"/><ref name="CalEPA2017"/>. [[Wikipedia: Fenton's reagent | Fenton-like chemistry]] (i.e., Fe(II) activated hydrogen peroxide) has been shown to degrade TCP in the laboratory with half-lives ranging from 5 to 10 hours<ref name="Tratnyek2010"/>, but field-scale demonstrations of this process have not been reported. Treatment of TCP with heat-activated or base-activated persulfate is effective but secondary water quality impacts from high sulfate may be a concern at some locations.
 +
 +
===Aerobic Bioremediation===
 +
No naturally occurring microorganisms have been identified that degrade TCP under aerobic conditions<ref name="SaminJanssen2012"/>. Relatively slow aerobic cometabolism by the ammonia oxidizing bacterium [[Wikipedia: Nitrosomonas europaea | Nitrosomonas europaea]] and other populations has been reported<ref name="Vanelli1990">Vannelli, T., Logan, M., Arciero, D.M., and Hooper, A.B., 1990. Degradation of Halogenated Aliphatic Compounds by the Ammonia-Oxidizing Bacterium Nitrosomonas europaea. Applied and Environmental Microbiology, 56(4), pp. 1169–1171. [https://doi.org/10.1128/aem.56.4.1169-1171.1990 DOI: 10.1128/aem.56.4.1169-1171.1990] Free download from: [https://journals.asm.org/doi/epdf/10.1128/aem.56.4.1169-1171.1990 American Society of Microbiology]&nbsp;&nbsp; [[Media: Vannelli1990.pdf | Report.pdf]]</ref><ref name="SaminJanssen2012"/>, and genetic engineering has been used to develop organisms capable of utilizing TCP as a sole carbon source under aerobic conditions<ref name="Bosma2002">Bosma, T., Damborsky, J., Stucki, G., and Janssen, D.B., 2002. Biodegradation of 1,2,3-Trichloropropane through Directed Evolution and Heterologous Expression of a Haloalkane Dehalogenase Gene. Applied and Environmental Microbiology, 68(7), pp. 3582–3587. [https://doi.org/10.1128/AEM.68.7.3582-3587.2002 DOI: 10.1128/AEM.68.7.3582-3587.2002] Free download from: [https://journals.asm.org/doi/epub/10.1128/AEM.68.7.3582-3587.2002 American Society for Microbiology]&nbsp;&nbsp; [[Media: Bosma2002.pdf | Report.pdf]]</ref><ref name="SaminJanssen2012"/><ref name="JanssenStucki2020">Janssen, D. B., and Stucki, G., 2020. Perspectives of genetically engineered microbes for groundwater bioremediation. Environmental Science: Processes and Impacts, 22(3), pp. 487-499. [https://doi.org/10.1039/C9EM00601J DOI: 10.1039/C9EM00601J] Open access article from: [https://pubs.rsc.org/en/content/articlehtml/2020/em/c9em00601j Royal Society of Chemistry]&nbsp;&nbsp; [[Media: JanssenStucki2020.pdf | Report.pdf]]</ref>.
 +
 +
===Anaerobic Bioremediation===
 +
Like other CVOCs, TCP has been shown to undergo biodegradation under anaerobic conditions via reductive dechlorination by [[Wikipedia:Dehalogenimonas | Dehalogenimonas (Dhg)]] species<ref name="Merrill2019"/><ref name="Yan2009">Yan, J., B.A. Rash, F.A. Rainey, and W.M. Moe, 2009. Isolation of novel bacteria within the Chloroflexi capable of reductive dechlorination of 1,2,3-trichloropropane. Environmental Microbiology, 11(4), pp. 833–843. [https://doi.org/10.1111/j.1462-2920.2008.01804.x DOI: 10.1111/j.1462-2920.2008.01804.x]</ref><ref name="Bowman2013">Bowman, K.S., Nobre, M.F., da Costa, M.S., Rainey, F.A., and Moe, W.M., 2013. Dehalogenimonas alkenigignens sp. nov., a chlorinated-alkane-dehalogenating bacterium isolated from groundwater. International Journal of Systematic and Evolutionary Microbiology, 63(Pt_4), pp. 1492-1498. [https://doi.org/10.1099/ijs.0.045054-0 DOI: 10.1099/ijs.0.045054-0]  Free access article from: [https://www.microbiologyresearch.org/content/journal/ijsem/10.1099/ijs.0.045054-0?crawler=true Microbiology Society]&nbsp;&nbsp; [[Media: Bowman2013.pdf | Report.pdf]]</ref><ref name="Loffler1997">Loffler, F.E., Champine, J.E., Ritalahti, K.M., Sprague, S.J. and Tiedje, J.M., 1997. Complete Reductive Dechlorination of 1, 2-Dichloropropane by Anaerobic Bacteria. Applied and Environmental Microbiology, 63(7), pp.2870-2875. Free download from: [https://journals.asm.org/doi/pdf/10.1128/aem.63.7.2870-2875.1997 American Society for Micrebiology]&nbsp;&nbsp; [[Medeia: Loffler1997.pdf | Report.pdf]]</ref><ref name="Moe2019">Moe, W.M., Yan, J., Nobre, M.F., da Costa, M.S. and Rainey, F.A., 2009. Dehalogenimonas lykanthroporepellens gen. nov., sp. nov., a reductively dehalogenating bacterium isolated from chlorinated solvent-contaminated groundwater. International Journal of Systematic and Evolutionary Microbiology, 59(11), pp.2692-2697. [https://doi.org/10.1099/ijs.0.011502-0 DOI: 10.1099/ijs.0.011502-0] Free download from: [https://www.microbiologyresearch.org/content/journal/ijsem/10.1099/ijs.0.011502-0?crawler=true Microbiology Society]&nbsp;&nbsp; [[Media: Moe2009.pdf | Report.pdf]]</ref><ref name="SaminJanssen2012"/>. However, the kinetics are slower than for other CVOCs.  Bioaugmentation cultures containing Dehalogenimonas (KB-1 Plus, SiREM) are commercially available and have been implemented for remediation of TCP-contaminated groundwater<ref name="Schmitt2017">Schmitt, M., Varadhan, S., Dworatzek, S., Webb, J. and Suchomel, E., 2017. Optimization and validation of enhanced biological reduction of 1,2,3-trichloropropane in groundwater. Remediation Journal, 28(1), pp.17-25. [https://doi.org/10.1002/rem.21539 DOI: 10.1002/rem.21539]</ref>. One laboratory study examined the effect of pH on biotransformation of TCP over a wide range of TCP concentrations (10 to 10,000 µg/L) and demonstrated that successful reduction occurred from a pH of 5 to 9, though optimal conditions were from pH 7 to 9<ref name="Schmitt2017"/>. 
 +
 +
As with other microbial cultures capable of reductive dechlorination, coordinated amendment with a fermentable organic substrate (e.g. lactate or vegetable oil), also known as biostimulation,  creates reducing conditions in the aquifer and provides a source of hydrogen which is required as the primary electron donor for reductive dechlorination.
 +
 +
A 2016 field demonstration of ''in situ'' bioremediation (ISB) was performed in California’s Central Valley at a former agricultural chemical site with relatively low TCP concentrations (2 µg/L). The site was first biostimulated by injecting amendments of emulsified vegetable oil (EVO) and lactate, which was followed by bioaugmentation with a microbial consortium containing Dhg. After an initial lag period of six months, TCP concentrations decreased to below laboratory detection limits (<0.005 µg/L)<ref name="Schmitt2017"/>.
 +
 +
The 2016 field demonstration was expanded to full-scale treatment in 2018 with biostimulation and bioaugmentation occurring over several months. The initial TCP concentration in performance monitoring wells ranged from 0.008 to 1.7 µg/L. As with the field demonstration, a lag period of approximately 6 to 8 months was observed before TCP was degraded, after which concentrations declined over fifteen months to non-detectable levels (less than 0.005 µg/L). TCP degradation was associated with increases in Dhg population and propene concentration. Long term monitoring showed that TCP remained at non-detectable levels for at least three years following treatment implementation<ref name="Merrill2019"/>.
 +
 +
==Treatment Comparisons and Considerations==
 +
When selecting a technology for TCP treatment, considerations include technical feasibility, ability to treat to regulated levels, potential secondary water quality impacts and relative costs. A comparison of some TCP treatment technologies is provided in Table 2.
  
 
{| class="wikitable" style="float:right; margin-left:10px;text-align:center;"
 
{| class="wikitable" style="float:right; margin-left:10px;text-align:center;"
|+Table 2.  Advantages and limitations of TCP treatment technologies
+
|+Table 2.  Advantages and limitations of TCP treatment technologies<ref name="Kane2020"/>
 
|-
 
|-
 
! Technology
 
! Technology
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|}
 
|}
  
 +
==Summary==
 +
The relatively high toxicity of TCP has led to the development of health-based drinking water concentration values that are very low. TCP is sometimes present in groundwater and in public water systems at concentrations that exceed these health-based goals. While a handful of states have established MCLs for TCP, US federal regulatory determination is hindered by the lack of low-concentration occurrence data. Because TCP is persistent in groundwater and resistant to typical remediation methods (or costly to treat), specialized strategies may be needed to meet drinking-water-based treatment goals.  ''In situ'' chemical reduction (ISCR) with zero valent zinc (ZVZ) and ''in situ'' bioremediation have been demonstrated to be effective for TCP remediation.
  
 +
==References==
 +
<references />
  
There&nbsp;are&nbsp;two&nbsp;main&nbsp;approaches to downscaling. One method, commonly referred to as “statistical downscaling”, uses the empirical-statistical relationships between large-scale weather phenomena and historical local weather data. In this method, these statistical relationships are applied to output generated by global climate models. A second method uses physics-based numerical models (regional-scale climate models or RCMs) of weather and climate that operate over a limited region of the earth (e.g., North America) and at spatial resolutions that are typically 3 to 10 times finer than the global-scale climate models. This method is known as “dynamical downscaling”.  These regional-scale climate models are similar to the global models with respect to their reliance on the principles of physics, but because they operate over only part of the earth, they require information about what is coming in from the rest of the earth as well as what is going out of the limited region of the model. This is generally obtained from a global model.  The primary differences between statistical and dynamical downscaling methods are summarized in Table 1.
+
==See Also==
 
+
ATSDR Toxicological Profile: https://www.atsdr.cdc.gov/ToxProfiles/TP.asp?id=912&tid=186
It&nbsp;is&nbsp;important&nbsp;to&nbsp;realize that there is no “best” downscaling method or dataset, and that the best method/dataset for a given problem depends on that problem’s specific needs. Several data products based on downscaling higher level spatial data are available ([https://cida.usgs.gov/gdp/ USGS], [http://maca.northwestknowledge.net/ MACA], [https://www.narccap.ucar.edu/ NARCCAP], [https://na-cordex.org/ CORDEX-NA]). The appropriate method and dataset to use depends on the intended application. The method selected should be able to credibly resolve spatial and temporal scales relevant for the application. For example, to develop a risk analysis of frequent flooding, the data product chosen should include precipitation at greater than a diurnal frequency and over multi-decadal timescales. This kind of product is most likely to be available using the dynamical downscaling method.  SERDP reviewed the various advantages and disadvantages of using each type of downscaling method and downscaling dataset, and developed a recommended process that is publicly available<ref name="Kotamarthi2016"/>. In general, the following recommendations should be considered in order to pick the right downscaled dataset for a given analysis:
 
 
 
* When a problem depends on using a large number of climate models and emission scenarios to perform preliminary assessments and to understand the uncertainty range of projections, then using a statistical downscaled dataset is recommended. 
 
* When the assessment needs a more extensive parameter list or is analyzing a region with few long-term observational data, dynamically downscaled climate change projections are recommended.
 
 
 
==Uncertainty in Projections==
 
{| class="wikitable" style="float:right; margin-left:10px;text-align:center;"
 
|+Table 2.  Downscaling model characteristics and output<ref name="Kotamarthi2016"/>
 
|-
 
!Model or</br>Dataset Name
 
!Model<br />Method
 
!Output<br />Variables
 
!Output<br />Format
 
!Spatial</br>Resolution
 
!Time</br>Resolution
 
|-
 
| colspan="6" style="text-align: left; background-color:white;" |'''Statistical Downscaled Datasets'''
 
|-
 
| [https://worldclim.org/data/index.html WorldClim]<ref name="Hijmans2005">Hijmans, R.J., Cameron, S.E., Parra, J.L., Jones, P.G. and Jarvis, A., 2005. Very High Resolution Interpolated Climate Surfaces for Global Land Areas. International Journal of Climatology: A Journal of the Royal Meteorological Society, 25(15), pp 1965-1978.  [https://doi.org/10.1002/joc.1276 DOI: 10.1002/joc.1276]</ref>
 
|Delta||T(min, max,</br>avg), Pr||NetCDF||grid: 30 arc sec to</br>10 arc min||month
 
|-
 
| Bias Corrected / Spatial</br>Disaggregation (BCSD)<ref name="Wood2002">Wood, A.W., Maurer, E.P., Kumar, A. and Lettenmaier, D.P., 2002. Long‐range experimental hydrologic forecasting for the eastern United States. Journal of Geophysical Research: Atmospheres, 107(D20), 4429, pp. ACL6 1-15. [https://doi.org/10.1029/2001JD000659 DOI:10.1029/2001JD000659]&nbsp;&nbsp; Free access article available from: [https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2001JD000659 American Geophysical Union]&nbsp;&nbsp; [[Media: Wood2002.pdf | Report.pdf ]]</ref>
 
|Empirical Quantile</br>Mapping||Runoff,</br>Streamflow||NetCDF||grid: 7.5 arc min||day
 
|-
 
| [https://cida.usgs.gov/thredds/catalog.html?dataset=dcp Asynchronous Regional Regression</br>Model (ARRM v.1)]<ref name="Stoner2013">Stoner, A.M., Hayhoe, K., Yang, X., and Wuebbles, D.J., 2013. An Asynchronous Regional Regression Model for Statistical Downscaling of Daily Climate Variables. International Journal of Climatology, 33(11), pp. 2473-2494.  [https://doi.org/10.1002/joc.3603 DOI:10.1002/joc.3603]</ref>
 
|Parameterized</br>Quantile Mapping||T(min, max), Pr||NetCDF||stations plus</br>grid: 7.5 arc min||day
 
|-
 
| [https://sdsm.org.uk/ Statistical Downscaling Model (SDSM)]<ref name="Wilby2013">Wilby, R.L., and Dawson, C.W., 2013. The Statistical DownScaling Model: insights from one decade of application. International Journal of Climatology, 33(7), pp. 1707-1719. [https://doi.org/10.1002/joc.3544 DOI: 10.1002/joc.3544]</ref>
 
|Weather Generator||T(min, max), Pr||PC Code||stations||day
 
|-
 
| [https://climate.northwestknowledge.net/MACA/ Multivariate Adaptive</br>Constructed Analogs (MACA)]<ref name="Hidalgo2008">Hidalgo, H.G., Dettinger, M.D. and Cayan, D.R., 2008. Downscaling with Constructed Analogues: Daily Precipitation and Temperature Fields Over the United States. California Energy Commission PIER Final Project, Report CEC-500-2007-123. [[Media: Hidalgo2008.PDF | Report.pdf]]</ref>
 
|Constructed Analogues||10 Variables||NetCDF||grid: 2.5 arc min||day
 
|-
 
| [http://loca.ucsd.edu/ Localized Constructed Analogs (LOCA)]<ref name="Pierce2013">Pierce, D.W., Cayan, D.R. and Thrasher, B.L., 2014. Statistical Downscaling Using Localized Constructed Analogs (LOCA). Journal of Hydrometeorology, 15(6), pp. 2558-2585. [https://doi.org/10.1175/JHM-D-14-0082.1 DOI: 10.1175/JHM-D-14-0082.1]&nbsp;&nbsp; Free access article available from: [https://journals.ametsoc.org/view/journals/hydr/15/6/jhm-d-14-0082_1.xml American Meteorological Society].&nbsp;&nbsp; [[Media: Pierce2014.pdf | Report.pdf]]</ref>
 
|Constructed Analogues||T(min, max), Pr||NetCDF||grid: 3.75 arc min||day
 
|-
 
| [https://www.nccs.nasa.gov/services/data-collections/land-based-products/nex-dcp30 NASA Earth Exchange Downscaled</br>Climate Projections (NEX-DCP30)]<ref name="Wood2002"/>
 
|Bias Correction /</br>Spatial Disaggregation||T(min, max), Pr||NetCDF||grid: 30 arc sec||month
 
|-
 
| colspan="6" style="text-align: left; background-color:white;" |'''Dynamical Downscaled Datasets'''
 
|-
 
| [http://www.narccap.ucar.edu/index.html North American Regional Climate</br>Change Assessment Program (NARCCAP)]<ref name="Mearns2009">Mearns, L.O., Gutowski, W., Jones, R., Leung, R., McGinnis, S., Nunes, A. and Qian, Y., 2009. A Regional Climate Change Assessment Program for North America. Eos, Transactions, American Geophysical Union, 90(36), p.311.  [https://doi.org/10.1029/2009EO360002 DOI: 10.1029/2009EO360002]&nbsp;&nbsp; Free access article from: [https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2009EO360002 American Geophysical Union]&nbsp;&nbsp; [[Media: Mearns2009.pdf  | Report.pdf]]</ref>
 
|Multiple Models||49 Variables||NetCDF||grid: 30 arc min||3 hours
 
|-
 
| [https://cordex.org/about/ Coordinated Regional Climate</br>Downscaling Experiment (CORDEX)]<ref name="Giorgi2009">Giorgi, F., Jones, C., and Asrar, G.R., 2009. Addressing climate information needs at the regional level: the CORDEX framework. World Meteorological Organization (WMO) Bulletin, 58(3), pp. 175-183. Free access article from: [https://public.wmo.int/en/bulletin/addressing-climate-information-needs-regional-level-cordex-framework World Meteorological Organization]&nbsp;&nbsp; [[Media: Giorgi2009.pdf | Report.pdf]]</ref>
 
|Multiple Models||66 Variables||NetCDF||grid: 30 arc min||3 hours
 
|-
 
| [https://esrl.noaa.gov/gsd/wrfportal/ Strategic Environmental Research and</br>Development Program (SERDP)]<ref name="Wang2015">Wang, J., and Kotamarthi, V.R., 2015. High‐resolution dynamically downscaled projections of precipitation in the mid and late 21st century over North America. Earth's Future, 3(7), pp. 268-288.  [https://doi.org/10.1002/2015EF000304 DOI: 10.1002/2015EF000304]&nbsp;&nbsp; Free access article from: [https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2015EF000304 American Geophysical Union]&nbsp;&nbsp; [[Media: Wang2015.pdf | Report.pdf]]</ref>
 
|Weather Research and</br>Forecasting (WRF v3.3)||80+ Variables||NetCDF||grid: 6.5 arc min||3 hours
 
|}
 
A&nbsp;primary&nbsp;cause&nbsp;of&nbsp;uncertainty in climate change projections, especially beyond 30 years into the future, is the uncertainty in the greenhouse gas (GHG) emission scenarios used to make climate model projections. The best method of accounting for this type of uncertainty is to apply a climate change model to multiple GHG emission scenarios (see also: [[Wikipedia: Representative Concentration Pathway]]).
 
  
The&nbsp;uncertainties&nbsp;in&nbsp;climate&nbsp;projections over shorter timescales, less than 30 years out, are dominated by something known as “internal variability” in the models. Different approaches are used to address the uncertainty from internal variability<ref name="Kotamarthi2021"/>. A third type of uncertainty in climate modeling, known as scientific uncertainty, comes from our inability to numerically solve every aspect of the complex earth system. We expect this scientific uncertainty to decrease as we understand more of the earth system and improve its representation in our numerical models.  As discussed in [[Climate Change Primer]], numerical experiments based on global climate models are designed to address these uncertainties in various ways. Downscaling methods evaluate this uncertainty by using several independent regional climate models to generate future projections, with the expectation that each of these models will capture some aspects of the physics better than the others, and that by using several different models, we can estimate the range of this uncertainty.  Thus, the commonly accepted methods for accounting for uncertainty in climate model projections are either using projections from one model for several emission scenarios, or applying multiple models to project a single scenario.  
+
EPA Technical Fact Sheet: https://www.epa.gov/sites/production/files/2014-03/documents/ffrrofactsheet_contaminant_tcp_january2014_final.pdf
  
A comparison of the currently available methods and their characteristics is provided in Table 2 (adapted from Kotamarthi et al., 2016<ref name="Kotamarthi2016"/>).  The table lists the various methodologies and models used for producing downscaled data, and the climate variables that these methods produce.  These datasets are mostly available for download from the data servers and websites listed in the table and in a few cases by contacting the respective source organizations. 
+
Cal/EPA State Water Resources Control Board Groundwater Information Sheet: http://www.waterboards.ca.gov/gama/docs/coc_tcp123.pdf
 
 
The most popular and widely used format for atmospheric and climate science is known as [[Wikipedia:NetCDF | NetCDF]], which stands for Network Common Data Form. NetCDF is a self-describing data format that saves data in a binary format. The format is self-describing in that a metadata listing is part of every file that describes all the data attributes, such as dimensions, units and data size and in principal should not need additional information to extract the required data for analysis with the right software.  However, specially built software for reading and extracting data from these binary files is necessary for making visualizations and further analysis. Software packages for reading and writing NetCDF datasets and for generating visualizations from these datasets are widely available and obtained free of cost ([https://www.unidata.ucar.edu/software/netcdf/docs/ NetCDF-tools]). Popular geospatial analysis tools such as ARC-GIS, statistical packages such as ‘R’ and programming languages such as Fortran, C++, and Python have built in libraries that can be used to directly read NetCDF files for visualization and analysis.  
 
<br clear="left" />
 
 
 
==References==
 
<references />
 
==See Also==
 
  
[https://serdp-estcp.org/Program-Areas/Resource-Conservation-and-Resiliency/Infrastructure-Resiliency/Vulnerability-and-Impact-Assessment/RC-2242/(language)/eng-US Climate Change Impacts to Department of Defense Installations, SERDP Project RC-2242]
+
California Water Boards Fact Sheet: http://www.waterboards.ca.gov/drinking_water/certlic/drinkingwater/documents/123-tcp/123tcp_factsheet.pdf

Revision as of 20:16, 12 October 2021

1,2,3-Trichloropropane (TCP)

1,2,3-Trichloropropane (TCP) is a chlorinated volatile organic compound (CVOC) that has been used in chemical production processes, in agriculture, and as a solvent, resulting in point and non-point source contamination of soil and groundwater. TCP is mobile and highly persistent in soil and groundwater. TCP is not currently regulated at the national level in the United States, but maximum contaminant levels (MCLs) have been developed by some states. Current treatment methods for TCP are limited and can be cost prohibitive. However, some treatment approaches, particularly in situ chemical reduction (ISCR) with zero valent zinc (ZVZ) and in situ bioremediation (ISB), have recently been shown to have potential as practical remedies for TCP contamination of groundwater.

Related Article(s):

Contributor(s):

Key Resource(s):

  • Prospects for Remediation of 1,2,3-Trichloropropane by Natural and Engineered Abiotic Degradation Reactions. Strategic Environmental Research and Development Program (SERDP), Project ER-1457.[1]
  • Verification Monitoring for In Situ Chemical Reduction Using Zero-Valent Zinc, A Novel Technology for Remediation of Chlorinated Alkanes. Strategic Environmental Research and Development Program (SERDP), Project ER-201628.[2]

Introduction

Figure 1. Ball and stick representation of the molecular structure of TCP (Salter-Blanc and Tratnyek, unpublished)

1,2,3-Trichloropropane (TCP) (Figure 1) is a man-made chemical that was used in the past primarily as a solvent and extractive agent, as a paint and varnish remover, and as a cleaning and degreasing agent.[3]. Currently, TCP is primarily used in chemical synthesis of compounds such as polysulfone liquid polymers used in the aerospace and automotive industries; hexafluoropropylene used in the agricultural, electronic, and pharmaceutical industries; polysulfide polymers used as sealants in manufacturing and construction; and 1,3-dichloropropene used in agriculture as a soil fumigant. TCP may also be present in products containing these chemicals as an impurity[3][4]. For example, the 1,2-dichlropropane/1,3-dichloropropene soil fumigant mixture (trade name D-D), which is no longer sold in the United States, contained TCP as an impurity and has been linked to TCP contamination in groundwater[5][4]. Soil fumigants currently in use which are composed primarily of 1,3-dichloropropene may also contain TCP as an impurity, for instance Telone II has been reported to contain up to 0.17 percent TCP by weight[6].

TCP contamination is problematic because it is “reasonably anticipated to be a human carcinogen” based on evidence of carcinogenicity to animals[7]. Toxicity to humans appears to be high relative to other chlorinated solvents[6], suggesting that even low-level exposure to TCP could pose a significant human health risk.

Environmental Fate

TCP’s fate in the environment is governed by its physical and chemical properties (Table 1). TCP does not adsorb strongly to soil, making it likely to leach into groundwater and exhibit high mobility. In addition, TCP is moderately volatile and can partition from surface water and moist soil into the atmosphere. Because TCP is only slightly soluble and denser than water, it can form a dense non-aqueous phase liquid (DNAPL) as observed at the Tyson’s Dump Superfund Site[8]. TCP is generally resistant to aerobic biodegradation, hydrolysis, oxidation, and reduction under naturally occurring conditions making it persistent in the environment[1].

Table 1. Physical and chemical properties of TCP[9]
Property Value
Chemical Abstracts Service (CAS) Number 96-18-4
Physical Description
(at room temperature)
Colorless to straw-colored liquid
Molecular weight (g/mol) 147.43
Water solubility at 25°C (mg/L) 1,750 (slightly soluble)
Melting point (°C) -14.7
Boiling point (°C) 156.8
Vapor pressure at 25°C (mm Hg) 3.10 to 3.69
Density at 20°C (g/cm3) 1.3889
Octanol-water partition coefficient
(logKow)
1.98 to 2.27
(temperature dependent)
Organic carbon-water partition coefficient
(logKoc)
1.70 to 1.99
(temperature dependent)
Henry’s Law constant at 25°C
(atm-m3/mol)
3.17x10-4[3] to 3.43x10-4[10]

Occurrence

TCP has been detected in approximately 1% of public water supply and domestic well samples tested by the United States Geological Survey. More specifically, TCP was detected in 1.2% of public supply well samples collected between 1993 and 2007 by Toccalino and Hopple[11] and 0.66% of domestic supply well samples collected between 1991 and 2004 by DeSimone[12]. TCP was detected at a higher rate in domestic supply well samples associated with agricultural land-use studies than samples associated with studies comparing primary aquifers (3.5% versus 0.2%)[12].

Regulation

The United States Environmental Protection Agency (USEPA) has not established an MCL for TCP, although guidelines and health standards are in place[9]. TCP was included in the Contaminant Candidate List 3[13] and the Unregulated Contaminant Monitoring Rule 3 (UCMR 3)[14]. The UCMR 3 specified that data be collected on TCP occurrence in public water systems over the period of January 2013 through December 2015 against a reference concentration range of 0.0004 to 0.04 μg/L[15]. The reference concentration range was determined based on a cancer risk of 10-6 to 10-4 and derived from an oral slope factor of 30 mg/kg-day, which was determined by the EPA’s Integrated Risk Information System[16]. Of 36,848 samples collected during UCMR 3, 0.67% exceeded the minimum reporting level of 0.03 µg/L. 1.4% of public water systems had at least one detection over the minimum reporting level, corresponding to 2.5% of the population[15]. While these occurrence percentages are relatively low, the minimum reporting level of 0.03 µg/L is more than 75 times the USEPA-calculated Health Reference Level of 0.0004 µg/L. Because of this, TCP may occur in public water systems at concentrations that exceed the Health Reference Level but are below the minimum reporting level used during UCMR 3 data collection. These analytical limitations and lack of lower-level occurrence data have prevented the USEPA from making a preliminary regulatory determination for TCP[17].

Some US states have established their own standards including Hawaii which has established an MCL of 0.6 μg/L[18]. California has established an MCL of 0.005 μg/L[19], a notification level of 0.005 μg/L, and a public health goal of 0.0007 μg/L[20], and New Jersey has established an MCL of 0.03 μg/L[21].

Transformation Processes

Figure 2. Figure 2. Summary of anticipated primary reaction pathways for degradation of TCP. Oxidation, hydrolysis, and hydrogenolysis are represented by the horizontal arrows. Elimination (dehydrochlorination) and reductive elimination are shown with vertical arrows. [O] represents oxygenation (by oxidation or hydrolysis), [H] represents reduction. Gray indicates products that appear to be of lesser significance[1].

Potential TCP degradation pathways include hydrolysis, oxidation, and reduction (Figure 2). These pathways are expected to be similar overall for abiotic and biotic reactions[22], but the rates of the reactions (and their resulting significance for remediation) depend on natural and engineered conditions.

The rate of hydrolysis of TCP is negligible under typical ambient pH and temperature conditions but is favorable at high pH and/or temperature[1][22]. For example, ammonia gas can be used to raise soil pH and stimulate alkaline hydrolysis of chlorinated propanes including TCP[23]. Thermal Conduction Heating (TCH) may also produce favorable conditions for TCP hydrolysis[1][22].

Treatment Approaches

Compared to more frequently encountered CVOCs such as trichloroethene (TCE) and tetrachloroethene (PCE), TCP is relatively recalcitrant[24][1]. TCP is generally resistant to hydrolysis, bioremediation, oxidation, and reduction under natural conditions[1]. The moderate volatility of TCP makes air stripping, air sparging, and soil vapor extraction (SVE) less effective compared to other VOCs[24]. Despite these challenges, both ex situ and in situ treatment technologies exist. Ex situ treatment processes are relatively well established and understood but can be cost prohibitive. In situ treatment methods are comparatively limited and less-well developed, though promising field-scale demonstrations of some in situ treatment technologies have been conducted.

Ex Situ Treatment

The most common ex situ treatment technology for groundwater contaminated with TCP is groundwater extraction and treatment[25]. Extraction of TCP is generally effective given its relatively high solubility in water and low degree of partitioning to soil. After extraction, TCP is typically removed by adsorption to granular activated carbon (GAC)[24][26].

TCP contamination in drinking water sources is typically treated using granular activated carbon (GAC)[27].

In California, GAC is considered the best available technology (BAT) for treating TCP, and as of 2017 seven full-scale treatment facilities were using GAC to treat groundwater contaminated with TCP[28]. Additionally, GAC has been used for over 30 years to treat 60 million gallons per day of TCP-contaminated groundwater in Hawaii[29].

GAC has a low to moderate adsorption capacity for TCP, which can necessitate larger treatment systems and result in higher treatment costs relative to other organic contaminants[9]. Published Freundlich adsorption isotherm parameters[30] indicate that less TCP mass is adsorbed per gram of carbon compared to other volatile organic compounds (VOCs), resulting in increased carbon usage rate and treatment cost. Recent bench-scale studies indicate that subbituminous coal-based GAC and coconut shell-based GAC are the most effective types of GAC for treatment of TCP in groundwater[29][31]. To develop more economical and effective treatment approaches, further treatability studies with site groundwater (e.g., rapid small-scale column tests) may be needed.

In Situ Treatment

In situ treatment of TCP to concentrations below current regulatory or advisory levels is difficult to achieve in both natural and engineered systems. However, several in situ treatment technologies have demonstrated promise for TCP remediation, including chemical reduction by zero-valent metals (ZVMs), chemical oxidation with strong oxidizers, and anaerobic bioremediation[24][1].

In Situ Chemical Reduction (ISCR)

Reduction of TCP under conditions relevant to natural attenuation has been observed to be negligible. Achieving significant degradation rates of TCP requires the addition of a chemical reductant to the contaminated zone[24][1]. Under reducing environmental conditions, some ZVMs have demonstrated the ability to reduce TCP all the way to propene. As shown in Figure 2, the desirable pathway for reduction of TCP is the formation of 3-chloro-1-propene (also known as allyl chloride) via dihaloelimination, which is then rapidly reduced to propene through hydrogenolysis [24][1][32]. ZVMs including granular zero-valent iron (ZVI), nano ZVI, palladized nano ZVI, and zero-valent zinc (ZVZ) have been evaluated by researchers[24][1].

ZVI is a common reductant used for ISCR and, depending on the form used, has shown variable levels of success for TCP treatment. The Strategic Environmental Research and Development Program (SERDP) Project ER-1457 measured the TCP degradation rates for various forms of ZVI and ZVZ. Nano-scale ZVI and palladized ZVI increased the TCP reduction rate over that of natural attenuation, but the reaction is not anticipated to be fast enough to be useful in typical remediation applications[22].

Commercial-grade zerovalent zinc (ZVZ) on the other hand is a strong reductant that reduces TCP relatively quickly under a range of laboratory and field conditions to produce propene without significant accumulation of intermediates[22][33][34][24]. Of the ZVMs tested as part of SERDP Project ER-1457, ZVZ had the fastest degradation rates for TCP[1]. In bench-scale studies, TCP was reduced by ZVZ to propene with 3-chloro-1-propene as the only detectable chlorinated intermediate, which was short-lived and detected only at trace concentrations[32].

Navy Environmental Sustainability Development to Integration (NESDI) Project 434 conducted bench-scale testing which demonstrated that commercially available ZVZ was effective for treating TCP. Additionally, this project evaluated field-scale ZVZ column treatment of groundwater impacted with TCP at Marine Corps Base Camp Pendleton (MCBCP) in Oceanside, California. This study reported reductions of TCP concentrations by up to 95% which was maintained for at least twelve weeks with influent concentrations ranging from 3.5 to 10 µg/L, without any significant secondary water quality impacts detected[34].

Following the column study, a 2014 pilot study at MCBCP evaluated direct injection of ZVZ with subsequent monitoring. Direct injection of ZVZ was reportedly effective for TCP treatment, with TCP reductions ranging from 90% to 99% in the injection area. Concentration reduction downgradient of the injection area ranged from 50 to 80%. TCP concentrations have continued to decrease, and reducing conditions have been maintained in the aquifer since injection, demonstrating the long-term efficacy of ZVZ for TCP reduction[2].

Potential in situ applications of ZVZ include direct injection, as demonstrated by the MCBCP pilot study, and permeable reactive barriers (PRBs). Additionally, ZVZ could potentially be deployed in an ex situ flow-through reactor, but the economic feasibility of this approach would depend in part on the permeability of the aquifer and in part on the cost of the reactor volumes of ZVZ media necessary for complete treatment.

In Situ Chemical Oxidation (ISCO)

Chemical oxidation of TCP with mild oxidants such as permanganate or ozone is ineffective. However, stronger oxidants (e.g. activated peroxide and persulfate) can effectively treat TCP, although the rates are slower than observed for most other organic contaminants[1][26]. Fenton-like chemistry (i.e., Fe(II) activated hydrogen peroxide) has been shown to degrade TCP in the laboratory with half-lives ranging from 5 to 10 hours[1], but field-scale demonstrations of this process have not been reported. Treatment of TCP with heat-activated or base-activated persulfate is effective but secondary water quality impacts from high sulfate may be a concern at some locations.

Aerobic Bioremediation

No naturally occurring microorganisms have been identified that degrade TCP under aerobic conditions[25]. Relatively slow aerobic cometabolism by the ammonia oxidizing bacterium Nitrosomonas europaea and other populations has been reported[35][25], and genetic engineering has been used to develop organisms capable of utilizing TCP as a sole carbon source under aerobic conditions[36][25][37].

Anaerobic Bioremediation

Like other CVOCs, TCP has been shown to undergo biodegradation under anaerobic conditions via reductive dechlorination by Dehalogenimonas (Dhg) species[24][38][39][40][41][25]. However, the kinetics are slower than for other CVOCs. Bioaugmentation cultures containing Dehalogenimonas (KB-1 Plus, SiREM) are commercially available and have been implemented for remediation of TCP-contaminated groundwater[42]. One laboratory study examined the effect of pH on biotransformation of TCP over a wide range of TCP concentrations (10 to 10,000 µg/L) and demonstrated that successful reduction occurred from a pH of 5 to 9, though optimal conditions were from pH 7 to 9[42].

As with other microbial cultures capable of reductive dechlorination, coordinated amendment with a fermentable organic substrate (e.g. lactate or vegetable oil), also known as biostimulation, creates reducing conditions in the aquifer and provides a source of hydrogen which is required as the primary electron donor for reductive dechlorination.

A 2016 field demonstration of in situ bioremediation (ISB) was performed in California’s Central Valley at a former agricultural chemical site with relatively low TCP concentrations (2 µg/L). The site was first biostimulated by injecting amendments of emulsified vegetable oil (EVO) and lactate, which was followed by bioaugmentation with a microbial consortium containing Dhg. After an initial lag period of six months, TCP concentrations decreased to below laboratory detection limits (<0.005 µg/L)[42].

The 2016 field demonstration was expanded to full-scale treatment in 2018 with biostimulation and bioaugmentation occurring over several months. The initial TCP concentration in performance monitoring wells ranged from 0.008 to 1.7 µg/L. As with the field demonstration, a lag period of approximately 6 to 8 months was observed before TCP was degraded, after which concentrations declined over fifteen months to non-detectable levels (less than 0.005 µg/L). TCP degradation was associated with increases in Dhg population and propene concentration. Long term monitoring showed that TCP remained at non-detectable levels for at least three years following treatment implementation[24].

Treatment Comparisons and Considerations

When selecting a technology for TCP treatment, considerations include technical feasibility, ability to treat to regulated levels, potential secondary water quality impacts and relative costs. A comparison of some TCP treatment technologies is provided in Table 2.

Table 2. Advantages and limitations of TCP treatment technologies[2]
Technology Advantages Limitations
ZVZ
  • Can degrade TCP at relatively high and low concentrations
  • Faster reaction rates than ZVI
  • Material is commercially available
  • Higher cost than ZVI
  • Difficult to distribute in subsurface in situ applications
Groundwater
Extraction and
Treatment
  • Can cost-effectively capture and treat larger, more dilute
    groundwater plumes than in situ technologies
  • Well understood and widely applied technology
  • Requires construction, operation and maintenance of
    aboveground treatment infrastructure
  • Typical technologies (e.g. GAC) may be expensive due
    to treatment inefficiencies
ZVI
  • Can degrade TCP at relatively high and low concentrations
  • Lower cost than ZVZ
  • Material is commercially available
  • Lower reactivity than ZVZ, therefore may require higher
    ZVI volumes or thicker PRBs
  • Difficult to distribute in subsurface in situ applications
ISCO
  • Can degrade TCP at relatively high and low concentrations
  • Strategies to distribute amendments in situ are well established
  • Material is commercially available
  • Most effective oxidants (e.g., base-activated or heat-activated
    persulfate) are complex to implement
  • Secondary water quality impacts (e.g., high pH, sulfate,
    hexavalent chromium) may limit ability to implement
In Situ
Bioremediation
  • Can degrade TCP at moderate to high concentrations
  • Strategies to distribute amendments in situ are well established
  • Materials are commercially available and inexpensive
  • Slower reaction rates than ZVZ or ISCO

Summary

The relatively high toxicity of TCP has led to the development of health-based drinking water concentration values that are very low. TCP is sometimes present in groundwater and in public water systems at concentrations that exceed these health-based goals. While a handful of states have established MCLs for TCP, US federal regulatory determination is hindered by the lack of low-concentration occurrence data. Because TCP is persistent in groundwater and resistant to typical remediation methods (or costly to treat), specialized strategies may be needed to meet drinking-water-based treatment goals. In situ chemical reduction (ISCR) with zero valent zinc (ZVZ) and in situ bioremediation have been demonstrated to be effective for TCP remediation.

References

  1. ^ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 Tratnyek, P.G., Sarathy, V., Salter, A.J., Nurmi, J.T., O’Brien Johnson, G., DeVoe, T., and Lee, P., 2010. Prospects for Remediation of 1,2,3-Trichloropropane by Natural and Engineered Abiotic Degradation Reactions. Strategic Environmental Research and Development Program (SERDP), Project ER-1457. Website   Report.pdf
  2. ^ 2.0 2.1 2.2 Kane, L.Z., Suchomel, E.J., and Deeb, R.A., 2020. Verification Monitoring for In Situ Chemical Reduction Using Zero-Valent Zinc, A Novel Technology for Remediation of Chlorinated Alkanes. Strategic Environmental Research and Development Program (SERDP), Project ER-201628. Website   Report.pdf
  3. ^ 3.0 3.1 3.2 Agency for Toxic Substances and Disease Registry (ATSDR), 2021. Toxicological Profile for 1,2,3-Trichloropropane. Free download from: ATSDR   Report.pdf
  4. ^ 4.0 4.1 CH2M HILL, 2005. Interim Guidance for Investigating Potential 1,2,3-Trichloropropane Sources in San Gabriel Valley Area 3. Report.pdf   Website
  5. ^ Oki, D.S. and Giambelluca, T.W., 1987. DBCP, EDB, and TCP Contamination of Ground Water in Hawaii. Groundwater, 25(6), pp. 693-702. DOI: 10.1111/j.1745-6584.1987.tb02210.x
  6. ^ 6.0 6.1 Kielhorn, J., Könnecker, G., Pohlenz-Michel, C., Schmidt, S. and Mangelsdorf, I., 2003. Concise International Chemical Assessment Document 56: 1,2,3-Trichloropropane. World Health Organization, Geneva. Website   Report.pdf
  7. ^ National Toxicology Program, 2016. Report on Carcinogens, 14th ed. U.S. Department of Health and Human Services, Public Health Service. Free download from: NIH   Report.pdf
  8. ^ United States Environmental Protection Agency (USEPA), 2019. Fifth Five-year Review Report, Tyson’s Dump Superfund Site, Upper Merion Township, Montgomery County, Pennsylvania. Free download from: USEPA   Report.pdf
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See Also

ATSDR Toxicological Profile: https://www.atsdr.cdc.gov/ToxProfiles/TP.asp?id=912&tid=186

EPA Technical Fact Sheet: https://www.epa.gov/sites/production/files/2014-03/documents/ffrrofactsheet_contaminant_tcp_january2014_final.pdf

Cal/EPA State Water Resources Control Board Groundwater Information Sheet: http://www.waterboards.ca.gov/gama/docs/coc_tcp123.pdf

California Water Boards Fact Sheet: http://www.waterboards.ca.gov/drinking_water/certlic/drinkingwater/documents/123-tcp/123tcp_factsheet.pdf