Team:UESTC-China/description

Team:UESTC-China/Introduction - 2017.igem.org

Overview

The progress of the chemical industry and agriculture has brought great convenience to our lives. But a large number of chemical pollutants have been discharged through various means, most of them difficult to degrade and accompanied by toxicity, seriously polluting our environment. Among them, Organochlorine compounds is occupy a large part of the proportion. Through collecting questionnaire and soil research in most parts of China, our project is directed against 1,2,3-Trichloropropane - an organic chloride which is a less concerned and insecurity pollution. In this summer, we decided to use synthetic biology methods to achieve plant degradation of 1,2,3-trichloropropane by transferring three enzymes to tobacco to produce glycerol, which is environmentally friendly and recyclable.

The distributions of pollutant 1,2,3-TCP

1,2,3-Trichloropropane(TCP), an emerging organic pollutant, usually formed as industrial solvents[1] and also is a raw material for the production of 1,1,2,3-Tetrachloropropene and other chemical substances[2]. In agriculture, it has been one of the ingredients of soil fumigants, as well as a harmful byproduct for the production of other pesticides. The global yield of TCP reached about 50,000 tons annually[3] at present. Because it is biodegradation-recalcitrant[3] and will cause groundwater pollution and the damage of soil if it is discharged without treatment.

Table 1. Lethal concentration data. These experiments show that TCP is a DNA reactive carcinogen. [4]~[6]

Human data: It has been reported that objectionable ocular and mucosal irritation were experienced after 15 minutes of exposure to 100 ppm

Species Reference LC50(ppm) LCLo(ppm) Time Adjusted 0.5-hrLC (CF) Derived value
Mouse Izmerov et al. 1982 555 \ 2 hr 888 ppm (1.6) 89 ppm
Mouse McOmie & Barnes 1949 \ 5,000 20 min 4,350 ppm (0.87) 435 ppm
Rat McOmie & Barnes 1949 LC100: 700 \ 4 hr 1,400 ppm (2.0) 140 ppm
Mouse McOmie & Barnes 1949 LC100: 700 \ 4 hr 1,400 ppm (2.0) 140 ppm
Mouse McOmie & Barnes 1949 LC100: 340 \ 4 hr 680 ppm (2.0) 68 ppm
Rat Smyth et al. 1962 LC83: 1,000 \ 4 hr 2,000 ppm (2.0) 200 ppm
Rat UCC 1973 LC83: 5,600 \ 1 hr 7,000 ppm (1.25) 700 ppm

One of the most serious pollution incidents was happened at Californians. TCP was spread to all over California because the agricultural divisions of Dow Chemical and Shell started selling two soil fumigants (D-D and Telone) including TCP from the 1940s. Although TCP was banned from use in soil fumigants in the 1990s,there was a large amount of TCP remained and it was frequently detected in drinking water, threating to people's lives seriously[7].

Figure 1 This map was produced by KQED[7], drawing on information from the State Water Resources Control Board. It shows water systems where significant levels of the 123-TCP have been detected. Image courtesy KQED, whose reporter, Sasha Khokha, recently found her own water supply to be contaminated as part of a story on this issue.

What’s more, Dr. Qian Yong from China University of Geosciences has studied the behavior and relevant mechanism of TCP. At the ruins of a factory which was running from 1976 to 1979, he found TCP in high concentration(3890mg / L) underground in 2016[8].

Figure 2. The distribution of TCP contamination underground at this factory[8].

That tell us TCP can keep in the soil and groundwater for years, showing the great stability of TCP in the groundwater and soil. By the way, some researches show the adhesion of 1,2,3-TCP is very low[8], which means that it can easily spread into people's living area and threaten people's health because of its potential carcinogenicity and the huge damage to the kidney. The best evidence is that TCP has been detected around the world more and more frequently in the past decade.

Figure 3. The important report about TCP contamination[3]. We can learn about that the contamination of TCP are becoming more serious.

To sum up, we know that TCP is a very dangerous contaminant. However, governments don't pay enough attention to 1,2,3-TCP.Most counties even don't include 1,2,3-TCP into the pollutant detection list. Under these circumstances, we hope that we can attract attention of the society and contain the spread of 1,2,3-TCP pollution through this project.

Ways to treat 1,2,3-TCP

How do people solve TCP? Traditional remediation technology to treat 1,2,3-TCP includes granular activated carbon (GAC), dechlorination by hydrogen release compound (HRC®), reductive dechlorination by zero valent iron(ZVI) and so on. Most of them are inefficient and impractical. There are just a few methods such as ZVI that has a good efficiency. But all of them are cost and hard to large-scale deal with TCP in nature.[10]~[12]

Figure 4. Treatability tests with 1,2,3-TCP-contaminated groundwater/soil[10].

In that scenario, the concept of " Microbial remediation " began to be respected by people. Some studies have shown that 1,2,3 trichloropropane may be converted to CO2, H20 and HCl by biocatalytic action under the oxidative co-metabolism of O2 as the electron acceptor, so that people are mainly seeking to degrade in aerobic microorganisms method. Unfortunately, scientists have failed to enrich and screen aerobe which can degrade 1,2,3 - trichloropropane. However, they found several strains could degrade TCP in absolutely anaerobic environment . But this method, anaerobic microorganism degradation , hasn't been spread because of its harsh condition and low conversion efficiency. So there are some studies that want to introduce a series of enzyme genes into microorganisms such as Escherichia coli and Pseudomonas putida to degrade TCP. This method is efficient. But it has some limitations. First, these microoganisms have strict nutrient demand and weak competitiveness. Second, they may cause antibiotic resistance gene. Third, they usually depend on special inductions so that they can work. So, we hope to find a better method that can degrade TCP for a long time without extra resource[3]. In this time，Phytoremediation, a safe and long-lasting remediation strategy，go into our field of vision

Our strategy

As an emerging "Green remediation" technology, phytoremediation shows its own great potential. Compared with "Bioremediation", its advantages are very obvious. The most amazing one is that plants have a set of photosynthetic autotrophic system which means they can degrade TCP in a long time and just need a little nutrition input, This method is easier and cheaper. Plants can also stabilize soil and absorb CO2 while cleaning the environment.

Figure 5.The main models of phytoremediation strategy.

"Phytoremediation"[13] mainly contains four models: Phytoextraction, Phytostabilization, Phytovolatilization and Phytodegradation. Through analyzing physical and chemical properties of 1,2,3-TCP, we know that 1,2,3-TCP is unlikely to become concentrated in plants and aquatic organisms because it has a low estimated bioconcentration factor (BCF) and sticking coefficient. So it is difficult to degrade 1,2,3-TCP with phytoextraction and phytostabilization. Furthermore, it needs a complex system to deal with these plants if we choose phytoextraction and phytostabilization, which requires much time and effort. By the way, phytovolatilization is more unsuitable because 1,2,3-TCP , inhaled by ml9human body, would create more damage in the gas. Thus, we finally identified the strategy of phytodegradation. We introduce the gene of three enzyme-haloalkane dehalogenase(DhaA31), haloalcohol dehalogenase(HheC) and Epichlorohydrin epoxide hydrolase (EchA) into model plant- Nicotiana tabacum and transform 1,2,3-TCP into glycerol

References

  1. EPA. Technical Fact Sheet – 1,2,3-Trichloropropane (1,2,3-TCP), 2017.
  2. Liu FS. The comprehensive utilization of 1,2,3-Trichloropropane. Speciality Petrochemicals, 1995;2:11-4.
  3. Samin G, Janssen DB. Transformation and biodegradation of 1, 2, 3-trichloropropane (TCP). Environmental Science and Pollution Research, 2012. 1;19(8):3067-78.
  4. McOmie WA, Barnes TR. ACUTE AND SUBACUTE TOXICITY OF 1, 2, 3 TRICHLOROPROPANE IN MICE AND RABBITS. InFEDERATION PROCEEDINGS 1949 Jan 1 (Vol. 8, No. 1, pp. 319-319). 9650 ROCKVILLE PIKE, BETHESDA, MD 20814-3998: FEDERATION AMER SOC EXP BIOL. PROCEEDINGS (Vol. 8, No. 1, pp. 319-319). 9650 ROCKVILLE PIKE, BETHESDA, MD 20814-3998: FEDERATION AMER SOC EXP BIOL.
  5. UCC. Toxicology studies: 1,2,3-trichloropropane. New York, NY: Union Carbide Corporation, 1973.
  6. Smyth Jr HF, Carpenter CP, Well CS, Pozzani UC, Striegel JA. Range-finding toxicity data: List VI. American Industrial Hygiene Association Journal. 1962 Mar 1;23(2):95-107.
  7. Sasha Khokha . California Finally Begins Regulating Cancer-Causing Chemical Found in Drinking Water. KQED Science Menu, 2017.
  8. Qian Yong. Research on Environment Behavior of 1,2,3-Trichloropropane in Groundwater of a Contaminated Site with Chlorinated Pollutants. China University of Geosciences(Beijing). 2016
  9. Kang JW. Removing environmental organic pollutants with bioremediation and phytoremediation. Biotechnology letters, 2014. 1;36(6):1129-39.
  10. Tratnyek PG, Sarathy V, Fortuna JH. Fate and remediation of 1, 2, 3-trichloropropane. InInternational Conference on Remediation of Chlorinated and Recalcitrant Compounds, 6th, Monterey, CA 2008.
  11. Sarathy V, Salter AJ, Nurmi JT, O’Brien Johnson G, Johnson RL, Tratnyek PG. Degradation of 1, 2, 3-trichloropropane (TCP): hydrolysis, elimination, and reduction by iron and zinc. Environmental science & technology, 2009. 14;44(2):787-93.
  12. Sarathy V, Salter AJ, Nurmi JT, O’Brien Johnson G, Johnson RL, Tratnyek PG. Degradation of 1, 2, 3-trichloropropane (TCP): hydrolysis, elimination, and reduction by iron and zinc. Environmental science & technology, 2009. 14;44(2):787-93.
  13. Cherian S, Oliveira MM. Transgenic plants in phytoremediation: recent advances and new possibilities. Environmental science & technology, 2005. 15;39(24):9377-90.