Difference between revisions of "Team:UESTC-China/description"

Overview

Chemical industry brings us comfortable life, but it also let us pay a heavy price at the same time. A large number of chemical contaminants are discharge through various means, polluting our environment. And organic halide is important part in these pollution. Our project in this year is directed against 1,2,3-Trichloropropane – an organic chloride which is a less concerned but unsecured pollution. We intend to effectively degrade 1,2,3-trichloropropane by transferring it into a three-enzyme plasmid to the Nicotiana tabacum.

Harm of 1,2,3-TCP

1,2,3-Trichloropropane(1,2,3-TCP), an emergent organic pollutant, formed as a by-product during the synthesis of various chemicals and was present in commercial preparations of the soil fumigant 1,3-dichloropropene (also known under the trade name D-D).

Figure 1 The earliest record about 1,2,3-TCP is that it was spread to the fields around California

as a part of soil fumigants(D-D and Telone) produced by Dow Chemical and Shell.

Having detected frequently in various occasions in recent years, 1,2,3-TCP has gradually aroused people's attention in the world. Animal experiments show that it has a great deal of damage to livers and kidneys of the animals and makes them die at certain concentration. It has been classified as "likely to be carcinogenic to humans" by the EPA. Dr. Qian Yong the concentration up to 3890mg / L of 1,2,3-TCP from 5m to 15m underground at the ruins of a factory, running in the 1970s shows.

Figure 2 1,2,3-TCP flowed to the depths of the ground and kept about 30 years,

which make it easy enter into people’s life with groundwater.

The discovery proves the stability and permeability of 1,2,3-TCP. By the way, some researches show the adhesion of 1,2,3-TCP is very low, which means it easy to spread in nature and enters to people's life through a variety of ways such as groundwater, threatening people's health. The tap water around the world has been detected 1,2,3-TCP frequently, proving the harmfulness of 1,2,3-TCP.

Figure 3 The 1,2,3-TCP was frequently detected in the recent years

However, governments don't pay enough attention to 1,2,3-TCP. Some counties, like China and American, even don't include 1,2,3-TCP into the pollutant detection list. Under these circumstances, we hope that we can attract the attention of the society and contain the spread of 1,2,3-TCP pollution through this project.

Technology to treat 1,2,3-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 zinc and others. They have difference disadvantages such as inefficient, expensive or impractical. So it is hard to treat 1,2,3-TCP in large-scale. In recent years, the concept of "Bioremediation" has been respected by people. There is someone that has successfully introduced the genes of specific enzyme which can degrade 1,2,3-TCP into microorganism such as Escherichia coli, Pseudomonas putida. These strain are efficient. However, it’s shortcomings are also very obvious. First, the strain usually work in the bioreactor with favourable bacterial density and continuous nutrient input. It is very difficult and expensive to make it in nature. Second, some strain like Pseudomonas putida is a kind of pathogen and them may be create security issues. At last, the degradation of them will produce secondary pollution. On one word, the “Bioremediation” to 1,2,3-TCP isn’t a safe and efficient strategy for us now. So, we paid our attention to "phytoremediation", which hasn’t been tried.

Our strategy

Compared to "Bioremediation", the advantage is very obvious. The most important one is that plant has a set of photosynthetic autotrophic system which means it can degrade 1,2,3-TCP in a long time and just need little nutrition input, easier and cheaper. The plant can aslo stabilized soil and absorb CO2 while clean the environment. Furthermore, plant material can be reworks into wood chips, pulp and some of the plants that treat heavy metals, and heavy metals are recovered. "Phytoremediation" mainly contains four ways: Phytoextraction, Phytostabilization, Phytovolatilization, Phytodegradation.

Figure 4 The four main models of Phytoremediation

Combined with the physical and chemical properties of 1,2,3-TCP, we learn about that 1,2,3-TCP is unlikely to become concentrated in plants other aquatic organisms because it has a low estimated bioconcentration factor (BCF) and sticking coefficient(lgKoc). So it is difficult to treat 1,2,3-TCP using phytoextraction and phytostabilization. Moreover, it needs a complex system to deal with these plant if we choose phytoextraction and phytostabilization, which require much time and effort. By the way, phytovolatilization is more unsuitable because 1,2,3-TCP , inhaled by human body, will create more damage in the gas. Thus, we finally identified the strategy of phytodegradation. We introduce the gene of three enzyme-haloalkane dehalogenase(dhA31),haloalcohol dehalogenase(HheC) Epichlorohydrin epoxide hydrolase (echA) into model plant- Nicotiana tabacum and transform 1,2,3-TCP into glycerol.