The Problem

For over a century , dioxins – and specifically chlorinated dioxins – have been notorious as some of the most toxic and persistent environmental pollutants. Though some dioxins occur naturally, 2,3,7,8-tetrachlorodibenzodioxin (TCDD), the most toxic chemical of this family, is completely synthetic. These compounds are extremely stable, and due to their synthetic nature, many are not easily broken down by living organisms. Dioxins remain in our ecosystems for decades, causing harm to all that come in to contact with them.

The toxicity of TCDD is such that varying doses of the toxin had caused cancer in all animals tested. TCDD’s effect is widespread, reaching almost all of the internal organs, but in mammals mainly affects the liver. Birth defects as well as severe developmental issues have been observed in humans as well as other animals. TCDD is more toxic than Sodium Cyanide, ricin and even plutonium.

How is TCDD created?

TCDD is not, and has never been produced commercially except as a pure chemical for scientific research. It is, however, a byproduct of chlorophenols or chlorophenoxy acids which are produced as herbicides and fungicides. It may also be formed along with other polychlorinated dibenzodioxins (PCDD’s) and dibenzofuranes (PCDF’s) during incineration, especially if certain metal catalysts such as copper are present. Generally, small amounts of PCDD/Fs are formed whenever organic materials such as oxygen and chlorine are available at suitable temperatures. As a result of this, when organic material is burned in less-than-optimal conditions- open or building fires, domestic fireplaces, and poorly operated and designed solid waste incinerators- these chemicals are synthesized at the highest high rates. Historically, municipal and medical waste incineration was a central source of PCDD/Fs.

Other sources of PCDD/F include:
  ·Metal smelting and refining.
  ·Chlorine bleaching of pulp and paper - historically important source of PCDD/Fs to waterways.
  ·Synthesis side products of several chemicals, especially PCBs, chlorophenols, chlorophenoxy acid herbicides and hexachlorophene.
  ·Uncontrolled combustion, particularly open burning of waste ("backyard barrel burning"), accidental fires, wildfires.
  ·Engines using leaded fuel, which contained the additives 1,2-Dichloroethane and 1,2-Dibromoethane, (a practice no longer used).

Mode of action

TCDD and dioxin-like compounds act via a specific receptor present in all cells: the aryl hydrocarbon (AH) receptor. This receptor is a transcription factor which is involved in expression of genes; in fact, it has been shown that high doses of TCDD affects expression of several hundred genes in rats, increase some while decreasing others. Research shows a particularly strong effect on transcription of enzymes activating the breakdown of foreign and toxic compounds.

The method currently being employed to decontaminate soils in Vietnam involves the transport heavily contaminated soils to a castle-sized, makeshift “oven”. Once there, the soil is incinerated 350°C for months. Although this method successfully rids soils of their dioxin contaminants it is impractical for a number of reasons.

1. Only so much soil can be gathered for purification.
2. The process is detrimental to the soil, damaging both microbial communities and soil structure.
3. This method is unsustainable, and harmful to the environment at every stage.

Additionally, is important to note that dioxin pollution is found in small amounts nearly everywhere in the world- as such soil-burning would be far too inefficient and expensive to deal with these types of contaminations.

Our Solution

The biological solution we have designed is a novel enzymatic pathway capable of breaking down TCDD into harmless metabolites. We have identified a group of enzymes derived from different organisms that, when combined, completely degrade TCDD. We incorporated these enzymes into a single transgenic plant that can breakdown TCDD and dioxins, as well as detoxify chlorinated pollutants.

We chose plants as the host for this pathway for several reasons:

1. Plants are easy to track and control. Through various genetic and molecular methods, we can sterilize the plants to ensure our GMO’s don’t invade the ecosystem.

-By contrast, microbes require more intricate and complicated control mechanisms that hinder efficiency and flexibility regarding the implementation of our research.

2. Plants possess specific attributes that are critical to our project’s success.

-Plant root systems are efficient at accumulating dioxins from soil and water.
-Plants naturally contain useful enzymes, that aid in the breakdown of TCDD.

3. Utilizing plants, which sit at the bottom of the food chain, we can keep animals in polluted areas safe, and avoid bioaccumulation of TCDD.

Team:HebrewU/Description