Difference between revisions of "Team:Paris Bettencourt/Human Practices"

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@iGEM_Paris

Human Practices

Human Practices are a noticeable part of iGEM and more broadly of synthetic biology and science. The idea behind Human Practices is to investigate how our work will influence the world, what impact it will have and what good could the society benefit from it. It starts with reverse thinking, how does the world influence your work? What problem(s) does our project tackle? Our project, Frank&Stain, aims to find a biological way to degrade wine pigments, anthocyanins. But why caring so much about stains? Wine stains, among other stains, are difficult to remove after some time and people usually send their stained clothes to dry cleaners.

PERC

What is PERC?

Perchloroethylene (aka tetrachloroethylene or PERC) is the main chemical found in products used for dry cleaning worldwide. It acts as a solvent to remove stains from all types of fabrics, since it is an excellent solvent for organic materials. It is volatile, highly stable and non-flammable, reasons for which it is so widely used in this industry. The big selling point of this chemical is that it is quite effective and quite cheap, which means that almost all dry cleaners throughout the globe use it daily.
The problem is that PERC is quite toxic, both for humans and the environment. Like many other chlorinated hydrocarbons, PERC acts as a central nervous system depressant, and due to its volatile character, it can enter the body through both the respiratory system and dermal exposure. The World Health Organisation’s International Agency for Research on Cancer lists it as being a group A2 carcinogen, which means that it is “probably carcinogenic to humans”. It can also dissolve fats from the protective layer of the skin, potentially resulting in skin irritation. Animal studies have already shown evidence that exposure to PERC increases the risk of developing Parkinson’s disease in ninefold, and the compound has been shown to cause liver tumours in mice, and kidney tumours in rats. PERC is also labelled as toxic for the environment, since its degradation is quite slow, having an estimated atmospheric half-life of 100 days.

The predominant routes of exposure to PERC for the general population are the inhalation of the compound from both ambient and indoor environments, and ingestion, by drinking water contaminated with it. People working on the dry cleaning industry are, of course, exposed to higher levels of PERC than the general population, and, in addition, people residing near dry cleaning locations are also exposed to high levels, due to the volatile nature of the compounds and to vapour intrusion.

Because of all these reasons, the French government has set up as one of their goals for the Horizon 2020 the complete banning of PERC from dry cleaning establishments situated close to residential areas. Similar laws had been already passed in Denmark and the USA.

What are the effects of PERC on human health?

PERC’s mechanism of toxicity differs from tissue to tissue. The main two targets of PERC, in the human body, are neurological tissues and hepatic tissues.

In the case of the neurological effects, experimental studies in rodents have shown that PERC alters the fatty acid pattern of the brain’s phospholipids and amino acids. This explains its neurotoxic effects. Other studies propose that PERC might be incorporated into the brain membranes, hence altering the neural conduction velocity. PERC can also interfere with the voltage-gated channels and neuronal receptors of the nervous cells. Shafer et al. (2005) showed that PERC disturbs whole-cell calcium currents as well.

In contrast with these neurological effects, which are a result of PERC itself, the hepatic effects are a result of oxidative metabolites including trichloroacetic acid and dichloroacetic acid, which accumulate on the liver.

What are the effects of PERC on the environment?

PERC is a compound that tends to volatise quickly when released into water or soil. Furthermore, it is also mobile in soil and therefore has the potential of leaching bellow the soil surface and reaching groundwater, hence contaminating it. The United States’ Health and Human Services identified PERC in approximately 4% of aquifers in the latest US Geological Survey, showing that aquifer contamination is indeed a problem.
It can biodegrade to tricholoethylene, dichloroethylene, vynil chloride or ethane through dechlorination, but these compounds are not safer than PERC itself.

What alternatives exist already to PERC?

There are already some existing alternatives to the use of PERC in dry cleaning, but the scientific community is divided regarding their safety.

The first alternative is the use of liquid silicon instead of PERC. Silicon is a commonly used solvent, which we find in products such as cosmetics, deodorants and shampoos. It is both odourless and colourless making it in theory a perfect alternative to PERC. However, some scientists have expressed their concern over the use of this chemical since no complete analysis of its impact on humans has been performed to date. Furthermore, only some countries, such as Canada and the UK, have declared liquid silicon as not harmful for the environment, which shows that there is no global consensus on its safety. Furthermore, the European Chemical Agency has reported that liquid silicone is bioaccumulative. It is very difficult to break down and it is likely to accumulate in our bodies, which is why the EU’s Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) has called for further research.

Another existing alternative is wet cleaning. This method involves the use of gentle washing machines, water, biodegradable soaps and conditioners, and various types of pressing and re-shaping equipment specialised for different types of fabric and fibre types. This method is quite expensive because it requires the investment of acquiring different machines for different fabrics, and requires a lot of training for the operators.
Although a safe alternative for the environment, the specialised detergents and conditioners are mild and not as effective on getting rid of all stains, and many tailors do not recommend it as the process can harm sensible garments.