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iGEM Leiden Wiki / Project

The Project

Introduction

That's one small step for man, one giant leap for mankind – Neil Armstrong

15 July 1965, a memorable day for every human interested in our deep space. After six unsuccessful attempts, NASA's Mariner 4 finally managed to send back 21 pictures of the Martian surface. The first pictures ever taken from another planet from space. Since then our interests in this red planet never increased and now, after 46 unmanned missions, serious plans are being made to finally travel to this inhabited planet. In September, SpaceX will announce their plans to send humans to Mars by 2024 and start the colonization of this planet. But the questions might rise, which hurdles have to be overcome in order for us humans to survive this inhabited place and make the colonization a success? Synthetic Biology and Space colonization share a common feature; both seem like science fiction, but are actually happening right under our noses and will be the topic of our future. So why not combine these fields and make a contribution to Mars colonization? The subject we are working on will be one of the bigger problems for building a self-sufficient colony on the planet, the toxic compound perchlorate. Martian soil contains a fair amount of 0.5-1% of this anion, up to 10.000 times more compared to concentrations found on earth, which could make the cultivation of edible crops impossible. Also, perchlorate has been shown to play a role on earth and the awareness of the dangers of this toxin are growing.

Perchlorate

Perchlorate is a chemical anion, which consists of one chlorine atom and four oxygen atoms, written by the formula CLO4-. The salts, such as ammonium perchlorate (NH4ClO4) and sodium perchlorate (NaClO4), are extremely soluble in water and dissociate in their partner cation and the perchlorate anion relatively quick. This anion is very mobile and remains stable once formed. This may cause the accumulation of the toxin in surface and groundwater. Degradation of perchlorate under natural circumstances can take years to decades and also sorption to soils and sediments is not likely. Therefor perchlorate will persist in the environment for a long period of time. In fact, other than in some bacterial systems, perchlorate reduction is not observable, except when it is mixed with a hot and concentrated reducing agent, a solution which is explosive. ¹

Mars

Mars is there, waiting to be reached – Buzz Aldrin

May 2008 – This was the first time NASA’s Phoenix lander detected perchlorates in arctic Martian soil. Still, more recently, the space agency spotted perchlorates in the Gale Crates with their Curiosity Rover, which landed on the red planet in 2012. According to investigator at the University of Arizona, the high levels of perchlorate present in the Martian soil and dust particles would be toxic to humans. ² But how to avoid something so small, it gets stuck onto everything? These dust particles present on Mars as well as on the Moon, are approximately 1.6μm, by comparison sand has a range of 0.0625 mm to 2 mm. Due to this small size, they might cause some serious problems. With the first Moon mission, these particles had several consequences. The astronauts’ suits were embedded in dust, which could not be brushed off. Also the Lunar module, including the atmosphere the astronauts breathed, was full of dust. When exposed to pure perchlorate salts, such as these dust particles on Mars, the toxin can be absorbed through the skin and may enter the lungs. This may cause irritations of the eyes, mucus and skin and could result in coughing and short breathing. But there are also indirect effect of perchlorate present in these soils for the human settlement on Mars. If future calorizators ever want to cultivate edible crops from the grounds, detoxification is necessary. If not, crops could accumulate the toxic compound in their biomass and become a toxic source for humans. An irrigation study performed with lettuce grown in greenhouses on perchlorate soils with known concentrations, suggested an incorporation into plant tissue of a majority of the compound (around 79%). ³ However, the presence of perchlorates on Mars have some positive effects as well. For example, Perchlorates lower the freezing point of liquid water. With the salt concentrations, small amounts of water would make the water activity sufficient for the viability of terrestrial life on the planet. ⁴

Earth

Because of uncertainties about toxicity and health effect at low levels of perchlorate, as well as the effect on environment, this compound raises lots of concerns. On earth perchlorate salts are formed naturally in small amounts in our environment. However, the biggest source of perchlorate contamination arises from the use of nitrate fertilizers and the chemical industry. Here the compound is used for a variety of products, of which more than 90% is manufactured as ammonium perchlorate to be used as rocket and missile engine. Also in explosives, flares, fireworks and other industrial processes, this compound is commonly found. Every time someone illuminates beautiful blue-colored firework, think about perchlorate going in the air.

Figure 1. Sources of perchlorate contamination

In 1998 perchlorate was first detected in drinking water in the Southern US, after which the EPA (environmental protection agency) added the compound to its Contaminate candidate list (CCL). Most of the contamination could be associated with military activities. More recent studies found contamination of ground- and surface waters in at least 26 states, which serve as drinking water sources for more than 16 million people. ⁵ According to the EPA the estimated annual costs for public water systems to comply with a 4microgram/L of perchlorate limit are 120million dollar (in 2013). This is still less than the annual 320 million dollar costs of the Arsenic rule of 10 microgram/L. ⁶ In Europe perchlorate have also been detected in crops. According to the European Commission the presence of perchlorate in fruits and vegetables is more widespread than initially expected, mostly due to the use of certain fertilizers. The toxic compound have also been found in infant formulae, with mean concentrations of 10microgram/kg. ⁷

Health

If you get exposed to perchlorates, many factors contribute to the toxicity. Such factors include the physical form of the compound, the dose, the duration of exposure and how you come in contact with the salt. On earth people might get exposed to the toxin, by ingestion of contaminated food or drinking water. After which the perchlorates travel via the intestines to the bloodstream. If someone breaths in dust particles, such as the particles present on Mars, the toxin can enter the bloodstream via the lungs. When present in the bloodstream, the main target organ for the perchlorate toxicity is the thyroid gland. This gland is responsible for the synthesis of the thyroid hormone, for which it needs the ion Iodine. The hormone is necessary for our metabolism. Because of the similarity in size of Perchlorate ions and Iodine ions, the compound has the ability to interfere with the uptake of iodine ions by the thyroid gland. Thereby disrupting the production of thyroid hormones and thus disrupting your metabolism and indirectly other physiologic systems. The reference dose for perchlorates has been set at 0.007 milligrams per kilo (24.5ppb). However, further studies are necessary to be able to completely answer all questions regarding toxicity.

Mars will come to fear my botany powers. - Mark Watney, The Martian (2015)

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