Team:Leiden/TheProblem

iGEM Leiden Wiki : Project

The Problem

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. Our interest in this red planet never diminished and now, after 46 unmanned missions, serious plans are being made to finally travel to this inhabited planet. 27 September: SpaceX announced their plans to send humans to Mars by 2024 and start the colonization of this planet. But the question might rise: Which hurdles do we have to overcome in order to survive and make the colonization of Mars 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. We aim to get rid the toxic compound perchlorate. Martian soil contains a fair amount of up to 0.5-1% of this compound, which is 10.000 times more concentrated(?) compared to concentrations found on earth. Because of these high concentrations, cultivation of edible crops would be impossible. Also, there is an increased interest in perchlorate contamination of drinking water on earth toxicity. 7


Perchlorate

Perchlorate is a chemical anion, which consists of one chlorine atom and four oxygen atoms arranged in tetrahedral geometry (ClO4-) . 8 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. Due to the high activation energy associated with the reduction of perchlorate, the anion is very persistent in the environment. This causes the accumulation of the toxin in surface- and groundwater. The main source of perchlorate found in drinking water is primarily associated with releases of ammonium perchlorate by military operations and aerospace programs. It can be biologically degraded by a number of bacteria possessing perchlorate reductases, enzymes that facilitate the reduction of perchlorate. Unfortunately, many of these organisms prefer oxygen and require specific growth conditions to be able to reduce perchlorate. 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. 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 These dust particles, present on Mars as well as on the Moon, are approximately 1.6 µm. This is very small compared to sand particles, which have range of 0.0625 mm to 2 mm. Due to the small size of these dust particles, they can cause some serious health problems. 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 can cause irritations of the eyes, mucus and skin and could result in coughing and short breathing. During the first Moon mission, the astronauts’ suits were embedded in dust particles which could not be brushed off. Also the Lunar module, including the atmosphere the astronauts breathed, was full of dust. But there are also indirect effects of perchlorate salts present in Martian soil. If future colonizers 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


Earth

Perchlorate was added to the Contaminant Candidate List (CCL) for drinking water in 1998 by the US Environmental Protection Agency (EPA), after its presence was discovered in drinking water supplies in the southwest of the United States. 9 On earth perchlorate salts are formed naturally in small amounts in our environment. However, most of the perchlorate contamination is associated with military activities or defense contractors. 10 More than 90% of the perchlorate salts are manufactured as ammonium perchlorate to be used as rocket fuel, explosives and fireworks. 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. 4 According to the EPA the estimated annual costs for public water systems to comply with a 4 microgram/L of perchlorate limit are 120 million dollar (in 2013). This is still less than the annual 320 million dollar costs of the arsenic rule of 10 microgram/L. 5 In Europe perchlorates 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 compounds have also been found in infant formulae, with mean concentrations of 10 microgram/kg. 6


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. Because the perchlorate ion is similar to the iodide ion, it can be taken up in place of it by the thyroid gland. By doing this, perchlorate disrupts the production of thyroid hormones, thereby disrupting the metabolism and indirectly other physiologic systems. 11 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)


References:
  1. Space.com
  2. Hutchinson, S.L. (2004) A Study on the Accumulation of Perchlorate in Young Head Lettuce, final report - U.S. Environmental Protection Agency (September 2004) - June 18 2016
  3. Perchlorate in Drinking Water: Regulatory Update and Treatment Options
  4. American water works association: National perchlorate cost update
  5. EFSA (European Food Safety Authority). 2011. Scientific Opinion on the risks for public health related to the presence of zearalenone in food. EFSA J 9:1–124.
  6. Kucharzyk, K. H., Crawford, R. L., Cosens, B. & Hess, T. F. Development of drinking water standards for perchlorate in the United States. J. Environ. Manage. 91, 303–310 (2009)
  7. Pubchem
  8. US Environmental Protection Agency (1998): Drinking Water Contaminant Candidate List. Washington, DC, Doc No EPA/600/F-98/002
  9. Gullick RW, LeChevallier MW, Barhorst TS (2001): Occurrence of perchlorate in drinking water sources. J Am Water Works Assoc 93 (1) 66–77
  10. Wolff J (1998): Perchlorate and the thyroid gland. Pharmacol Rev 50, 89–105