Radiation Biology

Galactic cosmic radiation

Figure 1-21. Schematic representation of the sources of ionizing radiation in low Earth orbit.

Galactic cosmic radiation

Cosmic rays deflected by geomagnetic field

\ Inner H- trapped belt

Cosmic rays deflected by geomagnetic field j- South r Atlantic Anomaly even break apart its nucleus. It is when these events occur in body tissue that health effects may result if the cell's self-repair mechanism fails. The ionization process in living tissues consists of ejecting bound electrons from the cellular molecules, leaving behind chemically active radicals that are the source of adverse changes. Many of the radicals resulting from radiation injury are similar to those produced in normal metabolic processes, for which the cell has developed recovery mechanisms needed for long term survival. The substantive target of radiation injury is considered to be the DNA structure, which may be changed or injured directly by a passing ionized particle. The ability of the cell to repair the effects of ionization depends in part on the number of such events occurring within the cell from the passage of a single particle, and the rate at which such passages occur. During the repair process, gene translocation and other chromosome aberrations may occur.

A number of studies have identified an increased rate of unstable chromosomal aberrations in flying crewmembers and related these to cosmic radiation exposure. However, there is no epidemiological evidence to link these aberrations with the development of cancers. Nevertheless, a cell may become cancerous as a result of being irradiated, the likelihood being dependent upon the energy and the dose received. Also, a child conceived after exposure of a parent to ionizing radiation is at risk of inheriting radiation-induced genetic defects. These may take the form of anatomical or functional abnormalities apparent at birth or later in life.

Studies involving various animal models have been conducted. It has been determined that exposure to radiation during spaceflight induced mutations in Drosophila (Ikenaga et. al. 1997). Furthermore, the mutation rate in space for C. elegans was twice or three times as great as what would have been anticipated on the ground (Hartman et al. 2001).

Studies have also been conducted on primates. In one large experiment, 2-year old primates, Macaca mulatta, were subjected to varying levels of proton irradiation. Seventeen years later, mortality studies were conducted. The investigators determined that one of the leading causes of increased mortality was a significant increase in the incidence of endometriosis5 (48% in irradiated females compared to 0% in controls).

In a similar experiment done by Wood (1991), female rhesus monkeys were given total body exposures of protons of varying energies. The doses and energies of the radiation received were within the range that could

5 Endometriosis is a common medical condition where the tissue lining the uterus (the endometrium, from endo, "inside", and metrium, "mother") is found outside of the uterus, typically affecting other organs in the pelvis. The condition can lead to serious health problems, primarily pain and infertility. Endometriosis primarily develops in women of the reproductive age.

be received by an astronaut traveling in low Earth orbit (LEO) during a random solar flare event. The frequency of developing endometriosis was highly significant in the irradiated group versus the non-irradiated controls. The minimum latency period was found to be 7 years. The scientists concluded that the risk of endometriosis could not be ignored when weighing the importance of a mission versus the risk of delayed radiation effects in female astronauts. Other scientists too have the same opinion after having obtained similar results in their experiments.

Plant cells are affected by radiation, just like any other cells. Chromosome damage and abnormalities are seen in a variety of plants in space. In general, seeds are less sensitive than developing embryos or growing plants. This may be because their cells are not actively dividing.

Several studies have been done to try and determine which radiations are most damaging, or even whether the chromosome damage was solely due to radiation at all. Some studies showed that standard radioprotectant chemicals like cytosine, aminoethyliothiourea, and 5-methoxytryptamine did not stop the damage. Some of the flights on which damage was found were short enough that GCR dosages were low. Some of the chromosomal damage and abnormalities could be due to higher energy particles. Some other environmental factors, like microgravity, also remain a possibility (Thora and Scott 1990).

6 BIOTECHNOLOGY

6.1 Definition

Biotechnology is the application of engineering and technology to life sciences research. It is a set of techniques and equipment for rearranging and manufacturing biological molecules, tissues, and living organisms. Biotechnology uses living systems or derivatives of living systems to make a product or to perform a specific service. For example, the beer industry, which uses yeast to get a fermented brew, is, in a sense, a biotech industry that produces a product. The sewage disposal plant is also a service that is biotechnologically provided because microorganisms are used to remove a number of organics from the water to make the water drinkable once again, or at least amenable to reprocessing.

In the space environment, biotechnology uses microgravity or the technologies developed for the space environment to make new products or perform a specific service. We have seen that gas exchange and fluid flow in biological systems are greatly affected by fluid dynamics in a gravitational environment (see this Chapter, Section 2.2). Consequently, products that are extremely pure, flawless and/or contain smooth mixes of materials with different density are difficult or impossible to produce on Earth. But this is possible in microgravity. As described above, there are many different forces that act on liquids. In normal gravity, buoyancy-driven convection is the major mixer. In microgravity, however, surface tension, Marangoni convection, and diffusion can be the major forces of mixing. Also, containers are often not needed for microgravity processing. Instead, surface tension is used as the container. Consequently, there is no container contamination, and the heat or solution can be applied anywhere into the liquid being processed; hence, a better, purer product.

The major space applications in biotechnology are in the areas of protein crystals studies, tissue culture, and the improvement of technology such as electrophoresis.

51 Tips for Dealing with Endometriosis

51 Tips for Dealing with Endometriosis

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