Lion, Tigers, and Plants, Oh My!!

Modeling Biotic Uptake

So now that we've seen some of the outlying reasoning behind environmental modeling and what we are trying to prevent, I thought I'd move this blog in yet another direction. I've talked about radionuclide dispersion in air, water, and ground. Yes it can disperse in all those ways. Thus we, as nuclear educated people want to model such occurrences. We want to model the results due to these dispersions resulting from storage types, nuclear project types, normal operation, disasters, and leaks. But one that area of modeling that has seemed to interest me is the modeling of those true third-parties to our nuclear industry. How does the world's nuclear activities affect the biotic life here. How does it get dispersed after animals drink from a contaminated stream or plants are irrigated by contaminated ground water. I find that to be truly interesting for some reason and hopefully you do as well. I am impressed that even these effects are both monitored and modeled, effects that I didn't even think much about prior to this year. Of course, most of the studies are human centered. We care about the food chain of which we are a part of and usually the endpoint of. How does the beef from a cow that was eating radioactive feed affect us? What kind of variables do they track and model? If you think this is interesting, well you can keep reading and even glance through this enormous textbook here to sate your curiosity. I would recommend a glance through sections 2 & 3 that relate to plants and animals. That link goes rather in depth being even specific to each radionuclide and can give you more than you would want to know. However, today I just plan to give a quick overview of some of the thoughts and factors that are assessed when these effects are modeled. Mainly to avoid typing out a textbook of which I would not get paid for, I'll just try and hit some of the highlights that I found interesting. It should be noted that for some specific radionuclides there is not enough data in order to draw conclusion about how they transfer into plants and animals. Thus it is common to compensate by utilizing stable radionuclides that more data may be available for. Also chemical analogues can be used instead. For example, Radium is similar to Calcium and understanding Calcium absorption can then lead to Radium transfer data.

Plants

Plants are rather cool organisms for study. They absorb water and nutrients from the soil. Some nutrients can even be dissolved in the water and then absorbed by the plant. Thus it would make sense that a major area of study is what happens when plants absorb radionuclides on top of these nutrients. There also is a possibility for aerial deposition. The main goal of these studies are to figure out a transfer coefficient which would work out to be how much radionuclide enters a plant relative to how much was readily available. Eventually these plants with high transfer coefficients and high radionuclide concentrations come back to us into our own diets. With plants it is important to analyze what type of event the contamination is coming from and consequently what form or chemical species the contaminant will be in when it arrives at the plants. In this sense, the study has pointed identifying the contaminant as either oxides or activation/products. One group primarily would remain in an insoluble particulate form in the normal environment (pH and reductive capacity) and the other would mainly be dissolved. Some species may primarily exist in ionized forms which can aid in stability and assist in its bioavailability (unaltered absorption). Plants also have interesting methods in which they handle the contaminates. Chemical analogs are analyzed with them being transferred similar to the normal nutrients. Other contaminants that are not similar to the normally absorbed nutrients are seen as toxins. Sometimes they do enter and sneak past. Often they are blocked, remaining in the soil. But some do trickle by. Another mechanism is the selective absorption of the radioactive contaminant/chemical contaminant that is then neutralized or compartmentalized (locked up) in a safe place away from vital processes.

Animals

Of course animals are of great interest. With me being the arch-enemy of every vegetarian (you know who you are) out there, this type of modeling is of great interest. Actually I'm okay with vegetarians  as this means more meat for me. Mostly joking though as I am also concerned with the health of the animals themselves and modeling how they absorb under conditions is of great relevance. This study goes into cow milk, sheep milk, goat milk, beef, pork, lamb and such. All topics that again weren't at the top of my mind when I thought of environmental exposure and modeling. Studies are done to figure out transfer coefficients basing them off of the radioactivity of the selected food (milk, beef, etc) divided by the feed that was given to the animal. Of interest as well is the ratio of the chemical analogs such as Ra/Ca and Cs/K as this can be a direct indicator of absorption. Scientists can get an apparent absorption by seeing the radioactivity of the feed given and compare it to the fecal matter's radioactivity. Some magnitude of the difference can then be assumed to absorbed into circulation. Obviously, animals should not want radioactivity to settle into their tissue thus homeostatic processes exist to secrete the contaminants, This can be modeled as well as it is excreted through urinary and fecal processes. Actually pooling in the milk leading to excretion is another form of homeostatic control and removal or radionuclides. Getting averages for these excretion methods can help in modeling versus diffect levels of radioactive feed and different animals subjected to it.

All in all, this was just a brief exploration of the some environmental modeling. I hope you enjoyed it. If anything peaked your interest you can follow the previously mentioned link or go through the citation below. Thanks

Cited:
http://www.pnnl.gov/main/publications/external/technical_reports/PNNL-14321.pdf