PDS AP Environmental Science 5th Period 2010-11

What exactly is the fixed-dose procedure? In addition, if it is being performed on a variety of species, what exactly can be concluded from such a test?

I find the concept of threshold dose a little confusing.

Does it mean when a dose starts to have an effect or when a dose starts to have a visual effect? Because even before a dose has a visual effect it is having some effect it seems like. Could someone explain threshold dose and its definition a little better to me?

Yep, you gotta check this research out (brief ad shows before the news clip)…

A Taste for Booze: Monkeys Share a Human Vice

?!

Today we spent most of our time discussing the complications of LD50 tests. The notes are in the box if you weren’t there.

Our test subjects

Then, we spent a little time discussing animal testing, watching a few short videos to stimulate thought/discussion.

*If those videos on monkeys and spiders (wink) piqued your interest (or if you were absent), here are some other sources you might investigate:

For an in-depth overview (oxymoron?), try Wikipedia. Has some good data/graphs on which animals are used:
http://en.wikipedia.org/wiki/Animal_testing

Here is a statement from our Food and Drug Administration (FDA) on animal testing:
http://www.fda.gov/Cosmetics/ProductandIngredientSafety/ProductTesting/ucm072268.htm

The European Union has agressively fought animal testing:
http://www.cosmeticsdesign-europe.com/Products-Markets/EU-timetables-end-of-animal-testing

Here is a very pro-animal testing story from a British paper:
http://www.guardian.co.uk/science/2006/mar/04/businessofresearch.research

Here is a very anti-animal testing web page from PETA:
http://www.stopanimaltests.com/us-fda.asp

How do you feel?

If you want to know more, more, more, here is a link to a great Environmental Contaminants and Toxicology Reader at The Encyclopedia of the Earth web site. We’ve only scratched the surface, and this will give you a much more complete picture of toxicology studies and principles. Maybe a great review site before the AP Exam. LD50 is just one, very common way to rate acute toxicity, this site will show you others.

http://www.eoearth.org/article/Dose-response_relationship

So, today we discussed how children are likely to be more vulnerable than adults to the effects of environmental toxins.

Three reasons we discussed:
1. Age/developmental stage. Children don’t just pop out of the womb with fully developed detox organs (liver, kidneys, lungs) or immune systems, so they may react differently to a toxin than an adult.
2. “Living low” and oral habits. Very young kids (esp. those that haven’t learned to walk yet) spend a lot of time on the floor crawling, and can transfer trace toxins from hand to mouth often since that’s how they explore the world.
3. Pound for pound, they take in more of a toxin than adults do. If a 20 lb. child takes in 1 ounce of a toxin, then he receives a higher does than a 200 lb. man taking in the same amount. Make sense?

If you missed the video today, I don’t have a full digital version but you can get some tidbits at this EPA page under the link:
Chemicals – “NOW with Bill Moyers: Kids and Chemicals.”

If you are curious about chemicals in your own home, take a quick interactive tour of a typical house at this EPA website. Each room has a little surprise…

And, on a related note if here is a USA Today Special Report that allows you to check out how toxic the air is around any school (full of kids!). Just click the link below, then enter our school, our city, and our state and see what comes up…
Toxic Air and America’s Schools

If you missed the last two days, I kicked off our unit on toxicology. First, I laid out the 4 categories of hazards you text states might cause “harm:” biological, cultural, physical, and chemical. You had a good background in the biological (pathogens-infectious disease) hazards to health last year, so I plan to focus more on the chemical.

Universal Symbol for Toxic Substance

Image source: http://upload.wikimedia.org/wikipedia/commons/5/53/Skull_and_crossbones.svg

Second, I tried to deconstruct some of the language in your text concerning toxicology. I really don’t like the definition of a toxin from your text as it implies all toxins=poisons. Not all toxins are poisons, as typically a poison is absorbed in the gut after ingestion (or through the skin). I’m sure all of you can think of some that is “harmful” that you don’t have to ingest! So, in the most general sense, a toxin is a chemical (or form of energy) that causes “harm” at a certain dose. Some texts are particular about the terms, with toxin used for a chemical made by an organism and toxicant for a man-made chemical. Your text uses toxican most often. That led to the discussion of a phrase from the book: “The dose makes the poison.” This saying is attributed to Paracelsus. By this definition, any “chemical” could be “harmful.” So, water (seemingly harmless) could be poisionous!? Yes. If you have not heard of water poisoning or intoxication, check out this story. Conversely, something harmful like alcohol can be consumed often if the dose is small enough. So, toxicity is based on a dosage scale-chemicals are not simply “good” or “bad” for you. Doctors have to deal with this concept daily as the determine how much of a medicine a patient can take without causing “harm.”

So, is toxicology that simple? It’s just about the amount or concentration of a substance? No, of course not. I think this webpage gives a more complete account of factors that complicate if and when a “chemical” is “harmful:”

The Dose Makes the Poison-Or Does It?

* You can also ask a classmate for a list of the factors we came up with besides dose when you get back.