I know that we briefly described this in class today, but I am still a little confused on quantitative risk assessment. I understand that qualitative is when a person makes judgements on how hazardous substances are based on perceptions that really have no scientific data to back them up. But for quantitative, I have that the risk is measured by the probability of a person being exposed to the hazard divided by the probability of being harmed if exposed. Is that considered scientific data? So does that mean that quantitative assessment is based on only scientific fact rather than perception? I just need this to be clarified.
Today we discussed a few more factors that affect toxicity (see previous post), like route of exposure, persistence, and solubility. In particular, we made note of POPs (Persistent Organic Pollutants) like dioxin, PCBs, and DDT. Substances like these don’t break down in water quickly, and so may persist in the environment for years. Once inside organisms, they can bioaccumulate in fatty tissues (and eventually lead to biomagnification at higher trophic levels). Here is a clever video clip about biomagnification:
We also spent time discussing the complications of LD50 tests-some of them are mentioned in your lab notebook.
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:
Thursday and Friday, we watched a video and discussed reasons children are likely to be more vulnerable than adults to the effects of environmental toxins: 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, 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.”
On Friday we were discussing other factors mentioned in the video (and text) that may impact toxicity, like the timing of the dose, the persistence of the chemical, the solubility of the chemical (could lead to bioaccumulation/biomagnification), and any synergistic effects. Combined with the list above, we have quite a number of things that affect the toxicity of a chemical besides the dose. Regardless, the dose is the most common measure of toxicity, and that is done by conducting a LD50 dose-response study. The LD50 is also known as the median lethal dose.
We will do our own crude LD50 test to understand the process better. 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.
Today, after another preassessment acitvity, I introduced the study of “harmful chemcials” or toxicology.Toxins are lumped into several categories (below) in the text, but some chemicals trigger effects that place them in multiple categories.
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The quote “the dose makes the poison” is a paraphrase by the Renaissance “scientist,” Paracelsus (you gotta check out his real name). Basically, almost anything in large enough dose can be toxic (cause harm). Many students remembered this story, that shows even water can be toxic in large enough quantity. We noted some well-know examples that fit each category (above). Students are expected to be familiar with these examples on the AP exam, as well as the type of “harm” they can cause (besides death).
On Monday, I tried frame the study of human health and environmental risks. After a preassessment activity, I outlined the various types of hazards present in our environment using the concept map below. We spent the majority of our time discussing biological hazards-more specifically the pathogens that cause infectious (transmissible) diseases.
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Then, I challenged students to use the Centers for Disease Control website to look up some specifics on historical and emerging disease that tend to appear on the AP exam. The text notes that some bacterial diseases we thought we had under control, like tuberculosis, are making a comeback due to antibiotic resistance. You can watch a short video on the topic at this website-click on Video 6: Why Does Evolution Matter Now?