1
What are toxic substances and how do we make decisions regarding the risks of exposure to these chemicals? Why is the solubility of a toxic substance important to individuals and to ecosystems?
INFOGRAPHIC 3.2
Which of the following is true of all toxic substances?
They don’t readily break down through natural means.
They are synthetic chemicals; no natural substances are considered toxic.
They cause damage through immediate or long-term exposure.
They biomagnify up the food chain.
C
At low doses that don’t hurt test mice, a new pesticide can effectively control an insect pest that’s been ravaging local trees. However, when that pesticide is combined with another commonly used pesticide, it is very toxic to mice. In deciding to approve the pesticide for sale anyway, policy makers were applying:
the precautionary principle.
logical fallacies.
information literacy.
a risk assessment.
D
In what way does the story of BPA reflect the precautionary principle?
The precautionary principle is invoked when there is uncertainty in the severity of a particular threat but the potential for a serious outcome exists. By removing BPA from baby bottles before we had definitive evidence that it is a problem, we took a precautionary step to protect children from exposure. We don’t know for sure how much of a problem it is for children but by removing it, we have reduced their exposure and avoided the risk.
2
What is information literacy, and why is it important?
INFOGRAPHIC 3.1
Which of the following is a secondary source of information?
A blog in which the author enters personal observations on his day-to-day life
A magazine article that uses primary and secondary sources
A scholarly review article that references only peer-reviewed original research articles
A government website that cites original research and scholarly review articles
C
Why are tertiary information sources considered less reliable than primary or secondary sources?
Tertiary information sources are considered less reliable than primary or secondary sources because they draw from secondary sources, which are themselves “re-tellings” of the information from an original source, any errors in content or context can be perpetuated from the secondary source to the tertiary one.
What is peer review, and how does it increase the reliability of an information source?
In peer-review, experts in the field go over an article to determine if it warrants publication based on the soundness of the scientific investigation described and logic of the analysis. This increases the probability that good studies will be published, but bad ones will not.
3
What factors influence a chemical’s toxicity? How is toxicity determined?
INFOGRAPHICS 3.3, 3.4, AND 3.6
The toxicity of a chemical is evaluated using cells in culture or live animal subjects by creating a(n) _________; a high LD50 indicates ________.
in vitro study; a safe dose
dose analysis; a threshold dose
in vivo study; high toxicity
dose-response curve; low toxicity
D
Pesticides such as DDT are known to biomagnify in food chains. This means that:
organisms in lower food chain levels accumulate lethal doses of toxic substances.
organisms at higher food chain levels have more concentrated levels of toxic substances.
toxic substances build up in the tissue of an organism over the course of its lifetime.
the environment has higher concentrations of toxic substances than organisms in the food chain.
B
Why is it so hard to determine a safe exposure for a given chemical? How do regulators setting safe exposure standards deal with the uncertainty associated with these factors?
So many factors influence how toxic a chemical actually is (especially chemical interactions and variability among the individuals exposed) that is it impossible to determine experimentally exactly what a safe exposure would be. Still, we start with experimental studies to assess the toxicity of the substance and identify what might be a safe level of exposure or “dose”. That dose is then reduced a factor or 100 or even 1000 to accommodate the uncertainty inherent in the research results.
4
What are endocrine disruptors, and why is it often harder to determine a “safe dose” of them than it is to determine safe doses of other types of toxic substances?
INFOGRAPHIC 3.5
Why are toxicologists more concerned about exposure to BPA in children and infants than in adults?
BPA does not bind to receptors in adult cells.
BPA might interfere with normal development in the young.
Adults can break down and excrete BPA, whereas children cannot.
BPA is only found in products that children are exposed to, such as formula cans and baby bottles.
B
Why must a hormone and a hormone receptor be present for a hormone to have an effect?
While the hormone may be the chemical messenger that tells the cell what to do next, it can only deliver its message to the cell if it can bind to a receptor molecule in the cell.
5
How can we use critical thinking skills to logically evaluate the quality of information and its source? What common logical fallacies are used in presenting arguments?
TABLE 3.1
Pesticides help increase agricultural yields, but some people oppose their use because of their inherent toxicity. An argument against pesticide use that attacks the pesticide maker on the grounds that he or she is simply profit driven is:
an ad hominem attack.
an appeal to authority.
an appeal to ignorance.
a false dichotomy.
A
Identify and explain four tenets in critical thinking that can help you logically access and reflect on information in order to draw your own conclusions.
1. Be skeptical — don’t accept claims without evidence;
2. Evaluate any evidence presented to determine how well it supports the claims presented;
3. Be open minded — don’t let your preconceived notions color your evaluation;
4. Watch for author biases — identify any stake the author may have in the issue that might color his or her conclusions.
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