Closure sub-modules contain my responses to student questions and sometimes other material related to that module, which I realize I missed the first time around. The items that are important, in the sense they are part of course content, are indicated by two or more asterisks (***) and have been grouped first. Items that relate to administrative issues are grouped second. The answers to other questions are grouped last. Some of this last group is my philosophical rambling, which you might find interesting but of itself will not be on the tests unless it is later presented again.
*** Q. In the Dose-Response experiment does Cheech change the fishes for each dose experiment?
A. Yes, You would start with a new, unexposed batch of fish for each dosing level. The lesson did not make that clear.
*** Q. In the toxicology submodule you refer to a dose that effects 90% of test subjects as ED90, but in the homework you refer to the dose as EC90, are the interchangeable?
A. I should have been consistent. The "D" in "ED" stands for "dose," typically mg / kg of body weight. That is the terminology used for oral and dermal exposure of test animals. For inhalation exposure of land animals or water exposure of aquatic species, the term "EC" is used and it means "effective concentration," typically in ppm or mg / m^3.
*** Q. (Several questions regarding the electronic quiz, question 1, and acute exposure:)
A. Acute vs. chronic refers to the duration of the exposure, not the effect. Regarding the Dartmouth researcher who was exposed to dimethyl mercury that you read about, her exposure was seconds, but the effect, culminating in death, took months. Many acute exposures have a "latency" period before the effects are patent.
In the Law, the exposure specified as a one-time brief exposure to the chemical, and thus acute. The effect is measured at 14 days. Or rather lack of effect, if the animal is not dead before then. (See Blackboard announcement about hints.)
*** Q. "Are the terms "risk assessment" and "risk characterization" interchangeable, or are there notable differences? The terms appear in the NAS diagram.
A. Not exactly interchangeable. "Risk Assessment" refers to the entire process of determining the probability and severity of harm. "Risk Characterization" refers to the statement of the findings, which is the statement of the probability and severity of the harm and the statement of uncertainties.
*** Q. 1 ppm for water equal to mg/L, for soil it would be 1 mg/kg. What about gases? Is 1 ppm for gas equal to 1 mg/m^3?
A.. I avoid using ppm for water solutions. In order to use the term "parts per million [parts]", both numerator and denominator must be in the same units. If and only if one liter of the solution weighed exactly one kilogram, 1 ppm equals 1 mg / L. However, in many environmental measurements, the solution is very dilute and one liter weighs just about one kilogram, so ppm and mg/L are used interchangeably. For gases, I added a non-mandatory page about converting ppm to mg / m^3. One ppm of a gas is different than 1 mg / m^3, usually quite different.
Q. Will you leave all the modules posted on Blackboard throughout the semester? Or will you pull them off as you add new one's?
Q. In sub module 1C, the NOEL was noted at being the no observable effect level. Therefore, I am to assume that any dose higher than the NOEL would produce an effect and everything lower would have no observable effect. Does the no observable effect include long latency periods (such as causing cancer years later???)?
A. Very good questions, see above for part of my answer. You observed that the Consumer Product Safety law for "highly toxic" had a definite cut-off time for effects and only mentioned death as an effect. Lawyers, not toxicologists, write this type of definition. I just put it in the lesson to illustrate how those words were used and to get you to think about their meaning. For the definition of "toxic" it had any harmful effect and no cut off time, so any harmful effect at any time would require the toxic label. Of course there are no testing protocols specified, either.
Q. Would the NOEL also be considered the threshold level?
A. We will talk more about NOEL and thresholds. They are often used synonymously, but are not. The NOEL would refer to a particular experiment. These experiments test a series of progressively higher doses, starting with zero dose called the controls. The NOEL would be the highest of the doses that did not demonstrate an effect. Long ago, toxicologists would state a "no effect level." Since the philosophers tell us that any dose must have some effect, the terms "no observable effect " became standard. Sometimes the matter is expanded to "no observable adverse effect (NOAEL), which is more accurate. These terms are common to regulatory toxicologists who have to come up with some definite number. The terms would be meaningless, unless they are coupled with the particular laboratory experiments that were used to determine them. For chemicals suspected of being carcinogens, those protocols would specify observations for the lifetime of the animals.
A threshold would be the largest dose that produced no effect. It is a scientific concept that is not tied to any particular experiment, but would be stated for a particular animal species and other protocols. There is much scientific debate if carcinogens have thresholds. We will discuss this.
Q. What are the criteria for "effects" when an experiment is done to determine the NOEL up to EC90? What if different individuals within a species show different effects?
A. This is part of the reason that the choice of animal species is so important. Some strains of lab animals are inbred and most of the individuals will show the same effect. Other strains are outbred and there will be more variation in effect. You can also see why the choice of an "endpoint" is so critical. This is why death is such a convenient endpoint.
Q. Also, am I right to conclude that reversible effects are reversed once exposure has stopped? Do irreversible effects include effects that require intense medical treatment such as chemotherapy (in other words, are does reversible effects include only those effects which would naturally reverse on their own once exposure has ended? Blurry vision might revert back to normal vision after exposure whereas cancer may not be reversible if medical treatment is not seeked and even if it was it still might result in death or may eliminate someone's ability to reproduce.)
A. Again, reversible and irreversible are very general concepts. The effects would have to reverse sometime in the future and not be permanent. Similar to the question, is a seven-day test is chronic or acute, for an adverse effect that slowly reversed itself for years, you would better presenting that explicitly rather than trying to decide if it is reversible or irreversible. We will discuss cancer in much greater detail soon.
Q. Is the effective dose affecting 10% of the population meaning any type of observable effect except death.
A. You would include death as an "effect." Its just that death is such an easily observed endpoint, it is often specified and the LD is often used. Obviously ED is not very descriptive, unless you specify the effect.
Q. Regarding the scented candle issue, what are the quantified health risks associated with use of scented candles? Do the levels presented in the abstract represent a serious health risk?
A. Deep questions, but so deep, I can give shallow answers. The abstract about the candles presented no quantified health risk for the candles. The author did a chemical analysis of soot and other combustion products from a set of very different candles, and not unsurprising found different chemicals. Then the author presented the health effects from stated levels of these chemicals, where they were known. For the biggest issue, candle soot, there were no known health effects published, so the author used the data from diesel exhaust, a completely different compound. What the author presented were assumptions stacked on top of estimates over a layer of extrapolations. We will often see this. My guess is the original paper carefully stated all this. When you use the words "serious health risk" you are trying to determine the acceptability of the risk. In my house, the fire danger from candles is thousands of time greater than any likely health effects.
Q "toxic" and "highly toxic" are both defined in terms of human illness or death, but the homework question referred to the results of a rat test. Can you infer a chemical is toxic if rats are affected, or does there have to be direct proof that humans will suffer?
A. In this case the law of the land defined the terminology required to warn humans of the hazard in terms of animal testing. Almost all toxicology testing is done in animals and the choice of the correct "animal model" is most important. We will deal much more with this issue in a few weeks.
Q. If, in Environmental Engineering "sticking to ethics" is given a lot of importance then how would one defend the cruelty imparted to animals used for studying the affects of various "poisons"?
A. Animal testing is an important issue. Economics dictates minimizing animal testing, if in vitro testing will suffice. The animal quarters where I did my graduate work were better than my graduate student offices, better ventilation and climate control. Strict adherence to animal welfare controls is an important part of experimental procedures. If animals are stressed they may produce anomalous experimental results. I have never witnessed or heard of any cruel or base treatment of laboratory animals, other than what was required by the experiments. As a practical matter, whole animal testing is required for all foods, drugs, and cosmetics that people will be exposed to, in order to determine if they are "poisons" or better put, what the harmful dose is. It would be irresponsible to purposefully expose consumers without prior animal testing. For persons whose moral system puts humans on a higher plane than animals, I do not perceive any moral issues with testing animals. (A person who took pleasure in hurting mammals is rare, and this type of behavior upsets other people, so it is anti-social.)
On the other hand, persons whose moral system puts animals and humans on the same plane might have problems with animal testing. Biomedical research is probably not a good career choice for persons with this ethic.
Q. In the Minimata case, did Chisso Corporation ever pay the $100 million settlement suit?
A. I don't know. It is an interesting moral issue. Today, we regard almost any pollution as a crime or at least anti-social corporate behavior. That was not the case in the US until sometime in the 1960's. Engineers were taught, "The solution to pollution is dilution." Almost everyone accepted that some contamination was inevitable and required for economic progress. The situation in Japan was worse, with most industries and infrastructure damaged or destroyed by World War II. Now what happed (as I remember some readings I have never researched this is depth) Chisso and the government knew that they were polluting and the pollution was not against any Japanese law. When it became apparent that there might have been health effects, the government told the locals to stop fishing in the Bay and stop eating the fish from the bay. Chisso in turn paid the fishermen to not fish in the bay. The fishers may have not stopped fishing, the fish outside the bay may have had some contamination, and certainly some of the effects may have been due to exposure before the restrictions. The same is true of Love Canal in New York. Everything Hooker Chemical Co. did was legal when they did it. In addition, when the site was sold there was a deed restriction that should have prevented housing and certainly the school being built on the dump. That is one of the reasons that the RCRA law was passed.
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