Drinking Water Contamination With 1,4-dioxane on Long Island

Environmental Risk Assessment 656. Homework #1 (of 3). Due 2/16/22.
View the PBS news segment on drinking water contamination with 1,4-dioxane on Long Island. Kociba (1974) is an important study in the body of literature on the toxicity of 1,4-dioxane. The study is described in a fairly clear, straightforward manner. Please read the study critically and answer the following questions. For background only, I am also providing a copy of Argus (1973), which is referenced in Kociba (1974). Include any thoughtful questions about parts of the study that are not clear to you. We can also discuss any clarifications you need when in class on 2/9/22. Your answers will be due by 2/16/22.
The goal of the homework in this course is to go beyond facts and basic concepts and reach for some of the higher levels of “Bloom’s Taxonomy”: “apply,” “analyze,” and “evaluate.”
1 PURPOSE/RATIONALE
Why was this study done? What were the questions the investigators were trying to answer?
Since 1,4-dioxane is highly soluble, it is hard to treat water to remove it. Its properties also make it hard to detect because it is colorless. Furthermore, it can be present in drinking water in very small (though significant) amounts, which makes it even harder to detect via conventional methods (i.e. if you are not looking for it, you cannot find it immediately). Because of this, the EPA has declared 1,4-dioxane to be a potential cause of cancer (Weber & Fong, 2017). Ongoing research are present for looking for possible chemicals such as the 1,4-dioxane that may contaminate drinking water. Essentially, Kociba et al.’s study was done to assess the toxicity of 1,4-dioxane, to settle ongoing debates on whether or not it poses a significant risk to consumers. Specifically, the authors aimed to identify the levels at which 1,4-dioxane becomes toxic to rats before moving on to or supporting research assessing the same on humans.
2 METHODOLOGY
a. What type of study was this? Briefly describe the basic study design (agent(s); types and numbers of animals; route, frequency and length of dosing; and toxicological endpoints studied).
The study by Kociba et al. (1974) was an experimental study involving 60 male and 60 female rats as subjects (per treatment level), with varying treatment levels of 1,4-dioxane introduced through the rats’ drinking water. The experimental treatment levels were 1.0%, 0.1%, and 0.01% 1,4-dioxane in drinking water, while the control group received 0% of 1,4-dioxane in their drinking water. The rats were subjected to their respective assigned treatments for up to 716 days.
b. What were the doses of 1,4-dioxane used in the study, expressed as 1) concentration in water
(volume/volume), and as 2) daily dose of 1,4-dioxane mg/kg/day?
1 1%= 1mL/100mL solution ; 0.1%= 0.1mL/100mL solution ; 0.01%= 0.01mL/100mL solution
2 1%= 1015 mg/kg/day for males ; 1599 mg/kg/day for females
0.1%= 94 mg/kg/day for males ; 148 mg/kg/day for females
0.01%= 9.6 mg/kg/day for males ; 19 mg/kg/day for females
c. Was the dosing (route, magnitude, frequency, duration) appropriate to the purpose of the study? Why or why not?
Yes, it was appropriate because the main goal of the study is pointed towards potential toxicity to humans through drinking water, although the expriment was done on rats, for safety and ethical reasons.
d. The authors did not provide the calculation that they used to convert the dioxane water concentration to daily dose in mg/kg/day in the rats. What is the general formula you would use to derive average daily dose in mg/kg/day from the doses given in percent water to? [Note that the water concentration was formulated as percent by volume-to-volume (vol./vol.), NOT weight-to-volume (eg. g/liter), so you would need to use the density of the contaminant in mg/ml to get the mass (in mg) of contaminant.]
The density of 1,4-dioxane is 1.03g/mL. This means that for the 1% v/v dose, which is 1 mL per 100 mL of the solution, so the conversion would be about 1030 mg, which is close to the specified 1015mg requirement dose for the treatment (this may vary depending on how the researchers rounded off the values they used in the calculation).
3 RESULTS
a. What were the main outcomes of the study?
The main outcomes indicate that ingestion of 1,4-dioxane in toxic levels can cause liver and nasal tumors in rats. This means that the chemical does have toxic properties that can kill organisms such as rats, and this can indicate that there is indeed a possible for toxicity in humans too. The authors found that liver and kidney damage is possible as well, but not for those receiving the 0.01% and ...