Biology 5868 ID Exam 1 February 23, 2007

Transcription

1 Ecotoxicology Name KEY Biology 5868 ID Exam 1 February 23, 2007 Be as specific as possible for all answers. Most of the questions have multiple parts; make sure to answer each part! Use diagrams, flowcharts, and formulas where appropriate. Use the back of the pages if necessary (make sure to indicate the question being answered). Fill in (1 point each) + 1. NH would pass through a cell membrane faster than NH. True or False? ALAD-deficiency porphyria is a diagnostic biomarker for exposure to what contaminant? lead 3. Give an example of a volatile organic compound (VOC). CH 4, etc. 4. Dioxin is highly toxic to rats but only mildly toxic to humans. True or False? 5. What enzyme assay would you choose to detect benzo[a]pyrene exposure? Aryl Hydrocarbon Hydrogenase (also MFO, CYP450, EROD) 6. Vitellogenin can be used as a biomarker for estrogen exposure in female fathead minnows.true or False? 7. Name a common test organism in sediment toxicity assays. amphipod, Chironomus, Lumbriculus, etc. Definitions Define any four of the following terms: (3 points each) 8. Xenobiotic: A foreign chemical or material not produced naturally and not normally considered a constitutive component of a specific biological system. 9. Partition coefficient: A quantitative expression of concentration among phases at equilibrium. 10. Biogeochemical cycle: The natural movement of metals of different forms through earth, atmosphere, water, and biological systems. 11. Absolute bioavailability: The amount of a contaminant that can be assimilated by a particular organisms determined by direct injection into the bloodstream. 12. Activation: Biotransformation resulting in a more toxic product than the starting material. 1

2 Short Answer. Answer any six of the following questions. (6 points each) 13. Describe the formation and buildup of ozone in the lower atmosphere resulting from NO 2 degradation. - NO 2 is split by UV to NO and O - O combines with atmospheric O 2 to form O3 - normally, O 3 could combine with NO and recycle to NO 2, but NO can be removed from the lower atmosphere by reaction with contaminant hydrocarbon free radicals, leading to a buildup of O For one of the following metals, arsenic, cadmium, mercury, or lead, list one: 1) natural source of contamination: all - volcanoes, weathering 2) anthropogenic source of contamination: all - combustion of fossil fuels 3) common use: As - pesticide/preservatives; Cd - electrical parts; Hg - batteries; Pb - batteries 4) toxic action: As - inhibit SH-enzymes; Cd - inhibit SH-enzymes; Hg - inhibit SH-enzymes; Pb - CNS damage. Distinguish between steady state and chemical equilibrium. Which is more appropriate in describing bioaccumulation? Why? Equilibrium - substrate and product concentrations stay the same because of forward and reverse reactions Steady state - substrate and product concentrations stay the same because of constant additions of the former and removal of the latter. Steady state conditions more accurately describe bioaccumulation because of the dynamic effects of biotransformation, excretion, mobilization, etc. 16. Describe one pathway by which reactive oxygen species (oxygen radicals, hydroxyl radicals) can be metabolized. 1. superoxide dismutase, catalase 2. superoxide dismutase, glutathione peroxidase, glutathione reductase 17. Define Henry s law coefficient and describe the difference between compounds that have high or low Henry s law coefficients. Henry s law: H = P/C, P = vapor pressure, C = water solubility; a quantitative expression of a contaminants tendency to partition to the vapor or dissolved state high H - more in the vapor phase low H - more in the dissolved (e.g. aqueous) phase 18. Explain the concept of biomarker efficiency. How is biomarker efficiency calculated? Biomarker Efficiency - ability of a given biomarker to detect the relevant concentration (i.e. that which produces an effect of interest) of a given contaminant. E = U i/b i, where U i is the concentration at which the undesirable effect occurs, and B i is the concentration that the method can detect or predict 2

3 19. Describe the QSAR technique. Quantitative Structure Activity Relationship; based on the premise the molecules of similar structure will have similar functions (activities). Activities of untested molecules can be quantitatively estimated by comparing the known activities of their constituents. 20. List three mechanisms organisms use to detoxify (or reduce toxicity) of metals. Describe how each of these mechanisms results in a less toxic compound. binding to a protein (e.g. albumen); sequestration addition of an organic group; increases water solubility, excretion conversion to a sugar; increases water solubility, excretion binding to metallothionein; excretion biomineralization; sequestration 21. Describe the Equilibrium Partitioning method for estimating toxicity of contaminants in sediments. What partitioning coefficients are relevant for this technique? Considers that a given contaminant will be in equilibrium with all available phases in the sediment, including carbon-containing, water, and biological. Relevant partitioning coefficient: K oc Short Essay. Answer three of the following questions. ( points each) 22. Testing two species of seabirds revealed that they had accumulated different amounts of mercury, and you suspect that this may reflect differences in the trophic positions of the birds. 1) Describe how a nitrogen isotope ratio technique might be used to test this hypothesis (include in your answer either a formula describing a technique or a narrative explaining the concept); 2) construct an experiment that would use the isotope ratio technique to test your hypothesis (assume you have access to all supplies and biological materials necessary). The nitrogen isotope ratio technique presumes that 1) organisms at all trophic levels will take 14 in a uniform ratio of N: N, and 2) the lighter N isotope (e.g. N) will be preferentially excreted in all organisms. Therefore, the heavier N isotope ( N) will be over-represented as compared to atmospheric nitrogen at higher trophic levels, i.e. higher N: N ratios indicate higher trophic levels, and should thus also have higher Hg concentrations. Hypothesis: birds at higher trophic levels should have higher N: N ratios and contain more mercury. Formula: ä N = 1000 [( N sample)/( N sample)]/[( N air)/ N air)] -1 Narrative: trophic level can be determined by comparing the relative amounts of N in each sample, calculated by dividing the ratio N: N in each sample by the ratio N: N in air; higher net N will reflect higher trophic levels Experiment: Test identical tissue samples from both birds for N: N ratios Control tests include air N: N ratio assays Note - a complete experiment would also test organisms thought or known to be at higher and lower trophic levels in that ecosystem 3

4 23. You are testing small minnows in a large, natural lake ecosystem for exposure to contaminant X, which is known to have a LogP of 4. You find contaminant X at a concentration of 10 ìg/kg in the environmental matrix (i.e. water, sediment, and all other sources, including food), and of 37.5 ìg/kg in the minnow tissue samples. You also test blood samples and find high EROD activity, a small amount of X- OH, as well as high concentrations of X-glucuronate. What is the bioaccumulation factor for contaminant X? What are the ecotoxicological implications of these data? Bioaccumulation factor (BF = [X organism]/[x source]): 37.5 ìg/kg/10 ìg/kg = 3.75 EROD activity indicates that Phase I P450 enzyme systems (mixed function monooxygenases) have been induced and suggest that contaminant has been metabolized to a more water soluble form. X-OH suggests that the activity of the P450 was to hydroxylate contaminant X. High concentrations of X-glucuronate suggest that Phase II conjugation reactions have taken place, and that X-glucuronate will be excreted in the urine. LogP = 4 suggests that contaminant X would readily cross into cells and would bioaccumulate in lipids; Contaminant X might biomagnify at higher trophic levels (LogP = 4); minnows would probably be at lower trophic levels in a large natural lake ecosystem 24. CYP4501A1, heat stress proteins, and metallothioneins can each be used as molecular biomarkers for contaminant exposure. For any two of these molecules (or classes of molecules) describe their 1) structure (in general terms), 2) normal metabolic function, 3) toxicological function, 4) detection method (at least one), 5) characteristics that make it a good biomarker, and 6) characteristics that limit its usefulness as a biomarker. CYP4501A1: 1) Structure: protein; kda; contain heme (porphyrin) group; uses molecular oxygen as a terminal electron acceptor (i.e. functions as an oxidase); 2) Normal metabolic function: detoxification, oxidase in steroid, cholesterol, etc. synthesis 3) Toxicological function: performs enzymatic activities that increase water solubility 4) Detection methods: various enzyme assays (e.g. EROD), Western blots 6) Biomarker disadvantages: constitutive activity; non-specific Heat stress proteins: 1) Structure: proteins; various MW, e.g. ubiquitin (8.5 kda) - hsp 60, 70, 90, 100 (kda) 2) Normal metabolic function: assist folding proteins; degradation pathway (i.e. ubiquitin) 3) Toxicological function: participate in protein folding/re-folding; tagging proteins for disposal via lysosome/proteosome 4) Detection methods: Western blots 6) Biomarker disadvantages: constitutive activity; non-specific Metallothionein 1) Structure: proteins; 6-7 kda; 25% cysteine, no aromatic amino acids 2) Normal metabolic function: binds, transports metals 3) Toxicological function: binds, transports metals 4) Detection methods: cdna probes, Western blots 6) Biomarker disadvantages: constitutive activity; non-specific; can be induced in response to glucocorticoids, antioxidants 4

5 25. Several small raptors (birds of prey) were found either dead or near death in a mixed agricultural/ residential (e.g. suburban) region. The surviving birds did not eat, could not fly, and showed uncoordinated muscular activity, such as the inability to perch. Necropsies (autopsies) of the dead birds revealed no obvious pathologies or unusual parasitic infections. You, as the State Ecotoxicologist, suspect contaminant intoxication, and have access to the birds and to the areas where the birds were found. Form a hypothesis as to what contaminant(s) affected these birds and describe the evidence that you used to form that hypothesis. Form a plan to test your hypothesis and describe the steps you would take to accomplish your goal. Form at least one alternative hypotheses and describe the steps that would be necessary to distinguish this alternative hypothesis from your initial hypothesis. Hypothesis: Since the birds showed nervous system problems, they could have been exposed to an organophosphate or carbamate insecticide, probably through prey (small birds, rodents, insects, etc.). Note that organochlorine pesticides could also be implicated, but that these have been banned from use in the US. Alternative hypothesis: The raptors were exposed to another toxicological agent; e.g. other pesticide, metal (e.g. mercury, which affects the CNS). Testing: 1) Analyze the birds blood and tissues for A) insecticide residues; B) acetylcholinesterase activity; C) insecticide metabolites. 2) Test environmental samples (e.g. prey, plant matter, soil) for insecticide residues Alternative hypothesis tests: 3) Test the bird tissue for Hg and organic Hg; 4) Test prey species for Hg; 3) Look for possible sources of Hg in the proximity (e.g. seed dressings, etc.) 5