Date of Award


Degree Name

Master of Science


Geological Sciences


Elizabeth J. Walsh


The presence of 9 selected PPCPs (acetaminophen, caffeine, cotinine, codeine, fluoxetine, erythromycin, ciprofloxacin, sulfamethazine, and trimethoprim) was surveyed in water samples collected at four sites along the middle Rio Grande during two flow regimes (irrigation and non-irrigation). Water collection for PPCPs analyses were conducted from August 2010 through September 2011. Three of the sites were located upstream, in, and downstream of the El Paso, TX/Ciudad Juárez, MX metroplex. Site selection was based on their proximity to the metroplex and due to the fact that the Rio Grande in this region is an effluent receiver water system (IBWC, 2011). The fourth site was selected as a reference site since it is located approximately 160 km upstream of El Paso, TX and receives water from the Elephant Butte and Caballo reservoirs for irrigation purposes. EPA Method 1694 was used as a guide for analysis of PPCPs by HPLC MS/MS. Selected PPCPs were detected at least once at each sampling site although for some dates they were detected below limits of quantification. Concentrations of these PPCPs were found in the ng/L range with concentrations from 0.004 ng/L to 42.8 ng/L. Ciprofloxacin was found at the highest concentration in the Rio Grande at the American Dam sampling site during the 2011 irrigation season. Cotinine and codeine were consistently found in all four sampled sites during both flow regimes. Since the occurrence of PPCPs has been reported to occur in surface waters around the world and in this study, aquatic systems are of great concern due to the continuous input of these pollutants. The freshwater rotifer Plationus patulus, a basal member of riverine food webs, was used to test acute and chronic toxicity of 4 selected PPCPs (acetaminophen, caffeine, fluoxetine, and triclosan). Two geographically distinct P. patulus populations were tested. The first population was collected in a remote site of Mexico, south of Big Bend National Park, TX, and was used as a reference population since it was assumed that this site is free of PPCPs toxicants. The second population was collected in a highly urban reach of the Rio Grande within the El Paso, TX/Ciudad Juárez metroplex. Results from acute toxicity tests show that the P. patulus reference population is more sensitive to triclosan (LC50 = 0.13 mg/L) while the Rio Grande population was more sensitive to acetaminophen (LC50 = 121 mg/L). Both populations showed a similar LC50 for caffeine (Reference population LC50 = 423 mg/L; Rio Grande population LC50 = 419 mg/L). LC50 values for both populations indicate that P. patulus is less sensitive to acute exposure to acetaminophen and caffeine as compared to Daphnia magna while this rotifer species was more sensitive to fluoxetine and triclosan. In chronic exposures, there was generally a decrease in population growth for all four tested PPCPs in both P. patulus populations. For instance, chronic exposure to acetaminophen (10 mg/L, 15 mg/L, and 20 mg/L) in the reference population inhibited population growth at all tested concentrations starting on day 3 through day 6 of exposure while for the Rio Grande population growth was inhibited only at 15 mg/L and 20 mg/L starting on day 3 and continuing through day 6 of exposure. A second set of lower acetaminophen concentrations were tested in both populations (1 mg/L, 5 mg/L, and 10 mg/L) for which no significant population growth inhibition was determined for either population with the exception of the 10 mg/L treatment which inhibited population growth in the reference population as previously shown. For tested concentrations of caffeine (100 mg/L, 200 mg/L, and 300 mg/L), population growth was inhibited in 200 mg/L and 300 mg/L treatments for both populations. For the reference population, growth was inhibited on days 5 and 6 at 200 mg/L while at 300 mg/L negative rates of population increase were seen on days 4 through 6. Population growth of the Rio Grande population was inhibited at 200 mg/L on days 3 (86%), 4 (45%), 5 (44%), and 6 (52%) as compared to control treatment. Further at 300 mg/L, negative rates of population increase were seen on days 3, 4, and 6 while on day 5 population growth was inhibited 99% as compared to the control treatment. Chronic exposure to fluoxetine (0.005 mg/L, 0.010 mg/L, and 0.020 mg/L) was only tested in the Rio Grande population. This toxicant caused significant population growth inhibition at 0.020 mg/L on days 3 (26%), 4 (15%, 5 (15%), and 6 (16%) as compared to control treatment. Tested concentrations of triclosan (0.05 mg/L, 0.075 mg/L, and 0.10 mg/L) had the most deleterious effects on both populations. In the reference population, population growth was affected at all tested concentrations with growth inhibition at 0.05 mg/L over days 4 and 5 and with negative growth rates at 0.075 mg/L and 0.10 mg/L over days 4 - 6 of exposure. For the Rio Grande population, negative growth rates or no growth was observed at all tested concentrations. Sub-lethal effects observed for chronic exposure to acetaminophen, caffeine, and triclosan included decreases in egg production and increased incidence of egg detachment from ovigerous females. Overall, the reference population was more sensitive to the chronic exposure of selected PPCPs as compared to control treatments than the Rio Grande population as compared to control treatments. Although tested concentrations of selected PPCPs are higher than those occurring in the environment, the continuous introduction of these toxicants to aquatic ecosystems may still present a risk. In addition, additive effects of mixtures of these toxicants have shown greater toxicities as those determined for single chemicals. Thus the impacts of these toxicants need further investigation.




Received from ProQuest

File Size

126 pages

File Format


Rights Holder

Diana Angelica Martinez Gomez