Risk perceptions of drinking bottled vs. tap water in a low-income community on the US-Mexico Border.

BACKGROUND: Previous studies have shown that low-income Latinos generally drink bottled water over tap water and might be at increased risks for cavities from unfluoridated bottled water. In order to better design interventions, it is important to understand the risk perceptions of this unique high-risk yet historically marginalized group. METHODS: We interviewed low-income Latino households (n = 90) from Nogales, Arizona who primarily drink bottled water and asked them to evaluate potential health risks of drinking tap water compared to 16 other voluntary activities. Unpaired t-tests were used to determine if statistically significant (α = 0.05) differences occurred in perceived risk by drinking-water source and differences among demographic groups in their level of (dis)agreement with statements regarding tap or bottled water safety. To assess significant differences (α = 0.05) in perceived risks and voluntariness to engage in a number of activities, including drinking local tap water and drinking water in different geographic regions, a one-way analysis of variance (ANOVA) followed by Scheffe's post-hoc test (a conservative post-hoc test) with adjustment for the number of pairwise comparisons was used. RESULTS: Participants viewed bottled water to be significantly safer to consume than tap water (p < 0.001). On a Likert scale from 1 (low risk) to 5 (high risk), "drinking tap water in Nogales, Arizona" received an average score of 4.7, which was significantly higher than the average perceived risk of drinking San Francisco, California tap water (µ = 3.4, p < 0.001), and as risky as drinking and driving (µ = 4.8, p = 1.00) and drinking Nogales, Sonora, Mexico tap water (µ = 4.8, p = 1.00). Ninety-eight percent of participants feared that drinking local tap water could result in illness, 79% did not drink their water because of fear of microbial and chemical contamination and 73% would drink their water if they knew it was safe regardless of taste. CONCLUSIONS: These results suggest that fear of illness from tap-water consumption is an important contributing factor to increased bottled water use. Future efforts should focus on the development of educational and outreach efforts to assess the safety and risks associated with tap-water consumption.

Measured and Modeled Comparisons of Chemical and Microbial Contaminants in Tap and Bottled Water in a US-Mexico Border Community.

Tap water quality concerns and advertisements often drive increased bottled water consumption, especially in communities with historical tap water quality problems (e.g., Nogales, Arizona). The study objective was to assess contamination of municipal tap and bottled water in Nogales, Arizona. Bottled (sealed, open/partially consumed bottles, and reusable containers for vended water) and tap water samples were collected from 30 homes and analyzed for chemical and microbial contaminants. Fisher exact tests and Wilcoxon rank sum tests were used to compare proportions of positive samples and contaminant concentrations between tap and bottled water samples. While none of the chemical contaminants were above MCLs, there were statistically significantly greater concentrations and proportions of positive samples for some contaminants, including arsenic, in tap vs. bottled water. E. coli concentrations were >0 CFU/100mL in some unsealed bottled water samples but not for sealed bottles. This study demonstrates that 1) the measured concentrations in tap and bottled water likely pose low risks, as they are below the MCLs, 2) more education in this community on hygiene maintenance of refillable or opened bottled water containers is needed, and 3) using tap water over bottled water is advantageous due to likely lower E. coli risk and lower cost.

Comparison of Fluoride Levels in Tap and Bottled Water and Reported Use of Fluoride Supplementation in a United States-Mexico Border Community.

BACKGROUND: Compared to the general United States (U.S.) population, Arizona counties along the U.S.-Mexico border have a higher prevalence of dental caries, which can be reduced with adequate fluoride exposure. Because of concern regarding local tap water quality, fluoride-free bottled water consumption is common in this region, raising concern that families are not receiving adequate fluoride to promote dental health. OBJECTIVE: To evaluate the levels of fluoride in tap and bottled water as well as the use of fluoride supplements in an Arizona border community. METHODS: Low-income Latino households (n = 90) who report use of bottled water as their primary source of water intake were recruited. Participants completed a questionnaire about their and their children's dental histories and use of fluoride supplements. Water samples (bottled and tap) were collected from a subset of households (n = 30) for analysis of fluoride. RESULTS: Fluoride detection levels were significantly greater (p = 0.02, Fisher's exact test) in tap water (average = 0.49 mg/dL) than in bottled water, yet, the majority (22/30) were below the range for optimal dental health (0.7-1.2 mg/L). Concentration of fluoride in the majority (29/30) of bottled water samples was below the quantitative detection limit of 0.4 mg/L. Children were significantly less likely to have dental caries if they received fluoride varnishing treatments (p = 0.01, Fisher's exact test), lived in households that reported using fluoridated mouthwash (p < 0.001, Fisher's exact test), their parents received fluoride education (p = 0.01, Fisher's exact test), and their parents reported visiting a dentist yearly (p < 0.001, Fisher's exact test). Furthermore, none of the participants reported receiving recommendations from health-care providers about fluoride supplementation or variance in content by the type of water consumed. CONCLUSION: Although fluoride was significantly more likely to be detected in tap than bottled water, neither water source in this border community is likely to provide enough fluoride for optimal dental health. Low-income children in this region may benefit from regular access to fluoride varnishing treatments and/or use of fluoridated mouthwash, interventions that could be tested in future well-designed trials.

The DNA polymerases of Leishmania mexicana.

Two previously isolated DNA polymerases from the parasitic protozoan Leishmania mexicana were further characterized by exposure to inhibitors of mammalian DNA polymerases. DNA polymerase A, a high molecular mass enzyme, and DNA polymerase B, a beta-like DNA polymerase were compared to each other and to their mammalian counterparts regarding pH optimum, utilization of templates, and response to various inhibitors and ionic strengths. The results suggest that the DNA polymerases from L. mexicana differ from the host enzymes and may offer a target for chemotherapeutic intervention.

Isolation and partial characterization of a high-molecular-weight DNA polymerase from Leishmania mexicana.

This paper describes for the first time the isolation and characterization of a high-molecular-weight predominant DNA polymerase from the genus Leishmania, which are parasitic flagellated protozoa. Like mammalian DNA polymerase alpha, the leishmanial DNA polymerase, designated DNA polymerase A, is of high-molecular-weight, is sensitive to N-ethylmaleimide and is inhibited by high ionic strength. Unlike mammalian DNA polymerase alpha, but similar to the predominant DNA polymerase isolated from the related lower eukaryotic organisms, Trypanosoma cruzi and Crithidia fasciculata, the leishmanial DNA polymerase A is resistant to inhibition by aphidicolin, a potent inhibitor of DNA replication in mammalian cells and of DNA polymerase alpha. The DNA polymerase A was purified 28,000-fold and properties such as pH optimum, salt sensitivity, template requirements and response to DNA polymerase inhibitors were determined. A low-molecular-weight DNA polymerase was detected during the isolation procedures, but was separated from the polymerase A activity. Differences in responses to specific antisera and specific mammalian DNA polymerase alpha inhibitors suggest that the leishmanial high-molecular-weight A enzyme is sufficiently different to suggest this enzyme as a chemotherapeutic target.

Partial purification and characterization of a beta-like DNA polymerase from Leishmania mexicana.

Deoxyribonucleic acid polymerase beta (EC 2.7.7.7) from the lower eukaryotic parasitic protozoan Leishmania mexicana has been partially purified over 9,000 fold and characterized for the very first time. Like mammalian DNA polymerase beta the protozoan enzyme is of low molecular weight (40,000), has a broad pH range, and is resistant to inhibition by N-ethylmaleimide and aphidicolin. It is unlike mammalian DNA polymerase beta in utilization of various templates and response to various inhibitors and sensitivity to high ionic strength, but similar to a beta-like enzyme from a related organism Crithidia fasciculata. It is estimated that this enzyme constitutes 20% of the polymerase activity of the crude cell extract.

Isolation and characterization of DNA-dependent RNA polymerase III from Leishmania mexicana and inhibition by purine analogs.

A DNA-dependent RNA polymerase has been isolated and characterized from the parasitic flagellated protozoan Leishmania mexicana. The initial stages of purification utilized high-ionic-strength extraction and protamine sulfate treatment. The enzyme was further purified by differential elution by heparin-Sepharose, DEAE-Sephadex, and carboxymethyl-Sephadex chromatography. Analysis of the chromatographically purified RNA polymerase on nondenaturing gels revealed two electrophoretic forms. The enzyme isolated had characteristics of true DNA-dependent RNA polymerase since it required DNA and all four nucleoside triphosphates for synthesis of RNase-sensitive products. Analysis of ammonium sulfate and metal ion optima, as well as relative activities of the enzyme with Mn2+ versus Mg2+, gave results similar to those reported for other RNA polymerase IIIs in eucaryotes. Formycin A triphosphate was found to be a noncompetitive inhibitor of RNA polymerase III, and cordycepin triphosphate was found to be inhibitory, although the exact mode of inhibition was not determined.

The effect of formycin B on mRNA translation and uptake of purine precursors in Leishmania mexicana.

Formycin B is a structural analog of inosine that is a potent inhibitor of Leishmania multiplication. Formycin B is reportedly converted to formycin A nucleotides and incorporated into RNA by the organisms, and it is unclear whether the active form of the drug is the nucleoside itself or its several metabolites. We confirmed that formycin A nucleotides are formed by formycin B-exposed L. mexicana promastigotes, and determined that the intraparasite concentration of Formycin B and its metabolites was 6 times the extracellular formycin B concentration. Formycin B did not significantly inhibit purine nucleoside transport by intact promastigotes or purine base phosphoribosylation by parasite lysates. Thus, the nucleoside does not appear to inhibit these initial steps of purine nucleoside metabolism. Since RNA and protein synthesis in formycin B-treated intact promastigotes was found to be inhibited within 30 minutes, the effect of formycin A metabolites on leishmanial protein synthesis was investigated in in vitro protein synthesis experiments. Messenger RNA from formycin B-treated promastigotes was translated only 40% as efficiently as control promastigote mRNA by rabbit reticulocyte lysates. In addition, when formycin A-5'-triphosphate was preincubated with the rabbit reticulocyte lysates, translation of control mRNA was 86% inhibited. Formycin B toxicity to Leishmania promastigotes appears to be at least partially due to inhibition of protein synthesis by formycin A nucleotides and formycin A containing mRNA.