University of Waterloo

About: University of Waterloo is a education organization based out in Waterloo, Ontario, Canada. It is known for research contribution in the topics: Population & Poison control. The organization has 36093 authors who have published 93906 publications receiving 2948139 citations. The organization is also known as: UW & uwaterloo.

Long‐Term Performance of an In Situ “Iron Wall” for Remediation of VOCs

Abstract: The use of granular iron for in situ degradation of dissolved chlorinated organic compounds is rapidly gaining acceptance as a cost-effective technology for ground water remediation. This paper describes the first field demonstration of the technology, and is of particular importance since it provides the longest available record of performance (five years). A mixture of 22% granular iron and 78% sand was installed as a permeable “wall” across the path of a contaminant plume at Canadian Forces Base, Borden, Ontario. The major contaminants were trichloroethene (TCE, 268 mg/L) and tetrachloroethene (PCE, 58 mg/L). Approximately 90% of the TCE and 86% of the PCE were removed by reductive dechlorination within the wall, with no measurable decrease in performance over the five year duration of the test. Though about 1% of the influent TCE and PCE appeared as dichloroethene isomers as a consequence of the dechlorination of TCE and PCE, these also degraded within the iron-sand mixture. Performance of the field installation was reasonably consistent with the results of laboratory column studies conducted to simulate the field behavior. However, if a more reactive iron material, or a higher percentage of iron had been used, complete removal of the chlorinated compounds might have been achieved. Changes in water chemistry indicated that calcium carbonate was precipitating within the reactive material; however, the trace amount of precipitate detected in core samples collected four years after installation of the wall suggest that the observed performance should persist for at least another five years. The study provides strong evidence that in situ use of granular iron could provide a long-term, low-maintenance cost solution for many ground water contamination problems.

The relationship between habitual patient-reported symptoms and clinical signs among patients with dry eye of varying severity.

Abstract: PURPOSE. To investigate symptom profiles and clinical signs in subjects with dry eye and normal subjects in a cross-sectional multicenter study. METHODS. Subjects aged 35 to 65 were recruited according to dry eye diagnostic codes and telephone interview and completed the Dry Eye Questionnaire 2001, among others, and underwent dry eye clinical tests. RESULTS. Subjects (122) included 28 control subjects (C), 73 with non-Sjogren's keratoconjunctivitis sicca (non-SS KCS) and 21 with Sjogren's syndrome (SS). Subjects with SS or non-SS KCS reported discomfort and dryness most frequently and that many symptoms worsened over the day and were quite bothersome. Groups were significantly different in corneal fluorescein staining, conjunctival lissamine green staining, Schirmer 1 tear test, and tear break-up time (TBUT; X 2 and Kruskal-Wallis, P < 0.0001). Statistically significant, but moderate, correlations were found between the frequency and evening intensity of dryness and discomfort and TBUT, Schirmer's tear test, overall corneal fluorescein staining, and temporal lissamine green conjunctival staining (Spearman r = 0.31-0.45, P < 0.01). Symptoms were moderately to highly correlated with the clinician's global grading of severity and highly correlated to patient's self-assessment of severity (r = 0.46-0.86, P < 0.0001), whereas signs showed lower correlations (r = 0.22-0.46, P < 0.0001). CONCLUSIONS. Subjects with SS or non-SS KCS reported frequent and intense ocular surface symptoms in the evening, some of which correlated moderately with clinical test results. The global clinician grade of dry eye correlated more highly with patient symptoms than did clinical signs, suggesting that patient symptoms influence dry eye diagnosis and grading of dry eye more than clinical test results.