The objective of this study was to evaluate correlations between annual average daily traffic (AADT) and storm water runoff pollutant concentrations generated from California Department of Transportation (Caltrans) highway sites. Analyses of data collected from the Caltrans Cyear (1997-01) highway runoff characterization program revealed that, in general, pollutant concentrations from urban highways were higher than those found from non-urban highways. For a limited number of pollutants, however, the concentrations from norrurban highways were found to be higher than the concentrations from urban highways. No direct linear correlation was found between highway runoff pollutant event mean concentrations (EMCs) and AADT. However, through multiple regression analyses, it was shown that AADT has an influence on most highway runoff constituent concentrations, in conjunction with factors associated with watershed characteristics and pollutant build-up and wash oft The other noticeable factors shown ' (530) 7537030, e-mail: claua@lrr~a.corn to influence the accumulation of pollutants on highways were antecedent dry period, drainage area, maximum rain intensity, and land use.Keywords: Annual average daily traffic (AADT), highway runoff, linear regression model, multiple regression model, and pollutants.The California Department of Transportation (Caltrans) is engagd in a multi-year program of research and monitoring pertaining to the environmental effects of stormwater quality from transportation facilities. Part of Caltrans storm water quality research and monitoring program involves the characterization of highway runoff (Kayhanian et al., 2001). These monitoring studies were principally undertaken (i) to comply with the statewide National Pollution Discharge Elimination System (NPDES) storm water permit requirements, (ii) to address legal requirements, (iii) to aid in developing new treatment systems, (iv) to develop runoff load models, and (v) to fill data gaps in stormwater runoff characterization for statistical analysis. The information presented in this paper is based on a 4-year highway stormwater runoff characterization study that was undertaken during the 1997-01 rainy seasons from October through April.Caltrans monitoring data are analyzed on a regular basis to assess runoff characteristics. One question that is frequently asked i s whether a correlation exists between annual average daily traffic (AADT) and the concentrations of highway runoff pollutants. The current paper addresses this issue. METHODS Sampling ProceduresRepresentative highway sites and storm events were selected for event-based monitoring. There are a wide range of parameters that can potentially affect the quality of stormwater discharges including geographic location, climatic/ecologic conditions, hydrologic conditions, land use, and AADT. The highway sites were selected to represent the full range of physical parameters. In addition, the sites were selected as potential monitoring sites based on the ability of the sampling t...
Catalytic reactions of enzyme labels in enzyme-linked immunosorbent assays require a long incubation period to obtain high signal amplification. We present herein a simple immunosensing scheme in which the incubation period is minimized without a large increase in the detection limit. This scheme is based on electrochemical-enzymatic (EN) redox cycling using glucose oxidase (GOx) as an enzyme label, Ru(NH3)6(3+) as a redox mediator, and glucose as an enzyme substrate. Fast electron mediation of Ru(NH3)6(3+) between the electrode and the GOx label attached to the electrode allows high signal amplification. The acquisition of chronocoulometric charges at a potential in the mass transfer-controlled region excludes the influence of the kinetics of Ru(NH3)6(2+) electrooxidation and also facilitates high signal-to-background ratios. The reaction between reduced GOx and Ru(NH3)6(3+) is rapid even in air-saturated Tris buffer, where the faster competitive reaction between reduced GOx and dissolved oxygen also occurs. The direct electrooxidation of glucose at the electrode and the direct electron transfer between glucose and Ru(NH3)6(3+) that undesirably increase background levels occur relatively slowly. The detection limit for the EN redox cycling-based detection of cancer antigen 125 (CA-125) in human serum is slightly higher than 0.1 U/mL for the incubation period of 0 min, and the detection limits for the incubation periods of 5 and 10 min are slightly lower than 0.1 U/mL, indicating that the detection limits are almost similar irrespective of the incubation period and that the immunosensor is highly sensitive.
We compare herein biosensing performance of two electroreduction-based electrochemical-enzymatic (EN) redox-cycling schemes [the redox cycling combined with simultaneous enzymatic amplification (one-enzyme scheme) and the redox cycling combined with preceding enzymatic amplification (two-enzyme scheme)]. To minimize unwanted side reactions in the two-enzyme scheme, β-galactosidase (Gal) and tyrosinase (Tyr) are selected as an enzyme label and a redox enzyme, respectively, and Tyr is selected as a redox enzyme label in the one-enzyme scheme. The signal amplification in the one-enzyme scheme consists of (i) enzymatic oxidation of catechol into o-benzoquinone by Tyr and (ii) electroreduction-based EN redox cycling of o-benzoquinone. The signal amplification in the two-enzyme scheme consists of (i) enzymatic conversion of phenyl β-d-galactopyranoside into phenol by Gal, (ii) enzymatic oxidation of phenol into catechol by Tyr, and (iii) electroreduction-based EN redox cycling of o-benzoquinone including further enzymatic oxidation of catechol to o-benzoquinone by Tyr. Graphene oxide-modified indium-tin oxide (GO/ITO) electrodes, simply prepared by immersing ITO electrodes in a GO-dispersed aqueous solution, are used to obtain better electrocatalytic activities toward o-benzoquinone reduction than bare ITO electrodes. The detection limits for mouse IgG, measured with GO/ITO electrodes, are lower than when measured with bare ITO electrodes. Importantly, the detection of mouse IgG using the two-enzyme scheme allows lower detection limits than that using the one-enzyme scheme, because the former gives higher signal levels at low target concentrations although the former gives lower signal levels at high concentrations. The detection limit for cancer antigen (CA) 15-3, a biomarker of breast cancer, measured using the two-enzyme scheme and GO/ITO electrodes is ca. 0.1 U/mL, indicating that the immunosensor is highly sensitive.
In washing-free electrochemical detection, various redox and reactive species cause significant interference. To minimize this interference, we report a washing-free electrochemical immunosensor using flavin adenine dinucleotide (FAD)-dependent glycerol-3-phosphate dehydrogenase (GPDH) and glycerol-3-phosphate (GP) as an enzyme label and its substrate, respectively, because the reaction of FAD-dependent dehydrogenases with dissolved O2 is slow and the level of GP preexisting in blood is low (<0.1 mM). A combination of a low electrocatalytic indium-tin oxide (ITO) electrode and fast electron-mediating Ru(NH3)6(3+) is employed to obtain a high signal-to-background ratio via proximity-dependent electron mediation of Ru(NH3)6(3+) between the ITO electrode and the GPDH label. Electrochemical oxidation of GPDH-generated Ru(NH3)6(2+) is performed at 0.05 V vs Ag/AgCl, at which point the electrochemical interference is very low. When a washing-free immunosensor is applied to cardiac troponin I detection in human serum, the calculated detection limit is approximately 10 pg/mL, indicating that the immunosensor is very sensitive in spite of the use of washing-free detection with a short detection period (10 min for incubation and 100 s for electrochemical measurement). The low-interference washing-free electrochemical immunosensor shows good promise for fast and simple point-of-care testing.
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