固相萃取/气相色谱/质谱法测定饮用水中毒死蜱

建立了检测饮用水中毒死蜱的固相萃取/气相色谱/质谱法,该方法对毒死蜱的测定下限可达0.000 6 mg/L,远低于国标法的0.002 mg/L。线性范围为0.5～5.0 mg/L,样品平均加标回收率在74.86%～86.14%之间,测定结果的相对标准偏差<5.4%。该方法简单、灵敏度高、准确、重现性好,可用于饮用水中痕量毒死蜱的测定。     

Flow injection determination of p-aminophenol at trace level using inhibited luminol-dimethylsulfoxide-NaOH-EDTA chemiluminescence

A novel flow injection procedure was developed for the determination of p-aminophenol (PAP) based on the inhibition by PAP of the chemiluminescence from luminol-dimethylsulfoxide (DMSO)-NaOH-EDTA system. The method has merits of higher sensitivity, wider linear range, simpler procedure, and a more rapid analyzing speed. It is applicable for the determination of PAP in the range of 2.5 x 10(-10)-5.0 x 10(-8) g mL(-1) with a detection limit of 1.9 x 10(-10) g mL(-1). The relative standard deviation (RSD) for 5.0 x 10(-9) g mL(-1) PAP is 0.78% (n=15). The method has been successfully used to determine PAP in industrial wastewaters and environmental waters. Additionally, the inhibition mechanism was also discussed briefly.     

Detection of tannic acid at trace level in industrial wastewaters using a highly sensitive chemiluminescence method

A novel flow injection procedure was developed for the determination of tannic acid in industrial wastewaters based on the enhancement by tannic acid of the chemiluminescence from luminol-K3Fe(CN)6-OH- system. The method has the merits of higher sensitivity, higher selectivity, wider linear range, simpler instrumentation. It is applicable for the determination of tannic acid in the range of 3.0 x 10(-10)-1.0 x 10(-7) mol/L with a detection limit of 1.0 x 10(-10) mol/L. The relative standard deviation is 2.7% for the determination of 1.0 x 10(-8) mol/L tannic acid (n = 11). The method has been successfully used to determine tannic acid at trace level in industrial wastewaters from brewery and tannery.     

Extraction and determination of mercury from spring water,beverage and rice samples using combined microwave-assisted cloud point and dispersive-solid phase extraction in micellar media

The determination of inorganic mercury species in water, beverages and foods has been a special research priority in recent years because mercury, as a highly carcinogenic species, even in trace concentration, has high adverse effects on the body of living organisms. In this research, combining two extraction techniques, including microwave-assisted cloud point extraction and dispersive-solid phase extraction (MA-CP-dSPE), for the separation and pre-concentration of mercury in environmental samples is presented. This method is based on the dispersion of nanoparticles in micellar media in the presence of a novel mono-thiosemicarbazone Schiff base (2 N′-[4-diphenylamino]benzylidene) hydrazinecarbothiohydrazide) ligand. Using the experimental conditions defined in the optimization, the method allowed mercury determination from 0.020 to 350 mg/L with a detection limit of 0.005 mg/L. The accuracy of the procedure was tested by analysing certified reference material. The method was successfully applied to copper determination in spring water, beverage and rice samples.     

Determination of EDTA species in water by square-wave voltammetry using a chitosan-coated glassy carbon electrode

The electrochemical behavior of Fe(EDTA)(-/2-) on a chitosan-coated glassy carbon electrode (GCE) and the determining method of the EDTA species in water samples by square-wave voltammetry (SWV) have been investigated. Fe(EDTA)(-) can be adsorbed on the positively charged chitosan membrane assembled on a GCE and be reduced at a potential of -0.095V vs. Ag/AgCl. On the chitosan-coated GCE, the cathodic stripping peak current is proportional to the concentration of EDTA after the operating parameters of SWV were optimized. The measuring range of EDTA was from 2.0x10(-6) to 8.0x10(-5)mol/L with a correlation coefficient of r=0.998 and a detection limit of 2.0x10(-7)mol/L. The relative standard deviation was less than 6.4% (n=5) and the recovery was in the range of 98-105% for the determination of practical samples. The result was consistent with that from the HPLC method.     

Analysing transformation products of herbicide residues in environmental samples

High-performance liquid chromatography (HPLC) methods were developed for the optimised determination of five herbicide residues (dichlorprop, isoproturon, mecoprop, metsulfuron-methyl and 2,4,5-T) and major metabolites. These compounds represent important groups of herbicides and several residues have been found as contaminants in groundwater. The methods make it possible to study these herbicides and several transformation products through simultaneous detection and quantification. Culture media as well as cleaned up extracts from sediment and groundwater can be analysed. Using HPLC with UV detection the general limit of quantification was 1.8 ng injected corresponding to a detection limit of 1-2 micrograms/l when analysing a cleaned up extract from a 20 ml water sample. The method was verified by analysing herbicide residues in groundwater collected from a wetland area. Cleaning up 20 ml groundwater with a residue level of 25 micrograms/l the general recovery was within 58-82%.     

Pharmaceutical and personal care products in tile drainage following land application of municipal biosolids

Land application of municipal biosolids (sewage) is a common farming practice in many parts of the world. There is potential for transport of pharmaceuticals and personal care products (PPCPs) from agricultural fields to adjacent surface waters via tile drainage systems. In this study, liquid municipal biosolids (LMB) (total solids=11,933 mg L(-1)), supplemented with selected PPCPs and the fluorescent dye tracer rhodamine WT (RWT), were applied to tile drained fields using two land application approaches. Objectives included evaluating the relative benefits of land application practices with respect to reducing PPCP loadings to tile drains, evaluating PPCP persistence in tile water, and determining whether rhodamine WT can be used to estimate PPCP mass loads in tile. The PPCPs examined included an antibacterial agent used in personal care products (triclosan), a metabolite of nicotine (cotinine), and a variety of drugs including two sulfonamide antimicrobials (sulfapyridine, sulfamethoxazole), a beta-blocker (atenolol), an anti-epileptic (carbamazepine), an antidepressant (fluoxetine), analgesic/anti-inflammatories (acetaminophen, naproxen, ibuprofen), and a lipid-regulator (gemfibrozil). Maximum observed PPCP concentrations in the spiked LMB were about 10(3) ng g(-1) dry weight. PPCPs were shown to move rapidly via soil macropores to tile drains within minutes of the land application. Maximum observed PPCP concentrations in tile effluent associated with the LMB application-induced tile flow event were approximately 10(1) to 10(3) ng L(-1). PPCP mass loads, for the application-induced tile-hydrograph event, were significantly (p<0.1) higher for surface spreading over non-tilled soil (incorporation tillage occurring 20 h post-application), relative to aerating soil immediately prior to surface spreading using an AerWay slurry deposition system. PPCP concentrations that were detected above the limit of quantitation (LOQ) in tile water during several precipitation-induced tile flow events that occurred post-application, included: triclosan (max. approximately 1.5 x 10(2) ng L(-1)), carbamazepine (max. approximately 7 x 10(1) ng L(-1)), atenolol (max approximately 4 x 10(1) ng L(-1)), and cotinine (max approximately 2 x 10(1) ng L(-1)). In spite of their presence in biosolids, the other PPCPs were not observed above LOQ concentrations during these events. PPCP concentrations were predicted from RWT concentrations over a 40 day study period. Tile mass loads as a percent of PPCP mass applied to soil ranged from 4.2%+/-SD of 9.2% to 7.1%+/-10.9% for the AerWay system and surface spreading plus incorporation treatments, respectively.     

AA3流动分析仪在地表水总磷测定中的应用

建立了应用AA3流动分析仪测定地表水中总磷的分析方法,发现采用AA3测定总磷的最低检出限为0.007 mg/L,测定结果的相对标准偏差值小于1%,地表水加标回收率在90%～110%之间,说明AA3测定地表水中的总磷具有较高的重现性和精密性。     

Kinetics of triclosan oxidation by aqueous ozone and consequent loss of antibacterial activity: relevance to municipal wastewater ozonation

Oxidation of the antimicrobial agent triclosan by aqueous ozone (O(3)) was investigated to determine associated reaction kinetics, reaction site(s), and consequent changes in antibacterial activity of triclosan. Specific second-order rate constants, k(O(3)), were determined for reaction of O(3) with each of triclosan's acid-base species. The value of k(O(3)) determined for neutral triclosan was 1.3(+/-0.1)x10(3)M(-1)s(-1), while that measured for anionic triclosan was 5.1(+/-0.1)x10(8)M(-1)s(-1). Consequently, triclosan reacts very rapidly with O(3) at circumneutral pH (the pH-dependent, apparent second-order rate constant, K(app,O(3)) , is 3.8x10(7)M(-1)s(-1) at pH 7). The pH-dependence of K(app,O(3)) and comparison of triclosan reactivity toward O(3) with that of other phenolic compounds indicates that O(3) reacts initially with triclosan at the latter's phenol moiety. k(O(3)) values for neutral and anionic triclosan were successfully related to phenol ring substituent effects via Brown-Okamoto correlation with other substituted phenols, consistent with electrophilic attack of the triclosan phenol ring. Biological assay of O(3)-treated triclosan solutions indicates that reaction with O(3) yields efficient elimination of triclosan's antibacterial activity. In order to evaluate the applicability of these observations to actual wastewaters, triclosan oxidation was also investigated during ozonation of effluent samples from two conventional wastewater treatment plants. Nearly 100% triclosan depletion was achieved for a 4 mg/L(8.3x10(-5)mol/L)O(3) dose applied to a wastewater containing 7.5 mg/L of DOC, and approximately 58% triclosan depletion for dosage of 6 mg/L(1.3x10(-4)mol/L)O(3) to a wastewater containing 12.4 mg/L of DOC. At O(3) doses greater than 1mg/L(2.1x10(-5)mol/L), hydroxyl radical reactions accounted for <35% of observed triclosan losses in these wastewaters, indicating that triclosan oxidation was due primarily to the direct triclosan-O(3) reaction. Thus, ozonation appears to present an effective means of eliminating triclosan's antibacterial activity during wastewater treatment.     

Decolorization and toxicity of reactive anthraquinone textile dyes under methanogenic conditions

Reductive decolorization of two anthraquinone reactive dyes (Reactive Blue 4, RB4; Reactive Blue 19, RB19) under methanogenic conditions was performed using a mixed, methanogenic culture. Decolorization of the two anthraquinone dyes was investigated to evaluate the rate and extent of color removal as well as to assess possible toxic effects of the dyes and their decolorization product(s) on the methanogenic culture as a function of initial dye concentration ranging from 50 to 300 mg x L(-1). A dextrin/peptone mixture was used as the carbon and electron source. A high rate and extent of color removal was achieved ranging from 4.3 to 29.9 mg x L(-1)h(-1) and 73-91% for RB4, and 13.0-74.4 mg x L(-1)h(-1) and 90-95% for RB19. Initial RB4 concentrations up to 100 mg x L(-1) did not result in any significant inhibition. Both the 200 and 300 mg x L(-1) RB4-amended cultures, and all RB19-amended cultures resulted in severe inhibition of both acidogenesis and methanogenesis. Sequential dye addition at 300 mg x L(-1) for both RB4 and RB19 resulted in accumulation of volatile fatty acids (VFAs) and a very low methane production at the end of the first dye addition after 44 days of incubation. However, at the end of the second dye addition, after a relatively long incubation (384 days), recovery of methanogens in the RB4-amended culture was observed in contrast to the complete inhibition of methanogenesis in the RB19-amended culture. Therefore, RB19 resulted in a higher degree of inhibition of both acidogenesis and methanogenesis than RB4. Addition of dextrin/peptone to dye-inhibited cultures resulted in acidogenesis and a gradual recovery of methanogenesis (mainly aceticlastic methanogenesis) in the RB4-inhibited culture, and a slow recovery of acidogenesis but no recovery of methanogenesis in the RB19-inhibited culture. In contrast, addition of 80% H(2)-20% CO(2) gas to dye-inhibited cultures resulted in recovery of hydrogenotrophic methanogenesis in both the RB4- and RB19-inhibited cultures. In spite of the relatively severe inhibition of the two anthraquinone dyes on the mixed, methanogenic culture, a high extent of color removal was achieved.     

Inactivation of Legionella pneumophila and Pseudomonas aeruginosa: evaluation of the bactericidal ability of silver cations

In this study, silver cations dissolved as silver nitrate at various concentrations were exposed to Legionella pneumophila, Pseudomonas aeruginosa, and Escherichia coli to quantitatively estimate the bactericidal ability of silver. Observed data were analyzed using a newly developed model (Cs x T) that introduced a specific amount of chemisorbed silver onto a bacterial cell (Cs), which represented the chemisorption properties of silver on the bacterial cell body. Silver cations were rapidly chemisorbed onto bacterial cells after injection into samples, and Cs values (initial concentration of silver was 0.1 mg Ag/l) were calculated as 1.810 x 10(-6) (L. pneumophila), 1.102 x 10(-6) (P. aeruginosa), and 1.638 x 10(-6) microg Ag/cell(i) (E. coli) after incubation for 8 h. During that time, the three tested bacteria were completely inactivated under the detection limit (>7.2 log reduction). Based on the calculated Cs values, bacterial tolerance against silver was estimated by using the equation (Cs x T) multiplying the Cs values with exposure time (T). The Cs x T values well represented the bactericidal abilities of silver against the tested bacteria. The demanded Cs x T values to accomplish a 1 log inactivation (90% reduction) of L. pneumophila, P. aeruginosa, and E. coli (the initial numbers of bacteria were 1.5 x 10(7) CFU/ml, approximately) were estimated as 2.44 x 10(-6), 0.63 x 10(-6), and 0.46 x 10(-6) microgh/cell(i) of silver. The values were significantly reduced to 1.54 x 10(-6), 0.31 x 10(-6), and 0.25 x 10(-6) microgh/cell(i), respectively, with simultaneous injection of silver and copper. This study shows the successful quantitative estimation of the bactericidal ability of silver by applying the newly developed model (Cs x T). Among the tested bacteria, L. pneumophila showed the strongest tolerance to exposure of the same concentration of silver.     

Occurrence of nine nitrosamines and secondary amines in source water and drinking water: Potential of secondary amines as nitrosamine precursors

Due to their high carcinogenicity, the control of nitrosamines, a group of disinfection by-products (DBPs), is an important issue for drinking water supplies. In this study, a method using ultra-performance liquid chromatography-electrospray ionization tandem mass spectrometry was improved for simultaneously analyzing nine nitrosamines in source water and finished water samples of twelve drinking water treatment plants (DWTPs) in China. The method detection limits of the nine target analytes were 0.2-0.9 ng/L for the source water samples and 0.1-0.7 ng/L for the finished water samples. Of the nine nitrosamines, six (N-nitrosodimethylamine (NDMA), nitrosodiethylamine (NDEA), N-nitrosomorpholine (NMor), N-nitrosodi-n-butylamine (NDBA), N-nitrosomethylethylamine (NMEA), and N-nitrosodiphenylamine (NDPhA)) were detected. The total nitrosamine concentrations in source water and finished water samples were no detection-42.4 ng/L and no detection-26.3 ng/L, respectively, and NDMA (no detection-13.9 ng/L and no detection-20.5 ng/L, respectively) and NDEA (no detection-16.3 ng/L and no detection-14.0 ng/L, respectively) were the most abundant. Meanwhile, the occurrence of nine secondary amines corresponding to the nine nitrosamines was also investigated. All of them except for di-n-propylamine were detected in some source water and finished water samples, and dimethylamine (no detection-3.9 μg/L and no detection-4.0 μg/L, respectively) and diethylamine (no detection-2.4 μg/L and no detection-1.8 μg/L, respectively) were the most abundant ones. Controlled experiments involving chloramination of four secondary amines confirmed that dimethylamine, diethylamine, morpholine and di-n-butylamine in water can form the corresponding nitrosamines, with diethylamine and morpholine showing significantly higher yields than dimethylamine which has already been identified as a precursor of NDMA. This study proved that diethylamine, morpholine and di-n-butylamine detected in raw water would be one of the important the precursors of NDEA, NMOR and NDBA, respectively, in drinking water.     

Hybrid flotation--membrane filtration process for the removal of heavy metal ions from wastewater

A promising process for the removal of heavy metal ions from aqueous solutions involves bonding the metals firstly to a special bonding agent and then separating the loaded bonding agents from the wastewater stream by separation processes. For the separation stage, a new hybrid process of flotation and membrane separation has been developed in this work by integrating specially designed submerged microfiltration modules directly into a flotation reactor. This made it possible to combine the advantages of both flotation and membrane separation while overcoming the limitations. The feasibility of this hybrid process was proven using powdered synthetic zeolites as bonding agents. Stable fluxes of up to 80l m(-2)h(-1) were achieved with the ceramic flat-sheet multi-channel membranes applied at low transmembrane pressure (<100 mbar). The process was applied in lab-scale to treat wastewater from the electronics industry. All toxic metals in question, namely copper, nickel and zinc, were reduced from initial concentrations of 474, 3.3 and 167mg x l(-1), respectively, to below 0.05 mg x l(-1), consistently meeting the discharge limits.     

Pollutant removal from municipal sewage lagoon effluents with a free-surface wetland

This research project was initiated to refine the knowledge available on the treatment of rural municipal wastewater by constructed wetlands. To determine the treatment capacity of a constructed wetland system receiving municipal lagoon effluents, the wetland was monitored over one treatment season, from May 19 to November 3, 2000. The wetland system consisted of a three-cell free-surface wetland, phosphorus adsorption slag filters and a vegetated filter strip. Bimonthly water samples at the inlet and outlet of each component of the wetland system were analysed for biochemical oxygen demand, nitrate and nitrite, ammonia and ammonium, total Kjeldahl nitrogen (TKN), total suspended solids (TSS), total phosphorus (TP), ortho-phosphate (ortho-PO(4)), fecal coliforms (FCs) and Escherichia coli. The free-surface wetland cells treating the lagoon effluents achieved removals as follows: biochemical oxygen demand (34%), ammonia and ammonium (52%), TKN (37%), TSS (93%), TP (90%), ortho-PO(4) (82%), FCs (52%) and E. coli (58%). The wetland cells reduced total nitrogen, TP and biochemical oxygen demand to levels below the maximum permissible levels required for direct discharge to nearby receiving waters (TN<3.0 mg x L(-1), TP<0.3 mg x L(-1), BOD(5)<3.0 mg x L(-1)). The vegetated filter strip treating the effluents from the wetland cells achieved removals as follows: biochemical oxygen demand (18%), ammonia and ammonium (28%), TKN (11%), TSS (22%), TP (5%), FCs (28%) and E. coli (22%). It may therefore serve as an additional treatment stage further reducing the concentrations of these mentioned parameters. The slag filters reduced TP in the lagoon effluents by up to 99%, and, in this study, were concluded to be effective phosphorus adsorbers.     

Daily intake of manganese by the adult population of Mumbai

The daily intake of manganese (Mn) estimated through air, water and duplicate dietary analysis is found to range from 0.67 to 4.99 mg with a mean value of 2.21 mg. Ingestion through food contributed to the predominant fraction of the intake. The turnover rate of Mn through blood is approximately 2 h, based on the mean concentration of Mn in blood of 1.54 microg l(-1). The average concentrations of Mn in water and air were approximately 1.42 microg l(-1) and 37 ng m(-3), respectively. The daily intake of Mn by the adult population of Mumbai is closer to the lower bound of the recommended limit of 2-5 mg. Electro Thermal Atomic Absorption Spectrophotometry (ET-AAS), has been used for the determination of Mn in a variety of environmental and human biological fluids. The detection limit of Mn for a volume injection of 20 microl is 2 pg absolute. The precision of the method is established by analyzing a synthetic mixture containing various elements in different quantities (0.5-10 ppm) and is found to be within +/- 8%. The reliability of estimation is further assessed through the analysis of Standard Reference Materials (SRMs) of soil, hay, milk powder and fish tissue obtained from IAEA.     

微波消解/流动注射光度法在线测定水中的总氮

利用微波在线消解水样，将流动注射分析技术与分光光度法相结合，建立了一种在线测定水中总氮的快速分析方法。在优化试验条件下，该方法对TN的检出限为0．04mg／L，对总氮含量为0．491mg／L的标准样品测定11次的相对标准偏差为1．2％。采用该方法测定河水、生活污水、工业废水水样中的TN含量，其相对标准偏差≤1％，加标回收率为97％～101％，结果令人满意。     

NMR spectroscopy for determination of cationic polymer concentrations

Organic polyelectrolytes are utilized extensively in wastewater treatment, but their fate after use is poorly understood. Analytical methods used for polymer determination in less complex systems appear to fail in application to wastewater systems, contributing to the lack of knowledge. Thus, the development of 1H NMR spectroscopy is reported here for specifically quantitating certain cationic flocculant polymers in environmental samples. Proton observe frequencies of 250 or 400 MHz proton were used. A copolymer of acrylamide and acryloyloxyethyltrimethylammonium chloride was used, representative of cationic flocculant polymers possessing quaternary ammonium groups with terminal methyls that provide a sharp singlet at a chemical shift of approximately 3.06 ppm. A strong linear relationship was demonstrated between polymer concentration and either height or area of this peak. Recoveries were up to 96% at higher concentrations (250 mg/L), and were greater than when using viscosity or charge titration methods for polymer determination. Lesser recoveries at lower concentrations (70% at 5 mg/L) were attributed to adsorptive losses. The detection limit of this method was determined to be <0.5 mg/L. Use of the method was exemplified by analysis of anaerobically digested sludges for residual polymer following a range of dosages, showing the resulting isotherm.     

Laboratory investigation of the phosphorus removal (SRP and TP) from eutrophic lake water treated with aluminium

Mechanisms involved in phosphorus (P) removal from eutrophic lake water with aluminium (Al) were assessed by jar tests. For this purpose, eutrophic lake water enriched with soluble reactive phosphorus (SRP), algae or sediments in order to mimic the various conditions found in shallow eutrophic lakes was studied. Total phosphorus (TP) removal was reached after floc settling, the maximal TP removal efficiency (90-95%) was obtained for an Al concentration ranging from 2 to 5 mg L(-1), depending on the organic matter (OM) origin (algae or sediments). Algae appeared to limit macro-floc formation (those able to settle). In contrast, in the presence of sediments, macro-floc formation was favoured at low Al dose (2-3 mg L(-1) Al). High SRP removal was obtained with the lowest Al dose (1 mg L(-1) Al) and remained greater than 60% for an SRP concentration up to 350 microg L(-1). SRP removal was not influenced by the OM origin. The experimental data and literature were used to suggest a hypothetical model for floc formation and P removal with Al under the conditions observed in treated lakes.     

Occurrence and removal of N-nitrosamines in wastewater treatment plants

The presence of nitrosamines in wastewater might pose a risk to water resources even in countries where chlorination or chloramination are hardly used for water disinfection. We studied the variation of concentrations and removal efficiencies of eight N-nitrosamines among 21 full-scale sewage treatment plants (STPs) in Switzerland and temporal variations at one of these plants. N-nitrosodimethylamine (NDMA) was the predominant compound in STP primary effluents with median concentrations in the range of 5-20 ng/L, but peak concentrations up to 1 μg/L. N-nitrosomorpholine (NMOR) was abundant in all plants at concentrations of 5-30 ng/L, other nitrosamines occurred at a lower number of plants at similar levels. From concentrations in urine samples and domestic wastewater we estimated that human excretion accounted for levels of <5 ng/L of NDMA and <1 ng/L of the other nitrosamines in municipal wastewater, additional domestic sources for <5 ng/L of NMOR. Levels above this domestic background are probably caused by industrial or commercial discharges, which results in highly variable concentrations in sewage. Aqueous removal efficiencies in activated sludge treatment were in general above 40% for NMOR and above 60% for the other nitrosamines, but could be lower if concentrations were below 8-15 ng/L in primary effluent. We hypothesize that substrate competition in the cometabolic degradation explains the occurrence of such threshold concentrations. An additional sand filtration step resulted in a further removal of nitrosamines from secondary effluents even at low concentrations. Concentrations released to surface waters were largely below 10 ng/L, suggesting a low impact on Swiss water resources and drinking water generation considering the generally high environmental dilution and possible degradation. However, local impacts in case a larger fraction of wastewater is present cannot be ruled out.     

Nitrate flux from aquifer storage in excess of baseflow contribution during a rain event

Nitrate flux from a bedrock aquifer due to a storm was calculated by hydrograph separation. The hydrograph generated by a 20-mm rain in Cedar River of Iowa was separated into the following three components: the constant baseflow, the rainwater, and the water released from aquifer in excess of baseflow. The separation was conducted by using oxygen isotopes, dissolved nitrate, and stream discharge. The peak discharge was 33h long. During this period, the water released from the aquifer storage in excess of baseflow was 36% of the total discharge. The rainwater and the pre-storm baseflow equivalents were 17% and 47%, respectively. The nitrate concentrations in the instantaneous discharge ranged between 8.6 and 10.0 mg/L. The average concentrations in the rainwater and the baseflow were 3.7 and 9.8 mg/L, respectively. A total of 3.6 x 10(5) mol of nitrate was transported by the stream during the 33 h of peak discharge. Approximately 35% (1.3 x 10(5) mol) of this mass was derived from the aquifer storage in excess of baseflow contribution. The rainwater and the constant baseflow equivalentswere 7% (2.6 x 10(4) mol) and 58% (2.1 x 10(5) mol), respectively. The release of a significant amount of nitrate from the aquifer suggests that the local geology is favorable for vertical recharge of rainwater which causes an increased fluid pressure within the aquifer forcing ground water to discharge laterally into the stream. Such observation also implies that the aquifer is effectively flushed out during storms, thus restricting long term build-up of nitrate from agricultural sources.