Nitrate Concentrations In Samples Research Articles

Effective correction of dissolved organic carbon interference in nitrate detection using ultraviolet spectroscopy combined with the equivalent concentration offset method.

Nitrate contamination in water sources poses a substantial environmental and health risk. However, accurate detection of nitrate in water, particularly in the presence of dissolved organic carbon (DOC) interference, remains a significant analytical challenge. This study investigates a novel approach for the reliable detection of nitrate in water samples with varying levels of DOC interference based on the equivalent concentration offset method. The characteristic wavelengths of DOC were determined based on the first-order derivatives, and a nitrate concentration prediction model based on partial least squares (PLS) was established using the absorption spectra of nitrate solutions. Subsequently, the absorption spectra of the nitrate solutions were subtracted from that of the nitrate-DOC mixed solutions to obtain the difference spectra. These difference spectra were introduced into the nitrate prediction model to calculate the equivalent concentration offset values caused by DOC. Finally, a DOC interference correction model was established based on a binary linear regression between the absorbances at the DOC characteristic wavelengths and the DOC-induced equivalent concentration offset values of nitrate. Additionally, a modeling wavelength selection algorithm based on a sliding window was proposed to ensure the accuracy of the nitrate concentration prediction model and the equivalent concentration offset model. The experimental results demonstrated that by correcting the DOC-induced offsets, the relative error of nitrate prediction was reduced from 94.44% to 3.36%, and the root mean square error of prediction was reduced from 1.6108 mg L-1 to 0.1037 mg L-1, which is a significant correction effect. The proposed method applied to predict nitrate concentrations in samples from two different water sources shows a certain degree of comparability with the standard method. It proves that this method can effectively correct the deviations in nitrate measurements caused by DOC and improve the accuracy of nitrate measurement.

Biofilm Growth in Two Streams Draining Mountainous Permafrost Catchments in NE Greenland

AbstractThe objective of this study was to evaluate how stream water nutrient concentrations influence biofilm accrual in streams draining mountainous permafrost headwaters. We selected six stream locations in the Zackenberg area (NE Greenland, 74°N) subjected to a gradient in the areal contribution of different geomorphological units in the watersheds and channel stability. We used nutrient diffusing substrates to evaluate biofilm growth (autotrophic and total biomass). We found elevated stream nitrate concentrations in samples from upstream reaches draining larger areas of solifluction sheets and bare rock and with higher channel instability. Nitrate had the highest standardized effect on autotrophic biofilm growth on control disks. However, stream biofilm growth was not nutrient limited as shown by the absence of an increase in biofilm biomass as a response to the experimental nutrient additions. The response to nutrient additions via diffusing substrates depended on the altitude gradient. Overall, our results showed stream nitrogen availability to be one of the main drivers of algal biofilm accrual in high‐Arctic streams, suggesting that the predicted changes in nutrient exports induced by climate change will have strong impacts on the biogeochemistry and ecological functioning of high‐Arctic streams.

The concentration and health risk assessment of nitrate in vegetables and fruits samples of Iran

This investigation was aimed to assess nitrate concentration and its health risk in vegetable and fruit samples collected from Iran. The mean nitrate level in samples ranged from 66.70 to 1072.60 mg kg−1. The nitrate concentration in samples including leek (1070.79 ± 404.22 mg k−1 (carrot (339.50 ± 400.84 mg k−1), and watermelon (90.00 ± 136.73 mg kg−1) was higher while in other samples, including potato (129.30 ± 86.51 mg kg−1), onion (82.25 ± 92.22 mg kg−1), tomato (110.93 ± 166.08 mg kg−1), lettuce (1072.60 ± 644.17 mg kg−1), and melon (66.70 ± 45.41 mg kg−1) were lower than the permissible limit. The EDI and target hazard quotient (THQ) of nitrate (2.25 mg/kg bw/day) was less than EDI value (3.70 mg/kg bw/day) and 1, respectively.

Measuring nitrate concentration in wastewaters with high chloride content

ABSTRACTThe presence of chloride ions in wastewaters in concentrations above 50 mg/L poses interference in several methods used for the measurement of nitrate-nitrogen. The aim of this study was to characterise the reliability and costs of some commonly available methods for the analysis of nitrate concentration in landfill leachate which contains high chloride levels. To investigate the effect of chloride interference, several widely used methods [ion chromatography (IC), continuous flow analysis (CFA), the German standard method (DIN), cuvette test (CUV), standard addition method (SAM) and reflectometric test (REF)] were used to measure the nitrate concentration in synthetic solutions containing varying concentrations of chloride and nitrate-nitrogen. Nitrate recoveries of the various methods were found to decrease in the following rank order: CUV (>95%) > IC (>90%) > CFA (89%) > DIN (88%) > REF (70%) > SAM (<80%). In the second part of the study, the same methods were used to measure nitrate concentrations in samples of biologically nitrified landfill leachate with and without chloride elimination. For leachate samples without chloride elimination, CUV results were well correlated (linear regression) with IC results (slope = 1.02/R2 = 0.99) but to lesser extents with results obtained by CFA (0.91/0.86), DIN (0.89/0.97) and REF (0.86/0.77), and not correlated with SAM (0.74/–1.3). The incurred measurement costs per sample (in Euros) for the methods were as follows: CFA (<0.1) < DIN (0.6) < REF (0.7) < SAM (3) < CUV (3.8) < IC (15). Cuvette tests are recommended as the method of choice due to their accuracy and lower cost than IC.

Integrated approach to investigation of occurrence and quality of groundwater in Ogbomoso North, Southwestern Nigeria

An integrated approach involving electrical resistivity, hydrogeologic, hydrogeochemical and remote sensing has been employed to investigate the occurrence, facies, quality and hydrogeologic systems of the aquifer units of groundwater in the low latitude crystalline basement complex terrain of Ogbomoso North, Southwestern Nigeria. Vertical electrical soundings (VES) were conducted at 56 locations across the study area using Schlumberger electrode configuration with a maximum current electrode separation of 240 m along northeast–southwest azimuth. The layering models obtained from the interpretation of VES data were used to construct the 2-D geoelectric section for the study area. The static water level, depth, geographic coordinates and elevations of 130 hand-dug wells within the study area were also measured to construct the groundwater flow map. Hydrogeochemical studies involved in situ measurements of such parameters as electrical conductivity (EC), acidity (pH) and total dissolved solid (TDS) using calibrated WTW Conductivity/TDS meter (LF 90) sand HACH pH Sension meter, respectively, and laboratory analysis of 25 representative water samples for anion and cation concentration. Prominent lineaments were also mapped from side-looking airborne radar imagery of the area and used to obtain the lineaments orientations and joints systems vide Rose diagram. Interpretation of the VES data revealed a three- to four-layer earth model with the three-layer resistive–conductive–resistive geoelectrical signature as the most dominant constituting 62 % of the entire apparent resistivity curves. The fractured/weathered basement constitutes the aquifer units (confined/unconfined) while the conductive zones comprise clay/sandy clay/clayey sand. The 2-D geoelectric section revealed lenses of sand and clay, sand atoll and fresh/fracture basement at different depths. The lineament length varied from 0.72 to 1.39 km and 0.11 to 0.56 km for long and short lineaments, respectively. The long lineaments trend in the east–west direction and indicated shallow weathering while the short lineaments trend NW–SE and NE–SW directions indicating deep weathering in such directions. Two joint systems trending NW–SE and NE–SW as well as joints in the E–W direction were also revealed. The direction of groundwater flow was southward and westward with the recharge areas along topographic high trending NE–SW. The EC, pH and TDS ranged between 0.10 and 1.58 mS/cm, 5.0 and 7.3 and 60 and 920 mg/l, respectively, with corresponding mean of 0.60 ± 0.06 mS/cm, 6.8 ± 0.10, and 342 ± 34 mg/l. The anionic dominance was of the order CO3 2− > Cl− > NO3 − > SO4 2− > PO4 3− > Fl− and the concentrations of the cations were of the order Ca2+ > Na+ > K+. Furthermore, all the elemental concentrations were within the World Health Organization standard limit for drinking water save for high nitrate concentration in samples collected from very few locations. Twelve groundwater facies were identified each representing different rock types and products of weathering. The groundwater is localized within the fractured/weathered basement with moderately thick overburden and capable of sustaining industrial development, increasing urbanization as well as providing access to clean water. The corroboration between the joint system and the direction of groundwater flow indicated the groundwater flow is structural controlled.

Residence time as a key for comprehensive assessment of the relationship between changing land use and nitrates in regional groundwater systems

In this study, an approach is put forward to study the relationship between changing land use and groundwater nitrate contamination in the Sanjiang Plain. This approach emphasizes the importance of groundwater residence time when relating the nitrates to the changing land use. The principles underlying the approach involve the assessment of groundwater residence time by CFCs and the Vogel age model and the reconstruction of the land use at the groundwater recharge time by interpolation. Nitrate trend analysis shows that nitrates have begun to leach into the aquifers since agricultural activities boomed after the 1950s. Hydrochemical analysis implies that the possible process relating to the nitrate reduction in the groundwater is the oxidation of Fe(ii)-silicates. However, the chemical kinetics of the oxidation of Fe(ii)-silicates is slow, so this denitrification process contributes little to the nitrate variations. Stepwise regression shows that the nitrate concentrations of samples had no direct relationship with the land use at the groundwater sampling time, but had a relatively strong relationship with the land use at the groundwater recharge time. Dry land is recognized as the dominant factor contributing to the elevated concentration of nitrates. The nitrogen isotope for nitrate (δ(15)N-NO3) gives a more direct result of the identification of nitrate sources: the use of manure in agricultural activities. Principle component (PC) regression shows that the process of the dry land exploitation is the major process that controls the nitrate contamination in the Sanjiang Plain.

Evaluation of nitrate concentration in groundwater and drinking water distribution network of Robat-Karim City, Tehran Province, Iran

The aim of this study was to evaluate the amount of nitrate concentration in groundwater resources (wells) and drinking water distribution network of Robat-Karim city of Tehran Province, Iran. The study was accomplished during 8 months (March–Oct 2009). For this purpose, 40 samples from groundwater resources (wells) and 32 samples from water distribution network were collected and analyzed. In this study, a spectrophotometer was used for nitrate analysis of all samples. Based on the results of this study, the maximum, minimum and mean amounts of nitrate concentrations in wells and distribution network samples were 5.9, 0.2, 2.1 and 4, 1.4, 2.05 mg NO3−-N/L, respectively. The amounts of nitrate concentrations in all samples were much lower than its permissible levels in national and international standards.

The impact of agriculture on ground water quality of Canal area, Bikaner

This paper is aimed at the assesment of nitrate in ground water by various pollution sources such as fertilizer, pesticide and insceticide. 16 water samples were obtained from tube well and hand pumps situtaed at cultivated farms and near villages from Khajuwala (located at canal project area in Bikaner distric of Rajastan state). Water samples were collected in July, Oct (2005) and Jan (2006) and were analyzed for nitrate. Some samples were found to contain nitrate above the permissible limit prescribed by WHO, IS and other organizations. Nitrate concentration in samples of well water situated in cultivated area is found higher than in village area. It was also found to be more in handpump samples than in tube well water sample. This result indicates that nitrate concentration has positive correlation with the use of fertilizers & negative correlation with depth of water table. Nitrate concentration was found to enhance after the monsoon period in the month of Oct (2005), which proves the phenomenon of agricultural leaching of nitrate.

Statistical Analysis of Nitrate Movement through the Soil in Central Kansas

An earlier investigation by the Kansas Geological Survey in central Kansas studied the movement of nitrate from fertilizer through soil into the groundwater. Nitrate concentrations in soil water were measured on samples collected at three locations during a three-year span, from sets of lysimeters buried at different depths. Although patterns seemed apparent in the resulting measurements, no statistical analyses were performed to test their significance; this re-study of the data uses analyses of variance to test for differences in nitrate concentration attributable to time and to depth in the soil. The mean nitrate concentration of samples collected in the first year of the experiment was significantly higher than the means of second and third year samples at all three locations, perhaps reflecting the confounding influence of a previous flooding experiment. ANOVAs of depth across years determined few significant differences in nitrate concentration with depth. The wintertime gap in measurements and unequal sampling through time precludes formal time-series analyses, but graphs of concentration versus time show that peak concentration occurs at later times with increasing depth, and that maximum concentration decreases with depth. These statistical analyses support the conclusions from the original investigation.

Screening Nitrate in Forages with a Test Strip: Collaborative Study

A collaborative study was conducted for screening nitrate in forages with a commercially available test strip. The method involves extracting a finely ground sample with deionized water. The test strip is dipped in the sample extract. The color of the reaction zone on the test strip changes from white to pink or purple depending on the nitrate concentration in sample extract. The nitrate present in the extract is determined by comparing the color of the test strip to the color scale on the test strip container. Six blind quintuplicates of forage samples were analyzed by 20 collaborators. Nitrate concentrations in forage samples tested ranged from < 1000 ppm nitrate to > 10,000 ppm nitrate on dry matter basis. Each collaborator was asked to assign each sample to one of the 4 following nitrate concentration ranges: (1) < 1000 ppm, (2) 1000 to 5000 ppm, (3) > 5000 ppm to 10,000 ppm, and (4) > 10,000 ppm. Nineteen of 20 collaborators reported results. Results from 2 laboratories were rejected as outliers by inspection and chi 2 test. Sensitivity rates (p+) ranged from 0.965 to 0.998, with standard errors of 0.006 to 0.16. Specificity rates (p-) ranged from 0.991 to 0.997 for the 4 ranges, with standard errors of 0.003 to 0.006. False-positive rates (pf+) ranged from 0.006 to 0.046, with standard errors of 0.006 to 0.025. False-negative rates (pf-) ranged from 0.003 to 0.007, with standard errors of 0.003 to 0.006. Screening nitrate in forages with a test strip has been adopted first action by AOAC INTERNATIONAL.