Nitrate Accumulation Research Articles

Features of growing red beet and carrot in the conditions of the south-western part of the Central region of the Russian Federation

Relevance and methodology. The article presents the results of the study of economically valuable signs of red beet and carrot when grown in the conditions of the south-western part of the Central region of the Russian Federation. The aim of scientific researches was to conduct phytosanitary monitoring of crops, study the species composition of harmful organisms and the relative resistance of varieties and hybrids of vegetable root crops to harmful organisms in the Bryansk region. The estimation on level of ecotoxicant accumulation during cultivation was carried out. The researches were carried out in 2018–2020 in the stationary field of the Bryansk State Agrarian University.Results. As a result of the researches, the species composition of harmful organisms on the variety samples of red beet and garden carrot was established. In the conditions of the Bryansk region, according to the signs of "root crop mass" and "commercial yield" on average over the years of research varieties and hybrids of garden carrots Mars F1, Kupar F1, Nadezhda F1, Shantene korolevskaya, Nante, Minor were identified. Insignificant population of willow-carrot aphid — Cavariella aegopodii (Skop.) —was established on plants of varieties Nante, Nantskaya 4, Marlinka, Minor and hybrid Nadezhda F1. The Nante variety with a high content of carotene (185.1 mg/kg), dry matter (13.3%), low accumulation of nitrates (11.0 mg/kg) and relative resistance to pests was selected according to the results of biochemical analysis. The development of red beet cercosporosis (R) was found to be at a level of 1.6 to 11.3%, while the prevalence of the disease ranged from 22.7 to 76.9%. The variety samples Mulatka, Lyubava and Nezhnost(R 2–2.4%) were slightly affected. A high degree of the disease prevalence was noted in the varieties Nesravnennaya, Gospadynya, Bordo 237. The samples Mulatka, Kreolka, Gospadynya, Lyubava, Nesravnennaya were selected according to the mass of the root crop and resistance to harmful organisms.

Контроль вмісту нітратів у харчових продуктах – актуальні питання

Abstract. Nitrates are natural metabolic products of all plants. They are vital to plants – without them their normal growth and development is impossible. However, the uncontrolled use of nitrogen fertilizers has led to their uncontrolled accumulation in food products. When eating vegetables with high amounts of nitrates, they are partially restored to nitrites in the intestinal tract, and the latter, entering the bloodstream cause diseases – methemoglobinemia. Therefore, quantitative and qualitative determination of nitrates and nitrites in plant and animal products, water and soils are relevant today. Based on the analysis of scientific literature, the essence of the problem of excessive accumulation of nitrates in agricultural products and their negative impact on human health is highlighted. Aim. The aim of the research was to determine experimentally the concentration of nitrates and nitrites in plant and animal products, water and soils, to compare it with the maximum allowable concentration as required by Commission Regulation (EU) No 1258/2011 on maximum nitrate content in vegetables and by State sanitary rules and regulations on Maximum Permissible Levels of Certain Contaminants in Food, approved by the Order of the Ministry of Health of Ukraine of May 13, 2013 No 368 (as amended by the order of the Ministry of Health of Ukraine of May 22, 2020 No 1238). Materials and Methods. Sources of information retrieval in printed and electronic publications, databases search engines, methods of analysis, comparison and generalization of data. Photometric method. Results. The analysis of the value of nitrates in nature, sources of this substance in food was conducted; normalization of the content of nitrate components, the problem of plant products quality decline due to the uncontrolled use of fertilizers was studied; the content of nitrates in plant and animal products; the harmful effects of products with high nitrate content were considered; a comprehensive assessment of nitrate content in plant products was carried out; comparative characteristics of methods for determination of nitrate compounds were given; the consequences of consumption of products with high nitrate content were analyzed. Conclusions. The problem of nitrate pollution is becoming increasingly significant, because the amount and speed of the nitrate nitrogen cycle in the environment is constantly increasing, which increases its impact on natural systems and the possibility of nitrate accumulation in crop products, humans and animals. Therefore, the implementation of analytical control of food and environmental objects is important to obtain objective information about the content of man-made pollutants, which are nitrates and nitrites. Key Words: nitrates, maximum permissible level, nitrate compounds, nitrate pollution.

Spatio-temporal variation of C-PM2.5 (composition based PM2.5) sources using PMF*PMF (double-PMF) and single-combined PMF technique on real-time non-refractory, BC and elemental measurements during post-monsoon and winter at two sites in Delhi, India

Delhi's post-monsoon and winter haze reduces visibility, causes health hazards, and interrupts usual routines. Multiple source apportionment (SA) studies recently apportioned sources and discussed organic and elemental PM source characteristics independently. To design effective pollution control strategies, it's important to obtain a comprehensive picture of particulate matter (PM2.5) sources by doing SA on consolidated data that combines organics, inorganics, black carbon (BC), and metals. In this study, we tried to improve the understanding of PM2.5 sources by performing double-PMF (D-PMF) analysis on a consolidated dataset encompassing non-refractory PM2.5 factors, elements, and BC. Real-time instrumentation (HR-ToF-AMS, Xact, and Aethalometer) were used at two urban sites (IITD and IITMD) in Delhi during post-monsoon and winter seasons. The hourly average C-PM2.5 (Composition based PM2.5 is sum of NR-PM2.5, BC and metals) at IITD for the overall study period (1st Oct 2019 to 8th Jan 2020) was 91.9 ± 56.5 μg m−3, while at IITMD for the overall sampling period (31st Oct 2019 to 31st Dec 2019) was 105.2 ± 61.2 μg m−3. The sources identified by the double-PMF at both sites were road dust, traffic, secondary nitrate, secondary sulfate, oxidized organic aerosol (OOA), biomass burning (BB), and industrial. In contrast, fireworks were only resolved at IITD, and secondary chloride at IITMD. At IITD, the temporal variation of sources was noted between the post-monsoon, Diwali, and winter seasons. The secondary nitrate (17%, 15.8 ± 9.4 μg m−3) and BB (39.4%, 36.6 ± 43.6 μg m−3) were dominant during winter suggest the rapid-nighttime oxidation with favourable low temperature condition and increased heating activities, while OOA (33.4%, 17.2 ± 8.0 μg m−3) and secondary sulfate (12.7%, 6.5 ± 4.4 μg m−3) were dominating during the post-monsoon at IITD due to the high photochemical oxidation and long-range transport. The fireworks (22.2%, 26.6 ± 43.8 μg m−3) contributed a major fraction of sources during Diwali at IITD. For the concurrent measurement period (14th Nov 2019 to 31st Dec 2019) at both the sites, the mean hourly average concentration (C-PM2.5) was 102.2 ± 53.2 μg m−3 at IITD and 99.7 ± 59.6 μg m−3 at the IITMD site. Secondary nitrate and secondary sulfate were prevalent at IITMD, while OOA and traffic dominated at IITD. D-PMF improved interpretation of sources such as the SO4_OA and NO3_OA contributions to industrial sources (Pb-rich and Zn-rich) indicate the possibility of sulfate and nitrate accumulation on metal-rich particles (for example, the formation of ZnSO4 and PbSO4). The signals of NO3_OA in the fireworks factor are due to the gunpowder (KNO3), while HOA and BBOA suggest the role of burn-related organics. The elemental ratios K/Pb (17 at IITD) and K/As (137 at IITMD) in the secondary sulfate source from D-PMF further highlighted the role of coal combustion. The D-PMF results were in excellent agreement with single PMF on combined data (SC-PMF) done as a part of an extended study.

The effect of reservoir expansion from underground karst cave to surface reservoir on water quality in southwestern China.

Due to the excessive exploitation of traditional energy sources, the attention paid to water energy has increased in recent years. As an important means to effectively utilize water energy, reservoirs play an important role in drinking water, irrigation, flood control, and drought resistance. However, utilizing reservoirs often led to water quality issues resulting from the interaction of nutrients and hydrological conditions, especially due to the special structure of karst areas. Because of the change of hydrological conditions by the effect of dam construction, the dynamic of water quality will be more obvious in karst areas with a fast exchange of water and contaminants between underground and surface streams. In the present study, the change in water quality of a karst reservoir, the Muzhu Reservoir in the Houzhai Catchment, was studied. Long-term monitored datasets (1981-2002) and water quality datasets of more recent years were used to assess the effect on the water quality of reservoir expansion from the underground reservoir to the surface reservoir in a karst area. Long-term series datasets had shown that the hydro-chemistry type had been changed from HCO3-·SO42--Ca2+·Mg2+ type to HCO3--Ca2+ type in the short term after the reservoir's expansion. The chemical components of water originating from a rock background reduced markedly after the reservoir's expansion, whereas the content of the anthropogenic contribution in the water decreased after the expansion, except in April and May. Isotopic characteristics showed that δ15N-NO3- and δ18O-NO3- values were positively correlated before and after the reservoir expansion, but the slope of the linear regression before the expansion was 0.34, while the slope of the linear regression before the expansion was close to 0.7. This indicated that although denitrification and assimilation may occur simultaneously after the reservoir's expansion, the role of denitrification on nitrate removal decreased, which resulted in nitrate accumulation in the karst reservoir. The results highlighted that nitrate accumulation in karst reservoirs should be monitored to decrease nitrate concentration in the future.

Prediction of Residual NPK Levels in Crop Fruits by Electronic-Nose VOC Analysis following Application of Multiple Fertilizer Rates

The excessive application of nitrogen in cucumber cultivation may lead to nitrate accumulation in fruits with potential toxicity to humans. Harvested fruits of agricultural crops should be evaluated for residual nitrogen, phosphorus, and potassium (NPK) nutrient levels. This is necessary to avoid nutrient toxicity from the consumption of fresh produce with excessive nutrient levels. Electronic noses are instruments well-suited for the nondestructive detection of fruit and vegetable quality based on volatile organic compound (VOC) emissions. This proof-of-concept study was designed to test the efficacy of using an electronic nose with statistical regression models to indirectly predict excessive fertilizer application based on VOC emissions from cucumber fruits grown under controlled greenhouse conditions to simulate field conditions but eliminate most environmental variables affecting plant volatile emissions. To identify excess nitrogen in cucumber plants, five different levels of urea fertilizer application rates were tested on cucumbers (control without fertilizer, 100, 200, 300, and 400 kg/ha). Chemometric methods, such as the partial least squares regression (PLSR) method, the principal component regression (PCR) method, and the multiple linear regression (MLR) method, were used to create separate regression models to predict nitrogen (N), phosphorus (P), and potassium (K) levels in cucumber fruits following application of different fertilizer rates to greenhouse soils. The correlation coefficients for the MLR model (based on the optimal parameters of PCR and PLSR) were 0.905 and 0.905 for the calibration sets and 0.900 and 0.900 for the validation sets, respectively. The nitrogen prediction model for fruit nitrates was more accurate than other nutrient models. The proposed method could potentially be used to indirectly detect excessive use of fertilizers in cucumber field crops.

Impact of substrate depth and fertilizer type on growth, production, quality characteristics and heavy metal contamination of tomato and lettuce grown on urban green roofs

Urban farming on rooftops is a contemporary approach that combines the benefits of green roofing with food production within the city sprawl. The present study aims at assessing plant growth, nutritional value, and consumer safety of two vegetables, lettuce (Lactuca sativa L.) and tomato (Solanum lycopersicum L.) grown on urban green roof. Treatments included: (a) two substrate depths (7.5 and 15 cm) and (b) three types of fertilization (granulated complex fertilizer [GF], slow nitrogen release complex fertilizer [SR], and liquid fertigation [LF]). Measurements included plant growth, total fresh yield, dry weight, and quality characteristics such as nutrient content, nitrate accumulation in lettuce and firmness, and total soluble solids [TSS] in tomatoes. Production safety was evaluated through tissue analyses of the edible parts for heavy metal residues. Results showed that 15 cm substrate depth improved the total yield for both vegetables, and the firmness of tomato fruit, compared to 7.5 cm depth. Fertilization type had no impact on tomato productivity but GF increased TSS in tomato fruits while LF enhanced lettuce yield. The deeper substrate increased N, P, K, Ca, Mg in lettuce leaves but only P and Mn in tomato fruits. In contrast, fertilization type affected leaf nutrient levels in lettuce, where N, P, and Mg were increased using LF. In tomato, the LF increased the fruit P, K, Ca, Mg, and Fe concentration. LF increased the concentration of nitrates in lettuce to levels exceeding the maximum safety limits according to the European Food Safety Authority (EFSA) but not according to EU regulation No 1258/2011. The leaf Mn concentrations in lettuce were higher than the health limits for young children in all measured samples irrespective of the experimental treatments. Selenium (Se) exceeded the health limits in tomato fruits for adults and toddlers using SR but only for toddlers using LF, while GF maintained the Se content below the safety levels. Lead (Pb) and aluminium (Al) were high for both vegetables but did not exceed the EFSA safety limits for adults. However, Pb exceeded the EU Commission Regulation No 420/2011 limit, for both vegetables and fertilization treatments. Washing the leaves of lettuce reduced only Fe and Al concentration but the remaining elements were unaffected. In conclusion, our results suggest that lettuce and tomato of adequately high quality for human consumption can be produced on urban green roofs with shallow substrate depths ranging from 7.5 to 15 cm but, further research is needed to ensure production safety.

The impact of short-term nitrogen starvation and replenishment on the nitrate metabolism of hydroponically grown spinach

Nitrate is used as a source of supplemental nitrogen for plants, but it can also contribute to nitrate accumulation in green vegetables, which is unhealthy for humans. This study involves short nitrogen starvation and nitrogen replenishment treatments to minimize the nitrate content in spinach (Spinacea oleracea L.) in order to maximize nitrogen consumption and reduce the nitrate content. For this purpose, five different nitrogen application levels (N0 = 0 mmol·L−1, N4 = 4 mmol·L−1, N8 = 8 mmol·L−1, N12 = 12 mmol·L−1, N16 = 16 mmol·L−1) were used in hydroponic culture, in order to screen out the appropriate nitrogen application level of spinach and carry out short-term nitrogen starvation and replenishment treatment, the nitrate and nitrite contents, nitrate reductase and nitrite reductase activities, nitrate reductase gene and nitrite reductase gene were measured every 5 days, and plant growth was monitored during the experiment together with morphological adaptations at the root level. Our results showed that N8 level of the five nitrogen levels was the most effective for the growth of hydroponic spinach. In contrast to the N8 level, spinach roots and leaves thrive healthier after subsequent short-term nitrogen starvation and replenishment (N8*), optimum nitrate metabolism and key enzymes, and decreased expression levels of NR and NiR genes after nitrogen deprivation, however, their expression increased after nitrogen replenishment. It indicated that NR and NiR genes can be used as a reference gene to reduce the nitrate content in vegetables. In conclusion, our results provided a practical approach for optimum nitrate fertilization that will not only improve spinach growth but also reduce nitrate content harmful for human intake.

The nitrate uptake and growth of wheat were more inhibited under single-layer graphene oxide stress compared to multi-layer graphene oxide

Although the phytotoxicity of graphene-based materials has been investigated extensively, the effects of different graphene-based materials on nutrient uptake in plants remain unclear. Here, we analyzed the differences in phytotoxicity between single-layer graphene oxide (sGO) and multi-layer graphene oxide (mGO) by analyzing the growth status and nitrate (NO3–) accumulation in wheat plants at 0, 100, 200, 400, and 800 mg L−1 graphene oxide supply. Both sGO and mGO displayed concentration-dependent inhibitory effects on biomass, root length, number of lateral roots, and nitrogen (N) nutrient status. Treatment with 400 mg L−1 sGO caused 0.9-, 1.3-, and 1-fold higher reductions in NO3–-N, assimilated N, and total N concentrations in roots, respectively, than mGO treatment. Analysis of root oxidative stress and in situ NO3– uptake revealed that sGO caused more significant damage to the root tip and a lower NO3– net influx rate than mGO. In addition, the expression of NO3– transporter (NRT) genes in roots, including NRT1.5, NRT2.1, NRT2.2, NRT2.3, and NRT2.4, under sGO treatment were lower than those under mGO treatment. Overall, sGO treatment induced a more severe inhibitory effect on root growth and NO3– uptake and accumulation than mGO treatment, accompanied by significant suppression of the expression of NRTs in sGO-treated roots. This study provides a physiological and molecular basis for studying the phytotoxic effects of various sizes of graphene oxide.

Quantitative identification of nitrate and sulfate sources of a multiple land-use area impacted by mine drainage

The rapid increase in urbanization and intensive coal mining activities have accelerated the deterioration of surface water quality. Environmental problems caused by the accumulation of nitrate and sulfate from natural, urban, and agricultural sources have attracted extensive attention. Information on nitrate and sulfate sources and their transformations is crucial for understanding the nitrogen and sulfur cycles in surface water. In this study, we monitored nitrate and sulfate in three representative rivers in mining cities in northern China. The main pollution sources and biogeochemical processes were identified by using stable isotopes (δD, δ18OH2O, δ15N, δ18ONO3, δ34S and δ18OSO4) and hydrochemistry. The contribution of natural and anthropogenic sources was quantitatively estimated based on a Bayesian mixed model. The results indicated a large variation in sulfate and nitrate sources between the different rivers. Nitrate in the Tuohe River mainly derived from manure/sewage (57.9%) and soil N (26.9%), while sulfate mainly derived from manure/sewage (41.7%) and evaporite dissolution (26.8%). For the Suihe River, nitrate was primarily sourced from chemical fertilizer (37.9%) and soil nitrogen (34.8%), while sulfate was mainly sourced from manure/sewage (33.1%) and chemical fertilizer (21.4%). For the Huihe River, nitrate mainly derived from mine drainage (56.6%) and manure/sewage (30.6%), while sulfate predominantly originated from mine drainage (58.3%) and evaporite dissolution (12.9%). Microbial nitrification was the major pathway for the migration and transformation of nitrate in the surface water. However, denitrification and bacterial sulfate reduction (BSR) did not play a significant role as aerobic conditions prevailed. In this study, we elucidated the sources and transformation mechanisms of nitrate and sulfate. Additionally, we provided a reference for formulating a comprehensive strategy for effective management and remediation of surface water contaminated with nitrate and sulfate in mining cities.

Denitrification performance and bacterial ecological network of a reactor using biodegradable poly(3-hydroxybutyrate-co-3-hydroxyvalerate) as an electron donor for nitrate removal from aquaculture wastewater

Nitrate accumulation is a common phenomenon in aquaculture that can lead to eutrophication of surrounding water bodies. This study used poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) as a carbon source and substrate and performed a microbial co-occurrence network ecological analysis to elucidate the denitrification processes in two packed-bed reactors with different salinities. The denitrification rate reached maximum values of 0.438 and 0.446 kg m−3 d−1 in reactor I (salinity 0 ‰) and reactor II (salinity 20 ‰), respectively. Although ammonia was formed in both systems based on dissimilation nitrate reduction to ammonia (DNRA), the concentration was very low (2.47 ± 1.99 and 2.84 ± 1.79 mg L−1); moreover, the nitrite content was average (1.01 ± 0.87 and 0.96 ± 0.86 mg L−1). These results suggested that denitrification dominated in both reactors. PHBV generally presented a stable release of DOC, although a sharp increase was observed in the start-up period of reactor II. 16S rRNA results showed that reactor I had richer microbial diversity than reactor II. Among the top ten taxa, Betaproteobacteria was the dominant class in reactor I while Gammaproteobacteria was the dominant class in reactor II. In the stable period, Thauera and Denitromonas was the most abundant genera in reactor I and reactor II, respectively. In addition, the bacterial co-occurrence network showed that reactor I had a more complex node and edge network and faster start-up time compared to reactor II; however, reactor II had a more stable nitrogen removal capacity. Higher expression of NorB and NosZ genes in reactor II indicated higher efficient denitrification in seawater system. The SEM and FTIR showed bacterial development and materials surface erosion. These findings verified the denitrification performance and niche differences between freshwater and seawater environments.

Effects of Molybdenum Fertilizer Combined with Bacillus subtilis Strain on the Growth of Chinese Cabbage and the Content of Nitrate in Soil

With increasing nitrogen application in soil, the problem of nitrate accumulation in soil and vegetable bodies has become increasingly serious. In this study, Bacillus subtilis (B. subtilis) Strain11 was isolated and studied for its effects in combination with Molybdenum (Mo) on the growth of Chinese cabbage and soil nitrate content. The results showed that the strain effectively increased the growth, height, and moisture content of Chinese cabbage by 27% and 2.5%, respectively, compared to the control. Mo application alone reduced soil nitrate accumulation and increased root length, height, chlorophyll content, and moisture content of Chinese cabbage, with an optimal rate of 0.8–1.2 mg/kg soil. The application of Mo fertilizer in combination with the Bacillus strain was the most effective in increasing plant height and root length of Chinese cabbage, which were 1.49 times and 1.68 times that of the control, respectively. The proportion of dry matter, the average fresh weight, and the dry weight under this treatment were 9.01%, 5.83 g/plant, and 0.53 g/plant, respectively, higher than the rest. At harvest, the highest ammonium-nitrogen content in this treatment group was 8.56 mg/kg, and the soil nitrate reduction reached 40.68%. In conclusion, Mo fertilizer at a rate of 0.8 mg Mo/kg soil, in combination with B. subtilis Strain11, was recommended for the remediation of nitrate-contaminated soils.

Enhanced nitrogen removal in mainstream deammonification systems at ambient temperature by novel modified carriers and differentiation of microbial community transformation

Zeolite-modified polyurethane (ZP) carriers and zeolite/tourmaline-modified polyurethane (ZTP) carriers were proposed to enhance mainstream deammonification. The system with ZTP carriers was rapidly established in 28 days with a nitrogen removal rate (NRR) of 0.150 kg N·(m3·d)−1. Moreover, the facilitative effect of tourmaline was suggested by the highest humic acid peak intensity and more balanced potential activity. Besides, SEM-EDS analysis revealed carrier characteristic improvement was achieved in both novel carriers while maintaining an excellent spatial structure. Moreover, the microbial analysis suggested that both modified carriers support the substrate supply to anaerobic ammonium oxidizing bacteria (AnAOB) by enhancing dissimilatory nitrate reduction to ammonium and partial denitrification under nitrate accumulation conditions. Nevertheless, the ZTP system had a greater advantage over maintaining the original AnAOB (Candidatus Jettenia) and ammonium oxidizing bacteria (Nitrosomonas) abundance. Overall, this study provides ZTP carriers with great potential for facilitating the establishment of mainstream deammonification at full-scale WWTPs.

Survival strategies of Nitrospira in a stable nitritation-denitritation system treating low-strength fermented wastewater

Mainstream nitritation and denitritation can save aeration energy and carbon sources, but it is difficult to eliminate nitrite-oxidizing bacteria. Except for nitrite oxidation, Nitrospira may benefit from mixotrophic lifestyles. In our previous study, stable NOB suppression was achieved in a multi-cycle sequencing batch reactor (MCSBR) treating fermented low-strength wastewater. However, abundant Nitrospira was always detected, which was contrary to the negligible nitrate accumulation. Batch tests indicated that only acetate could be consumed by the enriched Nitrospira within six hours. In another batch test within six days, nitrate was fully or partially denitrified to nitrite after adding formate or acetate, while Nitrospira decreased 86.5 % and 28.7 % respectively. After adding formate, two hydrogenotrophic denitrifiers Hydrogenophaga and Methyloversatilis highly proliferated, but only Hydrogenophaga was also found in the MCSBR. Therefore, Nitrospira might still grow through nitrite oxidation, while the generated nitrate was timely reduced by Hydrogenophaga in the presence of simple organic carbons, or directly survived by heterotrophic acetate metabolism.

NITRATE CONTENT IN VEGETABLES IN WATER-INRATED WATER BODIES OF THE NORTHERN AND INGULETSKY GOK

The content of nitrates in vegetables is a rather urgent problem and is of interest to structures that control and regulate the possible consequences of an excessive amount of nitrates for human health. The main causes and features of food pollution are shown: irrigation of fields with water containing wastewater from industrial enterprises, excessive and uncontrolled use of fertilizers, conditions for growing vegetables and seasonality.The process of environmental pollution with nitrates, in particular, surface water resources, is considered. An analysis of the suitability of surface water for irrigation was carried out near the villages of Andreevka, Shevchenkovskoye, Zavyalovka, Annensky quarry and Ternovsky district of Krivoy Rog and showed that the content of nitrates does not exceed the MPC. The reasons for the accumulation of nitrates in plant products are shown. The transformations of nitrate ions and their toxic effect on the human body are given. The paper also outlines the main ways to reduce the content of nitrates in crop production. A quantitative analysis of nitrate ions in vegetable raw materials in the spring-autumn period was carried out: cucumbers, cabbage, potatoes, tomatoes, carrots and onions by the iodometric method, the express method based on the use of a diphenylamine reagent and the express method. method using the GreenTest nitrate tester, grown on the territory near such enterprises as the Northern and Ingulets GOK. The content of nitrates exceeds MPC in early potatoes and tomatoes.

Research Progress on Cu-Based Catalysts for Electrochemical Nitrate Reduction Reaction to Ammonia

Since the conventional Haber-Bosch ammonia synthesis loop suffers from harsh process conditions, high energy consumption, and heavy pollution, the artificial catalytic synthetic NH3 has emerged as a promising alternative method for producing NH3. Meanwhile, nitrate (NO3–) accumulation in the environment causes serious problems involving health and environmental issues. The urgent need to eliminate NO3– and produce NH3 perfectly caters to the NO3– reduction reaction (NO3RR) via an attractive electrocatalytic route. Cu-based catalysts exhibit an inhibiting effect on hydrogen evolution, rapid reduction kinetics, and stable catalytic performance, revealing remarkable advantages for NO3RR. In this review, we summarize the recent achievements of Cu-based catalysts in electrocatalytic NO3RR, discuss the detection methods for evaluating NO3RR performance, and introduce the fundamentals for understanding the thermodynamics and kinetics. This review can provide guidance and help for the rational design and development of non-noble metal catalysts in electrocatalytic NO3RR to NH3.

Agronomic and environmental benefits of ‘re-using’ a biodegradable mulching film for two consecutive lettuce cycles

Biodegradable films are a valuable and sustainable alternative to plastic films for mulching soils since they avoid the environmental and economic problems related to plastic removal and disposal. Nevertheless, the fast degradation of such materials could make them unsuitable for mid- to long-term use. In a field experiment, the agronomic performance of a biodegradable mulching film (MB) was compared to that of conventional low-density polyethylene (LDPE) film for two consecutive lettuce cycles (winter and spring). In the conditions of this trial, MB showed good resistance to atmospheric agents, with a reduction of its integrity and mechanical properties only after six months. The effects on soil temperature and lettuce yield did not differ from those obtained with LDPE films. The effect on harvest timing was the same as that with LDPE in the spring cycle, while in the winter cycle, the harvest was delayed by about five days compared to LDPE. Mulching films reduced nitrate accumulation in leaves mainly during the winter cycle. However, the effect needs to be further explored with experiments in different pedoclimatic conditions that consider the effects of mulching on nitrification and nitrate-reductase activity that could be affected by changes in soil temperature and moisture. Highlights - Biodegradable mulching films (MB) showed good mechanical resistance in the medium-long term (2 consecutive lettuce cycles). - Decrease in integrity and resistance to tearing became significant after 150-170 days. - The effect of MB on lettuce yield quantity and quality was comparable with that using low-density polyethylene (LDPE) films. - The effects of both mulching films on leaf nitrate content need further research in different pedoclimatic conditions. - MB can be recommended since it reduces the economic and environmental costs of removal and disposal of LDPE films.

Patterns of long-term variations of nitrate concentration – Stream discharge relationships for a drained agricultural watershed in Mid-western USA

Nitrate Concentration–discharge (C-Q) relationshipshave been used to infer nitrate sources, storage, reactions, and transport in watersheds, and to reveal key processes that control runoff chemistry. Yet, studies on long-term nitrate C-Q relationships are limited due to scarce high frequency (e.g., daily) concentration data. In this paper, using a long-term high-frequency dataset (1976–2019) comprising stream flow and nitrate concentrations, we quantitatively analyzed the long-term variations of event-scale hysteresis patterns (quantified by hysteresis index, HI, and flushing index, FI) to infer the leaching mechanisms of nitrate in an artificially drained agricultural watershed in Mid-western U.S. Our results revealed that most events exhibited anti-clockwise behaviors (HI < 0), regardless of whether nitrate was flushed or diluted during events. This means that water with high levels of nitrate-N reaches the stream network slower than water with lower nitrate concentrations. Long-term mean FI was close to zero but had strong seasonal patterns with dilution patterns observed during Winter and Summer, and flushing patterns during late Spring and Fall. The consistently negative HI values regardless of the FI value gave a strong indication of the preponderant role of the near-drain zone that usually exhibits accelerated leaching and less accumulation of nitrate in the soil profile in these drained agricultural watersheds. Both HI and FI depicted strong but opposite seasonality because of weather patterns and agricultural activities, particularly N fertilization. Overall, our findings suggest a little evidence of the role of deep groundwater and instead a strong evidence of the role of subsurface drainage as the primary pathway for nitrate transport in drained agricultural watersheds. Therefore, artificial drainage could dampen N legacy caused by the historically intensive N fertilization in drained agricultural landscapes.

Biochar-based molybdenum slow-release fertilizer enhances nitrogen assimilation in Chinese flowering cabbage (Brassica parachinensis).

Low molybdenum (Mo) bioavailability in acidic soil obstructs vegetable nitrogen assimilation and thus increases the health risk of vegetable ingestion due to nitrate accumulation. Constantly providing available Mo in acidic soil is a challenge for decreasing nitrate accumulation in vegetables. In this study, three Mo application methods, including biochar-based Mo slow-release fertilizer (Mo-biochar), seed dressing, and basal application, were investigated to enhance Mo bioavailability in acidic soil and nitrogen assimilation in Chinese flowering cabbage (Brassica parachinensis). The results showed that Mo-biochar constantly and sufficiently supplied Mo nutrients throughout the growing period of Brassica parachinensis, as evidenced by the soil available Mo, plant Mo uptake, and Mo values. The improved Mo supply was attributed to the alleviation of acidic soil (pH from 5.10 to 6.99) and the slow release of Mo adsorbed on biochar. Mo-biochar increased the nitrate reductase (NR) activity by 238.6% and glutamate dehydrogenase activity by 27.5%, indicating an enhancement of the rate-limiting steps of nitrogen assimilation, especially for nitrate reduction and amino acid synthesis. The increase in Mo-containing NR could be directly ascribed to the high level of Mo in Brassica parachinensis. Compared with the control, the nitrate content of Brassica parachinensis decreased by 42.9% due to the nitrate reduction induced by increased NR. Additionally, Mo-biochar was beneficial to vegetable growth and quality. In contrast, the transformation from NO3- to NH4+ was blocked with Mo seed dressing and basal application because of low Mo bioavailability in the soil, resulting in a high nitrate content in Brassica parachinensis. Conclusively, Mo-biochar can slowly release Mo and improve the neutral environment for Mo bioavailability, which is an effective strategy to mitigate the high nitrate accumulation of vegetables planted in acidic soil.

Nitrate transport behavior behind subsurface dams under varying hydrological conditions.

The construction of subsurface dams for controlling seawater intrusion triggers the accumulation of nitrate upstream of a dam. This is raising the concerns about nitrate contamination in those regions of coastal aquifers that are supposed to be used as a fresh groundwater source behind a subsurface dam. Research on this subject has been mostly restricted to the use of a simplified sea boundary (e.g., static and no slope), ignoring sea level fluctuations driven by tides. In this study, the combined effect of tides and subsurface dams on nitrate pollution in upstream groundwater was examined through laboratory experiments and numerical simulations. The results revealed that the difference in the extent of nitrate contamination under various conditions (i.e., static, tidal, static with a dam, and tidal with a dam) was related to the temporal pollution behavior. In the early stage, nitrate contamination in upstream groundwater was essentially identical for different scenarios. Both tides and subsurface dams were found to increase nitrate contamination in upstream aquifers. The extent of nitrate contamination increased with higher tidal amplitudes, whereas the increment was more evident for a large tidal amplitude. The effects of tides and subsurface dams on nitrate contamination were also regulated by the locations and infiltration rates of the pollution source. Interestingly, under the joint action of tides and subsurface dams, the increment in the extent of nitrate pollution was greater than the sum of their individual effects. The increased pollutions caused by subsurface dams and tides were quantified as 9.47% and 37.22%, respectively, whereas the increased value caused by their joint action was measured as 51.10%. These findings suggest that tidal activity should not be overlooked when assessing nitrate contamination in upstream groundwater.

Agricultural practices regulate the seasonality of groundwater-river nitrogen exchanges

Soil System Budgets (SSB) of nutrients are generally performed annually over arable land to infer their use efficiency and water pollution risk in highly exploited agricultural watersheds. They are seldom partitioned into seasonal budgets and matched with seasonal nutrient transport in adjacent river reaches. We calculated seasonal soil nitrogen (N) budgets in a Mincio River sub-basin (Italy), and we analyzed the dissolved inorganic N net export in the river reach draining such sub-basin. Our results show seasonal differences of SSB with N excess in winter and even more in spring, equilibrium among sources and sinks during autumn and N deficit during summer. Seasonal inorganic N loads transported by the river were not correlated with SSB as they peaked in late summer and were at their minimum in early spring. Fertilization uncoupled to significant uptake supports N excess in winter and spring, whereas crop uptake uncoupled to N inputs supports summer N deficit. Nitrification cannot explain nitrate accumulation in the river reach, suggesting alternative dynamics driving the local hydrology. Flood irrigation results in large soil nitrate solubilization, transport and in upward migration of the groundwater piezometric head during spring and summer periods. River water is likely replaced by nitrate-rich groundwater when the groundwater recharge exceeds a certain threshold coinciding with late summer. Irrigation is then interrupted and the piezometric head, together with nitrate exchange, decreases. This work suggests that a deep understanding of N dynamics in agricultural watersheds with flooding irrigation on permeable soils needs the reconstruction of the vertical pathways of nitrate and of river-groundwater interactions. Moreover, the partitioning of annual into seasonal N budgets and their combination with irrigation practices allows the identification of hot moments in N cycling. Agricultural practices minimizing nitrate excess, its mobility and the risk of surface and groundwater pollution are suggested for this area.