Elevated Nitrate Research Articles

Nitrogen and oxygen isotopes in nitrate in the groundwater and surface water discharge from two rural catchments: implications for nitrogen loading to coastal waters

In Prince Edward Island, Canada, widespread intensive potato production has contributed to elevated nitrate concentrations in groundwater and streams, and eutrophic or anoxic conditions occur regularly in several estuarine systems. In this research, the stable isotopes of nitrogen and oxygen in nitrate in intertidal groundwater discharge and stream water were used, in conjunction with water quality and quantity data and land use information, to better understand the characteristics of nitrate delivered to two small estuaries with contrasting land use in their contributory catchments. Most of the water samples collected during the two-year study had isotopic signatures that fell in the range expected for nitrate derived from ammonium-based fertilizers (26.5 % of the samples) or in the overlapping range formed between ammonium-based fertilizers and nitrate derived from soil (64 % of the samples). Overall, isotopic signatures spanned over relatively narrow ranges, and correlations with other water quality parameters, or catchment characteristics, were weak. Nitrate in groundwater discharge and surface water in the Trout River catchment exhibited significantly different isotopic signatures only for the nitrogen isotope, while in the McIntyre Creek catchment groundwater discharge and surface water had similar isotopic signatures. When the isotopic results for the waters from the two catchments were compared, the surface waters were found to be similar, while the isotopic signatures of nitrate in groundwater were distinct only for the nitrogen isotope. Denitrification in the two study catchments was not evident based on the isotopic results for nitrate; however, in the case of the Trout River catchment, where a small freshwater pond exists, an average nitrate load reduction of 14 % was inferred based on a comparison of nitrate loads entering and leaving the pond. Overall, it appears that natural attenuation processes, occurring either in the streams or groundwater flow systems, do not significantly reduce nitrate loading to these estuaries.

An efficient incentive of Nitrate and Fluoride on Organic highland cropping systems

Exerting necessitated concentrations of Nitrate and fluoride to the organic highland cropping systems is a vital management technique. All the chemical elements of the earth's crust occur in widely differing omnipresent concentrations, due to their different nuclear chemical formation and geochemical history. The use of biological nitrogen and fluoride inputs complicates its balancing act due to dandier uncertainty in inorganic Nitrogen and Fluoride availability. The growers to strike maintain Nitrogen provisioning to support crop growth and retention of limit pollution followed by fluoride associated soils. Due to various activities of the man in domestic field, agriculture area and industrial establishment the environment around us consisting soil, water and air gets polluted. Fluoride inexhaustible concentrations forbid the growth of crop even though nitrates reposit in the cultivated soils. The purpose of this project was to establish kinetics when nitro fluorides associated in the highland soils to different crop systems towards environmental pollutions. Cordia Africana and alfalfa are the plants which make soil to get enrichment of Nitrates and deescalate of concentrations of fluorides from cultivated soils through its decomposition. This entire study went on its conventionally tilled crops followed by Cordia Africana and alfalfa stems and leaf particles. Surface soil nitrate concentrations were measured weekly, biweekly by volumetric analysis and nitrate leaching was estimated from tension Lysimeters which were buried at the soil bedrock interface. Subsequently by using Orion 720A fluoride ion meter, de- escalated concentrations of fluorides have been measured. The demonstrated concentrations of Soil in NO3 variables, coefficients of variations from the mean concentrations across all samplings have been recorded sporadically. The total area of the soil bed was maintained the same P H values until project was completed by weigh Lysimeters. The timing of elevated Nitrate concentrations (10-15PPM) and the concentrations of fluoride in deeper soil water corresponds with fallow periods. These dynamics will assist growers in adapting the timing management operations and reduces nitrate departures.

Developing a Vegetable Fertility Program Using Organic Amendments and Inorganic Fertilizers

This review integrates information from common organic amendments used in conventional vegetable production, including 1) cover crops (legumes and nonlegumes), 2) compost generated from yard wastes, biosolids, municipal solid waste (MSW), animal manures, and other biodegradable waste by-products, and 3) raw animal manure (with and without bedding). Environmental monitoring has shown elevated nitrate concentration to be widespread in both surface and groundwater, often occurring in regions with concentrated horticultural production. Therefore, the objective of this review was to calculate the nutrient content from organic amendments, since these are not considered nutrient sources. Common organic amendments affect soil bulk density, water-holding capacity, soil structure, soil carbon content, macro- and micronutrients, pH, soluble salts, cation exchange capacity (CEC), and biological properties (microbial biomass). The first step in building a conventional tomato (Solanum lycopersicum) fertility program will be to take a soil sample and send it to a soil laboratory for a nutrient analysis. These results should be compared with the local crop recommendations. Second, select the organic amendments based on local cover crop suitability and availability of compost, raw animal manure, or both. Then, determine the nutrients available from cover crops and other applied organic amendments and use inorganic fertilizer sources to satisfy the crop nutrient requirements not supplied from these other sources.

Hydrogeochemistry and Isotopic Tracing of Nitrate Contamination of Two Aquifer Systems on Jeju Island, Korea

The groundwater of Jeju Island (Republic of Korea) is vulnerable to contamination because its aquifers are mainly composed of highly permeable geological units and its agricultural fields are often exposed to excessive use of predominantly synthetic fertilizers. In the Gosan area of Jeju Island, we investigated nitrate contamination in both a perched aquifer above an impermeable clay bed and the regional groundwater beneath this aquitard. The δO and δD values indicate that the perched groundwater is recharged by local precipitation, whereas the regional groundwater is recharged mainly by regional flow from an adjacent mountainous region. The perched groundwater contained very high NO-N concentrations of up to 87 mg/L. The isotopic composition of nitrate in the perched groundwater showed that synthetic fertilizers applied in high excesses of crop N needs were the main cause of aquifer pollution. Elevated nitrate concentrations were also observed in the regional groundwater especially after precipitation events. Concentration and isotopic data revealed that the inflow of shallow perched groundwater along the poorly cemented or uncemented annulus of regional groundwater wells was one of the main reasons for the nitrate contamination observed in the regional groundwater. In both aquifers, δN and δO values showed that the sources of nitrate were derived from synthetic fertilizers that had been recycled in the soil zone by nitrification and in some portions of the perched aquifer (dissolved oxygen concentrations <2 mg/L) indicated that denitrification occurred locally.

Influence of nitrate supplementation on VO2 kinetics and endurance of elite cyclists

The present study examined if an elevated nitrate intake would improve VO(2) kinetics, endurance, and repeated sprint capacity in elite endurance athletes. Ten highly trained cyclists (72 ± 4 mL O(2) /kg/min, mean ± standard deviation) underwent testing for VO(2) kinetics (3 × 6 min at 298 ± 28 W), endurance (120 min preload followed by a 400-kcal time trial), and repeated sprint capacity (6 × 20 s sprints, recovery 100 s) during two 6-day periods in randomized order with a daily ingestion of either 0.5 L beetroot (BR) juice to increase nitrate levels or a 0.5 L placebo (PLA) drink with blackcurrant juice. Plasma NOx (nitrate + nitrite) levels were higher (P < 0.01) in BR (147 ± 102 and 159 ± 103 μM after 4 and 6 days of beverage intake, respectively) compared with PLA (41 ± 10 and 40 ± 7 μM). VO(2) kinetics and exercise economy were the same in BR and PLA. Time-trial performance was similar with an average completion time of 18:20 and 18:37 min:s in BR and PLA, respectively, with average power outputs of 290 ± 43 W in BR and 285 ± 44 W in PLA. Peak and mean power during repeated sprinting were similar in BR and PLA. In contrast to observations in moderately trained subjects intake of BR juice had no effect on VO(2) kinetics and performance in elite cyclists.

Effectiveness of purolite A500PS and A520E ion exchange resins on the removal of nitrate and phosphate from synthetic water

Water pollution due to the excessive presence of nutrients (nitrogen and phosphorus) is a serious environmental worldwide problem, because both species are implicated in the eutrophication of receiving surface waters and elevated nitrate concentration in drinking water can be toxic to infants. The removal efficiencies of nitrate and phosphate from water spiked with different ratios and concentrations of these nutrients by two ion-exchange resins (Purolite A500PS and Purolite A520E) were studied in batch kinetics and equilibrium adsorption experiments. Both purolites were found to be selective towards nitrate removal at all ratios of nitrate to phosphate in solution. Purolite A520E showed higher (<85%) removal efficiency of nitrate than Purolite A500PS (about 65%) from a solution containing 20 mg N/L as nitrate and 10 mg P/L as phosphate at a resin dose of 1.5 g/L. However, Purolite A500PS showed higher (65%) removal of phosphate than Purolite A520E (48%). Langmuir and Freundlich isotherm models fitted well for the adsorption of nitrate on Purolite A520E (R2 = 0.95–0.96). However, the adsorption of nitrate on Purolite A500PS can be explained satisfactorily only by Freundlich model (R2 = 0.98). The adsorption of phosphate on the resins fitted well to Freundlich model (R2 = 0.90) for Purolite A500PS as well as for Purolite A520E (R2 = 0.90). The adsorption of phosphate and nitrate on both ion-exchange resins was much better described by pseudo-second-order kinetic model (R2 ⩾ 0.99) than by pseudo-first-order kinetic model (R2 = 0.25–0.94).

Evaluation of the origin of nitrate influencing the Ključ groundwater source, Serbia

This paper describes the use of the dual isotope method involving δ(15)N and δ(18)O measurements of dissolved nitrates to assess the origin and fate of groundwater nitrate at the Ključ groundwater source, Serbia. A sampling campaign was conducted in September 2007 during flow conditions obtaining groundwater from observation wells and river water fed by a shallow aquifer hosted in alluvial (sandy-gravel) sediments. Nitrate isotope ratios ranged from +5.3 to +16.9‰ and δ(18)O(NO(3)) values varied from -2.3 to +5.0‰. Two major contamination sources were identified with isotopic compositions characteristic for nitrate derived from nitrification of soil organic nitrogen (+5.3 to +7.8‰ for δ(15)N) resulting in nitrate concentrations of 33.6 and 78.8 mg/L and nitrate derived from animal wastes or human sewage, e.g. via septic systems, yielding δ(15)N values of +9.9 to +11.9‰ and elevated nitrate concentrations of 31.2-245.8 mg/L. The occurrence of nitrification and denitrification was also revealed based on concentration and isotope data for dissolved nitrate.

Effect of Nitrogen Fertilizer on the Levels of Some Nutrients, Anti-nutrients and Toxic Substances in Hibiscus sabdariffa

The presence of antinutrients and toxic substances in vegetables limits the derivable benefits from vegetables. The levels of these substances in vegetables are influenced by the nature of soil in which the vegetables are grown. The effect of applied nitrogen fertilizer on the levels of some antinutrients and toxic substances is investigated with a view to determine the appropriateness or otherwise of the application of nitrogen fertilizer in growing vegetables. Pot experiments were conducted to determine the effect of soil nitrogen levels on soluble and total oxalates, cyanide, nitrate and some micronutrients namely, vitamin C, β-carotene (precursor of vitamin A) and mineral elements (Fe, Mg, Zn, Cu, Ca, Na and K) in Hibiscus sabdariffa. The leaves of the vegetable were harvested and analysed at market maturity (vegetative phase) and fruiting (reproductive phase) of the plant development. Results obtained showed that the applied nitrogen fertilizer significantly elevated nitrate and β-carotene contents, while it decreases the levels of vitamin C, soluble and total oxalates in the vegetable. The levels of cyanide and mineral elements were not significantly affected by the applied nitrogen fertilizer.

Vulnerability of Recently Recharged Groundwater in Principle Aquifers of the United States To Nitrate Contamination

Recently recharged water (defined here as <60 years old) is generally the most vulnerable part of a groundwater resource to nonpoint-source nitrate contamination. Understanding at the appropriate scale the interactions of natural and anthropogenic controlling factors that influence nitrate occurrence in recently recharged groundwater is critical to support best management and policy decisions that are often made at the aquifer to subaquifer scale. New logistic regression models were developed using data from the U.S. Geological Survey's National Water-Quality Assessment (NAWQA) program and National Water Information System for 17 principal aquifers of the U.S. to identify important source, transport, and attenuation factors that control nonpoint source nitrate concentrations greater than relative background levels in recently recharged groundwater and were used to predict the probability of detecting elevated nitrate in areas beyond the sampling network. Results indicate that dissolved oxygen, crops and irrigated cropland, fertilizer application, seasonally high water table, and soil properties that affect infiltration and denitrification are among the most important factors in predicting elevated nitrate concentrations. Important differences in controlling factors and spatial predictions were identified in the principal aquifer and national-scale models and support the conclusion that similar spatial scales are needed between informed groundwater management and model development.

Linkages between denitrification and dissolved organic matter quality, Boulder Creek watershed, Colorado

Dissolved organic matter (DOM) fuels the majority of in‐stream microbial processes, including the removal of nitrate via denitrification. However, little is known about how the chemical composition of DOM influences denitrification rates. Water and sediment samples were collected across an ecosystem gradient, spanning the alpine to plains, in central Colorado to determine whether the chemical composition of DOM was related to denitrification rates. Laboratory bioassays measured denitrification potentials using the acetylene block technique and carbon mineralization via aerobic bioassays, while organic matter characteristics were evaluated using spectroscopic and fractionation methods. Denitrification potentials under ambient and elevated nitrate concentrations were strongly correlated with aerobic respiration rates and the percent mineralized carbon, suggesting that information about the aerobic metabolism of a system can provide valuable insight regarding the ability of the system to additionally reduce nitrate. Multiple linear regressions (MLR) revealed that under elevated nitrate concentrations denitrification potentials were positively related to the presence of protein‐like fluorophores and negatively related to more aromatic and oxidized fractions of the DOM pool. Using MLR, the chemical composition of DOM, carbon, and nitrate concentrations explained 70% and 78% of the observed variability in denitrification potential under elevated and ambient nitrate conditions, respectively. Thus, it seems likely that DOM optical properties could help to improve predictions of nitrate removal in the environment. Finally, fluorescence measurements revealed that bacteria used both protein and humic‐like organic molecules during denitrification providing further evidence that larger, more aromatic molecules are not necessarily recalcitrant in the environment.

Salinity and nitrate concentration on the growth and carotenoids accumulation in a strain of Dunaliella salina (Chlorophyta) cultivated under laboratory conditions

1 - The effect of salinity (9, 14, and 22 % NaCl w/v) and nitrate concentration (882, 435 and 212 imol L-1) on the growth and production of carotenoids was studied in a wild strain of Dunaliella salina Teod. isolated from solar salterns on the Tyrrhenian coast (Tarquinia – Central Italy). 2 - The alga was grown in batch culture at relatively low illumination (40 imol photon m-2s-1). The total content of carotenoids produced from the alga and the amount of all-trans-â-carotene, the isomer showing a relevant commercial value, were determined by UV-Vis spectrophotometry and HPLC analysis. 3 - The highest growth rate in this strain of D. salina was obtained at salinity of 22% NaCl w/v and elevated nitrate concentration (882 imol L-1); a relatively high cell density was also observed at higher salinity and reduced nitrate concentrations. Low nitrate concentration negatively affected growth, but enhanced the carotenoids accumulation in the cells. 4 - The highest concentration of carotenoids (17 pg/cell) was observed in the 28 day old cultures in the late stationary phase at 22% NaCl w/v and 212 imol L-1 nitrate concentration. Also the average of all-trans-â-carotene on total carotenoids was enhanced by low nitrate concentration changing from 5% in 28 day old cultures at 22% salinity and 882 imol L-1 N, to 37% in 28 day old cultures at 22% NaCl w/v and lower nitrate concentration (212 imol L-1).

Temperature responses of growth, photosynthesis, fatty acid and nitrate reductase in Antarctic and temperate Stichococcus

Stichococcus, a genus of green algae, distributes in ice-free areas throughout Antarctica. To understand adaptive strategies of Stichococcus to permanently cold environments, the physiological responses to temperature of two psychrotolerants, S. bacillaris NJ-10 and S. minutus NJ-17, isolated from rock surfaces in Antarctica were compared with that of one temperate S. bacillaris FACHB753. Two Antarctic Stichococcus strains grew at temperature from 4 to 25°C, while the temperate strain could grow above 30°C but could not survive at 4°C. The photosynthetic activity of FACHB753 at lower than 10°C was less than that of Antarctic algae. Nitrate reductase in NJ-10 and NJ-17 had its optimal temperature at 20°C, in comparison, the maximal activity of nitrate reductase in FACHB753 was found at 25°C. When cultured at 4-15°C a large portion of unsaturated fatty acids in the two Antarctic species was detected and the regulation of the degree of unsaturation of fatty acids by temperature was observed only above 15°C, though the content of the major unsaturated fatty acid αC18:3 in FACHB753 decreased with the temperatures elevated from 10 to 25°C. Elevated nitrate reductase activity and photosynthetic rates at low temperatures together with the high proportion of unsaturated fatty acids contribute to the ability of the Antarctic Stichococcus to thrive.

Dissimilatory nitrate reduction pathways in an oligotrophic freshwater ecosystem: spatial and temporal trends

Elevated nitrate (NO3 � ) concentrations can cause eutrophication, which may lead to harmful algal blooms, loss of habitat and reduction in biodiversity. Denitrification, a dissimilatory process that removes NO3 � mainly as dinitrogen gas (N2), is believed to be the dominant NO3 � re- moval pathway in aquatic ecosystems. Evidence suggests that a less well-studied process, dissimila- tory nitrate reduction to ammonium (DNRA), which retains nitrogen (N) in the system, may also be important under favorable conditions. Using stable isotope tracers in sealed microcosms, we mea- sured the potential for NO3 � losses due to DNRA and denitrification in an oligotrophic freshwater ecosystem. We took sediment and water samples at runoff and baseflow, across several ecotypes. Our objective was to quantify the relative importance of DNRA compared to denitrification with changes in ecotype and season. Potential denitrification rates ranged from 0 to 0.14 ± 0.03 µgN gAFDM �1 d �1 . Potential DNRA rates ranged from 0 to 0.0051 ± 0.0008 µgN gAFDM �1 d �1 . Denitrifica- tion losses peaked at the inflow stream ecotype at 96.2% of total dissimilatory NO3 � removal, whereas losses due to DNRA peaked in the lake ecotype at 34.4%. When averaged over the entire system, denitrification peaked at baseflow (31.2%), while DNRA peaked at runoff (2.9%). Although NO3 � transformations due to denitrification were higher than DNRA in all ecotype and temporal comparisons, our results suggest that DNRA is also important under favorable conditions.

Flow Injection Assessment of Nitrate Contents in Fresh and Cooked Fruits and Vegetables Grown in Fiji

Nitrates form part of the essential chemistry of soils and plants. Thus, plant roots are able to absorb nitrate directly from the soil. It has been discovered that human nitrate intake is mainly from vegetables. Vegetables play an important role in human nutrition since they are an outstanding source for vitamins, minerals, and biologically active compounds. In risk assessment of nitrate contents, this study reports the nitrate levels of 8 commonly consumed fruits and vegetables grown in Fiji, tomato (Lycopersicon esculentum), eggplant (Solanum melongena), capsicum (Capsicum annuum var. grossum), breadfruit (Artocarpus altilis), long bean (Vigna sesquipedalis), jackfruit (A. heterophyllus), pumpkin (Cucurbita pepo), and cucumber (Cucumis sativus). The effects of different types of cooking methods, baking, boiling, and frying, have also been studied. The validated flow injection analysis technique has been used to quantify the nitrate-N levels in the chosen products following nitrate extraction using the activated carbon technique. The mean values of nitrate levels in fresh products ranged from 25.83 to 281.02 mg NO(3) (-) kg(-1) . The study shows that boiling reduced nitrate contents by 65.37% to 25.25%. The frying in soy bean oil elevated nitrate contents from 354.79% to 86.69%, but after baking, nitrate contents remained almost constant with slight increasing trend in the case of tomato (19.97%). The nitrate levels published in the literature for the same types of fruits and vegetables studied have also been reviewed and compared. The average nitrate-N values were comparable or lower than overseas data, but did not present unpredictably high values, that is, they were below the risk level.

Retraction Note: Groundwater contaminations and health perspectives in developing world case study: Gaza Strip

Groundwater is the only source of water in the Gaza Strip. The results of a 10-year monitoring program revealed that more than 90% of the available water is not suitable for drinking purposes as a result of elevated chemical contaminants as well as microbiological organisms. The archives of the local hospitals showed catastrophic records on diseases caused by water directly and indirectly. Methemoglobinemia and dental fluorosis are well-known diseases caused by elevated nitrate and fluoride, respectively. Water-borne diseases are currently high and will increase if water, sanitation, and food-control services are not restored, or are allowed to deteriorate further. Heavy use and misuse of banned and prohibited pesticides may show other hard diseases in the near future. Geography, politics, and war combine to make the Gaza Strip a worst-case scenario for water-resource planners. Urgent alternative water resources should be secured and the human health should be given the highest priority.

Removal of highly elevated nitrate from drinking water by pH-heterogenized heterotrophic denitrification facilitated with ferrous sulfide-based autotrophic denitrification

The performance of acetic acid-supported pH-heterogenized heterotrophic denitrification (HD) facilitated with ferrous sulfide-based autotrophic denitrification (AD) was investigated in upflow activated carbon-packed column reactors for reliable removal of highly elevated nitrate (42mgNO3-Nl−1) in drinking water. The use of acetic acid as substrate provided sufficient internal carbon dioxide to completely eliminate the need of external pH adjustment for HD, but simultaneously created vertically heterogenized pH varying from 4.8 to 7.8 in the HD reactor. After 5-week acclimation, the HD reactor developed a moderate nitrate removal capacity with about one third of nitrate removal occurring in the acidic zone (pH 4.8–6.2). To increase the treatment reliability, acetic acid-supported HD was operated under 10% carbon limitation to remove >85% of nitrate, and ferrous sulfide-based AD was supplementally operated to remove residual nitrate and formed nitrite without excess of soluble organic carbon, nitrite or sulfate in the final effluent.

Elevated Plasma Nitrate Levels Are Associated with Decompensated Heart Failure and with Oral Nitrate Therapy in Chronic Heart Failure

Elevated Plasma Nitrate Levels Are Associated with Decompensated Heart Failure and with Oral Nitrate Therapy in Chronic Heart Failure

The effect of air supply on nitrogen removal using a biological filter proposed for ventilated pit latrines

Pit latrines are the most commonly used sanitation systems in many developing countries. Various researchers have reported elevated nitrate concentrations in groundwater in the vicinity of pit latrines and this could pose a serious health risk to the users of the water source. Faecal sludge from pit latrines contains high concentrations of nitrogen and organicmatter (3-5 g·l-1 N and 20-50 g·l-1 COD); however, it is produced at a very low rate (1.5 l·capita-1·d-1) relative to that of waterborne sewage systems. A pit latrine basically only confines the waste and no real treatment takes place. In this research the nitrogen was removed in a biological filter using a combination of nitrification and denitrification processes. The aim of this investigation was to determine the effect of air supplied at different rates, namely, 0, 0.3, 1.0 and 2.0 m3·h-1 N, on the biological filtration process. The application rate was 0.04 m3·m-2·d-1. More than 90% removal of nitrogen was observed at an air supply rate of 1.0 m3·h-1 N. At lower air supply rates nitrification was not complete. At an air supply rate of 2.0 m3·h-1 nitrogen removal was also approx. 90%, but the biological filter only became stable after about 2 months of operation, possibly due to desiccation of the biomass.

Microarray analysis of P450 upregulation in honey bee following neonicotinoid treatment

ontent, but had no relevant influence on protein content. Sulfate nrichment caused only a moderate increment of proteins. Photoynthetic light use efficiency and vitality index of photosynthetic pparatus revealed a positive influence of elevated nitrate conent, while an excessive phosphate and sulfate supply moderately ecreased quantumyield efficiency. Our resultsmay be used to iniiate evaluation of efficiency of high-scale cultivation of this algal train for bioremediation of wastewater and biomass production. oi:10.1016/j.copbio.2011.05.203

Nitrate‐Induced Goiter in Captive Whitespotted Bamboo Sharks Chiloscyllium plagiosum

Elasmobranch susceptibility to goiter formation in captive environments has been well documented. Until recently, most public aquariums operated under the belief that the etiology of goiter in elasmobranchs was nutritional and specifically caused by insufficient dietary iodine. Recent studies have demonstrated that high environmental nitrate (NO3-N) inhibits the ability of the thyroid gland to utilize available iodide, resulting in thyroid gland overstimulation by thyroid stimulating hormone and ultimately leading to the development of goiter. The objective of this study was to evaluate the effects of high environmental nitrate concentrations on thyroid function in juvenile whitespotted bamboo sharks Chiloscyllium plagiosum. In July 2008, five juveniles (80-150 g) were exposed to a low-nitrate environment (NO3-N concentration < 1 mg/L of water) and five were exposed to an elevated-nitrate environment (NO3-N = 70 mg/L) for 29 d in a flow-through natural seawater system. Nitrate exposure did not affect growth rates (e.g., weight, length, and condition factor) and did not alter free plasma thyroxine concentrations during the 29-d experimental period. However, histological examination of thyroid glands from sharks exposed to elevated nitrate revealed the development of diffuse hyperplastic goiter. With increasing restrictions on water use, most modern aquaria operate as recirculating systems, which results in higher and more chronic nitrate exposure for captive animals. Goiter is one of the most common health problems in captive elasmobranchs, and this study suggests that nitrate exposure is an important factor in the etiology of this disease.