Nitrate in drinking water and risk of death from bladder cancer: an ecological case-control study in Taiwan

Nitrate in groundwater and agricultural products: intake and risk assessment in northeastern Iran

The suitability of groundwater and agricultural products for human consumption requires determining levels and assessing the health risks associated with potential pollutants. Here, particularly pollution with nitrate still remains a challenge, especially for those urban areas suffering from insufficient sewage collection systems, resulting in contaminating soil, endangering food safety, and deteriorating drinking water quality. In the present study, nitrate concentrations in the commonly consumed fruit and vegetable species were determined, and the results, together with the groundwater nitrate levels, were used to assess the associated health risks for Mashhad city residents. For this assessment, 261 water samples and 16 produce types were used to compute the daily intake of nitrate. Nitrate in groundwater was analyzed using a spectrophotometer, and produce species were examined using High-Performance Liquid Chromatography. Ward's hierarchical cluster analysis was applied for categorizing produce samples with regard to their nitrate content. Additionally, to account for the sanitation hazards associated with groundwater quality for drinking purposes, total coliform and turbidity were also assessed using the membrane filter (MF) technique and a nephelometer, respectively. Nitrate concentrations exceeded the prescribed permissible limits in 42% of the groundwater wells. The outcomes also exhibit significantly higher nitrate accumulation levels in root-tuber vegetables and leafy vegetables compared to fruit vegetables and fruits. Using cluster analysis, the accumulation of nitrate in vegetables and fruits was categorized into four clusters, specifying that radish contributes to 65.8% of the total content of nitrate in all samples. The Estimated Daily Intake (EDI) of nitrate and Health Risk Index (HRI) associated with consumption of groundwater exceeded the prescribed limit for the children's target group in Mashhad's south and central parts. Likewise, EDI and HRI values for produce consumption, in most samples, were found to be in the tolerable range, except for radish, lettuce, and cabbage, potentially posing risks for both children and adult consumers. The total coliforms in groundwater were found to violate the prescribed limit at 78.93% of the sampling locations and were generally much higher over the city's central and southern areas. A relatively strong correlation (R² = 0.6307) between total coliform and nitrate concentrations suggests the release of anthropogenic pollution (i.e., sewage and manure) in the central and southern Mashhad.

Nitrate and nitrite contamination in drinking water and cancer risk: A systematic review with meta-analysis

BACKGROUND

Pollution of water sources, largely from wide-scale agricultural fertilizer use has resulted in nitrate and nitrite contamination of drinking water. The effects on human health of raised nitrate and nitrite levels in drinking water are currently unclear.

OBJECTIVES

We conducted a systematic review of peer-reviewed literature on the association of nitrate and nitrite in drinking water with human health with a specific focus on cancer.

METHODS

We searched eight databases from 1 January 1990 until 28 February 2021. Meta-analyses were conducted when studies had the same exposure metric and outcome.

RESULTS

Of 9835 studies identified in the literature search, we found 111 studies reporting health outcomes, 60 of which reported cancer outcomes (38 case-control studies; 12 cohort studies; 10 other study designs). Most studies were set in the USA (24), Europe (20) and Taiwan (14), with only 3 studies from low and middle-income countries. Nitrate exposure in water (59 studies) was more commonly investigated than nitrite exposure (4 studies). Colorectal (15 studies) and gastric (13 studies) cancers were the most reported. In meta-analyses (4 studies) we identified a positive association of nitrate exposure with gastric cancer, OR = 1.91 (95%CI = 1.09-3.33) per 10 mg/L increment in nitrate ion. We found no association of nitrate exposure with colorectal cancer (10 studies; OR = 1.02 [95%CI = 0.96-1.08]) or cancers at any other site.

CONCLUSIONS

We identified an association of nitrate in drinking water with gastric cancer but with no other cancer site. There is currently a paucity of robust studies from settings with high levels nitrate pollution in drinking water. Research into this area will be valuable to ascertain the true health burden of nitrate contamination of water and the need for public policies to protect human health.

Nitrate adsorption onto surface-modified red mud in batch and fixed-bed column systems: equilibrium, kinetic, and thermodynamic studies

This research aimed to develop a novel composite as a low-cost adsorbent for the removal of nitrate ion from aqueous solutions. The characterization of this composite (composition of red mud with dimethyldioctadecylammonium bromide (DDAB)) was performed by XRF, XRD, FTIR, and BET analyses. The most influential variables on nitrate adsorption, including contact time, solution acidity, adsorbent amount, and temperature were studied. The maximum amount of nitrate adsorbed onto the prepared adsorbent was obtained at pH 5.5 and contact time 30 min. The heterogeneous adsorption occurred during the uptake of nitrate. The results of kinetic study revealed that intra-particle diffusion was the major limitation for nitrate adsorption rate. The values of thermodynamic parameters illustrate the non-spontaneous, associative, and exothermic adsorption process. Increasing the temperature enhances the tendency of the process to non-spontaneously. Research on fixed-bed column has been done under different initial nitrate concentrations. The adsorption capacity of nitrate was increased with an increase in the initial concentration of nitrate. The results of column data were successfully explained using the Thomas and Yoon-Nelson models.

Evaluation of natural attenuation-potential and biogeochemical analysis in nitrate contaminated bedrock aquifers by carbon source injection

In this study, the natural attenuation potential and biogeochemical analysis of nitrate contaminated bedrock aquifers by injection of carbon sources was evaluated. The denitrification capacity was assessed by injecting different carbon sources (succinate, acetate, fumarate) into the groundwater. Acetate was identified as the optimum source of electron donors for microbial metabolic processes, as it improved the effect of nitrate removal and microbial activity in the groundwater. In addition, when acetate was injected with a C/N ratio = 2.1:1, the ratio of denitrifying bacteria was the greatest (C/N 2.1 (2.1%) > C/N 4.2 (1.9%) > C/N 7.0 (0.9%) > control (0.7%)). Reflecting the geochemical characteristics of the bedrock aquifer environment, acetate was injected into groundwater at the research site to activate biological heterotrophic denitrification. As a result, the nitrate reduction rate was 0.377 g-N/day (YP-3), while the rate in groundwater unaffected by acetate was significantly lower, at 0.028 g-N/day (YP-4) over the same reaction time. In particular, the ratio of Dechloromonas denitrificans sp., which is a representative denitrification bacteria involved in anaerobic reduction of nitrate, increased (before injection: 0.0089%, after injection: 1.3067%). Expression of the nosZ gene, which is involved in the denitrification pathway (N₂O → N₂), increased from 4.82 Log (gene copies L^-1) to 9.71 Log (gene copies L^-1). Together, these results demonstrate that denitrification in bedrock aquifers can be activated by injection of carbon sources and identified the genetic reason for that denitrification.

Concurrent removal of nitrate, arsenic and iron from simulated and real-life groundwater to meet drinking water standards: Effects of operational and environmental parameters

The aim of this work was to study concurrent removal of nitrate, arsenic and iron in an attached growth reactor (AGR) based on bio-sulphidogenesis treating simulated and real-life ground water. A lab-scale bioreactor system was monitored for a period of 511 days under conditions identical to those prevailing at full-scale to assess the relative influence of empty bed contact time (EBCT) (20-90 min), backwash strategies (water-nitrogen and water-air), temperature (20-50 °C), pH (6.6-8.4) and shut down on reactor performance and recovery. Complete removal of nitrate (50 mg/L) and over 95% removal of iron (3 mg/L) occurred. Arsenic removal efficiency was around 99% (500 μg/L) and treated water arsenic concentration was in compliance with the World Health Organization and Indian Standard of 10 μg/L. Port sampling along the depth of bioreactor shows shifting of terminal electron accepting process zones at lower EBCT of 20 min and after air assisted backwashing. The temperature range of 20-50 °C and pH range of 6.6-8.4 were applicable for arsenic removal in natural conditions. Precipitated biosolids were analysed using electron microscopy. Biogenic sulphides resulted in the precipitation of arsenosulphides and iron sulphides, which concurrently removed arsenic and iron. This study suggests that a sulphidogenic bioreactor may help to set the basis for concurrent removal of nitrate, arsenic and iron from real-life groundwater using mixed biofilm bacterial community.

Environmental justice and drinking water quality: are there socioeconomic disparities in nitrate levels in U.S. drinking water?

BACKGROUND

Low-income and minority communities often face disproportionately high pollutant exposures. The lead crisis in Flint, Michigan, has sparked concern about broader socioeconomic disparities in exposures to drinking water contaminants. Nitrate is commonly found in drinking water, especially in agricultural regions, and epidemiological evidence suggests elevated risk of cancer and birth defects at levels below U.S. EPA's drinking water standard (10 mg/L NO3-N). However, there have been no nationwide assessments of socioeconomic disparities in exposures to nitrate or other contaminants in U.S. drinking water. The goals of this study are to identify determinants of nitrate concentrations in U.S. community water systems (CWSs) and to evaluate disparities related to wealth or race/ethnicity.

METHODS

We compiled nitrate data from 39,466 U.S. CWSs for 2010-2014. We used EPA's Safe Drinking Water Information System (SDWIS) to compile CWS characteristics and linked this information with both city- and county-level demographic data gathered from the U.S. Census Bureau. After applying multiple imputation methods to address censored nitrate concentration data, we conducted mixed-effects multivariable regression analyses at national and regional scales.

RESULTS

5.6 million Americans are served by a CWS that had an average nitrate concentration ≥ 5 mg/L NO3-N between 2010 and 2014. Extent of agricultural land use and reliance on groundwater sources were significantly associated with nitrate. The percent of Hispanic residents served by each system was significantly associated with nitrate even after accounting for county-level cropland and livestock production, and CWSs in the top quartile of percent Hispanic residents exceeded 5 mg/L nearly three times as often as CWSs serving the lowest quartile. By contrast, the percent of residents living in poverty and percent African American residents were both inversely associated with nitrate.

CONCLUSIONS

Epidemiological evidence for health effects associated with drinking water above 5 mg/L NO3-N raises concerns about increased risk for the 5.6 million Americans served by public water supplies with average nitrate concentrations above this level. The associations we observed between nitrate concentrations and proportions of Hispanic residents support the need for improved efforts to assist vulnerable communities in addressing contamination and protecting source waters. Future studies can extend our methods to evaluate disparities in exposures to other contaminants and links to health effects.

Evaluation of nitrate and phosphate adsorption on Al-modified biochar: Influence of Al content

Biochars with different Al contents (i.e., 5, 10, 15, and 20 wt%) were prepared to evaluate their adsorption capacities for nitrate (NO₃^-) and phosphate (PO₄^3-) from eutrophic water. Several techniques, including N₂ adsorption-desorption, X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectrometry, were applied to characterize the physical-chemical properties of the biochars. We found that the NO₃^- and PO₄^3- adsorptions significantly improved on the Al-modified biochars because of their multifunctional and surface charge properties. In single-solute adsorption, 15 Al/BC and 20 Al/BC exhibited optimal NO₃^- and PO₄^3- adsorption capacities, respectively. In bi-solute coadsorption, the PO₄^3- adsorption on the biochar was less affected with the coexistence of NO₃^-, whereas the coexistence of PO₄^3- had a significant impact on the NO₃^- adsorption. The optimal solution pH for NO₃^- adsorption was 6, and pH < 6 was advantageous to PO₄^3- adsorption. In the kinetic study, the pseudo-second-order model could describe the NO₃^- and PO₄^3- adsorptions on biochar well, indicating that chemical adsorption was the main adsorption mechanism. The Langmuir-Freundlich model agreed well with the NO₃^- and PO₄^3- adsorptions on the biochars, and the maximum adsorption capacities for NO₃^- and PO₄^3- reached 89.58 mg/g and 57.49 mg/g, respectively. Therefore, the Al-modified biochar was a good choice for the remediation of eutrophic water.

Impacts of zeolite, alum and polyaluminum chloride amendments mixed with agricultural wastes on soil column leachate, and CO2 and CH4 emissions

This study aimed to quantify leaching losses of nitrogen (N), phosphorus (P) and carbon (C), as well as carbon dioxide (CO₂) and methane (CH₄) emissions from stored slurry, and from packed soil columns surface applied with unamended and chemically amended dairy and pig slurries, and dairy soiled water (DSW). The amendments to the slurries, which were applied individually and together, were: polyaluminum chloride (PAC) and zeolite for pig and dairy slurry, and liquid aluminium sulfate (alum) and zeolite for DSW. Application of pig slurry resulted in the highest total nitrogen (TN) and nitrate-nitrogen (NO₃-N) fluxes (22 and 12 kg ha^-1), whereas corresponding fluxes from dairy slurries and DSW were not significantly (p < 0.05) higher than those from the control soil. There were no significant (p < 0.05) differences in leachate N losses between unamended and amended dairy slurries, unamended and amended pig slurries, and unamended and amended DSW. There were no leachate P losses measured over the experimental duration. Total cumulative organic (TOC) and inorganic C (TIC) losses in leachate were highest for unamended dairy slurry (82 and 142 kg ha^-1), and these were significantly (p < 0.05) reduced when amended with PAC (38 and 104 kg ha^-1). The highest average cumulative CO₂ emissions for all treatments were measured for pig slurries (680 kg CO₂-C ha^-1) followed by DSW (515 kg CO₂-C ha^-1) and dairy slurries (486 kg CO₂-C ha^-1). The results indicate that pig slurry, either in raw or chemically amended form, poses the greatest environmental threat of leaching losses and gaseous emissions of CO₂ and CH₄ and, in general, amendment of wastewater with PAC, alum or zeolite, does not mitigate the risk of these losses.

Nitrate and Nitrogen Oxides: Sources, Health Effects and Their Remediation

Increased use of nitrogenous (N) fertilizers in agriculture has significantly altered the global N-cycle because they release nitrogenous gases of environmental concerns. The emission of nitrous oxide (N2O) contributes to the global greenhouse gas accumulation and the stratospheric ozone depletion. In addition, it causes nitrate leaching problem deteriorating ground water quality. The nitrate toxicity has been reported in a number of studies showing the health hazards like methemoglobinemia in infants and is a potent cause of cancer. Despite these evident negative environmental as well as health impacts, consumption of N fertilizer cannot be reduced in view of the food security for the teeming growing world population. Various agronomic and genetic modifications have been practiced to tackle this problem. Some agronomic techniques adopted include split application of N, use of slow-release fertilizers, nitrification inhibitors and encouraging the use of organic manure over chemical fertilizers. As a matter of fact, the use of chemical means to remediate nitrate from the environment is very difficult and costly. Particularly, removal of nitrate from water is difficult task because it is chemically non-reactive in dilute aqueous solutions. Hence, the use of biological means for nitrate remediation offers a promising strategy to minimize the ill effects of nitrates and nitrites. One of the important goals to reduce N-fertilizer application can be effectively achieved by choosing N-efficient genotypes. This will ensure the optimum uptake of applied N in a balanced manner and exploring the molecular mechanisms for their uptake as well as metabolism in assimilatory pathways. The objectives of this paper are to evaluate the interrelations which exist in the terrestrial ecosystems between the plant type and characteristics of nutrient uptake and analyze the global consumption and demand for fertilizer nitrogen in relation to cereal production, evaluate the various methods used to determine nitrogen use efficincy (NUE), determine NUE for the major cereals grown across large agroclimatic regions, determine the key factors that control NUE, and finally analyze various strategies available to improve the use efficiency of fertilizer nitrogen.

Re-evaluation of sodium nitrate (E 251) and potassium nitrate (E 252) as food additives

The Panel on Food Additives and Nutrient Sources added to Food (ANS) provided a scientific opinion re-evaluating the safety of sodium nitrate (E 251) and potassium nitrate (E 252) when used as food additives. The current acceptable daily intakes (ADIs) for nitrate of 3.7 mg/kg body weight (bw) per day were established by the SCF (1997) and JECFA (2002). The available data did not indicate genotoxic potential for sodium and potassium nitrate. The carcinogenicity studies in mice and rats were negative. The Panel considered the derivation of an ADI for nitrate based on the formation of methaemoglobin, following the conversion of nitrate, excreted in the saliva, to nitrite. However, there were large variations in the data on the nitrate-to-nitrite conversion in the saliva in humans. Therefore, the Panel considered that it was not possible to derive a single value of the ADI from the available data. The Panel noticed that even using the highest nitrate-to-nitrite conversion factor the methaemoglobin levels produced due to nitrite obtained from this conversion would not be clinically significant and would result to a theoretically estimated endogenous N-nitroso compounds (ENOC) production at levels which would be of low concern. Hence, and despite the uncertainty associated with the ADI established by the SCF, the Panel concluded that currently there was insufficient evidence to withdraw this ADI. The exposure to nitrate solely from its use as a food additive was estimated to be less than 5% of the overall exposure to nitrate in food based on a refined estimated exposure scenario. This exposure did not exceed the current ADI (SCF, 1997). However, if all sources of exposure to dietary nitrate are considered (food additive, natural presence and contamination), the ADI would be exceeded for all age groups at the mean and the highest exposure.

The drinking water disparities framework: on the origins and persistence of inequities in exposure

With this article, we develop the Drinking Water Disparities Framework to explain environmental injustice in the context of drinking water in the United States. The framework builds on the social epidemiology and environmental justice literatures, and is populated with 5 years of field data (2005-2010) from California's San Joaquin Valley. We trace the mechanisms through which natural, built, and sociopolitical factors work through state, county, community, and household actors to constrain access to safe water and to financial resources for communities. These constraints and regulatory failures produce social disparities in exposure to drinking water contaminants. Water system and household coping capacities lead, at best, to partial protection against exposure. This composite burden explains the origins and persistence of social disparities in exposure to drinking water contaminants.

Enhanced removal of nitrate from water using surface modification of adsorbents--a review

Elevated concentration of nitrate results in eutrophication of natural water bodies affecting the aquatic environment and reduces the quality of drinking water. This in turn causes harm to people's health, especially that of infants and livestock. Adsorbents with the high capacity to selectively adsorb nitrate are required to effectively remove nitrate from water. Surface modifications of adsorbents have been reported to enhance their adsorption of nitrate. The major techniques of surface modification are: protonation, impregnation of metals and metal oxides, grafting of amine groups, organic compounds including surfactant coating of aluminosilicate minerals, and heat treatment. This paper reviews current information on these techniques, compares the enhanced nitrate adsorption capacities achieved by the modifications, and the mechanisms of adsorption, and presents advantages and drawbacks of the techniques. Most studies on this subject have been conducted in batch experiments. These studies need to include continuous mode column trials which have more relevance to real operating systems and pilot-plant trials. Reusability of adsorbents is important for economic reasons and practical treatment applications. However, only limited information is available on the regeneration of surface modified adsorbents.

Nitrates in drinking water and the risk of death from brain cancer: does hardness in drinking water matter?

The objectives of this study were to (1) examine the relationship between nitrate levels in public water supplies and risk of death from brain cancer and (2) determine whether calcium (Ca) and magnesium (Mg) levels in drinking water might modify the influence of nitrates on development of brain cancer. A matched cancer case-control study was used to investigate the relationship between the risk of death from brain cancer and exposure to nitrates in drinking water in Taiwan. All brain cancer deaths of Taiwan residents from 2003 through 2008 were obtained from the Bureau of Vital Statistics of the Taiwan Provincial Department of Health. Controls were deaths from other causes and were pair-matched to cancer cases by gender, year of birth, and year of death. Information on the levels of nitrate-nitrogen (NO₃-N), Ca, and Mg in drinking water was obtained from Taiwan Water Supply Corporation (TWSC). The municipality of residence for cancer cases and controls was presumed to be the source of the subject's NO₃-N, Ca, and Mg exposure via drinking water. Relative to individuals whose NO₃-N exposure level was <0.38 ppm, the adjusted OR (95% CI) for brain cancer occurrence was 1.04 (0.85-1.27) for individuals who resided in municipalities served by drinking water with a NO₃-N exposure ≥ 0.38 ppm. No marked effect modification was observed due to Ca and Mg intake via drinking water on brain cancer occurrence.

Developing biomarkers for improved diagnosis and treatment outcome monitoring of bladder cancer

IMPORTANCE OF THE FIELD

A non-invasive marker for the follow-up and diagnosis of bladder cancer is highly needed. Several markers have been studied with regard to sensitivity and specificity in detecting bladder cancer. Comparison of studies is complicated by limited data on tumor characteristics and treatment details. Many studies do not differentiate between primary and recurrent tumors, nor is the performance of the studied marker assessed separately in superficial and invasive or high- versus low-grade tumors.

AREAS COVERED IN THIS REVIEW

The field of bladder cancer biomarker research from the past 15 years. WHAT THE READER GAIN: A summary of the current field of bladder biomarker research with concluding remarks on some specific challenges in developing biomarkers for improved diagnosis and monitoring the disease.

TAKE HOME MESSAGE

In general, the best new markers give higher sensitivity than urinary cytology, but specificity is usually lower. By using new markers, the intervals between follow-up cystoscopies can be increased and the detection of relapse can be improved. But to date no non-invasive biomarker has proven to be sensitive and specific enough available to replace cystoscopy, neither in the diagnosis nor in the follow-up of bladder cancer. However, new marker combinations and algorithms for risk assessment hold promise for the future.

Environmental factors and genetic susceptibility promote urinary bladder cancer

Cancer of the urinary bladder is the second most common malignancy of the genitourinary tract, currently accounting for up to 5% of all newly diagnosed tumours in the western world. Urinary bladder carcinogenesis seems to develop from the interaction of environmental exposure and genetic susceptibility. Smoking, specific industrial chemicals, dietary nitrates and arsenic represent the most important exogenous risk factors. Chromosomal abnormalities, silencing of certain genes by abnormal methylation of their promoter region, alterations in tumour suppressor genes and proto-oncogenes that induce uncontrolled cell proliferation and reduced apoptosis, are molecular mechanisms that have been reported in bladder carcinogenesis. In this article, we discuss the environmental risk factors of bladder cancer and we review the genetic and epigenetic alterations, including aberrant DNA methylation and deregulation of microRNAs expression. We also discuss the role of p53 and retinoblastoma suppressor genes in disease progression. Finally, we present recent reports on the use of molecular profiling to predict disease stage and grade and direct targeted therapy.

Nitrates in municipal drinking water and non-Hodgkin lymphoma: an ecological cancer case-control study in Taiwan

The relationship between nitrate levels in drinking water and increased risk of non-Hodgkin lymphoma (NHL) development has been inconclusive. A matched cancer case-control and a nitrate ecology study was used to investigate the association between mortality attributed to NHL and nitrate exposure from Taiwan's drinking water. All deaths due to NHL in Taiwan residents from 2000 through 2006 were obtained from the Bureau of Vital Statistics of the Taiwan Provincial Department of Health. Controls were deaths from other causes and were pair-matched to the cases by gender, year of birth, and year of death. Each matched control was selected randomly from the set of possible controls for each case. Data on nitrate-nitrogen (NO(3)-N) levels of drinking water throughout Taiwan were collected from the Taiwan Water Supply Corporation (TWSC). The municipality of residence for cancer cases and controls was presumed to be the source of the subject's nitrate exposure via drinking water. The adjusted odds ratios (OR) for NHL death for those with high nitrate levels in their drinking water, as compared to the lowest tertile, were 1.02 (0.87-1.2) and 1.05 (0.89-1.24), respectively. The results of the present study show that there was no statistically significant association between nitrates in drinking water at levels in this investigation and increased risk of death attributed to NHL.

Nitrate in drinking water and risk of death from pancreatic cancer in Taiwan

The relationship between nitrate levels in drinking water and risk of pancreatic cancer development remains inconclusive. A matched case-control and nitrate ecology study was used to investigate the association between mortality attributed to pancreatic cancer and nitrate exposure from Taiwan's drinking water. All pancreatic cancer deaths of Taiwan residents from 2000 through 2006 were obtained from the Bureau of Vital Statistics of the Taiwan Provincial Department of Health. Controls were deaths from other causes and were pair-matched to the cases by gender, year of birth, and year of death. Each matched control was selected randomly from the set of possible controls for each case. Data on nitrate-nitrogen (NO(3)-N) levels of drinking water throughout Taiwan were collected from Taiwan Water Supply Corporation (TWSC). The municipality of residence for cancer cases and controls was assumed to be the source of the subject's nitrate exposure via drinking water. The adjusted odds ratios and confidence limits for pancreatic cancer death for those with high nitrate levels in their drinking water, as compared to the lowest tertile, were 1.03 (0.9-1.18) and 1.1 (0.96-1.27), respectively. The results of the present study show that there was no statistically significant association between the levels of nitrate in drinking water and increased risk of death from pancreatic cancer.

Nitrates in drinking water and risk of death from rectal cancer in Taiwan

The relationship between nitrate levels in drinking water and rectal cancer development has been inconclusive. A matched case-control and nitrate ecology study was used to investigate the association between mortality attributed to rectal cancer and drinking-water nitrate exposure in Taiwan. All deaths due to rectal cancer of Taiwan residents from 1999 through 2003 were obtained from the Bureau of Vital Statistics of the Taiwan Provincial Department of Health. Controls were deaths from other causes and were pair matched to the cancer cases by gender, year of birth, and year of death. Each matched control was selected randomly from the set of possible controls for each case. Data on nitrate-nitrogen (NO3-N) levels in drinking water throughout Taiwan were collected from Taiwan Water Supply Corporation (TWSC). The municipality of residence for cancer cases and controls was assumed to be the source of the subject's nitrate exposure via drinking water. The adjusted odds ratios for rectal cancer death for those with high nitrate levels in their drinking water, as compared to the lowest tertile, were 1.22 (0.98-1.52) and 1.36 (1.08-1.70), respectively. The findings of this study warrant further investigation of the role of nitrates in drinking water in the etiology of rectal cancer in Taiwan.