Category Archives: Nitrate

Biological Methods for Removing Nitrate from Drinking Water

Rezvani F, Sarrafzadeh MH, Ebrahimi S, Oh HM. Nitrate removal from drinking water with a focus on biological methods: a review. Environ Sci Pollut Res Int. 2017 May 31. doi: 10.1007/s11356-017-9185-0.

This article summarizes several developed and industrial technologies for nitrate removal from drinking water, including physicochemical and biological techniques, with a focus on autotrophic nitrate removal. Approaches are primarily classified into separation-based and elimination-based methods according to the fate of the nitrate in water treatment. Biological denitrification as a cost-effective and promising method of biological nitrate elimination is reviewed in terms of its removal process, applicability, efficiency, and associated disadvantages. The various pathways during biological nitrate removal, including assimilatory and dissimilatory nitrate reduction, are also explained. A comparative study was carried out to provide a better understanding of the advantages and disadvantages of autotrophic and heterotrophic denitrification. Sulfur-based and hydrogen-based denitrifications, which are the most common autotrophic processes of nitrate removal, are reviewed with the aim of presenting the salient features of hydrogenotrophic denitrification along with some drawbacks of the technology and research areas in which it could be used but currently is not. The application of algae-based water treatment is also introduced as a nature-inspired approach that may broaden future horizons of nitrate removal technology.

Nitrate in Drinking Water and Colorectal Cancer; Indonesia

Fathmawati, Fachiroh J, Gravitiani E, Sarto. Nitrate in drinking water and risk of colorectal cancer in Yogyakarta, Indonesia. Journal of toxicology and environmental health. Part A. 2017 Jan 17:1-9. doi: 10.1080/15287394.2016.1260508.

Nitrate concentration in well water in Yogyakarta, Indonesia, and its surroundings tended to increase rapidly from time to time, and it may be associated with an elevated risk for several types of cancer. The purpose of this study was to examine the association between nitrate in drinking water and colorectal cancer (CRC) risk occurrence. A case-control study was conducted in Yogyakarta Special Province. Pathologically confirmed 75 CRC patients and 75 controls were consulted and their individual well water was sampled and examined for nitrate concentrations. Logistic regression analysis was conducted to establish the association between nitrate and CRC risk development. There was a significant correlation between nitrate in drinking water and CRC occurrence, and this value was relatively stable after being adjusted for protein intake, smoking history, age, and family history of cancer. These findings demonstrated that the risk of CRC development was fourfold among those with >10 years of nitrate exposure from well water compared with those with ≤10 years of nitrate exposure. Consequently, a significant association between nitrate in drinking water and occurrence of CRC in Yogyakarta was established.

Drinking Water Nitrate and Colorectal Cancer Risk

Studies such as this are an enormous undertaking and authors are to be commended for their effort. Assessing actual exposure is typically the weakest component as personal interviews and after-the-fact surveys are known to be unreliable. Water system monitoring records are not intended to represent human exposure. This could sway the subtle associations reported here up or down. At best it can be concluded that additional study should be considered. But even if the associations reported here were much higher or much lower, such results could be misleading given the inherent limitations of the study design. This comment is not intended as a criticism of this work. But recognition of the realities associated with this type of epidemiological study. Learn what we can from it and then move on.

Espejo-Herrera N, Gràcia-Lavedan E, Boldo E, Aragonés N, Pérez-Gómez B, Pollán M, Molina AJ, Fernández T, Martín V, La Vecchia C, Bosetti C, Tavani A, Polesel J, Serraino D, Gómez Acebo I, Altzibar JM, Ardanaz E, Burgui R, Pisa F, Fernández-Tardón G, Tardón A, Peiró R, Navarro C, Castaño-Vinyals G, Moreno V, Righi E, Aggazzotti G, Basagaña X, Nieuwenhuijsen M, Kogevinas M, Villanueva CM. Colorectal cancer risk and nitrate exposure through drinking water and diet. International Journal of Cancer. 2016 Mar 8. doi: 10.1002/ijc.30083.

Ingested nitrate leads to the endogenous synthesis of N-nitroso compounds (NOCs), animal carcinogens with limited human evidence. We aimed to evaluate the risk of colorectal cancer (CRC) associated with nitrate exposure in drinking water and diet. We conducted a case-control study in Spain and Italy during 2008-2013. Hospital-based incident cases and population-based (Spain) or hospital-based (Italy) controls were interviewed on residential history, water consumption since age 18, and dietary information. Long-term waterborne ingested nitrate was derived from routine monitoring records, linked to subjectś residential histories and water consumption habits. Dietary nitrate intake was estimated from food frequency questionnaires and published food composition databases. Odd ratios (OR) were calculated using mixed models with area as random effect, adjusted for CRC risk factors, and other covariables. Generalized additive models (GAMs) were used to analyze exposure-response relationships. Interaction with endogenous nitrosation factors and other covariables was also evaluated. We analyzed 1869 cases and 3530 controls. Average waterborne ingested nitrate ranged from 3.4 to 19.7 mg/day, among areas. OR (95% CIs) of CRC was 1.49 (1.24, 1.78) for >10 vs. ≤5 mg/day, overall. Associations were larger among men vs. women, and among subjects with high red meat intake. GAMs showed increasing exposure-response relationship among men. Animal-derived dietary nitrate was associated with rectal, but not with colon cancer risk. In conclusion, a positive association between CRC risk and waterborne ingested nitrate is suggested, mainly among subgroups with other risk factors. Heterogeneous effects of nitrate from different sources (water, animal and vegetables) warrant further research.

Nitrate and Bladder Cancer Risk Remains Inconsistent

When study after study reveal inconsistent results perhaps it is time to look head in a different direction.

Espejo-Herrera N, Cantor KP, Malats N, Silverman DT, Tardón A, García-Closas R, Serra C, Kogevinas M, Villanueva CM. Nitrate in drinking water and bladder cancer risk in Spain. 2015 Feb;137:299-307. doi: 10.1016/j.envres.2014.10.034. Epub 2015 Jan 16.

BACKGROUND: Nitrate is a widespread contaminant in drinking water and ingested nitrate under conditions resulting in endogenous nitrosation is suspected to be carcinogenic. However, the suggested association between nitrate in drinking water and bladder cancer remains inconsistent. We evaluated the long-term exposure to drinking water nitrate as a risk factor for bladder cancer, considering endogenous nitrosation modifiers and other covariables.

METHODS: We conducted a hospital-based case-control study of bladder cancer in Spain (1998-2001). Residential histories and water consumption information were ascertained through personal interviews. Historical nitrate levels (1940-2000) were estimated in study municipalities based on monitoring records and water source. Residential histories of study subjects were linked with nitrate estimates by year and municipality to calculate individual exposure from age 18 to recruitment. We calculated odds ratios (OR) and 95% confidence intervals (CI) for bladder cancer among 531 cases and 556 controls with reliable interviews and nitrate exposure information covering at least 70% of years from age 18 to interview.

RESULTS: Average residential levels ranged from 2.1mg/L to 12.0mg/L among regions. Adjusted OR (95%CI) for average residential levels relative to ≤ 5 mg/L were 1.2 (0.7-2.0) for >5-10mg/L and 1.1 (0.6-1.9) for >10mg/L. The OR for subjects with longest exposure duration (>20 years) to highest levels (>9.5mg/L) was 1.4 (0.9-2.3). Stratification by intake of vitamin C, vitamin E, meat, and gastric ulcer diagnosis did not modify these results. A non-significant negative association was found with waterborne ingested nitrate with an OR of 0.7 (0.4-1.0) for >8 vs. ≤ 4 mg/day. Adjustment for several covariables showed similar results to crude analyses.

CONCLUSION: Bladder cancer risk was inconsistently associated with chronic exposure to drinking water nitrate at levels below the current regulatory limit. Elevated risk is suggested only among subjects with longest exposure duration to the highest levels. No evidence of interaction with endogenous nitrosation modifiers was observed.

Modeled Nitrate Occurrence is Unrepresentative of Actual N-nitroso Compound Exposure

This study models nitrate occurrence in private wells in Iowa for the purpose of exposure assessment. Like other epidemiology studies it heads down the limited pathway of an ecologic study design. Modeled nitrate occurrence in wells does not represent actual exposure to N-nitroso compounds or even to nitrate. Application of this work in a cancer cohort assessment can at best only generate hypotheses. As an aside, an r-square = 0.77 still generates a very large confidence interval at any level of significance.

Wheeler DC, Nolan BT, Flory AR, DellaValle CT, Ward MH. Modeling groundwater nitrate concentrations in private wells in Iowa. The Science of the Total Environment. 2015 Jul 29;536:481-488. doi: 10.1016/j.scitotenv.2015.07.080.

Contamination of drinking water by nitrate is a growing problem in many agricultural areas of the country. Ingested nitrate can lead to the endogenous formation of N-nitroso compounds, potent carcinogens. We developed a predictive model for nitrate concentrations in private wells in Iowa. Using 34,084 measurements of nitrate in private wells, we trained and tested random forest models to predict log nitrate levels by systematically assessing the predictive performance of 179 variables in 36 thematic groups (well depth, distance to sinkholes, location, land use, soil characteristics, nitrogen inputs, meteorology, and other factors). The final model contained 66 variables in 17 groups. Some of the most important variables were well depth, slope length within 1km of the well, year of sample, and distance to nearest animal feeding operation. The correlation between observed and estimated nitrate concentrations was excellent in the training set (r-square=0.77) and was acceptable in the testing set (r-square=0.38). The random forest model had substantially better predictive performance than a traditional linear regression model or a regression tree. Our model will be used to investigate the association between nitrate levels in drinking water and cancer risk in the Iowa participants of the Agricultural Health Study cohort.

Agricultural Buffers to Reduce Groundwater Nitrate

At first look studies like are promising. But this approach assumes that (1) the crops grown in the buffer area do not leach nitrate or other contaminants and (2) the “integrated model” represents reality. It does not. It may be useful at this point, but any use of an agricultural buffer to grow “cash” crops must pass the economic test of the free market.

Megan M. Mayzelle, Joshua H. Viers, Josué Medellín-Azuara, Thomas Harter. Economic Feasibility of Irrigated Agricultural Land Use Buffers to Reduce Groundwater Nitrate in Rural Drinking Water Sources. Water 2015, Vol. 7 Issue 1, p12-37.

Agricultural irrigation leachate is often the largest source for aquifer recharge in semi-arid groundwater basins, but contamination from fertilizers and other agro-chemicals may degrade the quality of groundwater. Affected communities are frequently economically disadvantaged, and water supply alternatives may be too costly. This study aimed to demonstrate that, when addressing these issues, environmental sustainability and market profitability are not incompatible. We investigated the viability of two low impact crops, alfalfa and vineyards, and new recharge basins as an alternative land use in recharge buffer zones around affected communities using an integrated hydrologic, socio-geographic, and economic analysis. In the southern Central Valley, California, study area, alfalfa and vineyards currently constitute 30% of all buffer zone cropland. Economic analyses of alternative land use scenarios indicate a wide range of revenue outcomes. Sector output gains and potential cost saving through land use conversion and resulting flood control result in gains of at least $2.3 billion, as compared to costs of $0.3 to $0.7 billion for treatment options over a 20 year period. Buffer zones would maintain the economic integrity of the region and concur with prevailing policy options. Thus, managed agricultural recharge buffer zones are a potentially attractive option for communities facing financial constraint and needing to diversify their portfolio of policy and infrastructure approaches to meet drinking water quality objectives.

Click here for paper (Open Access).


San Joaquin Valley Study of Low Birth Weight and Nitrate

If a forest fire is serious it can be seen from miles away. Perhaps when none is seen there is no serious fire there at all.

This abstract does not mention what constitutes an “unsafe level”. Presumably this would be the drinking water MCL of 10 mg/L but perhaps the “safe” level is higher than the MCL. Like most studies of this type the presumption is that there must be a problem we just have not looked close enough.

Blake SB. Spatial relationships among dairy farms, drinking water quality, and maternal-child health outcomes in the San Joaquin Valley. Public Health Nurs. 2014 Nov-Dec;31(6):492-9. doi: 10.1111/phn.12166.

OBJECTIVE: Access to clean and affordable water is a significant public health issue globally, in the United States, and in California where land is heavily used for agriculture and dairy operations. The purpose of this study was to explore the geographic relationships among dairy farms, nitrate levels in drinking water, low birth weight, and socioeconomic data at the ZIP code level in the San Joaquin Valley.

DESIGN AND SAMPLE: This ecological study used a Geographic Information System (GIS) to explore and analyze secondary data.

MEASURES: A total of 211 ZIP codes were analyzed using spatial autocorrelation and regression analysis methods in ArcGIS version 10.1.
RESULTS: ZIP codes with dairies had a higher percentage of Hispanic births (p = .001). Spatial statistics revealed that ZIP codes with more dairy farms and a higher dairy cow density had higher levels of nitrate contamination. No correlation was detected between LBW and unsafe nitrate levels at the ZIP code level.

CONCLUSION: Further research examining communities that use private and small community wells in the San Joaquin Valley should be conducted. Birth data from smaller geographic areas should be used to continue exploring the relationship between birth outcomes and nitrate contamination in drinking water.