Health aspects of nitrate in drinking water

The potential human health hazard of nitrates in drinking water: a media discourse analysis in a high-income country

BACKGROUND

Recent studies linking low levels of nitrate in drinking water to colorectal cancer have raised public concerns over nitrate contamination. The aim of this study was to analyze the media discourse on the potential human health hazard of nitrates in drinking water in a high-income country with a large livestock industry: New Zealand (NZ).

METHODS

Searches of media sources ("major newspapers") held by the Factiva database for the NZ setting in the five-year period 17 December 2016 to 20 December 2021.

RESULTS

The largest number of media items was observed for 2017 (n = 108), the year of a NZ general election, with a notable decrease in 2020 (n = 20) that was likely due to the Covid-19 pandemic, which dominated health media. However, the percentage of these media items with a health focus steadily increased over time, from 11.1% of all articles in 2017 to 51.2% in 2021. The most commonly mentioned health hazard was colorectal cancer, followed by methemoglobinemia. The temporal pattern of media items suggests that the release of scientific studies and scholarly blogs was associated with the publication of subsequent media items. Major stakeholders involved in the discourse included representatives of local and central government, environmental and recreational interest groups, researchers, local residents, agricultural interest groups, and health organizations. Māori (Indigenous New Zealanders) values or perspectives were rarely mentioned.

CONCLUSIONS

Analysis of major newspapers for a five-year period indicated that a wide range of expert comment and opinions were made available to the public and policy makers on the issue of nitrates in water. While many different stakeholder views were captured in the media discourse, there is scope for the media to better report the views of Māori on this topic. There is also a need for articles detailing the health issues to also refer to the environmental, recreational, and cultural aspects of protecting water quality to ensure that the public, policy makers, and regulators are aware of co-benefits.

From Classical to Advanced Use of Polymers in Food and Beverage Applications

Polymers are extensively used in food and beverage packaging to shield against contaminants and external damage due to their barrier properties, protecting the goods inside and reducing waste. However, current trends in polymers for food, water, and beverage applications are moving forward into the design and preparation of advanced polymers, which can act as active packaging, bearing active ingredients in their formulation, or controlling the head-space composition to extend the shelf-life of the goods inside. In addition, polymers can serve as sensory polymers to detect and indicate the presence of target species, including contaminants of food quality indicators, or even to remove or separate target species for later quantification. Polymers are nowadays essential materials for both food safety and the extension of food shelf-life, which are key goals of the food industry, and the irruption of smart materials is opening new opportunities for going even further in these goals. This review describes the state of the art following the last 10 years of research within the field of food and beverage polymer's applications, covering present applications, perspectives, and concerns related to waste generation and the circular economy.

Denitrification in a hypersaline lake-aquifer system (Pétrola Basin, Central Spain): the role of recent organic matter and Cretaceous organic rich sediments

Agricultural regions in semi-arid to arid climates with associated saline wetlands are one of the most vulnerable environments to nitrate pollution. The Pétrola Basin was declared vulnerable to NO3(-) pollution by the Regional Government in 1998, and the hypersaline lake was classified as a heavily modified body of water. The study assessed groundwater NO3(-) through the use of multi-isotopic tracers (δ(15)N, δ(34)S, δ(13)C, δ(18)O) coupled to hydrochemistry in the aquifer connected to the eutrophic lake. Hydrogeologically, the basin shows two main flow components: regional groundwater flow from recharge areas (Zone 1) to the lake (Zone 2), and a density-driven flow from surface water to the underlying aquifer (Zone 3). In Zones 1 and 2, δ(15)NNO3 and δ(18)ONO3 suggest that NO3(-) from slightly volatilized ammonium synthetic fertilizers is only partially denitrified. The natural attenuation of NO3(-) can occur by heterotrophic reactions. However, autotrophic reactions cannot be ruled out. In Zone 3, the freshwater-saltwater interface (down to 12-16 m below the ground surface) is a reactive zone for NO3(-) attenuation. Tritium data suggest that the absence of NO3(-) in the deepest zones of the aquifer under the lake can be attributed to a regional groundwater flow with long residence time. In hypersaline lakes the geometry of the density-driven flow can play an important role in the transport of chemical species that can be related to denitrification processes.

Nitrates in drinking water and methemoglobin levels in pregnancy: a longitudinal study

BACKGROUND

Private water systems are more likely to have nitrate levels above the maximum contaminant level (MCL). Pregnant women are considered vulnerable to the effects of exposure to high levels of nitrates in drinking water due to their altered physiological states. The level of methemoglobin in the blood is the biomarker often used in research for assessing exposure to nitrates. The objective of this study was to assess methemoglobin levels and examine how various factors affected methemoglobin levels during pregnancy. We also examined whether differences in water use practices existed among pregnant women based on household drinking water source of private vs. public supply.

METHODS

A longitudinal study of 357 pregnant women was conducted. Longitudinal regression models were used to examine changes and predictors of the change in methemoglobin levels over the period of gestation.

RESULTS

Pregnant women showed a decrease in methemoglobin levels with increasing gestation although <1% had levels above the physiologic normal of 2% methemoglobin, regardless of the source of their drinking water. The multivariable analyses did not show a statistically significant association between methemoglobin levels and the estimated nitrate intake from tap water among pregnant women around 36 weeks gestation (β = 0.046, p = 0.986). Four women had tap water nitrate levels above the MCL of 10 mg/L. At enrollment, a greater proportion of women who reported using water treatment devices were private wells users (66%) compared to public system users (46%) (p < 0.0001). Also, a greater proportion of private well users (27%) compared to public system users (13%) were using devices capable of removing nitrate from water (p < 0.0001).

CONCLUSION

Pregnant women potentially exposed to nitrate levels primarily below the MCL for drinking water were unlikely to show methemoglobin levels above the physiologic normal. Water use practices such as the use of treatment devices to remove nitrates varied according to water source and should be considered in the assessment of exposure to nitrates in future studies.

Electric prompting and control of denitrification

The effectiveness of a denitrification process which is driven and controlled by an electric current is demonstrated. Denitrifying microorganisms were immobilized on a carbon electrode and hydrogen was produced through the electrolysis of water. The hydrogen was utilized for the reduction of nitrate to N(2). The denitrification rate was a linear function of the electric current, and it was shown that about 1 mol of electron reduces 0.2 mol of nitrate to N(2) gas. These results exhibit that the proposed process is simple and feasible, especially for the treatment of low-strength nitrate solutions.

Groundwater contamination by microbiological and chemical substances released from hospital wastewater: health risk assessment for drinking water consumers

Contamination of natural aquatic ecosystems by hospital wastewater is a major environmental and human health issue. Disinfectants, pharmaceuticals, radionuclides and solvents are widely used in hospitals for medical purposes and research. After application, some of these substances combine with hospital effluents and, in industrialised countries, reach the municipal sewer network. In certain developing countries, hospitals usually discharge their wastewater into septic tanks equipped with diffusion wells. The discharge of chemical compounds from hospital activities into the natural environment can lead to the pollution of water resources and risks for human health. The aim of this article is to present: (i) the steps of a procedure intended to evaluate risks to human health linked to hospital effluents discharged into a septic tank equipped with a diffusion well; and (ii) the results of its application on the effluents of a hospital in Port-au-Prince. The procedure is based on a scenario that describes the discharge of hospital effluents, via septic tanks, into a karstic formation where water resources are used for human consumption. COD, Chloroform, dichlomethane, dibromochloromethane, dichlorobromomethane and bromoform contents were measured. Furthermore, the presence of heavy metals (chrome, nickel and lead) and faecal coliforms were studied. Maximum concentrations were 700 NPP/100 ml for faecal coliforms and 112 mg/L for COD. A risk of infection of 10(-5) infection per year was calculated. Major chemical risks, particularly for children, relating to Pb(II), Cr(III), Cr(VI) and Ni(II) contained in the ground water were also characterised. Certain aspects of the scenario studied require improvement, especially those relating to the characterisation of drugs in groundwater and the detection of other microbiological indicators such as protozoa, enterococcus and viruses.

Drinking-water nitrate, methemoglobinemia, and global burden of disease: a discussion

On behalf of the World Health Organization (WHO), I have undertaken a series of literature-based investigations examining the global burden of disease related to a number of environmental risk factors associated with drinking water. In this article I outline the investigation of drinking-water nitrate concentration and methemoglobinemia. The exposure assessment was based on levels of nitrate in drinking water greater than the WHO guideline value of 50 mg/L. No exposure-response relationship, however, could be identified that related drinking-water nitrate level to methemoglobinemia. Indeed, although it has previously been accepted that consumption of drinking water high in nitrates causes methemoglobinemia in infants, it appears now that nitrate may be one of a number of co-factors that play a sometimes complex role in causing the disease. I conclude that, given the apparently low incidence of possible water-related methemoglobinemia, the complex nature of the role of nitrates, and that of individual behavior, it is currently inappropriate to attempt to link illness rates with drinking-water nitrate levels.

Contribution of environmental factors to cancer risk

Environmental carcinogens, in a strict sense, include outdoor and indoor air pollutants, as well as soil and drinking water contaminants. An increased risk of mesothelioma has consistently been detected among individuals experiencing residential exposure to asbestos, whereas results for lung cancer are less consistent. At least 14 good-quality studies have investigated lung cancer risk from outdoor air pollution based on measurement of specific agents. Their results tend to show an increased risk in the categories at highest exposure, with relative risks in the range 1.5-2.0, which is not attributable to confounders. Results for other cancers are sparse. A causal association has been established between exposure to environmental tobacco smoke and lung cancer, with a relative risk in the order of 1.2. Radon is another carcinogen present in indoor air which may be responsible for 1% of all lung cancers. In several Asian populations, an increased risk of lung cancer is present in women from indoor pollution from cooking and heating. There is strong evidence of an increased risk of bladder, skin and lung cancers following consumption of water with high arsenic contamination; results for other drinking water contaminants, including chlorination by-products, are inconclusive. A precise quantification of the burden of human cancer attributable to environmental exposure is problematic. However, despite the relatively small relative risks of cancer following exposure to environmental carcinogens, the number of cases that might be caused, assuming a causal relationship, is relatively large, as a result of the high prevalence of exposure.

The use of epidemiological concepts and techniques to discern factors associated with the nitrate concentration of well water on swine farms in the USA

This epidemiological study investigates the relationship between various factors associated with swine farms and the nitrate concentration of well water in the USA. Through a random sampling procedure, 605 swine farms located in 18 states were selected for inclusion in this study. A total of 631 well water samples were collected from these farms and tested for a variety of elements and compounds. The concentrations of nitrate, nitrite, sulfate, chloride, sodium, potassium, ammonia, fluoride, bromide and lithium were determined by an ion chromatograph while an inductively coupled argon plasma emission spectrophotometer was used to determine the concentrations of calcium, magnesium, barium, zinc, iron and phosphate. Data concerning various farm factors were gathered via a personally administered questionnaire. The data were examined using both multiple linear regression and logistic regression. Results indicate that 53.6% (338/631) of the wells contained detectable levels of nitrate, 11.7% (74/631) had nitrate levels exceeding 45 ppm and 4.3% (27/631) exceeded 100 ppm. Logistic models demonstrated an association between nitrate concentrations > 45 ppm, increasing water potassium levels and wells < 100 ft deep. Nitrate levels > 100 ppm were related to increasing water concentrations of potassium, magnesium, barium and zinc, wells 6-10 years old, increasing distance from the study farm to the nearest cattle farm and a greater distance to the nearest waterway located off the study farm. A negative association was seen between nitrate concentrations > 100 ppm, the water level of sulfate, and the use of the same well to supply both the household and livestock. Multiple linear regression models revealed a positive association between increasing nitrate concentration and the water levels of chloride, calcium, zinc and the greater number of miles from the study farm to the nearest farm with cattle or sheep. A negative association was noted between the concentration of well water nitrate and the water levels of sulfate and ammonia, the use of water treatment, the number of miles to the nearest farm with poultry, the employment of water treatment and the use of the same well to supply water to both livestock and the household.

Evaluation of the nitrate drinking water standard with reference to infant methemoglobinemia and potential reproductive toxicity

In view of published results of epidemiologic studies which suggested an association between nitrate in drinking water and human malformations, an assessment of the toxicology of nitrates and nitrites in relation to possible adverse effects on reproduction and development was performed. The current water standard for nitrate is based on protection from methemoglobinemia. A review of the animal data failed to provide evidence for teratogenic effects attributable to nitrate or nitrite ingestion. Adverse reproductive effects reported occurred at doses that were about one thousand times and higher than the estimated human intake. Neither nitrate nor nitrite in experimental animals concentrated in the mammary gland or milk. The present assessment concludes that the maximum contaminant level of 45 ppm nitrate ion, or 10 ppm nitrate-nitrogen, adequately protects the very young from nitrate-induced toxicity, both pre- and postnatally.

Nitrates, nitrites and gastric cancer in Great Britain

Nitrate and nitrite were measured in the saliva of two populations who differed in their risk of developing gastric cancer. Surprisingly, the levels of both ions were significantly higher in the low-risk group.

Epidemiological monitoring: methods for analysing routinely-collected data

Morbidity and mortality statistics are routinely collected in many countries. These data may be arranged in a number of ways, for example, classified by area of residence, or occupation of the person concerned, or by the time-period during which the relevant event occurred. Judicious use of such data enables disease to be monitored and may draw attention to the adverse effects of harmful agents in the environment. This paper describes the different methods of analysing data for such purposes, giving examples of their application and discussing their relative merits. Particular reference is made to the data-collecting systems in England and Wales and to the statistical aspects of monitoring disease.