Manganese (Mn) in Drinking Water

by Dr. Yasir

Background

Manganese (Mn) is among the most abundant elements on Earth that occur in the form of various rock minerals, in soil depending on the geological composition of the region, in water, particularly the groundwater sources, and in dissolved form as Mn²⁺ ions or as colloids, in sediments and biological systems. In drinking water, its occurrence is mainly dependent on regional geology and proximity to Mn-containing rocks and minerals. Mn gets enriched in drinking water systems through natural and anthropogenic sources. Some notable sources of its enrichment include geological formation, leaching and runoff processes, industrial activities, municipal distribution, and water treatment systems. In general, the drinking water Mn concentration may range from very low to high. The World Health Organization (WHO) has set a permissible limit of 0.4 mg/L in drinking water. However, it is important to mention that based on regional variability, various states, and regions have set their regulatory limits for Mn in drinking water.

Water with elevated Mn levels has a brown-to-black appearance making it aesthetically unfair for drinking purposes. Mn possesses high biological significance to the human body due to its essential role in many metabolic reactions due to reason, its low concentrations detected in drinking water do not pose any serious health concerns to humans therefore considered unharmful. However, health concerns arise when the Mn is taken in high concentrations and for a long period of time which may result in some serious health problems. For example, various studies have reported neurological effects among children and infants exposed to high Mn levels resulting in developmental delays, cognitive impairments, and motor coordination problems. However, the exact threshold levels for Mn have not been set so far due to individual variability to disease susceptibility and demands extensive scientific research and debate. As mentioned, the Mn levels detected in drinking water are not a general cause of concern. However, regular monitoring of public and private wells for Mn can ensure its safe supply to the consumers as well as may help in establishing threshold biological limits of toxicity to humans. In addition to neurological effects, some other health implications have also been associated with elevated Mn intake.

These include cardiovascular, respiratory, and reproductive disorders. However, the evidence in this regard is very weak, and particularly in the context of drinking water exposure and associated health effects, no epidemiological study has been reported so far to address the health issues. In the US, Mn can be present in drinking water sources, especially in regions with geological formations and industrial activities. The USEPA has established a secondary maximum contaminant level (SMCL) of 0.05 mg/L or 50 parts per billion (ppb) for Mn in drinking water to address the aesthetic issues associated with Mn including discoloration and taste. However, these guidelines may vary among states as different states have set their local MCL for Mn based on its occurrence in drinking water. Furthermore, Mn also shows chemical synergies with other metals especially Fe due to the reason it is recommended the concentration of both Fe and Mn must not exceed 500 µg/L in drinking water. Although, the contaminant levels in drinking water are well communicated with the consumers by local drinking water suppliers to ensure the safe supply, however, if a consumer has any concerns related to Mn levels in their drinking water, they are recommended to contact local authorities and get their water tested. If elevated levels are detected, water must be treated through recommended drinking water treatment options and ensure that the Mn levels are lowered before the water is supplied to the consumers.

Scientific Aspects

Scientific evidence suggests various cellular and molecular mechanisms associated with Mn that are involved in toxic effects among humans when taken in excessive amounts. Some key mechanisms through which Mn causes toxicity in biological systems include i. generation of reactive oxygen species (ROS) causing oxidative stress which may result in mitochondrial dysfunction as well as cellular damage due to lipids, proteins, and DNA. These associated processes lead to oxidative stress and cellular dysfunctioning (Erikson et al. 2004; Farina et al. 2013; Li and Yang 2018). The mitochondrial dysfunction due to Mn accumulation in mitochondria can result in decreased ATP production in cells and affect the overall energy balance and metabolism (Malecki 2001; Warren et al. 2020). ii. Mn has also been reported to cause disruption in glutamate regulation which is an essential neurotransmitter in the brain causing damage to neurons and is responsible for various neurological disorders (Fitsanakis et al. 2006; Karki et al. 2013). iii. Excessive Mn exposure for long periods of time can also cause neuroinflammation by triggering inflammatory responses in the brain. This results in the release of pro-inflammatory cytokines and chemokines resulting in neuronal damage and neurotoxicity (Kirkley et al. 2017). Dopamine is an essential neurotransmitter involved in reward and movement control.

The dopamine synthesis in the brain gets altered under excessive Mn levels and is associated with Mn-induced parkinsonism (Prabhakaran et al. 2008; Tran et al. 2002). Recent findings also demonstrate that Mn may induce toxicity in humans through epigenetic mechanisms. These changes are associated with altered gene expression without altering the DNA sequences. Such effects are reported to be long-lasting and have the potential to be transferred from parents to offspring (Lindner et al. 2022; Tarale et al. 2016). Furthermore, microRNAs (miRNAs) are single-stranded, non-coding molecules involved in the regulation of gene expression. In vitro, findings suggest that the regulation of these molecules may get altered under excessive Mn levels in cells and hence affecting the protein synthesis process (Budinger et al. 2021; Harischandra et al. 2018; Tarale et al. 2018). Several processes are involved in the metabolism of Mn when entered the body. These metabolic processes involve the absorption of Mn in small intestines. This is followed by the distribution of absorbed Mn by binding to transferrin, an iron-transport protein which helps in transportation of Mn throughout the body. Furthermore, Mn also possesses affinity for basal ganglia region of the brain.

Following distribution, Mn get metabolized mainly in liver where it gets converted to various chemical complexes (Mn-oxalate, Mn-phosphate). Excess Mn is than excreted out from the body after being filtered from kidneys and excreted in the form of urine. An estimated half-life of Mn in humans is suggested between 15-20 days. Various factors determine the Mn metabolism including age, genetics, gender, nutritional status, exposure duration, and concentrations present in drinking water. Furthermore, more epidemiological research focusing on cross-sectional and case-control studies is required to demonstrate the extent of Mn toxicity associated with drinking water consumption. While Mn is an essential human nutrient, its excessive exposure has been linked to occupational and environmental sources. However, its levels detected in drinking water are usually not a serious public health concern but demand regular monitoring of public water supply systems to ensure Mn-free drinking water supply to the consumers.

Detection Methods and removal Strategies

Mn can be quantified in drinking water using various methods depending on desired results, sensitivity, technical support, and availability of suitable instruments to analyze the water sample. The methods range from simple field tests to professional water testing labs. Some commonly used methods to analyze drinking water Mn include simple and cost-effective colorimetric test kits for on-site measurements. These kits involve the addition of a reagent to a water sample that results in a color change proportional to Mn concentration in drinking water (Hatat-Fraile and Barbeau 2019). Electrochemical methods are also commonly used for the detection of Mn in a sample. The method is based on the application of a voltage to an electrode and the current response is proportional to the Mn concentration which can be used for quantitative analysis (Boselli et al. 2021; Crapnell and Banks 2022). For more sensitive and accurate detection of Mn, Atomic Absorption Spectrometry (AAS) is the most commonly used technique capable of quantifying Mn at ppb levels with high precision and accuracy. This method involves the measurement of light absorption by Mn atoms in a water sample (Rahman et al. 2021; Sharma and Tyagi 2013). Inductively Coupled Plasma (ICP) coupled with optical emission (OES) or a mass spectrometer (MS) is also a widely used analytical technique for Mn quantification and is capable of detecting Mn in drinking water at parts per billion (ppb) and (ppt) levels (Boselli et al. 2021; Rahman et al. 2015). However, the limitation of the technique includes its high operating costs and is recommended for analysis where highly precise results are desired.

Elevated Mn levels found in drinking water can be reduced by using various techniques depending on Mn concentration, available resources, and overall water chemistry. Some known approaches include i) oxidation and filtration which involves the conversion of soluble Mn²⁺ ions into insoluble MnO₂using chemical oxidants followed by filtration to remove Mn particles (Cheng et al. 2020; Tobiason et al. 2016). ii) coagulation and filtration involve the use of coagulants such as aluminum sulfate (alum) or Fe salts that coagulate Mn in drinking water which is then filtered using a suitable filtration system (McBeath et al. 2021). iii) ion exchange resins also work effectively to remove the dissolved Mn in drinking water in which the Mn ions are captured on a resin bed and removed from the water (Patil et al. 2016). iv) biological filtration involves the use of certain bacteria capable of oxidizing dissolved Mn in the water and is effective in removing low to moderate Mn levels in drinking water (Tobiason et al. 2016). The most widely used method for Mn removal includes reverse osmosis (RO) due to its wide applicability to remove a range of environmental contaminants from drinking water (Livinalli et al. 2023). However, the limitation of this method includes its expensive filters cost that needs to be replaced after intervals.

Public Perspective

Following frequently asked questions (FAQs) try to address some general public concerns in the US related to Mn in drinking water, especially in the NYC and NJ region.

What is Manganese, and why is it present in drinking water?

Mn is a naturally occurring metal found in rocks, soil, and water. It can enter drinking water sources through the dissolution of manganese-containing minerals in the environment as well as through human activities such as industries and water treatment processes.

Is Manganese in drinking water harmful to human health?

High Mn levels in drinking water are associated with human health risks. Its chronic exposure to elevated levels has been linked with neurological effects, especially among infants and children.

What are the signs of high Manganese levels in drinking water?

High Mn levels may cause discoloration, giving the water a brownish or blackish appearance. It can also affect the taste and odor of the water, causing a metallic or bitter taste and an unpleasant odor.

Can Manganese in drinking water cause stains or discoloration?

Yes, elevated manganese levels can cause staining on fixtures, plumbing, and laundry. The stains are typically brown or black in color.

How can I test the Manganese levels in my drinking water?

Water testing laboratories can analyze samples of your drinking water for Mn levels. You can contact local health departments or EPA certified water testing labs for assistance.

What are the acceptable Manganese levels in drinking water according to regulations?

In the United States, the EPA has established a non-enforceable secondary maximum contaminant level (SMCL) of 0.05 mg/L (50 ppb) for Mn in drinking water to address aesthetic concerns.

How can I remove Manganese from my drinking water?

Mn can be effectively removed from drinking water using methods such as oxidation and filtration, coagulation and filtration, ion exchange, or reverse osmosis. The choice depends on the specific water quality and treatment requirements.

Are there any health risks associated with using water with high Manganese levels for cooking or other household purposes?

The health risks from using water with high Mn levels for household purposes are generally low. However, it is advisable to consider alternative sources for drinking and cooking if Mn levels exceed the recommended limits.

Can water treatment plants remove Manganese from drinking water?

Yes, water treatment plants can employ various techniques, such as oxidation, filtration, and chemical treatment, to remove Mn from drinking water.

Does boiling water remove Manganese?

Boiling water does not effectively remove Mn. Mn is a dissolved contaminant, and boiling only eliminates microbes and volatile substances.

How often should I test my drinking water for Manganese?

The frequency of testing for Mn in drinking water depends on various factors, including the initial Mn levels, changes in water source, and local regulations. It is advisable to consult with local health authorities or water testing experts for specific recommendations.

Conclusion

Mn is a widely distributed element and has biological significance in humans due to its role in various metabolic reactions. Its levels in drinking water are generally found under safe limits. However, high levels of Mn exposure for longer periods of time is associated with health issues mainly neurological disorders among infants and children. There are few epidemiological studies conducted in this context to address Mn toxicity among exposed children and neonates. USEPA has set SMCL for Mn in drinking water to address aesthetic concerns. Regular monitoring of drinking water in the US is warranted to keep its levels under safe limits. If elevated levels are detected in a water sample, suitable drinking water treatment is recommended before its supply to the consumers. There is a need for systematic studies conducted in various studies focusing on human-exposed subjects through drinking water to address the detailed overview of the extent of Mn toxicity in the US.

References

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Dr. Rehman was born in Rawalpindi, Pakistan. He completed his MSc from PMAS – Arid Agriculture University Rawalpindi in 2011 where his thesis comprised a health risk assessment of subjects living in the vicinity of wastewater channels in urban settings and its relationship with the incidence of Malaria.

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