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Drinking Water

Nitrates in drinking water

October 10, 2012
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Nitrate results can be produced in one of multiple units of measure. As an example, mg/L (milligram per Liter) or ppm (parts per million) are cross comparative units and can be interchanged. ppb (parts per billion) and µg/L (micrograms per Liter) are also cross comparative.

Nitrates are a common contaminant frequently found in drinking water. Nitrate itself is not carcinogenic, but instead acts as a "pro-carcinogen," meaning that it reacts with other chemicals in our bodies to form carcinogenic compounds. Nitrate contamination of drinking water can occur in areas where nitrogen fertilizers are used. Naturally occurring nitrate levels in decomposing plants and vegetation can increase nitrate concentrations in the groundwater when it rains as well. Nitrates can be found in both areas of new construction (where houses are built on land previously used for farming) and can also be found in older wells where trees have grown around the well and have produced years of foliage drop. Fallen leaves that have decomposed into the soil can carry natural nitrates into the groundwater after it has rained. Concentrations of nitrate in rainwater of up to 50,000 ppb (parts per billion) have been observed in industrial areas. The nitrate concentration in surface water is normally low (0-18,000 ppb), but can reach high levels as a result of agricultural and refuse runoff or contamination from humans or wastes from sewer systems. In rural areas, naturally occurring animal waste from local herds or wild life can also contribute to increased nitrate concentrations.

Many homeowners are concerned that increased use of lawn fertilizers to produce picture perfect yards may be adding unnecessary risks to their groundwater too. Fertilizer usage may be a contributor to decreased water quality, but studies to prove the theory of lawn care contributing to nitrates are incomplete.

Analyzing regulations for nitrates

Only a laboratory analyzed drinking water test can accurately verify the presence and concentration of nitrates in a water source. Assumptions should not be made based on tests conducted from nearby wells because neighboring homes may have varying levels of nitrates in their wells. Therefore, each private well will need to be tested individually to verify nitrate concentrations. Low cost field tests should be avoided when working with a (health-related) primary drinking water standard like nitrates. Public water testing is different and results should show a common level between homes because single or combined water supplies may be blended producing a single common result after public water treatment.

The Maximum Contaminant Level (MCL) established by the Environmental Protection Agency (EPA) for nitrates is 10,000 ppb, but is just that: A maximum. Each drinking water contaminant has an MCL (enforceable regulation) and a Maximum Contaminant Level Goal (MCLG), i.e. a non-enforceable health goal. Oddly enough, the MCLG for nitrates is the same as the MCL of 10,000 ppb. This peculiar and potentially worrying fact is unique to nitrates. Many other drinking water contaminants have a much higher MCL than the corresponding MCLG. The reason nitrates lack a standard/goal difference, is presumably that the EPA established its MCL and MCLG using criteria based on the laboratory industry's ability to accurately test nitrates below 10,000 ppb.

In addition, studies conducted in the 1950s that included a group of 278 babies were the only references used by the EPA to establish the MCL for nitrates. Since the Safe Drinking Water Act (1974) included regulation for nitrate in the form of an MCL and MCLG in 1992, laboratory technology has improved. Laboratories can consistently produce accurate results as low as 500 ppb with the use of new and improved analytical methods. A possible second reason the EPA has not set a lower MCLG may be based on economics and the burden of cost to public water suppliers to produce safer water with less nitrates.

Nitrates are converted in the body to toxic nitrites, which at high levels prevent oxygen from moving from the blood to the body. High nitrate levels have been proven to cause methemoglobinemia, or blue baby syndrome, at nitrate levels above 10,000 ppb. It was perhaps these findings that the EPA used to establish this MCL.

New discoveries about nitrates

Since 1992, multiple studies have been produced that have demonstrated new findings that need to be considered by the EPA in the future. The EPA has suffered criticism from many health groups (including other branches of government) for including no margin of safety in a MLCG, which is typically a 10-fold safety factor, in the nitrate MCL and for its oversight in the protection of the public health. Other countries have adopted more protective standards: In Denmark, the guidance level is 5.6 mg/L; in Germany and South Africa, nitrate standards are only 4.4 mg/L, which is less than half of the current EPA MCL.

The Safe Drinking Water Act requires the EPA to review the primary drinking water standards every six years. Since 1996, two review periods have occurred in which nitrates were considered "not appropriate for revision at this time." It should be noted that the World Health Organization (WHO) has (a seemingly more appropriate) as needed, rolling standards review.

More recently, researchers from the National Institute of Health studied 21,977 older women in Iowa who had used the same water supply for more than 10 years. Women exposed to similar levels of nitrate, whether they drank from a public water supply or a private well, were included. The study determined cancer incidence using the state health registry and estimated nitrate intake from public drinking water sources using a public database of nitrate measurements. Dietary intake was measured through questionnaires.

The results of this study showed a nearly three-fold increase in thyroid cancer risk for women with more than five years usage of a public water supply with nitrate levels of 5 mg/L (equivalent to 5,000 ppb) or above. This is less than half the maximum contaminant level of nitrate in drinking water set by the EPA.

Researchers suggested that nitrate inhibits the thyroid gland's ability to use iodine. Iodine is a necessary mineral for proper thyroid hormone and gland function. This is one of the first studies to show a link between nitrates and thyroid cancer in humans. Animal studies with exposure to nitrates have been shown to cause thyroid tumors. In the U.S. the incidence of thyroid cancer has increased steadily since 1980. Thyroid cancer is the eighth most common cancer among women.

Relationship between nitrate and goitre

In 1956, a study described an association between high nitrate concentrations in drinking water and goitre (abnormal enlargement of the thyroid gland) incidence. Between 1987 and 1994, five studies found that inorganic nitrate in drinking water is a manifested factor of endemic goitre. A dose-response relationship could be demonstrated by both the experimental and epidemiological studies, establishing the theory that nitrate in drinking water has a stronger effect on thyroid function than nitrate in food. The differences in nitrate kinetics after ingestion through drinking water and through food could be the cause of the difference in thyroid effects.

Using the standards as set by the EPA for nitrates in public water it can be assumed that any water, private or public, could be as high as 9,999 ppb and be considered legal, usable water. There are even bottled water brands with elevated nitrate levels close to the 10,000 ppb MCL. Read the label the next time you have a bottle of Italian water with red or green labels. You may be surprised when you find 8,500 ppb in that $6 bottle.

Dealing with the facts

The good news for our industry is we have reached a point of information sharing through the Internet that allows everyone to have access to the facts. Any health conscious homeowner can search online and see that studies have produced associated risk for bladder cancer, stomach cancer and thyroidism at lower doses than the current EPA MCL. The public isn't agreeable to accepting this risk. A concerned consumer only has a few choices to avoid consuming nitrates from their water. Buying bottled water with proven reduced nitrate concentration is one option.

Since consumers cannot control the public water supplies delivered to their homes, their only other choice is to additionally treat the water after it enters their home. Private well owners who do not wish to use bottled water have control of their own destiny and must deal with the overall chemistry of their water supply, including nitrates.

Today's more conservative consumers are concerned about the health and safety of their families and thus are willing and able to support lower exposure levels based on their personal desires. This means that any home, whether using public water or a private water supply, has the potential to need a treatment system to remove nitrates. Water safety for the kitchen should be considered to be of the utmost importance when drinking water contaminants (such as nitrates) can adversely affect occupant health by ingestion.

The water used in the kitchen is the water most likely consumed via drinking, but via cooking as well. When water is boiled for cooking, nitrates increase as the water volume is reduced through evaporation. The three pathways for contaminant exposure are inhalation, adsorption and ingestion; nitrates must be ingested to cause health problems. Ingestion would be not only from drinking the water, but also from foods that were boiled in the water, which could become contaminated.

There is no need to do laboratory testing of public water because this information can be found in the Consumer Confidentiality Statement (CCS) from the water supplier. These reports should have accurate statements of concentration for nitrates and other regulated contaminants in the water they supply. Assuming the public water supply is below 10,000 ppb. There are field-testing devices for nitrates that could be considered to verify the need for treatment if the CCS is not available. With a private well, a laboratory report assessing the water quality for nitrates and a list of other contaminants should be secured before treatment is installed since the levels could be elevated above the EPA MCL — if this is the case a point-of-entry treatment is required.

Treatment options

For public or private water where nitrate levels are lower than 5,000 ppb, a point-of-use (POU) treatment, such as an RO system, for cooking and drinking water should be considered. The value behind using POU RO versus point-of-entry (POE) in homes with moderate levels of nitrates, between 2,000 ppb and 5,000 ppb, is that the consumer will get an additional benefit as the RO will reduce most contaminants (arsenic V, barium, cadmium, chromium III, chromium VI, copper, cyst, fluoride, lead, nitrate, nitrite, radium 226/228, selenium and TDS), producing a higher overall quality of water.

For typically less than $1,000 installed (and connected to ice makers or chilled water systems) the RO is an outstanding value. An RO should be considered an excellent addition to any home's POU drinking water supply. Don't forget to suggest a supplemental calcite cartridge after the RO to balance the pH and hardness. This should avoid warranty issues from refrigerator manufacturers.

If the nitrate levels reach a concentration of 5,000 ppb, whole-house treatment could be recommended. Some homeowners may insist on whole-house POE treatment regardless of nitrate concentrations. This would produce nitrate-free water for use at all locations in the home.

When treating with POE it is important to understand that the conditioner must be an anion type softener with a nitrate select resin. The salt setting for 14,000 ppb of nitrates, if set at 8 lbs., would produce 5,500 gallons of treated water. This should supply the average household with two to three weeks of treated water.

After installation

As a guide, this regeneration cycle could be adjusted to cycle every three weeks. This will decrease salt brining frequency for lower concentrations of backwash discharge into groundwater. If the anion nitrate system is preceded by a typical cation water softener, in most cases a neutralizer must follow the systems. This is required as the household water is deionized by the combination of a cation/anion system creating corrosive water starved for hardness and pH.

If left without the neutralizer unit the corrosive water could compromise the copper plumbing, creating obvious staining and possibly additional health concerns from dissolved copper or lead; an exception would be a water supply with unusually high hardness. Hardness and/or langelier index should be measured after treatment to verify the necessity of the neutralizer in those cases.

It is always recommended to have a laboratory evaluation of treated water after equipment installation or service. This laboratory test, proving the effectiveness of your services, not only makes you more professional, it reduces risk in verifying your commitment of safer water to your customers. The continued recommendation that the equipment be serviced and retested every year is also a good point for the safety of your clients.

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