Nitrates and Nitrites | Water & Food Testing

Q: Why are nitrates and nitrites regulated in drinking water?

The primary source of nitrate in drinking water is agricultural fertilisation — both synthetic nitrogen fertilisers and organic manures. Nitrate is highly soluble and mobile in soil; excess nitrate applied to farmland leaches through the soil profile into groundwater and is transported to surface water via runoff. Groundwater in intensive farming areas often has high and rising nitrate concentrations. Other sources include septic system effluent and natural geological deposits. The EU Nitrates Directive (91/676/EEC) was specifically enacted to address agricultural nitrate pollution of water bodies.

Q: What are the EU limits for nitrates and nitrites?

Plants absorb nitrate from soil as their primary nitrogen source for growth. Leafy vegetables — particularly spinach, lettuce, rocket, and celery — naturally accumulate nitrate in their tissues. The amount depends on: soil nitrate availability (influenced by fertilisation), plant species and variety, light intensity during growth (more light reduces nitrate accumulation as it drives nitrate assimilation into amino acids), and growing season. Winter-grown protected vegetables typically have higher nitrate content than summer outdoor crops, which is why EU regulation (EC) No 1881/2006 sets different limits for winter and summer harvests.

Q: How are nitrates and nitrites measured?

The health impact of dietary nitrate is nuanced. While excessive nitrate exposure (particularly as nitrite) can cause methaemoglobinaemia in vulnerable individuals and nitrosamines (carcinogens) from reactions with food amines, moderate dietary nitrate from vegetables may have beneficial cardiovascular effects through the nitrate-nitrite-nitric oxide pathway. EFSA and WHO have established an Acceptable Daily Intake (ADI) for nitrate of 3.7 mg/kg body weight per day (as nitrate ion). The primary concern is exposure via nitrate-contaminated water and from nitrite preservatives in processed meats, where nitrosamine formation risk is highest.

Q: What is the health risk from nitrates in food?

The most accurate and selective method for water analysis is ion chromatography (EN ISO 10304-1:2009), which simultaneously separates and quantifies nitrate, nitrite, and other anions in a single analysis. For routine monitoring, spectrophotometric methods using the Griess reaction (colorimetric measurement at ~543 nm after diazotisation) are widely used, often in automated flow injection systems (EN ISO 13395:1996). UV-Vis spectrophotometry at 220/275 nm provides rapid screening for nitrate in relatively clean water matrices. All methods require calibration with certified reference standards and uncertainty estimation in accredited laboratories.

Q: What are the main sources of nitrate contamination?

The EU Commission reduced permitted nitrite and nitrate levels as food additives in cured meats (under Regulation (EC) No 1333/2008) in 2023 to minimise consumer exposure to carcinogenic N-nitrosamines. Nitrite (used as E249/E250 for curing, colour preservation, and inhibition of Clostridium botulinum) reacts with secondary amines from meat protein under acidic conditions (cooking, stomach acid) to form N-nitrosamines, which IARC classifies as probable carcinogens (Group 2A). The new lower limits balance the food safety benefit of nitrite (anti-botulinal activity) against the nitrosamine formation risk, while also encouraging the development of alternative preservation technologies.

Nitrates (NO₃⁻) and nitrites (NO₂⁻) are inorganic nitrogen compounds that occur naturally in the environment and also enter the food chain through soil fertilisation, agricultural runoff, food preservation, and natural metabolic processes in plants. While small amounts of dietary nitrate are naturally present in vegetables and can have beneficial physiological effects, excessive exposure from water and food — particularly to nitrite — poses recognised health risks.

Key health concerns:

Methaemoglobinaemia (‘blue baby syndrome’): Nitrite (formed from nitrate by gut bacteria) reduces the oxygen-carrying capacity of haemoglobin. Infants under 3 months are particularly vulnerable due to foetal haemoglobin and low gut acidity.
Nitrosamines: Nitrite reacts with amines (from protein digestion) to form N-nitrosamines, some of which are carcinogenic. This reaction is particularly relevant for cured meat products preserved with nitrite additives.
Nitrate and nitrite testing is part of Ovalab’s water quality testing service and food analysis capabilities.

Analytical Methods

Nitrate and nitrite are determined by several validated analytical methods depending on the matrix (water, food) and concentration range:

Ion chromatography (IC — EN ISO 10304-1:2009): The preferred method for water analysis. Simultaneous determination of multiple anions (nitrate, nitrite, sulfate, chloride, fluoride, phosphate) in a single injection. Provides excellent selectivity and low detection limits (typically <0.1 mg/L). High throughput for environmental monitoring programmes.
Flow injection analysis / segmented flow analysis (EN ISO 13395:1996): Automated colorimetric methods for water analysis. Nitrite is determined directly by the Griess reaction (diazotisation with sulfanilamide and coupling with N-(1-naphthyl)ethylenediamine); nitrate is first reduced to nitrite by a cadmium reduction column, then determined the same way.
UV-Vis spectrophotometry (UV-Vis): Nitrate absorbs strongly at 220 nm and weakly at 275 nm; the 275 nm reading corrects for organic matter interference. Nitrite is determined by colorimetric Griess reaction at 543 nm. Both are fast, low-cost methods for routine water analysis.
ICP-OES (ICP-OES): Can determine total nitrogen in complex matrices; not typically the first-choice method for nitrate/nitrite but used when multi-element panels are required simultaneously.
Food matrices: For solid food samples, aqueous extraction is performed before analysis. Ion chromatography is the reference method under EU Regulation (EC) No 333/2007 for official control of nitrate in vegetables.

EU Regulatory Limits

Nitrate and nitrite limits are established across multiple EU regulatory frameworks:

Drinking water (Directive (EU) 2020/2184, Annex I, Part B):
— Nitrate: ≤50 mg/L as NO₃⁻ (parametric value)
— Nitrite: ≤0.5 mg/L as NO₂⁻ (parametric value); additionally ≤0.1 mg/L at the treatment plant exit
— Additional constraint: [NO₃⁻/50] + [NO₂⁻/3] ≤ 1 (combined exposure calculation)
Food contaminants — vegetables (Regulation (EC) No 1881/2006, as amended by Regulation (EU) No 1258/2011): Maximum levels for nitrate in fresh spinach, lettuce, and other leafy vegetables, with higher limits for winter harvest (lower light → higher nitrate accumulation). Example: fresh spinach 3,500 mg/kg (winter); fresh lettuce (protected) 4,000 mg/kg (winter).
Food additives — cured meat (Regulation (EC) No 1333/2008): Nitrite (E249, E250) and nitrate (E251, E252) are permitted preservatives in cured meats (bacon, ham, salami). EU Commission significantly reduced permitted levels in 2023 to minimise nitrosamine formation risk. Maximum added amounts vary by product category.
Nitrates Directive (91/676/EEC): Controls agricultural nitrate pollution of water bodies, requiring Member States to designate nitrate vulnerable zones (NVZs) and implement action programmes to limit nitrate runoff from farming.

Frequently Asked Questions

Why are nitrates and nitrites regulated in drinking water?

The primary source of nitrate in drinking water is agricultural fertilisation — both synthetic nitrogen fertilisers and organic manures. Nitrate is highly soluble and mobile in soil; excess nitrate applied to farmland leaches through the soil profile into groundwater and is transported to surface water via runoff. Groundwater in intensive farming areas often has high and rising nitrate concentrations. Other sources include septic system effluent and natural geological deposits. The EU Nitrates Directive (91/676/EEC) was specifically enacted to address agricultural nitrate pollution of water bodies.

What are the EU limits for nitrates and nitrites?

Plants absorb nitrate from soil as their primary nitrogen source for growth. Leafy vegetables — particularly spinach, lettuce, rocket, and celery — naturally accumulate nitrate in their tissues. The amount depends on: soil nitrate availability (influenced by fertilisation), plant species and variety, light intensity during growth (more light reduces nitrate accumulation as it drives nitrate assimilation into amino acids), and growing season. Winter-grown protected vegetables typically have higher nitrate content than summer outdoor crops, which is why EU regulation (EC) No 1881/2006 sets different limits for winter and summer harvests.

How are nitrates and nitrites measured?

The health impact of dietary nitrate is nuanced. While excessive nitrate exposure (particularly as nitrite) can cause methaemoglobinaemia in vulnerable individuals and nitrosamines (carcinogens) from reactions with food amines, moderate dietary nitrate from vegetables may have beneficial cardiovascular effects through the nitrate-nitrite-nitric oxide pathway. EFSA and WHO have established an Acceptable Daily Intake (ADI) for nitrate of 3.7 mg/kg body weight per day (as nitrate ion). The primary concern is exposure via nitrate-contaminated water and from nitrite preservatives in processed meats, where nitrosamine formation risk is highest.

What is the health risk from nitrates in food?

The most accurate and selective method for water analysis is ion chromatography (EN ISO 10304-1:2009), which simultaneously separates and quantifies nitrate, nitrite, and other anions in a single analysis. For routine monitoring, spectrophotometric methods using the Griess reaction (colorimetric measurement at ~543 nm after diazotisation) are widely used, often in automated flow injection systems (EN ISO 13395:1996). UV-Vis spectrophotometry at 220/275 nm provides rapid screening for nitrate in relatively clean water matrices. All methods require calibration with certified reference standards and uncertainty estimation in accredited laboratories.

What are the main sources of nitrate contamination?

The EU Commission reduced permitted nitrite and nitrate levels as food additives in cured meats (under Regulation (EC) No 1333/2008) in 2023 to minimise consumer exposure to carcinogenic N-nitrosamines. Nitrite (used as E249/E250 for curing, colour preservation, and inhibition of Clostridium botulinum) reacts with secondary amines from meat protein under acidic conditions (cooking, stomach acid) to form N-nitrosamines, which IARC classifies as probable carcinogens (Group 2A). The new lower limits balance the food safety benefit of nitrite (anti-botulinal activity) against the nitrosamine formation risk, while also encouraging the development of alternative preservation technologies.