C03030: Sampling for Nitrate in Lettuce and Spinach

Study Duration: 01 January 2003 to 31 July 2005

Contractor: ADAS

Nitrate is present in all vegetables naturally and also arises from the use of nitrogen fertilisers on crops. Vegetables, particularly green, leafy vegetables such as lettuce and spinach, contain the highest concentrations of nitrate and are a major source of nitrate in the diet. Although there are claims in the literature for deleterious effects of nitrate on consumer health, there are other studies that claim beneficial effects, especially when the nitrate is ingested as a component of vegetable matter rather than as an inorganic salt.

Since 1996, every Member State in the EU has been required to monitor and report on levels of nitrate in lettuce and spinach as part of a European Commission regulation which sets maximum levels. However, there is a high degree of variation in the results obtained by such sampling and while seasonal variation in crops and analytical methodology contribute to this variation, the sampling method used may also be a factor.

This project aims to investigate the potential sources of sampling variability for the analysis of nitrate in lettuce and spinach, and devise a recommended nitrate sampling plan for lettuce and spinach based on the results.

The conclusions for this project will be used to inform discussion on the European Commission Sampling Directive for nitrate in lettuce and spinach.

Field experiments will be used to examine the effect of plant variety, short-term fluctuations in light levels and time of day of harvest on the levels of nitrate in lettuce and spinach.
The number of plants sampled, the mass of plants sampled and the sampling pattern will also be investigated to determine the optimum sampling plan for nitrate surveillance.

This project aimed to investigate the potential sources of sampling variability for the analysis of nitrate in lettuce and spinach, and devise a recommended nitrate-sampling plan for lettuce and spinach based on the results.

Field experiments found plant variety to be a significant factor, suggesting surveillance results from different varieties in the same field should be treated as separate samples. Short-term fluctuations in light level (shading 24-48 hours before harvest) had little effect on nitrate levels compared with the large difference known to occur following dull periods 10-14 days before harvest. Although time of day of harvest appeared to influence nitrate levels, no significant trend could be determined. The report recommended that samples comprise a minimum of ten plants and a minimum weight of one kilogram, and that sampling should be carried out in a W or X pattern.

The conclusions of this project will be used to inform discussions on the European Commission Sampling Directive for nitrate in lettuce and spinach. This Directive will support the forthcoming amendment to the nitrate Regulation (563/2002), which amends Regulation 466/2001 setting maximum levels for certain contaminants in foodstuffs. This regulation will extend the derogation period (exemption from the limits on nitrate levels in lettuce and spinach) for the UK.

Although UK growers of lettuce and spinach apply a Code of Good Agricultural Practice, it has been found that produce may still fail to meet the limits for nitrates because of poor light conditions, such as those observed in the UK in winter or during cloudy spells in summer. However, based on levels reported in a survey of nitrate in lettuce and spinach sampled in 2004 (see link below), nitrate levels for UK consumers of lettuce and spinach would not cause even high-level consumers to exceed the Acceptable Daily Intake (ADI) set by the Scientific Committee for Food (SCF), justifying the UK�s use of the derogation. The maximum levels will still apply to lettuce and spinach imported into the UK from Member States and third countries.

Although the amended nitrate regulation will be directly applicable in the UK, it must be executed and enforced by a Statutory Instrument (SI). Owing to the tight timeframe for its implementation, it is intended to add this regulation to the SI currently being drafted that will update the Contaminants in Food Regulations of 2004, as amended.

The final report is available from the Agency's Information Centre. To obtain a copy, please contact the Enquiry Desk, Information Services, Food Standards Agency (tel: 020 7276 8181/8182 or email: infocentre@foodstandards.gsi.gov.uk

Contact: For any enquiries concerning this research project, please contact the relevant programme contact or email: science@foodstandards.gsi.gov.uk