Number 121 August 1997
MAFF UK - 1996/97 UK MONITORING PROGRAMME FOR NITRATE IN LETTUCE AND
SPINACH
Index to MAFF UK Food Surveillance Information
Sheets, 1997
See also:
91: MAFF UK -
Nitrate in vegetables (July 1996)
137:
MAFF UK - 1994 Total Diet Study - Nitrate and Nitrite (December 1997)
142: MAFF UK - Survey of Nitrite and
Nitrate in Bacon and Cured Meat Products (February 1998)
154: MAFF UK - 1997/98 UK Monitoring
Programme for Nitrate in Lettuce and Spinach (August 1998)
158: MAFF UK - Nitrate in Vegetables
(September 1998)
163: MAFF UK -
1997 Total Diet Study: Nitrate and Nitrite. (October 1998)
165: MAFF UK - Duplicate Diet Study of
Vegetarians-Nitrate Analyses (November 1998)
177: MAFF UK - Nitrate in Lettuce and
Spinach (May 1999)
Summary
The results of the 1996/97 UK Monitoring Programme for Nitrate in Lettuce
and Spinach are reported. Samples of glasshouse-grown lettuce, outdoor lettuce
and spinach were taken from six UK regions (i.e. Lancashire, Humberside, East
Anglia, South East, South West and Northern Ireland) by Trading Standards
Officers and analysed for nitrate by Public Analysts' laboratories. Most
samples contained nitrate concentrations below the maximum levels specified by
European Commission Regulation (EC) No 194/97. However, five of the 130 samples
of glasshouse-grown lettuce, two of the 86 samples of outdoor grown lettuce, two
of the 13 samples of fresh spinach and one sample of the 22 samples of processed
spinach exceeded these maximum levels. These results have been submitted to the
European Commission and will be used as part a future review of the Regulation.
Background
The 1996/97 UK Monitoring Programme for Nitrate in Lettuce and Spinach was
undertaken to obtain data on nitrate concentrations in UK crops and also to
assist in the design and implementation of the monitoring programme anticipated
to be required by European Commission Regulation (EC) No 194/97.1 This Regulation sets maximum levels for nitrate in
lettuce and spinach and has applied in the UK and other Member States since 15
February 1997 (Table 1). The Statutory Instrument (The
Contaminants in Food Regulations 1997 (S.I. [1997] No. 1499)) which
implements the Commission Regulation in the UK came into force on 4 July 1997.2 Data on nitrate levels in lettuce and spinach
obtained from Monitoring Programmes carried out in each Member State will be
used as part of the review of the Commission Regulation which will take place
before October 1998.1
Derogation
The UK is applying an optional derogation which allows lettuce and spinach
grown and sold in the UK to be exempt from the maximum levels specified by the
Commission Regulation. This is provided that nitrate concentrations in these
foods are acceptable from the point of view of public health and growers follow
the relevant Code of Good Agricultural Practice for the production of outdoor
lettuce, glasshouse-grown lettuce, and spinach.1
UK Monitoring Programme
The UK Monitoring Programme was carried out on behalf of MAFF by various
Local Authorities and was co-ordinated by Norfolk Trading Standards Department.
Samples were taken to be both representative of UK production of lettuce and
spinach and to obtain information on any regional differences in nitrate
concentrations. Samples were taken from growers by Local Authority enforcement
officers (Trading Standards Officers) in accordance with Council Directive
89/397/EEC on the official control of foodstuffs.3
Three types of produce were sampled: glasshouse-grown lettuce, outdoor
lettuce and spinach (fresh, frozen and canned). Samples were taken from six
regions of the UK: South East (i.e. Surrey and Sussex), Humberside (i.e.
Derbyshire and Lincolnshire), East Anglia (i.e. Norfolk, Essex and
Cambridgeshire), Lancashire (i.e. Lancashire, Powys and Durham), South West
(i.e. Wiltshire and Somerset) and Northern Ireland. No samples were taken from
Scotland as little lettuce and spinach is grown in there. Samples of
glasshouse-grown lettuce were taken throughout the year from June 1996 to March
1997, samples of outdoor lettuce from May to October 1996 and samples of fresh
spinach from July to December 1996.
Methods
Samples of lettuces and spinach were prepared and analysed in accordance
with the then draft European Commission document VI/4800/96 'Guidelines for
laboratories carrying out the determination of nitrate in lettuce and spinach:
EC monitoring programme.'4 These guidelines do
not specify particular analytical methods, but set criteria for analytical
performance (including recovery, reproducibility and repeatability) that should
be met by all methods used.
Samples were analysed by Public Analysts' laboratories. These laboratories
met the assessment criteria set out in Article 3 of Council Directive 93/99/EEC
relating to official food laboratories5 and
participated in and achieved satisfactory performances in the nitrate rounds of
the Food Analysis Performance Assessment Scheme (FAPAS).
Results
Glasshouse-grown Lettuce
A total of 130 samples of glasshouse-grown lettuces were taken from
Lancashire, Humberside, East Anglia, South East, South West and Northern
Ireland. The results of the analyses of these samples are summarised in
Table 2. Nitrate concentrations in glasshouse
lettuces were higher during the winter months (i.e. October to March), with a
mean level of 3066 mg/kg, than in the summer months (i.e. April to September),
when the mean nitrate level was 2237 mg/kg (Table 3).
Five of the 94 samples of winter-grown glasshouse lettuces exceeded the maximum
level (Table 2 and Table 3).
Nitrate levels varied between seasons. This effect was observed for each
region and for the UK as a whole. The mean nitrate concentrations detected for
glasshouse lettuces grown in all UK regions for each month between June 1996 and
March 1997 are summarised in Table 3. Nitrate
concentrations were greatest in glasshouse lettuces harvested in December,
January and February and lowest during July and August. These periods
correspond to seasons with low and high light levels, respectively. A similar
trend was observed in a previous MAFF survey of nitrate in retail samples of
lettuce.6 In addition, the only samples which
exceeded maximum levels were harvested in the months of December, January and
February.
There were no statistically significant differences between nitrate
concentrations in glasshouse lettuces grown in Lancashire, Humberside, East
Anglia, South East or South West regions. However, nitrate concentrations were
significantly lower in glasshouse lettuces from Northern Ireland (i.e. mean
concentration of 1881 mg/kg) than those from other UK regions (i.e. mean
concentration of 2883 mg/kg). This may be explained by the low number of
samples (i.e. six) taken from this region (Table 4).
Outdoor Lettuce
A total of 86 samples of outdoor lettuces were taken from Lancashire,
Humberside, East Anglia, South East, South West and Northern Ireland. The
results of the analyses of these samples are summarised in
Table 5. Two of the 40 samples obtained
between May and August exceeded the maximum level.
There was no observed seasonal trend in nitrate concentrations over the
growing period from May to October or any evidence of significant regional
differences in nitrate concentrations in outdoor lettuces.
The only significant difference in nitrate concentrations in outdoor
lettuces was between varieties. Iceberg lettuces were found to contain lower
nitrate concentrations than all other varieties (Table 6).
Spinach
Seventeen samples of UK-produced fresh, 13 samples of frozen and 9 samples
of canned spinach were taken and analysed for nitrate. Fresh spinach samples
were obtained from the South East and East Anglia. The results of these
analyses are summarised in Table 7. Two of the
13 samples of summer grown, fresh spinach exceeded the maximum level of 2500
mg/kg. No samples of winter grown spinach exceeded the maximum level of 3000
mg/kg. No regional or seasonal differences were observed for fresh spinach.
Frozen spinach samples were obtained from East Anglia and canned spinach
samples from East Anglia and Humberside. The results of nitrate analyses of
these samples are summarised in Table 8. One of the
13 samples of frozen spinach exceeded the maximum level.
Interpretation
Light appeared to be the main factor determining nitrate concentrations in
UK glasshouse-grown lettuces with a close inverse relationship observed between
hours of daylight and nitrate concentrations. Nitrate concentrations were
therefore higher in the winter months compared with glasshouse lettuces grown
during the summer (Table 3).
No regional or seasonal variations were observed for outdoor grown lettuces
or spinach (Tables 5, Table
6 and Table 7). However, this may be
partly explained by the shorter growing seasons of these crops and because
spinach samples were obtained from only two regions.
Nitrate levels in outdoor grown lettuces appeared to vary according to
variety. Iceberg lettuces tended to have lower nitrate concentrations than
other varieties (Table 6). This may be explained in
part by the practice of removing the outer leaves of these lettuces at harvest.
This effect was not observed in glasshouse-grown lettuces where similar
varieties are grown all year round.
The optional derogation from the Regulation which the UK is applying allows
lettuce and spinach grown and sold in the UK to be exempt from the maximum
levels, provided that their nitrate content is not so high as to present a risk
to health. Even those samples which contained nitrate at the highest
concentrations found in the 1996/97 Monitoring Programme would not cause an
average consumer to exceed the Acceptable Daily Intake (ADI) for nitrate, set by
the European Commission Scientific Committee for Food.7
Furthermore, the mean nitrate levels found in the 1996/97 Monitoring Programme
would not cause even high-level (97.5th percentile) consumers of lettuce or of
spinach to exceed the ADI.
Monitoring of UK-grown lettuce and spinach is continuing. The 1997/98 UK
Monitoring Programme for Lettuce and Spinach began in May 1997. The results
from the 1997/98 Monitoring Programme will be compared with those from the
1996/97 Monitoring Programme to determine the effectiveness of the Codes of Good
Agricultural Practice which growers have been implementing since March 1997.
Results of the 1997/98 Monitoring Programme will also be submitted to the
Commission to inform the review of the Regulation.
References
- European Commission (1997). Commission Regulation (EC)
No 194/97 of 31 January 1997. Official Journal of the European Communities No.
L 31/48.
- The Contaminants in Food Regulations 1997 (S.I.
[1997] No. 1499). HMSO.
- Council of the European Communities (1989). Council
Directive 89/397/EEC of 14 June 1989 on the official control of foodstuffs.
Official Journal of the European Communities No L 186/23.
- European Commission (1997). Guidelines for
Laboratories Carrying Out The Determination of Nitrate in Lettuce and Spinach:
EC Monitoring Programme. Document VI/4800/96
- Council of the European Communities (1993). Council
Directive 93/99/EEC of 29 October 1993 on the subject of additional measures
concerning the official control of foodstuffs. Official Journal of the European
Communities No L 290/14.
- Ministry of Agriculture, Fisheries and Food (1996).
Nitrate in Vegetables. Food Surveillance Information Sheet 91.
- Commission of the European Communities Scientific
Committee for Food (1995). Opinion on Nitrate and Nitrite, expressed on 22
September 1995. Annex 4 to Document III/5611/95
Contact Point
Further information can be obtained from:
Dr Gillian Ysart
MAFF, Food Contaminants Division
Room 238
Ergon
House, c/o Nobel House
17 Smith Square
London, SW1P 3JR.
Tel: +44 (0) 171 238 6756
Fax: +44 (0) 171 238 5331
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