Wageningen Academic
P u b l i s h e r s
World Mycotoxin Journal, May 2010; 3 (2): 157-168
Number of export almond lots rejected in the EU due to USA sampling plans and
aflatoxin contamination levels among lots tested
T. Whitaker1, A. Slate1, J. Adams2 and T. Birmingham2
!N.C.
State University, Biological and Agricultural Engineering Department, Box 7625, Raleigh, NC 27695-7625, USA;
Board of California, 1150 9th Street, Suite 1500, Modesto, CA 95354, USA; [email protected]
2Almond
Received: 2 March 2010 / Accepted: 26 April 2010
© 2010 Wageningen Academic Publishers
Abstract
In March 2010, the European Union (EU) modified their aflatoxin limits and sampling plans for almonds, pistachios,
and hazelnuts to closely resemble that developed by Codex in 2008. To assist the USA almond industry evaluate how
to modify their aflatoxin sampling plan to minimise USA lots rejected by the EU at import, studies were conducted to:
(a) develop a model to predict the number of USA almond lots rejected at origin and at destination by various Codex
style aflatoxin-sampling plans used by the USA where accept/reject limits vary from EU limits of 8 ng/g aflatoxin
Bj / 10 ng/g total aflatoxins (AFT) to 8, 6, 4, 2, and 0.5 ng/g AFT; (b) determine the effect of the level of aflatoxin
contamination among lots tested in the USA on the number of lots accepted and rejected at origin and at destination;
and (c) develop a method based upon lots rejected in the USA to predict the lots rejected several months later in
the EU. For a given USA crop contamination level, as the accept/reject limits of the USA sampling plan decreases
from 8 to 0.5 ng/g AFT, the number of lots rejected in the USA increases, the average aflatoxin concentration among
all lots accepted for export decreases, the number of lots rejected in the EU decreases, and the average aflatoxin
concentration among lots accepted in the EU decreases. For a given USA aflatoxin sampling plan used at origin, an
increase in the USA crop aflatoxin contamination level increases the number of lots rejected at origin, increases the
average aflatoxin concentration in USA lots accepted for export, increases the number of lots rejected in the EU, and
increases the average aflatoxin concentration among lots accepted in the EU. Graphical techniques were developed
to use the percentage of lots rejected in the USA to predict the percentage of USA lots rejected by the EU.
Keywords: aflatoxin, almonds, treenuts, maximum levels, Codex, export sampling plans
1. Introduction
Because aflatoxin is considered toxic and carcinogenic,
about 100 countries have established maximum levels or
regulatory limits for aflatoxin in food and feed products
(FAO, 2003). Maximum levels for aflatoxin not only vary
in magnitude, but vary with the type of aflatoxin being
controlled. Maximum limits can be based upon aflatoxin
Bj (AFBj), total aflatoxins (AFT = AFBj + AFB2 + AFGj
+ AFG2), or a combination of AFBt and AFT. When a
regulatory agency establishes regulatory limits for aflatoxin,
there is a ripple effect throughout the export market that
affects both the importer at destination and the exporter
at origin. The exporter usually samples bulk lots at origin
to ascertain if each lot's aflatoxin concentration is below
the importing country's regulatory limit. If the exporter's
sample test results indicate the lot is above the importing
country's regulatory limit, the lot will not be shipped to
the importer. The importer (or import control authorities)
will sample imported lots at destination to ascertain if
the aflatoxin concentration of the imported lot is below
the importing country's regulatory limit. If the importer's
sample test results indicate that the aflatoxin level in the
lot is above the regulatory limit, the lot is diverted from
the food chain by the importer, and subjected to additional
measures. It is possible that the imported product is shipped
back to the exporter or re-processed at destination using
proven sorting techniques to reduce contamination levels;
ISSN 1875-0710 print, ISSN 1875-0796 online, DO/ 10.3920/WMJ2010.1209
157
IVWiMeretal.
in extreme situations, the imported product could be
destroyed at destination. Lots that fail to test below the
regulatory limit at destination pose an economic burden
to both the exporter and the importer. The exporter must
pay the costs associated with the alternatives mentioned
above and the importer suffers from problems associated
with a loss in the consistency of supply.
Because there is variability associated with the sampling,
sample preparation, and analytical steps of the aflatoxin
test procedure (Whitaker et al., 2006), it is not possible
to determine the true aflatoxin level in a lot with 100%
certainty by measuring the aflatoxin concentration in
samples taken from the lot. As a result, some lots will be
misclassified by both the exporter and importer when using
sample test results to determine if the true lot aflatoxin
concentration is above or below a defined regulatory
limit. Two risks are associated with any sampling plan
design: (a) there is a chance that some good lots (lots with
aflatoxin levels below a regulatory limit) will be rejected
by the sampling plan (false positive) and (b) there is a
chance that some bad lots (lots with aflatoxin levels above
a regulatory limit) will be accepted by the sampling plan
(false negative). For sampling plans conducted at origin
by the USA exporter, a false positive (good lot rejected)
can be called the exporter's risk and a false negative
(bad lot accepted) can be called the importer's risk. As a
consequence of the random variation associated with the
aflatoxin test procedure (sampling, sample preparation, and
analysis), sampling product at origin doesn't guarantee that
all lots will be accepted by the importer when re-sampled
and tested for aflatoxin at destination (Whitaker et al.,
2006). It is inevitable that some lots tested at destination
will still be rejected even if the exporter and importer are
conducting their aflatoxin sampling programs according to
standard protocols and without mistakes. Unfortunately,
these rejections are sometimes incorrectly perceived as
a failure of the aflatoxin sampling program rather than
the result of random variability associated with sampling,
sample preparation, and analysis.
According to 2008 industry statistics (Almond Board of
California, 2009), USA almond growers produce over 80%
of the world's almond production. Of the total USA almond
production, approximately 70% went into the export market.
Western Europe is the largest importer of USA almonds
receiving 46% of the total USA export shipments. This
constitutes almost 11,000 lots exported to the EU during the
2008-2009 crop year (Note: a crop year spans two calendar
years, beginning August 1, 2008 approximately from the
beginning of harvest, through July 31,2009). Each export
lot destined for the EU is sampled and tested for aflatoxin
at origin to ascertain if the lot aflatoxin concentration will
comply with the EU ready-to-eat (RTE) limits of 2 ng/g
AFBj and 4 ng/g AFT.
158
In early 2010, the European Commission (EC) adopted
legislation changing their aflatoxin regulatory limits (EC,
2010a) and sampling plans (EC, 2010b) for treenuts to more
closely conform to that developed by the Codex Committee
on Contaminants in Foods (CCCF) and adopted by the
Codex Alimentarius Commission (CAC) in July 2008
(CCCF, 2008). The Codex aflatoxin sampling plan for RTE
treenuts (almonds, pistachios, and hazelnuts) requires that
two 10 kg samples both test less than 10 ng/g AFT (2x 10 kg
< 10 ng/g AFT) to accept the lot. The EU adopted the Codex
plan, but added an AFB1 limit of 8 ng/g. As a result, an RTE
almond lot requires two 10 kg samples to each test less than
both limits (8 ng/g AFBt and 10 ng/g AFT) for the lot to
be accepted into the food chain. For consistency, the USA
almond industry decided to modify their aflatoxin sampling
plan at origin in order to ascertain if lots exported to the EU
will meet the new EU aflatoxin regulatory limits of 8 ng/g
AFBj and 10 ng/g AFT for RTE almonds.
To assist the USA almond industry in the design of a new
aflatoxin sampling plan that would meet or exceed the
performance of the EU sampling plan and minimise lots
rejected by the EU at destination, a study was developed
with the following objectives: (a) develop a spreadsheet
model to predict the number of USA almond lots accepted
and rejected both at origin in the USA and at destination
in the EU by various Codex-style (2x10 kg) aflatoxinsampling plan designs used by the USA almond industry; (b)
determine the effect of the level of aflatoxin contamination
among all lots tested in the USA during a crop year on
the number of lots accepted and rejected at origin and at
destination; and (c) develop a method that uses sample test
results from the USA sampling program that USA almond
exporters can use in 'real-time' to predict the percentage of
lots that will be rejected several months later at destination
in the EU.
The study results can further provide exporters, importers,
and regulatory authorities with a better understanding
of how sampling plan designs and crop contamination
levels influence the number of lots rejected at origin and
at destination when both the exporter and the importer
are using standard sampling, sample preparation, and
analytical protocols to identify and reduce the number of
contaminated lots in the export market.
2. Methods
A flow chart describing the spreadsheet model that
simulates the aflatoxin testing of RTE almond lots in the
USA and in the EU during a given crop year is shown in
Figure 1. The simulation model not only computes the total
number of lots accepted and rejected at origin in the USA
and at destination in the EU during a given crop year, but
keeps track of the distribution among lots according to
their aflatoxin concentration that are tested, accepted, and
World Mycotoxin Journal 3 (2)
Almond lots accepted and rejected in the export market
Aflatoxin distribution among lots tested at origin
FLReu(C). Equations developed for the spreadsheet model
are given below.
The number of USA lots accepted by the USA sampling
plan at a given aflatoxin concentration C:
B
USA aflatoxin sampling plan
) = TLusFLus(C)PAas(C)
Lots rejected at origin
(1)
for C = 0,1,2,.... max. ng/g AFT.
Lots accepted for export to EU
The number of lots rejected by the USA sampling plan at
a given aflatoxin concentration C:
EU aflatoxin sampling plan
= TLUSFLUS(C)PRUS(C)
Lots rejected at destination
Lots accepted at destination
Figure 1. Flow diagram of spreadsheet model showing the
lots tested, accepted, and rejected in the USA (origin) and in
the EU (destination).
for C = 0,1, 2,..., max. ng/g AFT.
Total number of lots accepted in a crop year by the USA
sampling plan and exported to the EU:
Omax
(3)
c=o
Total number of lots rejected in a crop year by the USA
sampling plan and diverted from export:
rejected in the USA and in the EU. From the lot distribution
information, the amount of aflatoxin removed from or
remaining in the export market can also be computed.
The simulation starts with a known aflatoxin distribution
among USA lots in a given crop year, FLUS(C), which
is the fraction of total lots, TLus, at a given aflatoxin
concentration, C, (called the USA lot distribution). Each
lot is sampled and tested for aflatoxin at origin in the USA
during a given crop year. There is a chance that a given lot
in the USA lot distribution with aflatoxin concentration C
will be accepted with probability PA^C) or rejected with
probability PR^C) = (1 - PA,,, (C)) by the USA sampling
plan. The accept and reject probabilities are unique for the
design of the aflatoxin sampling plan (sample size, etc.),
regulatory limit, and the lot aflatoxin concentration C. As
a result, the USA lot distribution, FLUS(C), is partitioned
into a USA accepted lot distribution, FL\(C), and a USA
rejected lot distribution, FLRUS(C).
(2)
C=max
C=0
The number of lots accepted at destination by the EU
sampling plan at a given aflatoxin concentration C:
LAeu(Q=TLAusFLAus(C)PAeu(C)
(5)
for C=0,1, 2,..., max ng/g AFT.
The number of lots rejected at destination by the EU
sampling plan at a given aflatoxin concentration C:
LReu(C) = TLAUS FLAUS(C) PReu(C)
(6)
for C=0,1,2,..., max ng/g AFT.
Total number of lots accepted in a crop year by the EU
sampling plan at destination in the EU:
C=max
The distribution of lots accepted in the USA, FLA^C), is
exported to the EU (called the USA export lot distribution).
Once the USA export lot distribution arrives at destination
in the EU, all or a portion of the export lot distribution
is sampled and tested for aflatoxin by EU authorities.
Each lot in the USA export lot distribution, FLA^C),
will be accepted with probability PAeu(C) or rejected with
probability PReu(C) = (1 - PAeu (C)) by the EU sampling
plan. As a result, the USA export lot distribution is
partitioned by the EU sampling plan into an EU accepted lot
distribution, FLAeu(Q, and an EU rejected lot distribution,
World Mycotoxin Journal 3 (2)
TLAeu
= ZLAeu(Q
c=o
(7)
Total number of lots rejected in a crop year by the EU
sampling plan at destination in the EU:
C=max
c=o
The average aflatoxin concentration among lots tested,
accepted, and rejected in a crop year after each testing point
in the USA and in the EU can be calculated from the above
equations. The average aflatoxin concentration among all
lots before testing in the USA (ATL^) is:
159
I Whitaker Q[a\.
C=max
= £(FLUS(C)C)
c=o
(9)
The average aflatoxin concentration among all USA lots
accepted (ALAJ and rejected (ALRUS) in the USA for
export to the EU are:
C=max
(10)
00
C=max
C=0
(11)
The average aflatoxin concentration among all USA lots
exported to the EU and tested for aflatoxin in the EU is
also described by Equation 10.
The following information is needed for the development
of the spreadsheet model shown in Figure 1: (a) USA lot
distribution to be tested at origin (Box A), (b) the accept
and reject probabilities associated with a specific USA
aflatoxin sampling plan design used at origin (Box B), and
(c) the accept and reject probabilities associated with the
EU aflatoxin sampling plan design used at destination (Box
E). Once the information in Boxes A, B and E are known,
the remaining information in Boxes C, D, F and G can
be computed using Equations 1 to 11. Development of
information for the spreadsheet model (Boxes A, B and E)
is discussed below.
Aflatoxin distribution among USA lots to be tested for
export
The desire was to find at least four USA lot distributions
where the average aflatoxin concentration among all lots in
each crop (called the crop contamination level) varied from
some low value to some high value to demonstrate the effect
of crop contamination level on the number of lots accepted
and rejected at origin in the USA and at destination in
the EU. The California almond industry began testing all
export lots destined for the EU using USDA-approved
laboratories in September 2007. By the summer of 2009,
lots from three crop years, 2006,2007, and 2008 had been
sampled and tested for aflatoxin. As mentioned earlier,
a crop year spans two calendar years. Because sampling
started in late summer of 2007, most of the 2006 crop had
been marketed and only the remaining 1,519 lots from the
2006 crop were sampled and tested for aflatoxin prior to
export to the EU. The entire 2007 crop of 15,021 lots was
sampled and as of December 2009 a total of 11,078 lots of
the 2008 crop have been sampled and tested for aflatoxin
prior to export to the EU.
For a given crop year, the sample test results from the USA
almond industry sampling program (called Voluntary
Aflatoxin Sampling Plan or VASP by the California almond
industry) were used to estimate the USA lot distribution
160
identified for export to the EU. Three 5 kg laboratory
samples are taken from each lot destined for the EU and
tested for aflatoxin. The average of the three sample test
results was assumed to equal the lot aflatoxin concentration
in total aflatoxins. Therefore, the USA lot distribution was
assumed to equal the distribution among the averages of
the three sample test results for each lot. Table 1 shows the
number of lots sampled by crop year, the average AFT level
among all lots tested in each crop year, variance among all
lot concentrations, and the percentage of lots testing zero
AFT or non-detect.
From Table 1, it can be seen that the aflatoxin contamination
in the 2006 crop was higher than the aflatoxin contamination
in the 2007 and 2008 crops (based upon the average aflatoxin
concentration among all lots tested). To get a range in crop
contamination levels, it was decided to use the 2008 (0.42
ng/g AFT) and 2006 (1.26 ng/g AFT) sample averages to
construct two USA lot distributions. It was also decided to
construct two additional hypothetical USA lot distributions
where the average aflatoxin concentrations were at least two
times and four times the average aflatoxin concentration
of the 2006 lot distribution or 3.0 and 6.0 ng/g AFT. The
two hypothetical lot distributions were generated using the
compound gamma distribution (Giesbrecht and Whitaker,
1998; Whitaker et al,, 1996) where the parameters for the
compound gamma distribution were determined from the
mean and variance among lot aflatoxin concentrations
shown in Table 1. The compound gamma distribution was
chosen to generate the hypothetical lot distributions after
several skewed distributions such as the negative binomial
and lognormal distributions were investigated (Giesbrecht
and Whitaker, 1998; Whitaker et al, 1996).
Using four USA lot distributions with a wide range in
aflatoxin concentration (0.42 to 6.0 ng/g AFT) should
provide a reasonable demonstration of the effect of aflatoxin
Table 1. Number of lots tested before shipment to the European
Union, average aflatoxin concentration among all lots tested,
and the percent lots that tested zero (non-detect) aflatoxin for
the 2006,2007 and 2008 almond crops produced in the USA.
Crop
year
Number Average
Variance
of lots
aflatoxin
among lot
sampled concentration concentrations
(ng/gAFTp
Lots at zero
aflatoxin
concentration
(%)
2006
1,519
1.26
64.8
77.0
2007
15,021
0.47
21.5
90.4
20081
11,078
0.42
22.8
91.3
1 Lots from the 2008 crap year
are still being marketed.
2 Average aflatoxin concentration (total ng/g
AFT) among all lots
sampled for export.
World Mycotoxin Journal 3 (2)
Almond lots accepted and rejected in the export market
contamination in the USA lot distribution on lots accepted
and rejected at origin in the USA and at destination in the
EU. The four USA lot distributions, calculated with the
compound gamma distribution, are shown as cumulative
distributions in Figure 2. The USA lot distribution
information is used in Box A in Figure 1.
Accept and reject probabilities of USA and EU aflatoxin
sampling plans for RTE shelled almonds
Since the EU developed a sampling plan similar to the
Codex plan (two 10 kg laboratory samples taken from a lot
must each test less than 10 ng/g AFT (2x10 kg < 10 ng/g
AFT) for the lot to be accepted), but added a AFBj accept/
reject limit of 8 ng/g for RTE almonds (2x10 kg <, 8 ng/g
AFB1 / 10 ng/g AFT), a single EU aflatoxin sampling plan
design was evaluated in the spreadsheet model for use
at destination (2x10 kg < 8 ng/g AFBj / 10 ng/g AFT).
A Monte Carlo method was developed (Whitaker et
al., 2010) to predict the accept and reject probabilities
associated with the EU sampling plan using dual limits.
A plot of the accept probability, PAeu(C), associated with
the EU sampling plan versus lot concentration C (called an
operating characteristic or OC curve) is shown in Figure 3.
The accept probabilities associated with the EU sampling
plan are used in Box E (Figure 1).
The design of the Codex sampling plan for treenuts
influenced the 2010 EU aflatoxin sampling plan design
that in turn influences the aflatoxin sampling plan designs
considered by the USA almond industry to test USA lots
exported to the EU. Because the EU has decided to use a
AFBj accept/reject limit of 8 ng/g in addition to the 10 ng/g
AFT for RTE almonds, it was decided to evaluate five USA
aflatoxin sampling plans similar to the Codex plan where
two 10 kg samples must each test less than a single accept/
reject limit of 8, 6, 4, 2, and 0.5 ng/g AFT. A sixth USA
sampling plan design that was identical to the EU sampling
plan design with these dual limits was also evaluated. The
accept and reject probabilities for the five USA sampling
plan designs with single limits were computed using the
method used by CCCF to design harmonised aflatoxin
sampling plans for almonds, pistachios, and hazelnuts
(CCCF, 2008). The CCCF method of computing accept and
reject probabilities for almonds was based upon variance
and distribution data among sample test results published
by Whitaker et al. (2006). The six OC curves shown in
Figure 3 describe the accept and reject probabilities
associated with the six USA aflatoxin-sampling plan designs
considered for use by the USA almond industry at origin.
The accept and reject probabilities associated with each of
the six USA sampling plans are used in Box B in Figure 1.
aflatoxin concentration
2006 crop avg. aflatoxin concentration
.26 ng/g AFT
Hypothetical avg afla oxin concentration • 3.00 ng/g AFT
Hypothetical avg afla oxin concentration 6.00 ng/g AFT
o
50 >
i | . i . ,
|
. |
i i |
i i i | . ,i
Lot aflatoxin concentration (ng/g AFT)
Figure 2. Four USA almond lot distributions, according to the average aflatoxin crop contamination level among all lots, that are
tested prior to shipment to the European Union.
World Mycotoxin Journal 3 (2)
161
T.Whitakere\a\.
OC curves for VASP sampling plans
Shelled almonds
Laboratory sample size shown
Dry grind, 50 g test portion
Analysis, 1 aliquot, 22% reproducibility RSD
Maximum level shown (ng/g)
2x10kg<0.5T
0 I ' ' ' ' I ' ' ' '
10
15
20
25
Lot aflatoxin concentration (ng/g AFT)
Figure 3. Operating characteristic (OC) curves describing the probability of accepting almond lots by sampling plans used in the
USA and in the European Union. All sampling plans are a modification of the Codex aflatoxin sampling plan for treenuts where
two 10 kg samples must each test less than the accept/reject limit shown.
Export market assumptions for model development
Several basic assumptions had to be made about sampling
plans and export market conditions before simulations
were conducted:
a. Because the number of USA lots tested and accepted by
a USA sampling plan for export to the EU will vary from
one crop year to another, it was decided to make the total
number of USA lots tested in a crop year (TL^) vary with
crop contamination levels and sampling plan designs
such that 11,000 lots were always accepted (TLAUS) for
export to the EU in all 24 simulations (six USA sampling
plan designs by four crop contamination levels).
b. When USA lots are imported into the EU, the almond
industry estimates that approximately 5% of the imported
lots are sampled by EU authorities under random control
(EC, 2007). For each of the 24 simulations, three rates
of EU inspection were evaluated (2, 5, and 10%) for the
11,000 USA export lots sampled at destination in the
EU. It is assumed that the aflatoxin distribution among
the lots identified by the EU for testing at import is the
same as the aflatoxin distribution among the 11,000 lots
imported into the EU.
c. No biases or mistakes are associated with the sample
selection, sample preparation, or analytical methods
used by USA and EU authorities to test bulk lots for
aflatoxin.
Since the number of lots tested in the USA may vary
with crop year, and the number of USA lots tested in the
EU can vary due to regulatory decisions, the number of
lots accepted and rejected in the USA and in the EU was
converted to percentage of lots tested in the USA and in the
EU. The percentages can be converted back into number
of lots accepted and rejected in the USA and in the EU
once the actual number of lots tested in the USA and in
the EU is known.
3. Results and discussion
A total of 24 spreadsheet simulations (six USA sampling
plan designs times four USA crop contamination levels)
were run to solve for the number (percentage) of lots
accepted and rejected in the USA and in the EU and the
average aflatoxin concentration among lots accepted and
rejected in the USA and in the EU. Because of the size
and complexity of the output of a spreadsheet simulation
(approximately 10 columns by 70 rows), only a summary of
each of the 24 simulation results is shown in Tables 2 and 3.
These two tables contain the same simulation results, but
World Mycotoxln Journal 3 (2)
550 lots (m
Table 2. Effect of four different crop contamination levels and six differentLots
USA
sampling
rejected
2% plan designs on the number of lots accepted and rejected in the USA and in the European Union.
The number of lots accepted and rejected at destination in the EU is computed220
forlots
2,5,
(ntand 10% sampling rate with the new 2010 EU sampling plan (2x10 kg < 8 ng/g AFB^IO ng/g AFT).
Results sorted first by crop contamination level.
Crop avg.
USA sampling plan
USA (11 ,000 lots exported)
EU (11,000 lots imported), sampling plan: 2x10 kg & 8 ng/g AFB1 / 10 ng/g AFT
auaioxm ceinc.
(ng/g AFT)1
j
|
Average afla. o
rejects (ng/
"3
1
•3.
0.42
1.26
3.00
6.00
0.42
1.26
3.00
6.00
0.42
1.26
3.00
6.00
0.42
1.26
3.00
6.00
0.42
1.26
3.00
6.00
0.42
1.26
3.00
6.00
1 Average total
USA export 2x10 £ 8 AFB,/10AR
USA export 2x10 £ 8 AF^/10 AFT
USA export 2x10 £ 8 AFB,/10 AFT
USA export 2x 1 0 £ 8 AFB/1 0 AFT
USA export 2x10 £8 AFT
USA export 2x10 £8 AFT
USA export 2x10 £8 AFT
USA export 2x10 £8 AFT
USA export 2x10 £6 AFT
USA export 2x10 £6 AFT
USA export 2x10 £6 AFT
USA export 2x10 £6 AFT
USA export 2x10 £ 4 AR
USA export 2x10 £ 4 AR
USA export 2x10 £4 AFT
USA export 2x10 £4 AFT
USA export 2x10 £ 2 AR
USA export 2x10 £2 AFT
USA export 2x10 £ 2 AR
USA export 2x10 £2 AFT
USA export 2x10 £0.5 AFT
USA export 2x10 £0.5 AFT
USA export 2x10 £0.5 AFT
USA export 2x10 £0.5 AFT
11,149
11,446
12,024
12,942
11,153
11,461
12,061
13,012
11,178
11,529
12,203
13,254
11,225
11,644
12,417
13,598
11,374
11,935
12,854
14,206
11,983
12,943
14,029
15,498
!
149
446
1,024
1,942
153
461
1,061
2,012
178
529
1,203
2,254
225
644
1,417
2,598
374
935
1,854
3,206
983
1,943
3,029
4,498
J
1
Average afla. o
accepts (ng/
1.36
4.06
9.31
17.66
1.39
4.19
9.64
18.29
1.62
4.81
10.93
20.49
2.05
5.85
12.88
23.61
3.40
8.50
16.86
29.15
8.94
17.67
27.54
40.89
10
||
C3 5'
23.37
23,82
25.30
27.49
23.16
23.47
24.86
26.98
20.80
21.32
22.80
24.96
17.18
18,35
20.20
22.51
10.90
13.32
16.21
19.05
4.42
6.79
10.43
14.17
1
3
ta
0
11
0.15
0.38
0.77
1.44
0.15
0.36
0.73
1.35
0.13
0.32
0.63
1.17
0.12
0.27
0.52
0.95
0.10
0.21
0.39
0.69
0.08
0.16
0.25
0.41
3
0.51
1.54
3.56
6.94
0.48
1.46
3.38
6.59
0.42
1.26
2.92
5.74
0.34
1.03
2.38
4.71
0.24
0.73
1.69
3.37
0.13
0.40
0.91
1.85
I
I
1.1
3.4
7.8
15.3
1.1
3.2
7.4
14.5
0.9
2.8
6.4
12.6
0.7
2.3
5.2
10.4
0.5
1.6
3.7
7.4
0.3
0.9
2.0
4.1
I
I
2.8
8.5
19.6
38.2
2.7
8.0
18.6
36.3
2.3
6.9
16.1
31.6
1.9
5.6
13.1
25.9
1,3
4.0
9.3
18.5
0.7
2.2
5.0
10.2
o
2* •o
Tj
.3. §• P
5.6
16.9
39.2
76.4
5.3
16.1
37.2
72.5
4.6
13.9
32.2
63.1
3.7
11.3
26.2
51.8
2.7
8.0
18.5
37.1
1.5
4.4
10.1
20.3
•Z? 5"
0.11
0.25
0.46
0.81
0.11
0.24
0.44
0.78
0.10
0.22
0.41
0.71
0.09
0.20
0.36
0.61
0.08
0.18
0.29
0.49
0.07
0.14
0.22
0.34
~3 3'
8.59
8.89
9.34
9.95
8.19
8.49
8.93
9.51
7.43
7.74
8.16
8.70
6.50
6.83
7.23
7.72
5.21
5.57
5.95
6.38
3.41
3.81
4.18
4.54
CL
s-
53"
I
-i
CD"
3"
3s
CD
I
a
i
aflatoxin concentration: 2008 Crop - 0.42 ng/g AFT; 2006 Crop -1.26 ng/g AFT; hypothetical crops - 3.00 and 6.00 ng/g AFT.
CD
550 lots (nu
Lots rejected 2% I
220 tots (nu
The number of lots accepted and rejected at destination in the EU is computed for 2,5, and 10% sampling rate with the new 2010 EU sampling plan (2x10 kg 5 8 ng/g AFB.,/10 ng/g AFT).
Results sorted first by sampling plan design.
Crop avg.
USA sampling plan
USA (11,000 lots exported)
aflatoxin cone.
Average afla. cc
EU (11,000 lots imported), sampling plan: 2x10 kg £ 8 ng/g AFB1 / 10 ng/g AFT
rejects (ng/s
(ng/gAFT)'
|
i
t
i
a
0.42
0.42
0.42
0.42
0.42
0.42
1.26
1.26
1.26
1.26
1.26
1.26
3.00
3.00
3.00
3.00
3,00
3.00
6.00
6.00
6.00
6.00
6.00
6.00
Average afla. cc
accepts (ng/j
WM
3
9.64
1,061
12,061
9.31
1,024
12,024
17.67
1,943
0.21
8.50
0.27
5.85
149
153
178
225
374
983
446
461
529
644
935
11,149
11,461
USA export 2x10 5 8 AFT
11,983
11,446
USA export 2x10 5 0.5 AFT
USA export 2x10 £ 8 AFB^IO.SAFT
11,374
USA export 2x10 5 2AFT
11,225
USA export 2x10 54 AFT
11,178
USA export 2x10s6 AFT
11,153
USA export 2x10 s 8 AFB,/10 AFT
USA export 2x10 S 8 AFT
13,598
USA export 2x10 s 4 AFT
13,012
13,254
USA export 2x10 5 8 AFT
USA export 2x10 56 AFT
12,942
USA export 2x10 s 8 AFB^IO.S AFT
12,854
14,029
USA export 2x1052AFT
USA export 2x10 50.5 AFT
12,417
USA export 2x10 s 4 AFT
12,203
USA export 2x10 5 6 AFT
USA export 2x10 s 8 AFB.,/10.5 AFT
USA export 2x1058AFT
12,943
USA export 2x10sO,5 AFT
11,529
11,644
11,935
USA export 2x10 5 4 AFT
USA export 2x10 5 2 AFT
0.15
1.39
0.15
1.36
1.62
2.05
3.40
11
0.08
8.94
10.90
0.10
16.86
1,854
a
0.51
23.37
4.42
23.82
4.19
27.54
3,029
18.29
20.49
23.61
29.15
40.89
3
0.48
23.16
20.80
0.13
Lots
rejected (nu 17.18
0.12
23.47
0.36
0.38
4.06
4.81
17.66
1,942
2,012
2,254
2,598
3,206
4,498
—J
fe p
•3 3'
10.93
1,203
14,206
USA export 2x10 56 AFT
t
12.88
1,417
15,498
USA export 2x10 5 0.5 AFT
USA export 2x10 52 AFT
0.42
0.34
0.24
0.13
1.54
1.26
21.32
0.32
1.46
18.35
13.32
0.16
6.79
25.30
0.77
0.73
0.63
0.52
1.03
0.73
0.40
3.38
24.86
16.21
0.39
26.98
24.96
1.17
27.49
1.44
1.35
3.56
2.92
22.80
20.20
10.43
0.25
22.51
0.95
14.17
0.41
19.05
0.69
2.38
1.69
0.91
6.94
6.59
5.74
4.71
3.37
1.85
!!
1.1
1.1
0.9
0.7
0.5
0.3
3.4
3.2
2.8
2.3
1.6
0.9
7.8
7.4
6.4
5.2
3.7
2.0
15.3
14.5
12.6
10.4
7.4
4.1
^-
~ ET
PL f&
o S
§?
I
I
2.8
2.7
2.3
1.9
1.3
0.7
8.5
8.0
6.9
5.6
4.0
2.2
19.6
18.6
-3 3
5.6
5.3
4.6
3.7
2.7
1.5
16.9
16.1
13.9
11.3
8.0
4.4
39.2
37.2
26.2
13.1
32.2
16.1
76.4
38.2
10.1
9.3
5.0
36.3
31.6
18.5
72.5
63.1
37.1
18.5
51.8
25.9
10.2
20.3
0.11
0.11
0.10
0.09
0.08
0.07
0.25
0.24
0.22
0.20
0.18
0.14
0.46
0.44
0.41
0.36
0.29
0.22
0.81
0.78
0.71
0.61
0.49
0.34
It
8.59
8.19
7.43
6.50
5.21
3.41
8.89
8.49
7.74
6.83
5.57
3.81
9.34
8.93
8.16
7,23
5.95
4.18
9,95
9.51
8.70
7.72
6.38
4.54
' Average total atetoxin concentration: 2008 Crop - 0,42 ng/g AFT; 2006 Crop -1.26 ng/g AFT; hypothetical crops - 3.00 and 6.00 ng/g AFT.
Almond lots accepted and rejected in the export market
Table 2 results are sorted first by crop contamination level
and then by sampling plan design and Table 3 simulation
results are sorted first by sampling plan design and then
by crop contamination level. The entire spreadsheet
output for each of the 24 simulations can be obtained
upon request using the email address of one of the authors
([email protected]).
The first simulation in Table 2 is used as an example to
describe simulation results when the USA almond industry
uses a sampling plan identical to the EU aflatoxin sampling
plan design (2x10 kg < 8 ng/g AFBj / 10 ng/g AFT) to test
a USA crop that averages 0.42 ng/g AFT. The USA must
sample 11,149 lots in order to accept 11,000 lots for export
to the EU. The USA sampling plan removed 149 lots (1.36%)
from the export market and reduced the average aflatoxin
concentration from 0.42 ng/g AFT among all lots tested to
0.15 ng/g AFT among the 11,000 lots accepted for export
to the EU. The average aflatoxin concentration among
the 149 lots rejected for export in the USA was 23.4 ng/g
AFT. When the 11,000 USA lots are imported into the EU,
either 220,550 or 1,100 USA lots are tested for aflatoxin by
EU authorities based upon a 2, 5, or 10% inspection rate,
respectively. For a 5% EU inspection rate (550 lots), the
simulation predicts that 2.8 lots are rejected and 547.2 lots
are accepted by the EU sampling plan at destination. The
total number of lots accepted at destination is 10,997.2,
which is the 547.2 lots accepted by the EU sampling plan
plus the 10,450 lots not sampled. The EU rejected 0.51%
(2.8/550) of the lots tested at destination. The average
aflatoxin concentration among lots tested, accepted, and
rejected at destination by the EU sampling plan is 0.15,0.11
and 8.59 ng/g AFT, respectively. The percent lots rejected
at destination and the average aflatoxin concentration in
the lots tested, accepted, and rejected is the same regardless
of the inspection rate (2,5 or 10%) used by EU authorities
at destination.
Even though the USA rejected 1.36% of the lots tested at
origin and reduced the aflatoxin contamination by 64.2%
(0.42 vs. 0.15 ng/g AFT) when using an identical sampling
plan design at origin (2x 10 kg < 8 ng/g AfEl 110 ng/g AFT)
as that used by the EU at destination, the EU still rejects
0.51% of the USA lots tested at destination. These results
indicate that the USA cannot assume that all export lots will
be accepted at destination as a result of using a sampling
plan at origin that is equivalent (has the same level of false
positives and false negatives) to that used by the EU at
destination. The percentage of lots accepted and rejected
in the USA and in the EU for various USA sampling plan
designs and crop contamination levels (Tables 2 and 3) is
discussed below.
World Mycotoxin Journal 3 (2)
Effect of increasing the crop contamination level on lots
accepted and rejected at origin and at destination
Reviewing Table 2 it can be seen for a given USA sampling
plan design, as the crop contamination level increases from
0.42 to 6.0 ng/g AFT, the following happens:
1. More USA lots have to be sampled at origin to identify
11,000 lots for export (more USA lots are rejected at
origin from the export market).
2. The average aflatoxin concentration among the 11,000
lots identified for export increases.
3. The number or percentage of lots rejected by the EU at
destination increases.
4. The average aflatoxin concentration among all lots
accepted by the EU at destination increases.
Effect of decreasing the accept/reject limit of USA
sampling plans on lots accepted and rejected at origin
and at destination
Reviewing Table 3 it can be seen that for a given crop
contamination level, as the accept/reject limit decreases
from a dual limit of 8 ng/g AFBj /10 ng/g AFT to a single
limit of 8,6,4,2, or 0.5 ng/g AFT, the following happens:
1. More USA lots have to be sampled at origin to identify
11,000 USA lots for export (more USA lots are rejected
at origin from the export market).
2. The average aflatoxin concentration among the 11,000
USA lots identified for export decreases.
3. The number or percentage of lots rejected by the EU at
destination decreases.
4. The average aflatoxin concentration among all lots
accepted by the EU at destination decreases.
Reducing USA lots rejected in the EU
The USA almond industry would like to keep the percentage
of lots rejected by the EU as low as feasibly possible. Tables
2 or 3 show that simply having a USA sampling plan that
is equivalent to or exceeding the performance of the EU
sampling plan (2x10 kg S 8 ng/g AFBj / 10 ng/g AFT)
does not guarantee that no USA lots will be rejected at
destination or the percentage of USA lots rejected in the EU
will not exceed some predefined unacceptable level if crop
contamination levels exceed certain thresholds. Observing
results in Table 2 or 3 suggests that that the percentage
of lots rejected in the EU is a function of the average
aflatoxin concentration among all 11,000 lots accepted
in the USA for export. This can be better demonstrated
by plotting (Figure 4) the percentage of lots rejected in
the EU versus the average aflatoxin concentration among
all 11,000 lots exported to the EU for all 24 simulation
results in Table 2 or 3. Each point on the curve represents
a combination of a potential USA sampling plan design and
crop contamination level in Table 2 or 3. For example, a USA
sampling plan would have to keep the average aflatoxin level
165
IIMMeretal.
! All almond crops and all USA sampling plans
100% USA testing
7 ±-• EU testing: 2x10 kg <; 10T/8B1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
11
1.2
1.3
1,4
1.5
1.6
Avg. afiatoxin concentration of tote accepted in USA {ng/g AFT)
Figure 4. EU rejects versus average aflatoxin concentration in USA lots exported to the EU.
among the 11,000 lots accepted for export to the EU below
approximately 1.0 to 1.1 ng/g AFT to keep the percentage of
USA lots rejected by the EU at destination below 5% (Figure
4). As crop contamination level increases, USA sampling
plan would have to be designed (use more samples and/or
lower accept/reject limits) so that lots accepted for export
would average less than approximately 1.0 ng/g AFT. For
example, if the USA crop contamination level before testing
is 6.0 ng/g, a Codex style sampling plan (2x10 kg) with a 4
ng/g AFT accept/reject limit (2x 10 kg < 4 ng/g AFT) would
be required to keep the average aflatoxin concentration
among USA lots accepted for export below 1.0 ng/g and to
keep USA lots rejected in the EU below 5% (Table 2 or 3).
The USA sampling plan acts like a filter with varying
degrees of efficiency at removing aflatoxin contaminated
lots from the lot distribution being tested for possible export
to the EU. The percentage of lots rejected at destination
in the EU depends on the average aflatoxin contamination
among all 11,000 lots accepted for export to the EU, which
depends on the USA sampling plan design (as manifested
by the accept/reject limit or the percentage of USA lots
rejected at origin), which in turn depends on the USA crop
contamination level. The EU sampling plan design also acts
as a filter to remove contaminated lots at import. However,
the EU sampling plan design was not changed or was held
constant though all 24 simulations.
166
Predicting USA export lots rejected in the EU
Because of the time required to transport USA lots from
California to the EU, time for the EU to inspect USA
imported lots, and time for the EU to report inspection
results to the US, the USA almond industry cannot
determine the consequences (number or percentage of
lots rejected in the EU) of their sampling program for some
period of time after the lots have been tested for aflatoxin in
the USA. Using the observations in the previous paragraph
about the effects of USA crop contamination levels and
sampling plan designs on the percentage of lots rejected
in the EU, there may be a way for the almond industry as
a whole or for an individual exporter to predict in 'realtime' the percentage of lots that will be rejected several
months later at destination in the EU. These two methods
include keeping a record of either (a) the average aflatoxin
concentration among sample test results associated with all
USA lots tested for export (average aflatoxin concentration
among all sample test results is a measure of the crop
contamination level) or (b) the percentage of lots rejected
at origin in the USA.
Crop contamination levels (as measured by averaging all
sample test results) and percentage of USA lots rejected at
origin are two tangible parameters that can be measured
in 'real-time' during the marketing of export lots by an
World Mycotoxin Journal 3 (2)
Almond lots accepted and rejected in the export market
individual exporter or collectively by the industry as a
whole to predict the percentage of USA lots rejected in
the EU when those lots are eventually tested at a later date
in the EU.
From simulation results in Table 2 or 3, the percentage of
lots rejected in the USA and in the EU by each of the six
proposed USA sampling plan designs are plotted in Figure
5 versus crop contamination levels from 0.42 to 6.0 ng/g
AFT. There are two sets of curves shown in Figure 5, one
set of curves represents the percentage of lots rejected in
the USA and one set of curves represents the percentage of
lots rejected in the EU. Each curve in Figure 5 (for both the
USA and the EU set of curves) is associated with a specific
USA sampling plan design and provides an indication
how each proposed USA sampling plan would perform
(percent lots rejected) in the USA and in the EU for USA
crop contamination levels from 0.42 to 6.0 ng/g AFT.
Figure 5 can be used by the USA almond industry to keep
the percentage of lots rejected by the EU as low as feasibly
possible. If the USA almond industry plans to use a sampling
plan that is equivalent to the EU sampling plan (2x 10 kg <
8 ng/g AFBj /10 ng/g AFT), then that USA sampling plan
would be expected to keep USA rejects in the EU below 5%
for crop contamination levels up to 4.25 ng/g AFT (plan
1 in the EU set of curves). The USA almond industry will
reject about 12.8% of USA lots tested at origin (plan 1 in
the USA set of curves). For example, if the USA almond
industry is rejecting about 15% of lots tested for export
using a USA sampling plan that is identical to the EU plan
(plan 1 or 2x10 kg < 8 ng/g AFBt /10 ng/g AFT), then the
industry is sampling a USA crop that averages 4.95 ng/g
AFT (using plan 1 in the USA set of curves) and should
expect 5.9% of lots tested by the EU (using plan 1 in the
EU set of curves) to be rejected at destination (Figure 5).
If this predicted percentage of USA lots rejected in the EU
(5.9%) is unacceptable to the USA almond industry, they
would have to change their sampling plan by lowering
the accept/reject limit to 6 ng/g AFT (plan 3 or 2x10 kg
s 6 ng/g AFT), which will bring EU rejects down to 4.8%
when the USA is sampling a lot distribution at 4.95 ng/g
AFT. If the USA changes the sampling plan to 2x 10 kg <
6 ng/g AFT, then lots rejected in the USA would increase
from 15 to 17.5%. Reducing the accept/reject limit for the
USA sampling plan has a desirable effect of reducing lots
rejected at destination, but results in higher rejection rates
in the USA and greater economic burden on exporters.
Lots rejected in EU
Lots rejected in USA
USA almond
sampling plans
1: 2x10 kg s 8 ng/g AFB/10 ng/g AFT
2:2x10 kg <;8 ng/g AFT
3:2x10 kg £6 ng/g AFT
4:2x10 kg s 4 ng/g AFT
5:2x10 kg £2 ng/g AFT
6:2x1 Okg z 0.5 ng/g AFT
EU: 2x10 kg £ 8 ng/g AFB/10 ng/g AFT
0.0
15
20
25
Almond tots rejected (%)
Figure 5. USA lots rejected in the USA and in the EU for six different USA sampling plan designs and a range in USA crop
contamination levels.
World Mycotoxin Journal 3 (2)
167
IMiMeretal.
4. Conclusions
Simulation results show that even when the USA and the EU
are using the same sampling plan with accepted protocols
for sampling, sample preparation, and analytical methods
to detect aflatoxin in shelled RTE almond lots, USA lots
will be rejected at destination due to random variability
associated with the aflatoxin test procedure (sampling,
sample preparation, and analysis). The magnitude of the
USA lots rejected at destination depends on the USA crop
contamination level and the ability of the USA sampling
plan to detect and remove aflatoxin contaminated lots from
the export market. As the USA crop contamination level
increases, the accept/reject limit of the USA sampling plan
design will have to decrease to keep USA lots rejected in
the EU to acceptable levels.
After reviewing results of this study, the USA almond
industry decided to modify the pre-March 2010 sampling
plan (3x5 kg < 2.0 ng/g AFT) with a sampling plan identical
to the new post-March 2010 EU sampling plan (2x10 kg < 8
ng/g AFB1 /10 ng/g AFT). The percentage of lots rejected
in the EU is predicted to be minimal (less than 5%) unless
crop contamination levels are encountered that exceed 4.2
ng/g AFT on the average. Methods were developed using
the percentage of USA lots rejected at origin to help USA
exporters recognise when to adjust their aflatoxin sampling
plan design (lower the accept/reject limit) to keep USA lots
rejected in the EU at a minimum, which will help balance
the economic impact of increased rejections at origin. While
model results were specific to simulating the sampling of
RTE shelled almond destined for the EU, the model can be
used for other mycotoxins, other commodities, and other
destinations if the appropriate inputs can be provided.
References
Almond Board of California, 2009. Doc #5418. Almond Board of
California, Modesto, CA, USA.
Codex Committee on Contaminants in Foods (CCCF), 2008. Aflatoxin
sampling plans for aflatoxin contamination in ready-to-eat treenuts
and treenuts destined for further processing: almonds, hazelnuts,
and pistachios, Alinorm 08/31/41, Appendix IX, 31st CAC Session,
Geneva, Switzerland, 30 June to 4 July, 2008. Available at: www.
codexalimentarius.net/download/report/700/al31_41e.pdf.
168
European Commission (EC), 2007. Commission Decision 2007/5631
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Whitaker, T.B., Giesbrecht, F.G. and Wu, J., 1996. Suitability of several
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Whitaker, T.B., Slate, A.B., Hurley, J.M. and Giesbrecht, F.G., 2006.
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World Mycotoxin Journal 3 (2)