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CHANG ET AL.: JOURNAL OF AOAC INTERNATIONAL V OL. 99, NO . 4, 2016 1053
with degradation trend E at a concn, and among them, 9 and
21 pesticides were also in accordance with degradation trends
A and B, respectively, at b concn, accounting for 45.5 of
the 66 pesticides. Meanwhile, there were 40 pesticides in
accordance with degradation trend E at b concn, but only 3 and
5 of these pesticides corresponded with degradation trends A
and B, respectively, at a concn. At the same time, there were
24 pesticides in accordance with degradation trend E at both
concentrations, accounting for 36.4 and 60.0 of the pesticides
that were in accordance with degradation trend E at a and b
concns, respectively.
Degradation trend F.—Taking kresoxim-methyl as an
example, the pro¿les of degradation trend F are shown in
Figure 7. The concentrations of the degraded pesticides
presented as scatter points, and no degradation trend can
be found by any of the above-mentioned ¿tting curves with
R 2 values •0.4. The unsteadiness properties of these pesticides
in aged Oolong tea during storage might be the reason.
There were 16 pesticides at a concn and 24 pesticides at b
concn in accordance with degradation trend F, accounting for
5.9 and 8.9 of 271 pesticides, respectively. In addition, nine
pesticides were in accordance with degradation trend F at both
concentrations.
This discussion of degradation trends A–F indicates that the
271 pesticides studied here have relatively complex degradation
trends in aged Oolong tea, with various ¿tting curves at different
concentrations. Among the degradation trends A–F, degradation
trends A, B, and F had higher ratios than the others. All the
pesticides in accordance with degradation trends A, B, and E
decreased exponentially over 40 days and decreased mainly
exponentially or logarithmically over 120 days. In addition,
although no degradation trend was seen for the pesticides of
degradation trend D over 40 days, they decreased mainly
exponentially over 120 days. The conclusion is that pesticides
in tea degrade slowly, with concentrations of pesticides
decreasing within 4 months: at concentration a, the deviation
for each pesticide from day 1 to day 120 falls within the range
0.2–85.6 (mean, 36.4 ), whereas at concentration b , the
deviation for each pesticide from day 1 to day 120 falls within
the range 4.0–92.7 (mean, 50.8 ).
Pesticides in Different Classes
To further investigate the degradation trends, pesticides
in A–F aspects were divided into different classes according
to organonitrogen, organophosphorus, organochlorine,
organosulfur, carbamates, and pyrethroids, and “others.” Their
distributions can be found in Figures 8 and 9.
It is clear that most of the 271 pesticides are in the
organonitrogen, organophosphorus, and organochlorine classes;
therefore, the pesticides are discussed according to these three
classes. For the pesticides in degradation trend A, most were
organonitrogen and organophosphorus. For degradation trend B,
the number of organophosphorus and organochlorine pesticides
was equal but far below the number of organonitrogen pesticides.
The number of organochlorine pesticides for degradation trend
E was far higher than for organonitrogen and organophosphorus
pesticides, and the number of organophosphorus pesticides was
5 and 3 at a and b concns, respectively. The organophosphorus
and organochlorine pesticides can be further discussed for
degradation trends A and B combined (A/B) and E. At a
concn, 37.9 and 71.4 pesticides were organochlorine and
organophosphorus, respectively, for degradation trend A/B. At
the same time, 43.1 and 11.9 pesticides were organochlorine
and organophosphorus, respectively, for degradation trend
E. At b concn, the respective percentages of organochlorine
and organophosphorus pesticides for degradation trend A/B
were 41.8 and 71.8 . For degradation trend E, the respective
percentages for organochlorine and organophosphorus
pesticides were 34.5 and 7.7 . These results suggest that most
of the organophosphorus pesticides degraded in accordance
with degradation trends A and B in aged Oolong tea. In contrast,
most of the organochlorine pesticides decreased according to
degradation trend E in aged Oolong tea.
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Determination days were plotted as horizontal ordinates; residue
concentrations of pesticide were plotted as vertical ordinates.
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kresoxim-methyl) over (a) 40 days and (b) 120 days. Determination
days were plotted as horizontal ordinates; residue concentrations of
pesticide were plotted as vertical ordinates.
Figure 8. Distributions of pesticides according to different classes
within A–F aspects at a concn. For each degradation trend (x-axis),
percentages (y-axis) were calculated as the number of pesticides in
each class in accordance with the degradation trend multiplied by
100 and divided by the total number of pesticides in the class.
Figure 9. Distributions of pesticides according to different classes
within A–F aspects at b concn. For each degradation trend (x-axis),
percentages (y-axis) were calculated as the number of pesticides in
each class in accordance with the degradation trend multiplied by
100 and divided by the total number of pesticides in the class.