of life of the dolphins or a selective metabolization of the cis isomer after they reach
sexual maturity. An enrichment on the trans isomer of permethrin was also observed
in the samples of human milk from Mozambique [59].
The Mediterranean striped dolphins had EF cis ¼ 0.51 Æ 0.17 and
EF trans ¼ 0.47 Æ 0.10 for tetramethrin [8]. These values, corresponding to
a racemic mixture, agreed with the values reported for household insecticides
purchased in Spanish supermarkets [63], indicating no enantiomer-specific
accumulation of tetramethrin in the liver of the individuals. However, the EF cis
for permethrin in dolphins was 0.42 Æ 0.05, which was statistically lower
than 0.35 Æ 0.04 in commercial pesticides, suggesting enantiomer-specific
bioaccumulation of (1S,3S)-permethrin rather than (1R,3R)-permethrin in dolphin
liver.
On the other hand, whereas the R cis/trans values of permethrin in dolphins
and commercial pesticides were similar, tetramethrin showed higher values in
dolphin liver (1.88 Æ 0.52 > 0.32 Æ 0.09). These results suggest no selective
bioaccumulation of the permethrin enantiomers, contrary to what had been
reported for the Franciscana species in Brazil, and selective bioaccumulation of
cis-tetramethrin.
Moving on to fish, almost all the samples of Iberian river fish showed a
preference to bioaccumulate the cis isomers of pyrethroids, with maximum
R cis/trans values of 30 for cypermethrin, 1.3 for cyfluthrin and 11 for permethrin
[43]. Conversely, tetramethrin showed the opposed trend. The authors argued
that commercial mixtures might be rich in trans-tetramethrin as its 1R,3S
isomer has a stronger pesticide activity. Thus a low R cis/trans value could reflect
the environmental levels. The preference for cis-permethrin is a new situation
after seeing the preference for the trans isomer in Franciscana dolphins and
human milk from Mozambique and the lack of selectivity in the striped dolphins.
However, the cis preference was also reported for the samples of human milk [10].
Some studies on mice found that cis-permethrin was less metabolized than
trans-permethrin and more accumulative and toxic [64, 65].
It is important to note that commercial mixtures are rich in some cis isomers [63];
thus R cis/trans > 1 might just represent the environmental contamination. That is
why analysing environmental samples from the areas where biological samples are
collected would allow more accurate observations.
The EF cis1 for cyfluthrin was always below 0.39. On the other hand, the EF cis1 for
cypermethrin was always below 0.5, except for the catfish samples [43]. This might
suggest that enantiomer-selective bioaccumulation could depend on species,
as catfish samples were collected in the same locations as the rest [63].
Permethrin EF cis values were very different among the Iberian fish samples and
the sampling points [43]. For example, samples of catfish and barbel presented
higher content of (1R,3R,αR)-cyhalothrin in the first cis enantiomeric pair, while
the second cis pair appeared as a racemic mixture. However, the gudgeon samples,
which were not collected in the same location, presented a racemic mixture for the
first cis pair, but higher accumulation of (1R,3R,αS)-cyhalothrin in the second pair.
These variations could support the hypothesis of species-specific selectivity or
indicate different uses of commercial mixtures in the targeted locations.
216
Ò. Aznar-Alemany and E. Eljarrat
sexual maturity. An enrichment on the trans isomer of permethrin was also observed
in the samples of human milk from Mozambique [59].
The Mediterranean striped dolphins had EF cis ¼ 0.51 Æ 0.17 and
EF trans ¼ 0.47 Æ 0.10 for tetramethrin [8]. These values, corresponding to
a racemic mixture, agreed with the values reported for household insecticides
purchased in Spanish supermarkets [63], indicating no enantiomer-specific
accumulation of tetramethrin in the liver of the individuals. However, the EF cis
for permethrin in dolphins was 0.42 Æ 0.05, which was statistically lower
than 0.35 Æ 0.04 in commercial pesticides, suggesting enantiomer-specific
bioaccumulation of (1S,3S)-permethrin rather than (1R,3R)-permethrin in dolphin
liver.
On the other hand, whereas the R cis/trans values of permethrin in dolphins
and commercial pesticides were similar, tetramethrin showed higher values in
dolphin liver (1.88 Æ 0.52 > 0.32 Æ 0.09). These results suggest no selective
bioaccumulation of the permethrin enantiomers, contrary to what had been
reported for the Franciscana species in Brazil, and selective bioaccumulation of
cis-tetramethrin.
Moving on to fish, almost all the samples of Iberian river fish showed a
preference to bioaccumulate the cis isomers of pyrethroids, with maximum
R cis/trans values of 30 for cypermethrin, 1.3 for cyfluthrin and 11 for permethrin
[43]. Conversely, tetramethrin showed the opposed trend. The authors argued
that commercial mixtures might be rich in trans-tetramethrin as its 1R,3S
isomer has a stronger pesticide activity. Thus a low R cis/trans value could reflect
the environmental levels. The preference for cis-permethrin is a new situation
after seeing the preference for the trans isomer in Franciscana dolphins and
human milk from Mozambique and the lack of selectivity in the striped dolphins.
However, the cis preference was also reported for the samples of human milk [10].
Some studies on mice found that cis-permethrin was less metabolized than
trans-permethrin and more accumulative and toxic [64, 65].
It is important to note that commercial mixtures are rich in some cis isomers [63];
thus R cis/trans > 1 might just represent the environmental contamination. That is
why analysing environmental samples from the areas where biological samples are
collected would allow more accurate observations.
The EF cis1 for cyfluthrin was always below 0.39. On the other hand, the EF cis1 for
cypermethrin was always below 0.5, except for the catfish samples [43]. This might
suggest that enantiomer-selective bioaccumulation could depend on species,
as catfish samples were collected in the same locations as the rest [63].
Permethrin EF cis values were very different among the Iberian fish samples and
the sampling points [43]. For example, samples of catfish and barbel presented
higher content of (1R,3R,αR)-cyhalothrin in the first cis enantiomeric pair, while
the second cis pair appeared as a racemic mixture. However, the gudgeon samples,
which were not collected in the same location, presented a racemic mixture for the
first cis pair, but higher accumulation of (1R,3R,αS)-cyhalothrin in the second pair.
These variations could support the hypothesis of species-specific selectivity or
indicate different uses of commercial mixtures in the targeted locations.
216
Ò. Aznar-Alemany and E. Eljarrat