As observed in air and dust samples, a high contribution of trans-permethrin in
watershed river and sediment samples was observed after rains during the dry season
compared to the wet season [62]. According to the authors, extreme concentrations
of cis- and trans-permethrin (4,800 and 13,000 ng L
À1 , respectively) may be related
to application drift or product misuse.
Although sediment samples have a similar profile with a predominance of
trans-permethrin, Fig. 6 shows an atypical result (outlier) with a high contribution
of cis-permethrin in sediment samples carried with surface runoff from a commercial
nursery of plants [97]. According to the authors, permethrin is applied with the
planting mix material before seeding, and the required intensive irrigation results in a
heavy runoff. Therefore, the source of this sediment is from a contaminated soil,
which may explain the greater contribution of cis-permethrin in these sediment
samples, since a predominance of cis-isomers in soil samples has been described
[45, 96, 101]. Among sediment samples, trans-permethrin had the highest predominance (%EF trans ffi 100) in samples from Aiba Stream, Nigeria [98]. Although this
stream’s drainage basin is highly impacted by agricultural activities, according to the
authors, additional sources of pyrethroids may occur through their urban vector
control and domestic use and through untreated sewage discharge.
According to Fig. 6, cis-permethrin was predominant in biological samples, such
as human breast milk, dolphin tissues and commercial chicken eggs [90, 92, 93]. The
results are in agreement with the reported high degradation rate of trans-permethrin
in biological systems [15, 66]. Furthermore, a comparative study showed an increase
in the cis-cypermethrin epimers (1R-3R-αS and 1S-3S-αR) in human breast milk
samples compared to profiles found in commercial formulations [21]. Regarding the
above-mentioned findings, the main concern is the reported toxicity to mammals
related to the cis-enantiomers 1R-3R-permethrin and 1R-3R-αS-cypermethrin [15].
In wildlife, a great predominance of cis-isomers was also observed, such as in
bird egg samples (permethrin and cypermethrin) [99] and in river fish samples
(cypermethrin and cyfluthrin) [7]. However, for the specific compound tetramethrin,
commercial formulations have a much higher predominance (80:20 ratio) of 1Rtrans-enantiomers over 1R-cis-enantiomers [8]. According to the authors, it is
possible that the higher proportion of trans-tetramethrin in commercial formulations
has influenced the observed results [7, 99].
In a study of pyrethroid contamination in commercial chicken eggs [93], the
difference between the cypermethrin diastereomeric profile of a product applied
topically in chickens and that observed in egg samples from the same farm was
observed (Fig. 7a, b).
A higher percentage of cis-cypermethrin contribution was determined in the
egg sample (Fig. 7b) compared to the racemic formulation (Fig. 7a). The proportion
of the first cis-isomer (49%) compared to the total cypermethrin measured in the egg
sample is almost two times the proportion of the same isomer in the commercial
formulation (27%). Additionally, in a wide variety of contaminated food samples
(fish, beef, chicken and milk), a predominance of cis-cypermethrin [106] was
verified. However, the reference values for food safety – maximum residue limit
(MRL) and acceptable daily intake (ADI) – consider the sum of isomers
Stereoselectivity and Environmental Behaviour of Pyrethroids
167
watershed river and sediment samples was observed after rains during the dry season
compared to the wet season [62]. According to the authors, extreme concentrations
of cis- and trans-permethrin (4,800 and 13,000 ng L
À1 , respectively) may be related
to application drift or product misuse.
Although sediment samples have a similar profile with a predominance of
trans-permethrin, Fig. 6 shows an atypical result (outlier) with a high contribution
of cis-permethrin in sediment samples carried with surface runoff from a commercial
nursery of plants [97]. According to the authors, permethrin is applied with the
planting mix material before seeding, and the required intensive irrigation results in a
heavy runoff. Therefore, the source of this sediment is from a contaminated soil,
which may explain the greater contribution of cis-permethrin in these sediment
samples, since a predominance of cis-isomers in soil samples has been described
[45, 96, 101]. Among sediment samples, trans-permethrin had the highest predominance (%EF trans ffi 100) in samples from Aiba Stream, Nigeria [98]. Although this
stream’s drainage basin is highly impacted by agricultural activities, according to the
authors, additional sources of pyrethroids may occur through their urban vector
control and domestic use and through untreated sewage discharge.
According to Fig. 6, cis-permethrin was predominant in biological samples, such
as human breast milk, dolphin tissues and commercial chicken eggs [90, 92, 93]. The
results are in agreement with the reported high degradation rate of trans-permethrin
in biological systems [15, 66]. Furthermore, a comparative study showed an increase
in the cis-cypermethrin epimers (1R-3R-αS and 1S-3S-αR) in human breast milk
samples compared to profiles found in commercial formulations [21]. Regarding the
above-mentioned findings, the main concern is the reported toxicity to mammals
related to the cis-enantiomers 1R-3R-permethrin and 1R-3R-αS-cypermethrin [15].
In wildlife, a great predominance of cis-isomers was also observed, such as in
bird egg samples (permethrin and cypermethrin) [99] and in river fish samples
(cypermethrin and cyfluthrin) [7]. However, for the specific compound tetramethrin,
commercial formulations have a much higher predominance (80:20 ratio) of 1Rtrans-enantiomers over 1R-cis-enantiomers [8]. According to the authors, it is
possible that the higher proportion of trans-tetramethrin in commercial formulations
has influenced the observed results [7, 99].
In a study of pyrethroid contamination in commercial chicken eggs [93], the
difference between the cypermethrin diastereomeric profile of a product applied
topically in chickens and that observed in egg samples from the same farm was
observed (Fig. 7a, b).
A higher percentage of cis-cypermethrin contribution was determined in the
egg sample (Fig. 7b) compared to the racemic formulation (Fig. 7a). The proportion
of the first cis-isomer (49%) compared to the total cypermethrin measured in the egg
sample is almost two times the proportion of the same isomer in the commercial
formulation (27%). Additionally, in a wide variety of contaminated food samples
(fish, beef, chicken and milk), a predominance of cis-cypermethrin [106] was
verified. However, the reference values for food safety – maximum residue limit
(MRL) and acceptable daily intake (ADI) – consider the sum of isomers
Stereoselectivity and Environmental Behaviour of Pyrethroids
167