3.2 Aquatic Environments
Reports on pyrethroid occurrence in river sediments around the world point out a
relevant contribution of these compounds to contamination of aquatic ecosystems
[33, 58, 59]. Pyrethroids have high sorption potential in soils and can reach aquatic
environments mainly through spray drift and consequent via atmospheric deposition,
as well as rainfall and runoff events [43, 60–62].
Considering the effect of technical formulations, without an approach on single
stereoisomers, previous studies have noted the high toxicity of pyrethroids, mainly
to fish and aquatic arthropods [63]. On the other hand, chiral studies were performed
with Daphnia magna, a zooplanktonic crustacean with an important ecological role
as a food web base in freshwater aquatic environments [32]. In a chiral approach
with bifenthrin (10 μg L
À1 ), D. magna presented a low capacity for metabolism
of cis-isomers [36]. Among stereoisomers, 1R-cis-bifenthrin presented a high
bioaccumulation ratio and higher toxic effects on fecundity and survival compared
to 1S-cis enantiomers (Table 2). High toxicity was also reported in tests with
Ceriodaphnia dubia (a microcrustacean) and Daphnia magna exposed to 1R-cis
enantiomers of bifenthrin and permethrin, confirming the stereoselectivity on metabolism, bioaccumulation and toxicity in these aquatic organisms [22].
In a study with adult zebrafish (Danio rerio), significant oxidative stress was
observed in liver and brain tissues due to exposure to beta-cypermethrin racemic
formulation and single isomers: 1R-cis-αS and 1R-trans-αS [38]. These same enantiomers were more lethal in the acute toxicity test than their epimers 1S-cis-αR and
1S-trans-αR (Table 2).
The enantiomeric results of these studies are in agreement with the reported high
toxicity of 1R-cis (bifenthrin and permethrin), 1R-cis-αS and 1R-trans-αS enantiomers of cyhalothrin and cypermethrin in assays with species of different trophic
levels, such as microcrustaceans (Ceriodaphnia dubia and Daphnia magna)
[22, 36], shrimp [9], zebrafish [38], and tadpoles of anuran amphibian [40].
On the other hand, studies have shown that the S-configuration of C-1 at the
cyclopropane ring is associated with endocrine disruption in fishes (Table 2). The
enantiomer 1S-cis-bifenthrin (10 ng mL
À1 ) induced 123-fold greater oestrogenicity
compared to the 1R-enantiomers in Japanese medaka Oryzias latipes [39]. Additionally, 1S-cis enantiomers of permethrin induced significantly higher oestrogenic
activity compared to its epimer (1R-cis), as determined through assays performed
in vivo with Japanese medaka and in vitro with primary rainbow trout hepatocyte
[10]. Another study reported enantioselective oestrogenic effects in tests with
zebrafish exposed to 500 ng L
À1 of permethrin. Levorotary (À)-trans-enantiomers
induced the greatest oestrogenic activity compared to other permethrin enantiomers
[11]. According to the authors, (À)-trans-permethrin induced an oestrogenic effect
fourfold higher than the oestrogen 17-beta-estradiol at 50 ng L
À1 . The greatest
oestrogenic effects of levorotary (À)-trans-permethrin are comparable to the greater
oestrogenic effects of the 1S configuration of bifenthrin and permethrin [10, 39],
suggesting that both nomenclatures are related to the same configuration.
Stereoselectivity and Environmental Behaviour of Pyrethroids
161
Reports on pyrethroid occurrence in river sediments around the world point out a
relevant contribution of these compounds to contamination of aquatic ecosystems
[33, 58, 59]. Pyrethroids have high sorption potential in soils and can reach aquatic
environments mainly through spray drift and consequent via atmospheric deposition,
as well as rainfall and runoff events [43, 60–62].
Considering the effect of technical formulations, without an approach on single
stereoisomers, previous studies have noted the high toxicity of pyrethroids, mainly
to fish and aquatic arthropods [63]. On the other hand, chiral studies were performed
with Daphnia magna, a zooplanktonic crustacean with an important ecological role
as a food web base in freshwater aquatic environments [32]. In a chiral approach
with bifenthrin (10 μg L
À1 ), D. magna presented a low capacity for metabolism
of cis-isomers [36]. Among stereoisomers, 1R-cis-bifenthrin presented a high
bioaccumulation ratio and higher toxic effects on fecundity and survival compared
to 1S-cis enantiomers (Table 2). High toxicity was also reported in tests with
Ceriodaphnia dubia (a microcrustacean) and Daphnia magna exposed to 1R-cis
enantiomers of bifenthrin and permethrin, confirming the stereoselectivity on metabolism, bioaccumulation and toxicity in these aquatic organisms [22].
In a study with adult zebrafish (Danio rerio), significant oxidative stress was
observed in liver and brain tissues due to exposure to beta-cypermethrin racemic
formulation and single isomers: 1R-cis-αS and 1R-trans-αS [38]. These same enantiomers were more lethal in the acute toxicity test than their epimers 1S-cis-αR and
1S-trans-αR (Table 2).
The enantiomeric results of these studies are in agreement with the reported high
toxicity of 1R-cis (bifenthrin and permethrin), 1R-cis-αS and 1R-trans-αS enantiomers of cyhalothrin and cypermethrin in assays with species of different trophic
levels, such as microcrustaceans (Ceriodaphnia dubia and Daphnia magna)
[22, 36], shrimp [9], zebrafish [38], and tadpoles of anuran amphibian [40].
On the other hand, studies have shown that the S-configuration of C-1 at the
cyclopropane ring is associated with endocrine disruption in fishes (Table 2). The
enantiomer 1S-cis-bifenthrin (10 ng mL
À1 ) induced 123-fold greater oestrogenicity
compared to the 1R-enantiomers in Japanese medaka Oryzias latipes [39]. Additionally, 1S-cis enantiomers of permethrin induced significantly higher oestrogenic
activity compared to its epimer (1R-cis), as determined through assays performed
in vivo with Japanese medaka and in vitro with primary rainbow trout hepatocyte
[10]. Another study reported enantioselective oestrogenic effects in tests with
zebrafish exposed to 500 ng L
À1 of permethrin. Levorotary (À)-trans-enantiomers
induced the greatest oestrogenic activity compared to other permethrin enantiomers
[11]. According to the authors, (À)-trans-permethrin induced an oestrogenic effect
fourfold higher than the oestrogen 17-beta-estradiol at 50 ng L
À1 . The greatest
oestrogenic effects of levorotary (À)-trans-permethrin are comparable to the greater
oestrogenic effects of the 1S configuration of bifenthrin and permethrin [10, 39],
suggesting that both nomenclatures are related to the same configuration.
Stereoselectivity and Environmental Behaviour of Pyrethroids
161