pyrethroid bioavailability to microorganisms. Half-lives of bifenthrin, cypermethrin,
and permethrin in soils were 12–1,410, 14–106, and 5–55 days respectively, under
temperature conditions between 25 and 30
C (Table 2 in [63]). The biodegradation
rates in freshwater sediments have been seldom determined, and they are longer than
in soils [18]. Depending on conditions, long persistence was observed for bifenthrin
and permethrin. Under both aerobic and anaerobic conditions, and the half-life of
bifenthrin in sediment of drainage channels ranged from 8 to 17 months at 20
C,
while that of cis and trans permethrin varied between 2 to 13 months [65]. In liquid
media, bacteria (Bacillus, Brevibacillus, Ochrobactrum, Pseudomonas, Serratia,
and Sphingobium) and fungi (Cladosporium, Candida) degrade efficiently pyrethroids. At temperatures ranging from 27 to 38
C, most strains degraded pyrethroids
within 5 days, with the fastest degradation observed for permethrin in 3 days
[63]. However, the experimental conditions at which the experiments were carried
out were not the same as natural field conditions, where lower temperatures and
lower bacteria or fungi abundance can be expected to increase half-life of
pyrethroids.
6 Pyrethroid Occurrence in the Atmosphere
Because of their relatively low vapor pressure, pyrethroids are assumed to have low
tendency to volatilize during application, as well to revolatilize from soils or water
bodies [7]. During application, 20–30% of the applied doses can be emitted as
aerosols and drift away from their source by atmospheric transport [66]. Postapplication emissions have also been reported to occur via volatilization [67]. For
deltamethrin, having one of the lowest Henry’s law constant values among pyrethroids, it was experimentally demonstrated that 70% of deltamethrin sprayed on the
surface of the water was quickly emitted as aerosols [68]. Taken as a whole, these
evidences point to likely atmospheric emissions of pyrethroids, at least during and
shortly after application by spray broadcasting.
The widespread occurrence of pyrethroids in some areas also questions whether
their volatilization to the gas phase is possible, ensuing a likely atmospheric transport to proximate or remote ecosystems (see Sect. 7). A few reports have recently
evidenced that pyrethroids were present in the atmosphere, both as aerosols and as
vapors in the gas phase. The particle-bound fraction is susceptible to be atmospherically deposited or to be washed out by rain or snow whereas gas-phase pyrethroids
will be removed by photodegradation or air-soil, air-vegetation, or air-water diffusive exchange, probably resulting in longer atmospheric residence times
[69]. Table 3 reviews the concentrations of pyrethroid insecticides bounds to aerosols or as vapors. The first report of pyrethroids in the gas phase of Brazilian alpine
reserves showed that cypermethrin was the second pesticide in abundance, whereas
gas phase concentrations of legacy pollutants, such as chlordane, chlorinated cyclodienes and hexachlorobenzene, were around background levels [70]. In aerosols and
in the gas phase of Guangzhou (south China), eight pyrethroids were detected, and
Fate of Pyrethroids in Freshwater and Marine Environments
95
and permethrin in soils were 12–1,410, 14–106, and 5–55 days respectively, under
temperature conditions between 25 and 30
C (Table 2 in [63]). The biodegradation
rates in freshwater sediments have been seldom determined, and they are longer than
in soils [18]. Depending on conditions, long persistence was observed for bifenthrin
and permethrin. Under both aerobic and anaerobic conditions, and the half-life of
bifenthrin in sediment of drainage channels ranged from 8 to 17 months at 20
C,
while that of cis and trans permethrin varied between 2 to 13 months [65]. In liquid
media, bacteria (Bacillus, Brevibacillus, Ochrobactrum, Pseudomonas, Serratia,
and Sphingobium) and fungi (Cladosporium, Candida) degrade efficiently pyrethroids. At temperatures ranging from 27 to 38
C, most strains degraded pyrethroids
within 5 days, with the fastest degradation observed for permethrin in 3 days
[63]. However, the experimental conditions at which the experiments were carried
out were not the same as natural field conditions, where lower temperatures and
lower bacteria or fungi abundance can be expected to increase half-life of
pyrethroids.
6 Pyrethroid Occurrence in the Atmosphere
Because of their relatively low vapor pressure, pyrethroids are assumed to have low
tendency to volatilize during application, as well to revolatilize from soils or water
bodies [7]. During application, 20–30% of the applied doses can be emitted as
aerosols and drift away from their source by atmospheric transport [66]. Postapplication emissions have also been reported to occur via volatilization [67]. For
deltamethrin, having one of the lowest Henry’s law constant values among pyrethroids, it was experimentally demonstrated that 70% of deltamethrin sprayed on the
surface of the water was quickly emitted as aerosols [68]. Taken as a whole, these
evidences point to likely atmospheric emissions of pyrethroids, at least during and
shortly after application by spray broadcasting.
The widespread occurrence of pyrethroids in some areas also questions whether
their volatilization to the gas phase is possible, ensuing a likely atmospheric transport to proximate or remote ecosystems (see Sect. 7). A few reports have recently
evidenced that pyrethroids were present in the atmosphere, both as aerosols and as
vapors in the gas phase. The particle-bound fraction is susceptible to be atmospherically deposited or to be washed out by rain or snow whereas gas-phase pyrethroids
will be removed by photodegradation or air-soil, air-vegetation, or air-water diffusive exchange, probably resulting in longer atmospheric residence times
[69]. Table 3 reviews the concentrations of pyrethroid insecticides bounds to aerosols or as vapors. The first report of pyrethroids in the gas phase of Brazilian alpine
reserves showed that cypermethrin was the second pesticide in abundance, whereas
gas phase concentrations of legacy pollutants, such as chlordane, chlorinated cyclodienes and hexachlorobenzene, were around background levels [70]. In aerosols and
in the gas phase of Guangzhou (south China), eight pyrethroids were detected, and
Fate of Pyrethroids in Freshwater and Marine Environments
95