1.3 Synthetic Pyrethroids: Mode of Use
Currently, pyrethroids are applied through bath treatments using commercial product
doses of 0.3 mL m
À3 (active principle dose of 15 μg L
À1 ) for cypermethrin
(Betamax
® ) and between 0.2 mL m
À3 (active principle dose of 2 μg L
À1 ) (AMX
® )
and 0.3 mL m
À3 (active principle dose of 3 μg L
À1 ) (Deltafav
® ) for deltamethrin in
water. Suspended tarpaulins are used for these bath treatments, in which the fishnet is
raised to a depth of no more than 4 m to subsequently apply the doses indicated
above. The salmon exposure time to cypermethrin (Betamax
® ) is 30 min, while for
deltamethrin it is between 30 and 40 min [31]. Once the treatments are released, their
main mechanism of action on organisms involves interference in the central nervous
system, generating an interruption in the transmission of nerve impulses between
cells [32, 33].
The recommended treatment regime for sea lice using pyrethroids consists of a
“relatively high concentration at the levels of micrograms per liter–short duration
bath exposure” within skirted net pens, after which treatment water is released to
disperse into the surrounding marine environment [34, 35]. While pyrethroids such
as deltamethrin are highly effective treatments for ectoparasites such as sea lice, the
implications for nontarget species such as migratory salmonids and other commercial species that traverse multiple aquaculture areas are currently unclear.
2 Exposure Assessment: Approaches to Assess the Risk
of Pyrethroids in the Marine Ecosystem
The environmental fate of chemicals is determined by a combination of factors, of
which the most important are those related to the nature of the compound and the
environment. Physical and chemical properties define potential mobility and reactivity, while environmental variables determine the extent to which these potentials
are manifested [36]. Under field conditions, environmental variables (e.g., temperature, pH value, wavelength and radiation intensity, air–water exchange, turbulence,
organisms) are very complex to analyze and can produce significant changes in the
environmental behavior of chemicals. Therefore, the use of physical–mathematical
models is difficult in complex environmental chemistry, especially when a considerable number of details are required to successfully simulate the environment.
An alternative approach consists of developing simple, appraisable models that
simulate environments, in which the environmental variables are standardized and
reduced to their essentials (evaluative models). Initially, evaluative models were
developed as a means to interpret and understand the trends that govern the movement of chemical substances in the environment. Over time, this approach has
proved to be extremely reliable and versatile, to the extent that it has become
applicable not only in theoretical scenarios, but in local situations as well, providing
credible predictions at the actual-environment level. They tend to be very simple
182
F. Tucca and R. Barra
Currently, pyrethroids are applied through bath treatments using commercial product
doses of 0.3 mL m
À3 (active principle dose of 15 μg L
À1 ) for cypermethrin
(Betamax
® ) and between 0.2 mL m
À3 (active principle dose of 2 μg L
À1 ) (AMX
® )
and 0.3 mL m
À3 (active principle dose of 3 μg L
À1 ) (Deltafav
® ) for deltamethrin in
water. Suspended tarpaulins are used for these bath treatments, in which the fishnet is
raised to a depth of no more than 4 m to subsequently apply the doses indicated
above. The salmon exposure time to cypermethrin (Betamax
® ) is 30 min, while for
deltamethrin it is between 30 and 40 min [31]. Once the treatments are released, their
main mechanism of action on organisms involves interference in the central nervous
system, generating an interruption in the transmission of nerve impulses between
cells [32, 33].
The recommended treatment regime for sea lice using pyrethroids consists of a
“relatively high concentration at the levels of micrograms per liter–short duration
bath exposure” within skirted net pens, after which treatment water is released to
disperse into the surrounding marine environment [34, 35]. While pyrethroids such
as deltamethrin are highly effective treatments for ectoparasites such as sea lice, the
implications for nontarget species such as migratory salmonids and other commercial species that traverse multiple aquaculture areas are currently unclear.
2 Exposure Assessment: Approaches to Assess the Risk
of Pyrethroids in the Marine Ecosystem
The environmental fate of chemicals is determined by a combination of factors, of
which the most important are those related to the nature of the compound and the
environment. Physical and chemical properties define potential mobility and reactivity, while environmental variables determine the extent to which these potentials
are manifested [36]. Under field conditions, environmental variables (e.g., temperature, pH value, wavelength and radiation intensity, air–water exchange, turbulence,
organisms) are very complex to analyze and can produce significant changes in the
environmental behavior of chemicals. Therefore, the use of physical–mathematical
models is difficult in complex environmental chemistry, especially when a considerable number of details are required to successfully simulate the environment.
An alternative approach consists of developing simple, appraisable models that
simulate environments, in which the environmental variables are standardized and
reduced to their essentials (evaluative models). Initially, evaluative models were
developed as a means to interpret and understand the trends that govern the movement of chemical substances in the environment. Over time, this approach has
proved to be extremely reliable and versatile, to the extent that it has become
applicable not only in theoretical scenarios, but in local situations as well, providing
credible predictions at the actual-environment level. They tend to be very simple
182
F. Tucca and R. Barra