threshold values especially in suspended particles after rain events (in 80% of the
samples in Germany [31]).
Because pyrethroid pesticides have been quite often detected in streams, creeks,
and receiving rivers, they should also reach marine coastal waters. However,
research addressing the occurrence of pyrethroids in estuarine and marine environments is limited. Due to the dilution of river water into the sea, pesticides often fall
below detection limits. For instance, in seawater off Portugal, only two of the nine
targeted pyrethroids could be detected, and only one could be quantified, whereas
five were present in oysters [33]. Analytical difficulties may be a reason for the
scarcity of published data in seawater (Table 1).
A specific risk for the marine environment is associated with aquaculture treatment of salmon against ectoparasites [5, 57]. Formulations used in aquaculture
contain deltamethrin or cypermethrin together with emulsifiers for bath treatment
of caged fish. Once the treatment is over, the bath water is released into the seawater,
where pyrethroids are diluted by currents. In a case study in Canada, the deltamethrin
plume could be detected up to 5.5 h after emission and the plume extended a few km
away from the cages [5]. In this study, deltamethrin was emitted as a dissolved
pesticide, and it was monitored both in the dissolved phase and in the suspended
particles. Interestingly, deltamethrin concentration in the particle phase was approximately three to four times greater than in the aqueous phase, which demonstrates the
quick partition of pyrethroids to organic carbon in seawater and, thus, their affinity
for particles [5]. Variable responses of natural marine microbial communities to the
input of anti-lice pesticides have been evidenced in Southern Chile [58]. At some
locations and season, deltamethrin inputs resulted in an increase of carbon fixation
by photosynthesis, likely resulting from a decrease in arthropod grazing pressure;
however increase in carbon fixation was also observed at other sites and seasons. The
diverse responses observed evidenced complex relationships between environmental
factors (nutrient levels, zooplankton abundance, etc.) and pesticide impacts. These
responses of marine organisms, distinct from toxicity alone, need further research to
understand the overall impact of aquaculture and, more generally, of pyrethroid
emissions, on marine ecosystems. More detailed information on the effect of salmon
industry in the marine environment is presented elsewhere [6].
However difficult it is to detect pyrethroids in the marine environment, this task
should not be overlooked because marine crustaceans and fish have been reported to
be more susceptible to pyrethroids than freshwater ones [29, 34, 48].
4 Occurrence and Composition of Pyrethroids in Sediments
Table 2 documents pyrethroid occurrence in sediments. The solid phase of sediments
acts as a sorbent for pesticides and likely integrates over time water pyrethroid
concentrations in the overflowing water and also the accumulation of sinking
particles in sea and river beds. Because of their quick association to river sediment,
pyrethroid contamination of riverbed sediment has emerged as an important environmental threat to benthic organisms, and the literature reporting sediment toxicity
Fate of Pyrethroids in Freshwater and Marine Environments
91
samples in Germany [31]).
Because pyrethroid pesticides have been quite often detected in streams, creeks,
and receiving rivers, they should also reach marine coastal waters. However,
research addressing the occurrence of pyrethroids in estuarine and marine environments is limited. Due to the dilution of river water into the sea, pesticides often fall
below detection limits. For instance, in seawater off Portugal, only two of the nine
targeted pyrethroids could be detected, and only one could be quantified, whereas
five were present in oysters [33]. Analytical difficulties may be a reason for the
scarcity of published data in seawater (Table 1).
A specific risk for the marine environment is associated with aquaculture treatment of salmon against ectoparasites [5, 57]. Formulations used in aquaculture
contain deltamethrin or cypermethrin together with emulsifiers for bath treatment
of caged fish. Once the treatment is over, the bath water is released into the seawater,
where pyrethroids are diluted by currents. In a case study in Canada, the deltamethrin
plume could be detected up to 5.5 h after emission and the plume extended a few km
away from the cages [5]. In this study, deltamethrin was emitted as a dissolved
pesticide, and it was monitored both in the dissolved phase and in the suspended
particles. Interestingly, deltamethrin concentration in the particle phase was approximately three to four times greater than in the aqueous phase, which demonstrates the
quick partition of pyrethroids to organic carbon in seawater and, thus, their affinity
for particles [5]. Variable responses of natural marine microbial communities to the
input of anti-lice pesticides have been evidenced in Southern Chile [58]. At some
locations and season, deltamethrin inputs resulted in an increase of carbon fixation
by photosynthesis, likely resulting from a decrease in arthropod grazing pressure;
however increase in carbon fixation was also observed at other sites and seasons. The
diverse responses observed evidenced complex relationships between environmental
factors (nutrient levels, zooplankton abundance, etc.) and pesticide impacts. These
responses of marine organisms, distinct from toxicity alone, need further research to
understand the overall impact of aquaculture and, more generally, of pyrethroid
emissions, on marine ecosystems. More detailed information on the effect of salmon
industry in the marine environment is presented elsewhere [6].
However difficult it is to detect pyrethroids in the marine environment, this task
should not be overlooked because marine crustaceans and fish have been reported to
be more susceptible to pyrethroids than freshwater ones [29, 34, 48].
4 Occurrence and Composition of Pyrethroids in Sediments
Table 2 documents pyrethroid occurrence in sediments. The solid phase of sediments
acts as a sorbent for pesticides and likely integrates over time water pyrethroid
concentrations in the overflowing water and also the accumulation of sinking
particles in sea and river beds. Because of their quick association to river sediment,
pyrethroid contamination of riverbed sediment has emerged as an important environmental threat to benthic organisms, and the literature reporting sediment toxicity
Fate of Pyrethroids in Freshwater and Marine Environments
91