3 Environmental Fate
Environmental fate of pyrethroid insecticides occurs in different compartments,
water, soil, and air. They have been widely detected at the global scale, with most
reports being from China and the United States. In general, concentrations in soils
and sediment are higher than those of air and water, being pyrethroid levels two
orders of magnitude lower in water than in both soils and sediments [2]. In this
book there are different chapters dealing with this topic. “Fate of Pyrethroids in
Freshwater and Marine Environments”, “The Ecological and Evolutionary Implications of Pyrethroid Exposure: A New Perspective on Aquatic Ecotoxicity” and
“Environmental Risks of Synthetic Pyrethroids Used by the Salmon Industry in
Chile” were more focused on the water-soil system, whereas chapter “Indoor and
Outdoor Pyrethroid Air Concentrations” evaluates the impact in air.
Pyrethroids have high n-octanol-water partition coefficients (K ow ), with log
K ow values ranging from 4 to 7.5, indicating that these chemicals are much more
likely to partition into the sediment and sorb to particulate organic matter than to
remain in the water column [3]. However, and despite being highly lipophilic,
pyrethroids may remain in the water column for days to weeks and can produce
toxic effects at low concentrations. Generally, concentrations are under the 100 ng/L
range for water samples, being cyhalothrin and bifenthrin those reaching the highest
levels and also those more frequently exceeding regulatory threshold levels in
surface freshwater. Acute mortality has been documented far below 1 μg/L range
for fish and crustaceans [4], and acute toxicity has even been documented at levels
below 1 ng/L [5]. The potential combined acute and chronic effects on aquatic
ecosystems must be taken into account. It is also important to evaluate the possible
synergistic or antisinergic effects between different pyrethroid insecticides, as well
as among other different pollutants also present in aquatic ecosystems. Only taking
these effects into account, we will be able to correctly assess the real effects of these
compounds in aquatic media.
Most pyrethroids will be transported into sediments after entering water
bodies, while some will evaporate into the atmosphere or enter the ocean. A recent
review documented the occurrence of pyrethroids in sediments worldwide [6].
As expected and due to their lipophilicity, sediment concentration levels are higher
than those found in water samples, being generally under the 100 ng/g range.
Moreover, pyrethroid occurrence showed significant correlations with sediment
toxicity. The frequent occurrence at high concentrations of pyrethroids in sediments
from agricultural and residential areas constitutes a threat to freshwater ecosystems.
Historically, some pyrethroids were added to water directly as mosquito and
black fly larvicides, but their toxicity, hydrophobicity, and sediment persistence
have restricted their direct use in aquatic environments. However, in aquaculture,
pyrethroids are still added directly to the water to remove parasites from farmed
fish. Aquaculture is a locally direct source that likely constitutes an important
environmental burden for seawater, which it is very poorly surveyed.
Chapter “Environmental Risks of Synthetic Pyrethroids Used by the Salmon Industry in Chile” summarizes the effects of these applications, specifically the sea lice
Conclusions and Future Trends
309
Environmental fate of pyrethroid insecticides occurs in different compartments,
water, soil, and air. They have been widely detected at the global scale, with most
reports being from China and the United States. In general, concentrations in soils
and sediment are higher than those of air and water, being pyrethroid levels two
orders of magnitude lower in water than in both soils and sediments [2]. In this
book there are different chapters dealing with this topic. “Fate of Pyrethroids in
Freshwater and Marine Environments”, “The Ecological and Evolutionary Implications of Pyrethroid Exposure: A New Perspective on Aquatic Ecotoxicity” and
“Environmental Risks of Synthetic Pyrethroids Used by the Salmon Industry in
Chile” were more focused on the water-soil system, whereas chapter “Indoor and
Outdoor Pyrethroid Air Concentrations” evaluates the impact in air.
Pyrethroids have high n-octanol-water partition coefficients (K ow ), with log
K ow values ranging from 4 to 7.5, indicating that these chemicals are much more
likely to partition into the sediment and sorb to particulate organic matter than to
remain in the water column [3]. However, and despite being highly lipophilic,
pyrethroids may remain in the water column for days to weeks and can produce
toxic effects at low concentrations. Generally, concentrations are under the 100 ng/L
range for water samples, being cyhalothrin and bifenthrin those reaching the highest
levels and also those more frequently exceeding regulatory threshold levels in
surface freshwater. Acute mortality has been documented far below 1 μg/L range
for fish and crustaceans [4], and acute toxicity has even been documented at levels
below 1 ng/L [5]. The potential combined acute and chronic effects on aquatic
ecosystems must be taken into account. It is also important to evaluate the possible
synergistic or antisinergic effects between different pyrethroid insecticides, as well
as among other different pollutants also present in aquatic ecosystems. Only taking
these effects into account, we will be able to correctly assess the real effects of these
compounds in aquatic media.
Most pyrethroids will be transported into sediments after entering water
bodies, while some will evaporate into the atmosphere or enter the ocean. A recent
review documented the occurrence of pyrethroids in sediments worldwide [6].
As expected and due to their lipophilicity, sediment concentration levels are higher
than those found in water samples, being generally under the 100 ng/g range.
Moreover, pyrethroid occurrence showed significant correlations with sediment
toxicity. The frequent occurrence at high concentrations of pyrethroids in sediments
from agricultural and residential areas constitutes a threat to freshwater ecosystems.
Historically, some pyrethroids were added to water directly as mosquito and
black fly larvicides, but their toxicity, hydrophobicity, and sediment persistence
have restricted their direct use in aquatic environments. However, in aquaculture,
pyrethroids are still added directly to the water to remove parasites from farmed
fish. Aquaculture is a locally direct source that likely constitutes an important
environmental burden for seawater, which it is very poorly surveyed.
Chapter “Environmental Risks of Synthetic Pyrethroids Used by the Salmon Industry in Chile” summarizes the effects of these applications, specifically the sea lice
Conclusions and Future Trends
309