Entry into the marine environment
Synthetic pyrethroids are a group of chemicals
which act as neuropoisons, acting on the axons in
the peripheral and central nervous systems. They
are believed to interfere with sodium channels and
the permeability of nerve cells so affecting the
transmission of nerve impulses. Various pyrethroids
are commonly used as insecticides in a variety of
Some examples of pyrethroids commercially available
include allethrin, resmethrin, d-phenothrin and
tetramethrin (for insects of public health importance);
cypermethrin. deltamethrin, fenvalerate, cyhalothrin,
cyfluthrin, lambda-cyhalothrin and permethrin (mainly
for agricultural insect pests). Cypermethrin is
used in cage fish farming for sea lice treatments
and in sheep dip. Thus entry into the aquatic environment
may be through diffuse or point sources.
Recorded levels in the marine
Synthetic pyrethroids are not routinely monitored
for in the UK marine environment.
Fate and behaviour in the marine
The pyrethroids tend to be of low solubility and
adsorb readily to suspended solids and sediments.
Once adsorbed, they are thought to be less bioavailable.
However, at present no methods are available to
analyse or assess the bioavailable fraction of the
Pyrethroids are generally rapidly removed from
the water column (via degradation and sorption)
with half-lives of a few days. The half-lives of
pyrethroids adsorbed to suspended solids and sediments
tends to be considerably longer, i.e. several months.
Effects on the marine environment
Toxicity to marine organisms
An exhaustive literature review on the toxicity
of synthetic pyrethroids to marine organisms has
not been carried out for the purposes of this profile.
The information provided in this section is taken
from existing review documents (Zabel et al
1988, WHO 1989). The most sensitive groups of organisms
have been identified.
Both aquatic invertebrates (especially insects
and crustaceans) and fish have been found to be
highly sensitive to these chemicals. In addition,
based on their mode of action, effects on aquatic
mammals from certain pyrethroids could be expected.
However, data on such effects do not appear to be
As pyrethroids adsorb readily on sediments, there
is a need for sediment standards. There are some
concerns over bioavailability and the effects on
benthic and sediment dwelling organisms. This is
an area where investigations are on-going and the
results so far are uncertain.
Of the pyrethroids available for use in the UK,
only two (permethrin and cyfluthrin) currently have
statutory EQSs for the protection of aquatic life,
although standards for a few other pyrethroids (e.g.
cypermethrin) are under development.
Zabel et al (1988) reviewed data on the
toxicity of permethrin and cyfluthrin to marine
organisms and a summary of these conclusions is
presented below. In addition, cypermethrin is a
pyrethroid which is being increasingly used (such
as in formulations for use against ecotoparasites
on sheep and for sea lice treatments in cage fish
farming). Further information on this is also presented
Invertebrates were found to be more sensitive to
permethrin than fish. The lowest reported LC50 value
was 0.02 µg l-1 for newly-hatched
estuarine mysids (as the test result concentrations
were not analysed there was some uncertainty about
these). The LC50s for Crangon septemspinosa and
Pennies duorarum of 0.13 µg l-1
and 0.22 µg l-1, respectively,
were based on measured concentrations in the water.
Available data on the toxicity to aquatic organisms
was limited to two species of fresh water invertebrates
and three species of freshwater fish. Invertebrates
were the more sensitive organisms. Acute LC/EC50
values of >=5 ng l-1 were
found for freshwater organisms. No data were available
on the toxicity of cyfluthrin to saltwater organisms.
Available data on the toxicity of cypermethrin
to saltwater organisms indicate that acute LC50s
for crustaceans and fish range, in general, from
0.05 µg l-1 upwards (WHO
1989), although an LC50 as low as 0.005 µg
l-1 was reported for the mysid shrimp
Mysidopsis bahia (Hill 1985). In addition,
the LC50 for the lobster Homarus americanus could
be as low as 0.003 µg l-1,
based on a geometric mean of available toxicity
data (McLeese et al 1980).
SEPA Policy No. 30 provides EQSs for cypermethrin
on its use in cage fish farming. The SEPA Fish Farming
Manual describes the application of these EQSs.
The log Kows of these chemicals suggest that bioaccumulation
should be high. However, while there appears to
be uptake of some of these chemicals as a result
of rapid metabolism, bioaccumulation does not appear
to be a problem (WHO 1989).
Potential effects on the interest
features of European marine sites
Potential effects include:
- acute toxic effects on invertebrates, in particular
crustaceans, and fish at concentrations above
EQS values of 0.001 µg l-1
for cyfluthrin and 0.01 µg l-1
for permethrin in the water column. An EQS for
cypermethrin in under development;
- accumulation in sediments where concerns exist
about the effects of sediment dwelling organisms;
- identification of permethrin as an endocrine