Entry into the marine environment
Dichlorvos is a contact and stomach-acting insecticide
and is used as a household and public health insecticide.
Dichlorvos, as the active ingredient of Nuvan 500
EC (also known as Nuvan 50 EC and Aquaguard, 50%
wt/vol or 500 g ai l-1), was used extensively
in salmon farming to control the salmon louse Lepeophtheirus
salmonis (although it appears its use in this
industry is diminishing).
The principal, direct routes of entry for dichlorvos
into waters include industrial effluents and accidental
discharges (e.g. from pesticide manufacturing plants,
formulation plants and marketing outlets), use in
salmon fisheries, disposal of unused insecticide
and the cleaning of application and mixing equipment.
Dichlorvos may also indirectly enter the aquatic
environment via spray drift during application and
in land run-off.
Recorded levels in the marine
Monitoring data from the National Rivers Authority
and the National Monitoring Programme Survey of
the Quality of UK Coastal Waters are presented in
Appendix D. Only one water column concentration
was found to approach the EQS value (see Appendix
D). Monitoring data were not available for sediments
The available data suggest that concentrations
of dichlorvos in UK coastal and estuarine water
are unlikely to generally exceed relevant quality
standards derived for the protection of saltwater
Fate and behaviour in the marine
Dichlorvos is rapidly degraded in water both chemically
and biologically. The main degradation process is
hydrolysis. Persistence in water is low (days) and
depends on the pH and temperature (Jones and Stewart
The vapour pressure of dichlorvos is relatively
low so it is therefore unlikely that volatilisation
is a significant removal process from the aquatic
environment. Adsorption is not expected to be a
significant removal pathway due to the low octanol-water
(log Kow = 1.4) and soil organic carbon-water (log
Koc = 1.34) partition coefficients.
Effects on the marine environment
Toxicity to marine organisms
An exhaustive literature review on the toxicity
of dichlorvos 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 (Jones and Stewart 1996). The most
sensitive groups of organisms have been identified.
The principal source of dichlorvos in the marine
environment is the direct application to salmon
farms located in estuaries and coastal waters.
Only two studies investigating the toxicity of
dichlorvos to marine algae have been reported and
the results indicate a relatively high tolerance
compared to other phyla.
Jones and Stewart (1996) reviewed data on the toxicity
of dichlorvos to marine organisms. The authors concluded
that crustaceans were the most sensitive class.
The lowest acute 96 hour LC50 values for adult crustacean
species include 4 µg l-1
for the sand shrimp Crangon septemspinosa,
15 µg l-1 for the grass
shrimp Palaemonetes vulgaris (Eisler 1969),
4.4 µg l-1 for the shrimp
Crangon crangon and 9 µg l-1
for the amphipod Hyale nilssoni (Thain et
al 1990, McHenery et al 1990a).
Early life stages of the common lobster Homarus
gammarus show similar sensitivity to the effects
of dichlorvos as the adult sand shrimp. The 12,
24, 48 and 96 hour LC50s for stage 5 lobster larvae
were 53, 28, 11 and 5.7 µg l-1,
respectively (Ciba-Geigy SP 3560.25 cites in Jones
and Stewart 1996) and the corresponding calculated
12 and 96 hour NOEC values were 6.25 and 1.56 µg l-1,
respectively (McHenery et al 1990b).
Marine fish species appear to have similar sensitivities
to the toxic effects of dichlorvos as freshwater
fish species. Reported acute LC50 values for adult
fish range from 200 µg l-1
for striped mullet (Eisler 1970) to 5 mg l-1
for goby (Hirose and Kitsukawa 1976). Early life
stages of herring appear to be only marginally more
sensitive with a 96 hour LC50 of 122 µg l-1
(Ciba-Geigy SP 3560.25 cited in Jones and Stewart
Jones and Stewart (1996) concluded that bioaccumulation
in marine organisms was likely to be low.
Potential effects on interest features of European
Potential effects include:
- toxicity to invertebrates (particularly crustacea)
and fish to concentrations above the EQS of 0.04
(annual average) and 0.6 mg
l-1 (maximum allowable concentration)
in the water column.