Diuron and Linuron
Entry into the marine environment
Diuron and linuron are herbicides which are members
of what is usually known as the phenylurea group.
Diruon is also increasingly being used as a booster
biocide in antifoulant paints. Because of their
similar mode of action, a consideration of the effects
to the marine environment of both linuron and diuron
is discussed here.
These compounds are stable to hydrolysis in the
normal pH range and exist as the undissociated form
in natural waters. The vapour pressures at about
20 °C indicate negligible losses through vaporisation in the
environment, and sunlight-induced photochemical
decomposition is of relatively minor importance.
Phenylurea herbicides are easily taken up from
soil solution by the root systems of plants and
rapidly translocated into stems and leaves by the
transpiration system, moving primarily via the xylem.
Linuron and isoproturon, and to a lesser extent
other phenylurea derivatives, can also be taken
up through application to the leaves, especially
in the presence of surfactants.
The principal mode of action of these substances
is through disruption of photosynthesis, probably
by inhibition of an enzyme involved in the Hill
Lewis and Gardiner (1996) have reviewed data on
the use and fate and behaviour of these herbicides.
Diuron is used extensively on industrial land and
to a limited extent in agriculture. A major user
of diuron in the UK was British Rail to control
weed growth on railway tracks. Its 32,000 km
of track is sprayed annually, with 22 tonnes of
diuron used in 1991. This amount probably increased
as the triazine herbicides, atrazine and simazine,
were banned from August 1993 for non-agricultural
uses. Lewis and Gardiner (1996) were unable to estimate
the total amount of diuron used on industrial land
and around domestic buildings in the UK.
Little information is available on the quantities
of linuron used. However, Lewis and Gardiner (1996)
estimated that approximately 100 tonnes were used
on crops in 1992.
Linuron is mainly used as an agricultural herbicide
and, therefore, its main routes of entry into the
aquatic environment are likely to be run-off, leaching,
spray drift during application, washing down of
machinery used during application and accidental
Recorded levels in the marine
Monitoring data from the National Rivers Authority
(NRA) and the National Monitoring Programme Survey
of the Quality of UK Coastal Waters are presented
in Appendix D Monitoring data for diuron and linuron
were only available for the NRA survey. No water
column concentration was found to exceed the EQS
value (see Appendix D). Monitoring data were not
available for sediments or biota.
The available data suggest that concentrations
of diuron and linuron in UK coastal and estuarine
water do not exceed relevant quality standards derived
for the protection of saltwater life.
Fate and behaviour in the marine
Lewis and Gardiner (1996) found few data on the
fate and behaviour of these herbicides in water.
However, based on the information available, the
authors concluded that removal from water was likely
to be by biodegradation and adsorption, with half-lives
in the range of a few weeks to a few months reported.
Effects on the marine environment
Toxicity to marine organisms
An exhaustive literature review on the toxicity
of diuron and linuron 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 (Lewis and Gardiner
1996). The most sensitive groups of organisms have
Lewis and Gardiner (1996) reviewed the limited
data on the toxicity of linuron and diuron to saltwater
organisms. The authors concluded (although only
acute toxicity data were available) that the results
of Mayer (1987) for diuron and Kemp et al
(1985) for linuron suggested that these herbicides
may have similar toxicities to saltwater organisms.
In freshwaters, algae and macrophytes appear to
be the species most sensitive to these herbicides.
The lowest effect concentrations reported for these
species are approximately 20 µg l-1
and higher for all four herbicides.
Based on data for freshwater organisms, Lewis and
Gardiner (1996) concluded that because of a similar
mode of action, and because it is likely that they
could occur together in the aquatic environment,
it was possible that they could exert an additive
toxic effect on aquatic life when present together.
Sediment dwelling organisms
No data could be located.
Lewis and Gardiner (1996) found no data on the
bioaccumulation of these herbicides in saltwater
organisms. However, data for freshwater organisms
suggest bioaccumulation is unlikely to be significant
(reliable reported BCFs were <100), and therefore
likely to be the same for saltwater organisms.
Potential effects on interest
features of European marine sites
Potential effects include:
- toxic effects on algae and macrophytes at concentrations
above the EQS of 2 mg l-1 in the water column.