Trifluralin
Entry into the marine environment
Trifluralin is applied as a herbicide for pre-emergent
control of annual grasses and some broad leaved
weeds in a wide variety of vegetables and some fruit.
It is usually directly incorporated into soils,
although some trifluralin mixtures may be sprayed.
Trifluralin may enter the aquatic environment predominantly
via diffuse sources resulting from its recommended
use, e.g. in agricultural run-off bound mainly to
soil particles. Industrial discharges, accidental
spillages during transport, storage and use are
potential point sources of trifluralin contamination.
Recorded levels in the marine
environment
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. 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 trifluralin in UK coastal and estuarine waters
do not exceed relevant quality standards derived
for the protection of saltwater life.
Fate and behaviour in the marine
environment
Jones (1996) reviewed the fate and behaviour and
aquatic toxicity of trifluralin. Trifluralin is
readily adsorbed on solid surfaces. The solubility
and log Kow are also expected to be pH dependent.
A realistic value for solubility is likely to be
below 1 mg l-1 and for log Kow greater
than 4. The low vapour pressure indicates that loss
from the water phase by volatilisation will be slow.
Kearney et al (1977) studied the degradation
of trifluralin in model aquatic ecosystems containing
a variety of organic matter. The addition of 100
g loam containing 1 µg g-1
of labelled trifluralin to a 4 litre aquarium filled
with water resulted in a maximum water concentration
after 30 days of 7.5 µg l-1
based on 14C measurement. After 33 days, only degradation
products were isolated from the water and no trifluralin
was detected in fish placed in the tank for the
last 3 days of the test. As the experiment was carried
out in daylight, photolysis was probably the major
degradation process.
In the environment, biodegradation is not thought
to be an important pathway for the removal of trifluralin
from water or soils (Shuker and Hutton 1986). Photodecomposition
is the major degradation process for trifluralin
released into the aquatic environment (Helling 1976).
Kosinski (1984) added trifluralin to artificial
streams and calculated a half-life of less than
one hour. The rapid loss of chemical was attributed
to photodecomposition.
However, trifluralin present in the aquatic environment
is likely to be readily degraded by photolysis and
adsorbed onto sediments.
Effects on the marine environment
Toxicity to marine organisms
An exhaustive literature review on the toxicity
of trifluralin 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 1996). The most
sensitive groups of organisms have been identified.
Jones (1996) reviewed the aquatic toxicity of trifluralin.
Data for marine organisms were found to be limited.
Jones (1996) concluded that elevated trifluralin
concentrations in the marine environment were likely
to occur only in estuaries receiving significant
freshwater inputs contaminated with run-off from
agricultural land. Most of the trifluralin entering
marine waters is therefore likely to be adsorbed
on suspended solids and may therefore not be readily
bioavailable. Invertebrates and fish were found
to exhibit the greatest sensitivity.
Algae
Walsh (1972) reported that 2.5 mg l-1
of trifluralin reduced the growth of four marine
phytoplankton species by 50%. No other data were
found for marine algae.
Invertebrates
Liu and Lee (1975) exposed adults and larvae of
the mussel Mytilus edulis to trifluralin.
Larval growth was inhibited at 90 µg l-1
and 100 µg l-1 affected
the ability of adults to attach to glass. The corresponding
LC50 for adults was 240 µg l-1.
The effects of a technical mixture of trifluralin
(93% active ingredient) on eggs, larvae, juveniles
and adults of Cancer magister (Dungeness
crab) were investigated by Caldwell et al (1979).
Exposure to 590 µg l-1
for 24 hours in static water did not affect egg
hatching success or first stage zoeal motility.
In a further long-term continuous flow test with
larvae, juveniles and adults 220 µg l-1
produced 100% mortality of zoea after 8 days, whereas
exposure to 26 µg l-1
for 50 days produced no significant effects on survival
but significantly delayed the first molt. The survival
of juveniles exposed for 80 days to 590 µg l-1
and of adults exposed to 300 µg l-1
for 85 days was not affected. Based on the results
for the larval stages the MATC for the crab was
estimated to be 326 and <220 µg l-1.
Fish
Trifluralin was found to be very toxic to sheepshead
minnows Cyprinodon variegatus (Couch et
al 1979). Exposure to 5.5-31 µg l-1
for the initial 28 days of life resulted in acute
vertebral dysplasia which was thought to be a direct
result of the effect of trifluralin on the hormonal
control of calcium metabolism. High calcium levels
were found in the blood serum of adult sheepshead
minnows exposed to 16.6 µg l-1.
Wells and Cowan (1982) also reported spinal deformities
in minnows exposed to 16 µg l-1
for 51 days.
Parrish et al (1978) studied sheepshead
minnows exposed to trifluralin over a full life
cycle (166 days). Exposure to 17.7 µg l-1
caused significant mortality of adult fish, whereas
9.6 and 4.8 µg resulted in significantly
reduced growth and fecundity of adult fish, respectively.
In addition, significantly reduced hatching success
of embryos spawned by parent fish and survival and
growth of the second generation fish were observed
on exposure to 9.6 µg l-1.
From the results, an MATC of >1.3 and <4.8 µg l-1
was estimated for the sheepshead minnow.
Sediment-dwelling organisms
Trifluralin is likely to be absorbed to sediment
but no data could be located on the toxic effects
to sediment-dwelling organisms.
Bioaccumulation
No data on the bioaccumulation of trifluralin in
marine organisms could be located. However, it has
been demonstrated by Garnas (1976) that marine invertebrates
metabolise trifluralin via oxidative, reductive,
hydrolytic and conjugative pathways. High BCF (>1,000
for algae and fish) and slow depuration (generally
in the order of weeks) have been reported for freshwater
organisms. Therefore, there is potential for bioaccumulation,
although trifluralin is likely to be adsorbed to
sediment and therefore its bioavailability is uncertain.
Potential effects on interest
features of European marine sites
Potential effects include:
- toxic effects to algae, invertebrates and fish
at concentrations above the EQS of 0.1 mg l -1
(annual average) and 20 mg
l-1 (maximum allowable concentration)
in the water column;
- accumulation in sediments but there is no evidence
of effects on sediment-dwelling organisms;
- potential to bioaccumulate but there is no evidence
of bioaccumulation in marine organisms, including
fish, birds and Annex II sea mammals;
- trifluralin has been identified as an endocrine
disrupting substance and a precautionary approach
should be adopted in its control.
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References
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