Entry into the marine environment
Bentazone is a contact herbicide absorbed by the
leaves and is used to control broad leafed weeds
in winter and spring cereals. In 1992, 85 tonnes
of bentazone were used in Great Britain, which declined
to 73 tonnes in 1994. In 1994, it was the 40th
most commonly used active substance on arable crops
(PSD Data, Pers. Comm., Dr Marsden, DoE 1996).
The main mode of action of bentazone is by inhibition
of photosynthesis, causing depletion of carbohydrate
reserves and loss of chloroplast membrane integrity
(Fletcher and Kirkwood 1982).
The major diffuse sources of bentazone into the
aquatic environment are likely to be run-off from
soils or accidental over-spray as a result of its
use on agricultural land. Bentazone has a low affinity
for particulate or organic carbon material, log
Kow of 0.35, (RSC 1991); log Koc of 2.42 (Donigian
and Carsel 1987).
Recorded levels in the marine
Murgatroyd et al (1996) reported that no
exceedances to the EQS were measured in estuarine
or coastal waters by the NRA in 1993. In other parts
of Western Europe, up to 1 µg l-1
(Leistra and Boestsen 1989) of bentazone has been
recorded. However, in estuarine and coastal waters,
bentazone concentrations are generally below detection
limits (Readman et al. 1993).
The available data suggest that concentrations
of bentazone in UK coastal and estuarine waters
are unlikely to exceed relevant quality standards
derived for the protection of saltwater life.
Fate and behaviour in the marine
Murgatroyd et al (1996) reviewed the fate
and behaviour and aquatic toxicity of bentazone.
However, little information was available.
Photolysis appears to be the main abiotic degradation
process for bentazone (80% degradation of bentazone
in a 24 hour period when exposed to artificial
sunlight, Nilles and Zabik 1975), as in water, no
hydrolysis of 1 mg l-1 of bentazone
was observed after 122 days at 22 °C
(US EPA 1987).
Effects on the marine environment
Toxicity to marine organisms
An exhaustive literature review on the toxicity
of bentazone 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 (Murgatroyd et al 1996).
The most sensitive groups of organisms have been
Murgatroyd et al (1996) found no reliable
data on the toxicity of bentazone to marine organisms,
but concluded that bentazone was of low to moderate
toxicity to freshwater organisms, with acute effects
ranging from 10-6,232 mg l-1
(saltwater organisms are likely to exhibit similar
Algae appear to be the most sensitive species.
Bentazone affects algae through inhibition of photosynthesis
and, although no data are available, aquatic macrophytes
are likely to be of equal or greater sensitivity.
The majority of reliable toxicity data indicates
that invertebrates and fish are much less sensitive
to bentazone than algae.
Sediment dwelling organisms
No data could be located.
Murgatroyd et al (1996) found no data on
bioaccumulation in marine orgasms, but concluded,
based on evidence for freshwater organisms, that
the bioaccumulation potential for bentazone was
Potential effects on interest
features of European marine sites
Potential effects include:
- toxic effects on algae and macrophytes at concentrations
above the EQS of 500 mg l-1 (annual average) and 5,000
mg l-1 (maximum allowable concentration)
in the water column.