Entry into the marine environment
Malathion is a contact- and stomach-acting organophosphorus
pesticide which inhibits acetylcholinesterase (AChE)
activity, thus disrupting the nervous system and
making it toxic to all innervated animals. In higher
vertebrates, it is readily hydrolysed to inactive
derivatives. Malathion's broad-spectrum action has
led to widespread use against insect and other invertebrate
pests. In Europe, most malathion is used in agriculture,
principally against mite and insect pests of oilseed
rape, root crops, vegetables and fruits. Other uses
include domestic, horticultural and glasshouse pest
control (mostly against aphids), and application
against ectoparasites of humans and animals.
Malathion may enter the aquatic environment, either
directly in industrial effluents, or indirectly
in run-off from land or by deposition from the atmosphere
(following spray drift or in precipitation).
Recorded levels in the marine
80 river and estuary sites were sampled twice for
malathion over the winter of 1988-89 (SAC Scientific
1989 cited in Hedgecott (1991)). At 11 sites, malathion
was detected once, with a mean concentration of
1.5 ng l-1 (range 1.0 to 3.0 ng l-1).
At a 12th, malathion concentrations of 5.1 and 7.8
ng l-1 were recorded. At all other sites,
malathion was below the detection limit of 1 ng
l-1 (there is no further information
as to whether malathion was detected at any of the
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 data suggest that concentrations of malathion
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
The available data indicate that biodegradation
is an important removal process for malathion in
the aquatic environment, with various species of
bacteria and fungi able to utilise it as a source
of either carbon or phosphorus. Paris et al (1975a,
1975b) estimated half-lives for degradation by freshwater
bacteria of 28 and 41 hours (initial concentrations
approximately 1.5 and 1.1 mg l-1).
Efficient biodegradation has also been observed
in saline waters (Bourquin 1977). The Marine Biological
Association (MBA) (1979) report biodegradation rates
for estuarine and saltwater micro-organisms corresponding
to half-lives of 0.5 to 9 days and 3 to 12 days
or more, respectively.
Malathion has a low vapour pressure and does not
readily volatilise. Sorption to suspended solids
and sediments will account for some removal from
water. The major abiotic removal process in water
is hydrolysis. The MBA (MBA 1979) provides estimates
of half-lives in sea water, ranging from 7 to 40
days at 10 °C,
and from 2 to 9 days in sterile sea water at 25°C.
Effects on the marine environment
Toxicity to marine organisms
An exhaustive literature review on the toxicity
of malathion 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 (Hedgecott 1991). The most sensitive
groups of organisms have been identified.
The most sensitive saltwater organisms tested are
certain crustaceans, with lowest acute LC50s or
EC50s of 0.4 to 3.1 µg l-1
for Dungeness crabs Cancer magister and mysid
shrimps Mysidopsis bahia (Caldwell 1977,
Goodman et al 1988), and retarded development
of Dungeness crab eggs and larvae at 0.3 µg
l-1 (reported by MBA 1979). Hedgecott
(1991) concluded that early life stages of crustaceans
may be more sensitive than adult stages.
Fish species appear to be less sensitive with a
maximum acceptable concentration of 6 µg
l-1 reported for a full life cycle test
with sheepshead minnows Cyprinodon variegatus
(reported by Suter and Rosen 1988). An acute
LC50 of 300 µg l-1 has been
reported by the MBA (1979) for adult sheepshead
Hedgecott (1991) found no bioaccumulation data
for saltwater species, but concluded it would not
expected to differ greatly from that found for freshwater
organisms (i.e. low).
Potential effects on interest
features of European marine sites
Potential effects include:
- acute toxicity to invertebrate (particularly
crustacea) and fish to concentrations above the
EQS of 0.02µg l-1 (annual
average) and 0.5 µg l-1 (maximum
allowable concentration) in the water column.