Fenitrothion is a contact-acting organophosphorus pesticide which inhibits acetylcholinesterase (AChE) activity, thus disrupting the nervous system. In view of its broad-spectrum action, it is widely used against insect pests. Most fenitrothion applied in Europe is used in agriculture, but is also used in conjunction with pyrethroids to protect stored grain against insect damage, and in a number of domestic ant and fly killers.

Most input of fenitrothion into estuarine and marine waters is likely to be associated with river outflows.

Hedgecott (1996) reported limited information on the concentration of fenitrothion in marine waters. In a survey of 80 UK rivers and estuaries conducted in the winter of 1988-89, fenitrothion was below the detection limit of 10 ng l^-1 in all samples (SAC Scientific 1989).

The few data reported for aquatic (freshwater) sediments indicate low levels of adsorbed fenitrothion.

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 fenitrothion in UK coastal and estuarine water do not exceed relevant quality standards derived for the protection of saltwater life.

Hedgecott (1996) reviewed the fate and behaviour of fenitrothion. It is not particularly soluble, and combined with a log octanol-water partition coefficient (Kow) of 3.38, suggests a moderate tendency to associate with solids and organic matter. The low vapour pressure indicates a low tendency to volatilise.

Fenitrothion is readily degraded by micro-organisms found in sludge, soil and water via dealkylation, hydrolysis, oxidation and reduction. The main abiotic removal process acting on dissolved fenitrothion is photolysis, with carboxy fenitrothion as the main product. Weinberger et al (1982b) noted that fenitrothion dissolved in either fresh or estuarine water was reduced by 80% (from 2.5 to 0.5 mg l^-1) within six hours when exposed to natural sunlight in static laboratory systems. Degradation was more efficient in the estuarine water. In flowing systems, degradation was slower, possibly as a result of increased turbidity.

Caunter and Weinberger (1988) determined a half-life of about 31 hours for fenitrothion in the light in the laboratory, with photodegradation apparently being the major removal process. In the presence of algae, under similar conditions, the half-life was only about 16 hours. Sorption to the algae, and possibly also enhanced photodegradation following sorption, were responsible for this higher rate of loss.

Sorption to aquatic sediments (and soils) is directly related to their organic content and so varies between sites. Weinberger et al (1982a) considered sediments to be a major sink for fenitrothion in lake microcosms in both the laboratory and the field.

An exhaustive literature review on the toxicity of fenitrothion 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 1996). The most sensitive groups of organisms have been identified.

Persoone et al (1985) concluded that saltwater and freshwater crustaceans had similar sensitivities to fenitrothion, although this conclusion was based on limited data. Data suggesting similar sensitivities of fish were somewhat more extensive. There are too few recent data to assess the validity of these conclusions. However, Hedgecott (1996) concluded that data from laboratory studies indicated that certain species of arthropods were more sensitive to fenitrothion than any other tested freshwater organisms.

For the tiger shrimp Pennies japonicus Kobayashi et al (1985) obtained 50% survival times of approximately 24 hours at 1 µg l^-1 and 10 hours at 2 µg l^-1. Mayer (1987) reported an EC50 of 1.5 µg l^-1 for mobility of brown shrimps Pennies aztecus. For molluscs, Mayer (1987) reported a 96 hour EC50 of 450 µg l^-1 for shell deposition in juvenile oysters Crassostrea virginica.

Takimoto et al (1987) estimated 96 hour LC50s of 2.1 mg l^-1 and 2.6 mg l^-1 for adult killifish Oryzias latipes and mullet Mugil cephalus respectively when acclimated to and exposed in water of 23 ppt salinity. Equivalent LC50s in freshwater were similar, at 3.5 and 2.6 mg l^-1 respectively.

Hedgecott et al (196) observed low to moderate bioaccumulation in marine organisms.

The data on bioaccumulation of fenitrothion by marine organisms suggest similar levels as those in freshwater organisms, with BCFs of 179 and 303 for fish and 139 for the tiger shrimp (Takimoto et al 1987, Kobayashi et al 1985). Although the shrimp BCF is higher than the figures for similar freshwater invertebrates, the difference is not large. McLeese et al (1979) noted that uptake rates by soft-shelled clams Mya arenaria and mussels Mytilus edulis were quite low and excretion rates quite high. The authors suggested that water concentrations below 0.01 mg l^-1 were unlikely to result in significant contamination of tissues of these organisms.

Potential effects include:

• acute toxicity to invertebrates and fish at concentrations above the EQS of 0.01 mg l^-1 (annual average) and 0.25 mg l^-1 (maximum allowable concentration) in the water column.

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