Organophosphates are a group of chemicals which
act by inhibiting the enzyme acetylcholinesterase
(AChE) in the nervous system. Organophosphorus pesticides
are effective insecticides and are widely used in
the UK. However, they can have a harmful effect
on non-target organisms by inhibiting AChE activity.
Toxic effects of AChE inhibition vary with the degree
of exposure and the type and concentration of organophosphate
pesticide. Sub-lethal effects are poorly understood,
but have shown changes in behaviour, reproduction,
ability to cope with food and environmental stress,
leading to paralysis, convulsions and ultimately
The solubility, sorption, potential to bioaccumulate
and extent of toxicity to aquatic life tend to vary
according to the organophosphate. In addition, based
on their mode of action, effects on aquatic mammals
could be expected. However, data on such effects
do not appear to be available.
Azinphos-methyl, malathion, fenitrothion and dimethoate
have been identified as of potential concern in
the marine environment. Profiles of these organophosphates
are presented in sections linked below.
Azamethiphos is an organophosphate pesticide used
for the treatment of sea lice in cage fish farming.
The control of this substance in this application
is detailed in SEPA's Fish Farming Manual which includes operational
EQSs for azamethiphos (SEPA Policy No. 17). The
reader is referred to the Fish Farm Manual for further
information on this substance.