Organophosphorus and Carbamate Insecticides - Organic Pollutants: An Ecotoxicological Perspective - page 217

field may occur when animals or birds experience sufficiently high sublethal expo-
sures to them. It should be emphasized that lethal exposures to OPs have been widely
reported (Section 10.2.4); sublethal exposures must have been more common than
these. Also, the inhibition of oxidative detoxication can bring potentiation of other
readily degradable insecticides apart from CBs, such as pyrethroids and certain OPs.
The problem is that such potentiation is difficult to establish in the field.
CBs, like OPs, can cause a variety of sublethal neurotoxic and behavioral effects.
In one study with goldfish ( Carrasius auratus ), Bretaud et al. (2002) showed effects
of carbofuran on behavioral end points after prolonged exposure to 5 µg/L of the
insecticide. At higher levels of exposure (50 or 500 μg/L), biochemical effects were
also recorded, including increases in the levels of norepinephrine and dopamine in
the brain. The behavioral endpoints related to both swimming pattern and social
interactions. Effects of CBs on the behavior of fish will be discussed further in
Chapter 16, Section 16.6.1.
10.3.5 e c of l of g i c a l e f f e c T s
There have been a number of examples of birds and mammals being poisoned in the
field by the more toxic CBs when used in the recommended way. One such example
was the poisoning of about 100 black-headed gulls ( Larus ridibundus ) on agricul-
tural land by aldicarb (Hardy 1990). The compound had been applied as a granular
formulation to wet soil to control nematodes and insects in a sugar beet crop. Birds
apparently died from consuming granules directly and from feeding upon contami-
nated earthworms. In a field study conducted at Boxworth farm, Cambs, the highly
toxic CB methiocarb was shown to cause lethal poisoning of wood mice ( Apodemus
sylvaticus ) when used as a molluskicide (Greig-Smith et al. 1992b). The compound
had been broadcast on the soil surface as a 4% pelleted formulation. In a further
example, the movement of pesticides was studied from the land surface through a
soil that developed fissures, and then into neighboring water courses (Matthiessen et
al. 1995). Following heavy rains, the elution of carbofuran from a granular formula-
tion into water courses was sufficiently high to kill freshwater shrimps ( Gammarus
spp .) that had been deployed there.
Although the ability of highly toxic CBs to cause lethal poisoning in the field
has been clearly demonstrated, the ecological significance of such effects remains
unclear. In the case of the methiocarb poisoning of wood mice mentioned earlier,
population numbers before and after the application of the molluskicide were esti-
mated by trapping (Greig-Smith et al. 1992b). There was a rapid decline in numbers
immediately following application, but there was also a rapid recovery within a week
or so. In the longer run, the use of the molluskicide did not affect the size of the
mouse population in the treated area. In a more detailed study, it was found that
the broadcasting of molluskicide pellets altered the structure of the population; and
there was a higher proportion of juveniles in the wood mouse population following
broadcasting than in a control population. This change was not seen if pellets were
drilled instead of being broadcast.
The repeated use of carbofuran and other carbamates has been associated with
changes in the metabolic capacity of soil microorganisms (Suett 1986). Carbofuran