Organophosphorus and Carbamate Insecticides - Organic Pollutants: An Ecotoxicological Perspective - page 210

residues in carcasses of animals or birds found in the field do not provide reliable
evidence of the cause of death (cf. the persistent OCs). Supporting evidence, such as
inhibition of brain AChE activity, is usually needed to establish causality. From an
ecological point of view, such compounds appear less hazardous than compounds
such as dieldrin or heptachlor epoxide, which are both highly toxic and persistent.
There are, however, situations in which they may still cause ecological problems. If
they are applied to an area of farmland or to an orchard several times a year over
several years, effects may be seen on species of limited mobility, which are slow to
recolonize treated areas after OP residues have declined. This problem may be com-
pounded if other nonpersistent insecticides (e.g., carbamates and pyrethroids) are
also used. Effects of this kind have been reported from the Boxworth Experiment—a
long-term field experiment conducted by the Ministry of Agriculture, Fisheries, and
Food (MAFF) in Eastern England during 1982-1990 (Greig-Smith et al. 1992a). In
areas where OPs, pyrethroids, and carbamates were extensively used (“insurance
areas”), some nondispersive species, such as the ground beetles Bembidium obtusum
and Notiophilus biguttatus, fell drastically in numbers during the first 3 years, and
remained low or totally absent until the end of the experiment. In general, there was
a decline of predatory invertebrates in the area receiving the highest input of pesti-
cide (cf. the control area).
There is concern from an ecological point of view if a high proportion of the
population of a protected species is present in a particular area when a highly toxic
chemical is being used. An example of this problem was the heavy mortality of win-
tering greylag geese ( Anser anser ) and pink-footed geese ( Anser brachyrhynchus )
in east central Scotland during 1971-1972 (Hamilton et al. 1976). Deaths were due
to consumption by the geese of the OP carbophenothion, used as a seed dressing for
winter wheat and barley. The geese consumed uncovered seed, and also seedlings
with the contaminated seed coat still attached. It transpired that carbophenothion
was particularly toxic to geese belonging to the genus Anser , more toxic than had
been realized in the original risk assessment of the OP. Branta geese, such as the
Canada goose ( Branta canadensis ), were found to be less susceptible. It was esti-
mated that 60,000-65,000 wintering greylag geese, representing about two thirds
of the entire British population, came to this area of Scotland during autumn in the
early 1970s. Hundreds of birds died, and it was concluded that carbophenothion rep-
resented an unacceptable hazard to wintering Anser geese in east central Scotland.
Subsequently, the use of carbophenothion as a seed dressing for winter wheat or
barley was banned in the affected area.
Another example where OP spraying evidently caused ecological problems was
the large-scale application of fenitrothion to forests in New Brunswick, Canada
(Ernst et al. 1989; Chapter 15 in Walker et al. 2000, 2006). As described earlier
(Section 10.2.4), deaths of individual birds were attributed to acute poisoning by
the OP. The mortality rate due to poisoning, however, was not known, although the
levels of ChE inhibition measured in surveys suggested that it may have been high.
There was evidence for severe reproductive impairment in the white-throated spar-
row ( Zonotrichia albicollis ) associated with a mean brain AChE inhibition of 42%.
In general, many birds sampled in the area had 50% inhibition of brain AChE or
more, and it was suspected that sublethal effects on birds were widespread. Apart