Chemistry Reference
In-Depth Information
recorded, together with effects on EEG pattern and cognitive performance over a
12-month period (Muggleton et al. 2005). Initial inhibition of AChE was <82%,
but quickly returned to normal. Short-term changes in steep pattern were seen, but
there were no long-term changes in any of the measures made. It should be noted,
however, that inhibition of erythrocyte acetylcholinesterase is likely to be much
higher than inhibition of brain cholinesterase when animals are dosed in this way.
The authors note that there have been reports of long-term effects of low doses of
OPs on central nervous system (CNS) function, including steep, cognitive perfor-
mance, and EEG changes.
Turning now to effects upon fish, Beauvais et al. (2000) showed behavioral effects
following exposures of rainbow trout (
Oncorhynchus mykiss
) to diazinon and mala-
thion. In the case of the malathion treatment, no fish died. Sandahl et al. (2005) obtained
similar results when studying the response of juvenile coho salmon (
Oncorhynchus
kisutch
) to chlorpyrifos. The exposures were all sublethal with no deaths of fish even
at the highest exposure (2.5 μg/L). Significant correlations were observed between
percentage inhibition of brain cholinesterase and spontaneous feeding and swimming
behaviors. At the lowest level of exposure (0.6 μg/L), there was a significant reduction
in AChE activity and, associated with that, significant alterations in swimming and
feeding behaviors. Brain ACh-E was inhibited by 23 (±1%), whereas spontaneous
swimming rate was reduced by 27 (±5%) in the same treatment group (standard errors
in parentheses). Regarding feeding behavior, both the latency to strike and the strik-
ing rate were also significantly affected at this low dose.
In a further study on effects of anticholinesterases on the behavior of fish, cut-
throat trout (
Oncorhynchus clarki clarki
) were exposed to sublethal levels of the car-
bamate insecticide carbaryl (Labenia et al. 2007). In this case, however, significant
effects upon behavior were only demonstrated at high levels of brain cholinesterase
inhibition (above 70%). At this high level, effects were reported on both swimming
performance and avoidance of predation by lingcod (
Ophiodon elongates
). It is worth
mentioning that inhibition of the enzyme by carbamates is more readily reversible
than inhibition by OPs (Chapter 10, Section 10.3.4).
In a wide-ranging review, Grue et al. (1991) give many examples of studies that
have attempted to relate inhibition of cholinesterases by pesticides to physiological
and behavioral effects in mammals and birds. Behavioral effects measured in birds
included changes in walking, singing, and resting. Despite some examples from
well-designed studies in which a relationship was shown, generalizations proved dif-
ficult, and there was much evidence of intraspecific and interspecific variation in
responses to anticholinesterases. It was not possible to define critical levels of brain
cholinesterase activity across species with regard to sublethal effects. However, the
conclusion was that there were examples of the impairment of physiological function
and behavior once inhibition exceeds about 40%. Thus, these studies did not show
such high sensitivity to cholinesterase inhibition as was demonstrated in some of the
behavioral tests upon fish OPs discussed earlier, where there were clear indications
of effects at below 25% inhibition.
Hart (1993) reports a study of behavioral effects of the OP insecticide chlorfenvin-
phos on captive starlings (
Sturnus vulgaris
). Birds were dosed with 3-9 mg/kg of the
insecticide presented orally in the form of capsules. Behavioral effects were related
Search WWH ::
Custom Search