The exposure and toxicity of pesticides to amphibians

Amphibians and pesticides
2.2.1.3. Assimilation efficiencies for amphibians
Assimilation efficiency in southern toads (Bufo terrestris) fed house crickets was 73.70% (Smith
1976). While gut retention time was significantly longer at 20°C than at 30°C, assimilation efficiency
was not different over this temperature range.
The assimilation efficiencies of two African reed frog species when fed on flies (Musca) were
determined by Grafe et al (1992). Assimilation efficiencies in Hyperolius viridiflavus ommatostictus
were 85/6% for gravid females, 84.6% for post-reproductive females and 87.7% for males.
Assimilation efficiencies in at Hyperolius marmoratus taeniatus were 81.4% in juveniles, 84.3% in
gravid females, 86.3% in post-reproductive females and 84.9% in males.
The assimilation efficiency of several species fed on mealworms was determined by Dimmitt and
Ruibal (1980). Three temperatures from 20-30°C were used (Table 7).
Table 7: Assimilation efficiencies of amphibian species fed mealworms (Dimmitt and Ruibal
(1980)
Temperature during experiments 20°C 25°C 30°C
Species tested Assimilation efficiency (%)
Bufo boreas - - 94
Bufo cognatus 94 94 94
Bufo punctatus - - 92 -
Scaphiopus intermontanus - 84 -
Scaphiopus hammondi 94 90 -
Scaphiopus couchi - 92 95
In another species, the red-backed salamander (Plethodon cinereus) fed on fruit flies, temperature was
found to affect assimilation efficiency. Assimilation efficiency at 10, 15 and 20°C were 91.4, 85.9 and
79.8% for males and 89.3, 85.6 and 79.9% for females respectively.
The effect of food type on assimilation efficiency was shown by Dimmit and Ruibal (1980) when
Scaphiopus couchi was fed different foods. When fed mealworm larvae, assimilation efficiency was
92% but when fed adults the assimilation efficiency fell to 69%. When fed alate termites
(Gnathamitermes perplexus) assimilation efficiency was 89%, but for scarabs (Cyclocephala spp. or
Phyllophaga spp.) assimilation efficiency was 65-66%.
2.2.2. Dermal exposure
The risks to amphibians from dermal exposure to pesticides are higher than other groups due to a) the
lack of hairs, feathers or scales which may form a partial barrier to exposure and b) the presence of
specialised structures to enhance absorption (e.g. a vascularised pelvic patch). It can therefore be
assumed that should amphibians come into contact with a contaminated substrate that at least some
exposure will occur. A recent review of terrestrial risk (Bruhl et al. 2011) found that while dermal
exposure and uptake is a significant threat to amphibians, exposure and toxicity studies for terrestrial
life stages are scarce.
2.2.2.1. Literature found relating to dermal exposure
Forty-one references were found in the initial literature search relating to amphibian skin, dermal
uptake, pesticide effects on transport across the skin and dermal toxicity studies (Table 8).
Supporting publications 2012:EN-343 26
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