Identifying valid surrogates for amphibians and reptiles in pesticide toxicity assessment

Validity of fish, birds and mammals as surrogates for amphibians and reptiles in pesticide toxicity assessment

Environmental pollution is putting amphibians and reptiles at risk, yet these animals are not included in regulations regarding the environmental risk assessment (ERA) of pesticides.

The extent to which other species already used in pesticide toxicity assessment (including fish, birds and mammals) can serve as effective surrogates is currently under debate. This study conducts a systematic review of the available literature. The results reveal a positive correlation between toxicity recorded on fish and aquatic amphibians, but indicate that birds and mammals are generally not good surrogates for reptiles and terrestrial amphibians. Moreover, some chemical-dependent trends were detected, with a number of insecticides found to be more toxic to amphibians or reptiles than to potential surrogates.

These findings highlight an urgent need for further research to reduce uncertainties and contribute to future policymaking regarding the protection of amphibians and reptiles from potentially harmful pesticides.

2018 Study Abstract

Amphibians and reptiles are the two most endangered groups of vertebrates. Environmental pollution by pesticides is recognised as one of the major factors threatening populations of these groups. However, the effects of pesticides on amphibians and reptiles have been studied for few substances, which is partly related to the fact that these animals are not included in the mandatory toxicity testing conducted as part of environmental risk assessments of pesticides. Whether risks of pesticides to amphibians and reptiles are addressed by surrogate taxa used in risk assessment is currently under debate. In order to develop a scientifically sound and robust risk assessment scheme, information needs to be gathered to examine whether fish, birds and mammals are valid surrogates for amphibians and reptiles.

We updated a systematic review of scientific literature that was recently published compiling toxicity data on amphibians and reptiles. The outcome of this review was analysed with the purposes to

  1. compare endpoints from amphibians and reptiles with the available information from fish, birds and mammals,
  2. and develop species sensitivity distributions (SSDs) for those substances tested in at least six amphibian species (no substances were found tested in at least six reptile species) to identify a candidate amphibian model species to be used as surrogate in risk assessment.

A positive correlation was found between toxicity recorded on fish and amphibians, the former revealing, in general, to be more sensitive than the latter to waterborne pollutants. In the terrestrial environment, although birds and mammals were more sensitive than amphibians and reptiles to at least 60% of tested substances, just a few weak significant correlations were observed. As a general rule, homoeothermic vertebrates are not good surrogates for reptiles and terrestrial amphibians in pesticide risk assessment. However, some chemical-dependent trends were detected, with pyrethroids and organochlorine insecticides being more toxic to amphibians or reptiles than to birds or mammals. These trends could ultimately help in decisions about protection provided by surrogate taxa for specific groups of substances, and also to determine when risk assessment of pesticides needs to pay special consideration to amphibians and reptiles.

The outcome of this review reflects that there is still much information needed to reduce uncertainties and extract relevant conclusions on the overall protection of amphibians and reptiles by surrogate vertebrates.

Author: DES Daughter

Activist, blogger and social media addict committed to shedding light on a global health scandal and dedicated to raise DES awareness.

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