AMPHIBIAN TOXICOLOGY

Amphibian Toxicology

Amphibian Toxicology

Review Article on Amphibian Toxicology

Mann RM, Hyne RV, Choung CB, Wilson SP (2009) Amphibians and agricultural chemicals: Review of the risks in a complex environment. Environmental Pollution. 157, 2903-2927.

Introduction

Amphibians around different parts of the world are exposed to different kind of chemicals, fertilizer chemicals (chemicals used in fertilizers), Community effects, Abiotic/biotic stressors and pesticides which has greatly influenced their population and their health in many ways. Their population has been declining very fast all around the world especially in highly altered agricultural areas. The concentration of pesticides in the environment is often so elevated that it has caused transience among the amphibian population on a very large scale. This toxicity has upset their system in many ways including thyroid activity, retinoid pathways, sexual differentiation, impaired growth (deformity) and their development. It is clear that although a real connection between these chemicals and pesticides to the decline of these amphibians population and the effects on them is still not lucid because the actual effect of this toxicity remains unidentified, the extinction of some species and these abnormalities observed among some amphibians in both, adult and larval populations, especially in areas where these toxicity level is high. The following review will further explain how these chemicals, pesticides and agricultural chemicals influence the amphibian population and have upset their system.

Exposure to Pesticides

Pesticides have the effect of causing transience to amphibians and sometimes on a wide scale. Teratogenesis, abnormality in the sexual development, limb abnormalities and endocrine disruption were some of the widespread occurrences among these amphibians found among places with high concentration of pesticides.

Exposure to certain exogenous chemicals can cause manipulation in the timing of the metamorphosis of amphibians (Tadpoles) or prevent metamorphosis from happening completely and slow down thyroid activity, where as some environmental contaminants and some stress associated with natural conditions like drying of the pond and crowding of the pond can boost thyroid activity and affect the thyroid axis. The result of this accelerated metamorphosis is the development of undersized juveniles. The mechanism of how the thyroid axis is affected is still not clear.

Exposures to pesticides have also reported delayed metamorphosis among amphibians. Carbamate and Organophosphorus insecticides inhibit acetylcholine esterase and disrupt the neurological systems. They reduce the AChE activity according to laboratory studies and showed impaired behavioral responses, impaired growth and delayed metamorphosis.

There have been many malformations reports among amphibians like the malformation of the hind-limbs, deformed eyes in agricultural areas where several agricultural pollutants in the water were found. Although no causative agent was found for such deformities. Mineral deficiencies in water in these sites were also suggested as contributing factor in these deformities.

Impact of fertilizers

Chemicals used in fertilizers like ammonia, nitrite and nitrate have also shown some affects on amphibians. Methaemoglobinemia exposure to Nitrite is the cause of mortality among amphibians and their sluggish growth and development. But it is also found that amphibian larvae had shown tolerance to very high concentration of ...