Soil ecotoxicity of natural ester transformer liquids

Mineral oils have been used for decades as transformer fluids because of their excellent dielectric properties and availability. In the last decade natural ester transformer liquids have been introduced in the market. Natural ester transformer liquids are readily biodegradable fluids and induce very low toxicity levels against aquatic organisms like fish, algae or daphnia. On the other hand, the behavior of natural esters at the end of their life it is not fully understood because in service transformers containing natural esters have not reached that stage yet. Moreover, the interaction of natural esters with aquatic organisms has been thoroughly studied but that is not the case regarding soil organisms. This work presents the study of the behavior of natural esters, at the beginning and at the end of their life, in contact with water and soil organisms. The natural ester transformer liquid has been aged under severe oxidative conditions in order to obtain samples representing the state of the liquid well beyond the end of its life. Samples of non-aged and aged liquid have been tested according to OECD 207 and OECD 208 standards. OECD 207 standard defines the method for testing toxicity of chemicals to earthworms in an artificial soil test. OECD 208 test assesses effects on seedling emergence and early growth of higher plants following exposure to the test substance in the soil. The tests results demonstrate that the fluids are not classified as toxic for terrestrial organisms. The vegetable transformer fluid described in this work does not contain added antioxidants, including synthetic antioxidants, therefore enhancing the biodegradability and toxicity properties of the final product.