Toxicity And Bioaccumulation Of Bromadiolone, Fenvalerate And Paichongding To Earthworm Eisenia Fetida

The extensive usage of pesticides had caused serious environmental pollution and had been a great threat for the ecosystem. In this study, earthworm Eisenia foetida, one of the most common invertebrates used to assess the ecological risks of toxic substances in the soil ecosystem, was used as model organism to determine the adverse effect of three pesticides:bromadiolone, fenvalerate and paichongding, including acute toxicity, bodyweight change, oxidative damage and bioaccumulation.Bromadiolone, a potent second-generation anticoagulant rodenticide, has been extensively used worldwide for the field control of rodents.There are few data regarding the toxicity and bioaccumulation of bromadiolone to earthworms. In this study, we reported that bromadiolone was toxic to earthworms at 1 mg/kg soil, which isa likely concentration in the field following application of bromadiolone baits.Exposure to bromadiolone resulted in significant inhibition of earthworm growth. The antioxidant activities of superoxide dismutase (SOD) and catalase (CAT) were slightly activated in earthworms, while malondialdehyde (MDA) content was dominantly elevated over the duration of exposure. Bromadiolone in soil is bioaccumulative to earthworms. The BSAFs of bromadiolone were concentration dependent and BSAFs decreased as the level of bromadiolone in soil increased.These results suggest earthworms are not only the potential subject to primary poisoning but also the source of secondary exposure for insectivores and scavengers following application of bromadiolone.Fenvalerate is a typical chiral synthetic pyrethroid. Its Senantiomer, named as esfenvalerate, is the active ingredient as insecticide. In this study, we investigated the enantioselectivity toxicity between fenvalerate and esfenvalerate to Eisenia foetida and found out that fenvalerate were much more toxic than esfenvalerate. Further study indicates that both fenvalerate and esfenvalerate significantly inhibit the growth of earthworm with a longer exposure time and the esfenvalerate showed a stronger inhibition than fenvalerate. This result may be explained by the higher toxicity of esfenvalerate. Compared with fenvalerate, the earthworms under the exposure of esfenvalerate exhibited lower food intake, which had great impact on the synthesis and metabolism of protein,carbohydrate and fat, and therefore led to severer growth inhibition.For antioxidant enzyme activities, fenvalerate and esfenvalerate treated groups showed similar results. The CAT activity was inhibited at first, and followed by a dramatically inductionwith the extension of exposuretime. While the SOD activity increased during the whole exposure time. However, significant differences were observed at MDA contents exposed to fenvalerate and esfenvalerate, separately. The results suggest that the enantioselective toxicity should be taken into consideration when assessing ecological risks of chiral pesticide in the soil ecosystem. These findings suggested that SOD is a more sensitive biomarker for fenvalerate and MDA is a sensitive biomarker for esfenvalerate. With the increase of exposure time, fenvalerate and esfenvalerate in soil is bioaccumulative to earthworms. The BSAFs of fenvalerate is higher than esfenvalerate.The study indicated that enantiomer selectivity should be considered in the assessment of bioaccumulation of chiral pesticides.Paichongding is a novel pesticide developed in China independently. So far, there are no published studies reporting the toxicity of paichongding to earthworms. Paichongding is a kind of low toxic pesticidesand much less toxic than other nicotinoid insecticides.Toxic effect started to appear when the concentration of paichongding reached 50mg/kg or higher. Further studies indicated that a long time exposure of paichongding resulted in significant inhibition of earthworm growth. Moreover, the CAT and SOD activity in earthworms were significantly induced by paichongding. The notable effect of CAT activity on the lowest dose group (O.1mg/kg, 2d) suggested that CAT is a more sensitive biomarker. Obvious changes in the MDA content only observed on high concentration after long time exposure, which suggested MDA content as an insensitive biomarker to paichongding.This study enriches the toxicity data of earthworm as model organisms and provides detailed assessment of the ecological risks of the three pesticides in the soil ecosystem...