Lethal and sub-lethal effects of five pesticides used in rice farming on the earthworm Eisenia fetida

Abstract

The toxicity of five pesticides typically used in rice farming (trichlorfon, dimethoate, carbendazim, tebuconazole and prochloraz) was evaluated on different lethal and sub-lethal endpoints of the earthworm Eisenia fetida. The evaluated endpoints included: avoidance behaviour after an exposure period of 2 days; and mortality, weight loss, enzymatic activities (cholinesterase, lactate dehydrogenase and alkaline phosphatase) and histopathological effects after an exposure period of 14 days. Carbendazim was found to be highly toxic to E. fetida (LC50=2mg/kg d.w.), significantly reducing earthworm weight and showing an avoidance response at soil concentrations that are close to those predicted in rice-fields and in surrounding ecosystems. The insecticide dimethoate showed a moderate acute toxicity (LC50=28mg/kg d.w.), whereas the rest of tested pesticides showed low toxicity potential (LC50 values above 100mg/kg d.w.). For these pesticides, however, weight loss was identified as a sensitive endpoint, with NOEC values approximately 2 times or lower than the calculated LC10 values. The investigated effects on the enzymatic activities of E. fetida and the observed histopathological alterations (longitudinal and circular muscle lesions, edematous tissues, endothelial degeneration and necrosis) proved to be sensitive biomarkers to monitor pesticide contamination and are proposed as alternative measures to evaluate pesticide risks on agro-ecosystems.

Individual and combined effects of herbicide tribenuron-methyl and fungicide tebuconazole on soil earthworm Eisenia fetida

“…The use of pesticides in agriculture is a common practice to protect crops all over the world. However, despite their impacts on target species, pesticides potentially affect soil macro- and microorganisms 1 , 2 . This is because only 0.1% of an applied pesticide reaches the target organism whereas rest of it pollutes the surrounding air, water, and soil environments by different means 3 – 6 .…”

Ecotoxicological Tests as a Tool to Assess the Quality of the Soil

“…Terrestrial ecotoxicology uses ecotoxicological tests-internationally standardized by the International Organization for Standardization (ISO) and by the Organization for Economic Cooperation and Development (OECD)-which expose bioindicators (animals or plants) to soils contaminated with products or residues of interest in order to qualify and quantify the aforementioned negative effects. Different contamination levels are used in studies in this field [5,29,30]; therefore, Inferring the toxicity of the assessed substance and contributing to establish the limits of its use or disposal is possible.…”

“…Results: E. andrei reproduction was sensitive to dilute sediment samples presenting EC 20 = 1.26%, EC 50 = 2.94%. In addition, surviving earthworms showed visible morphological damage in their epidermis [29] The toxicity of five pesticides (trichlorfon, dimethoate, carbendazim, tebuconazole, and prochloraz) typically used in rice farming was evaluated through the mortality and body weight of E. fetida specimens 7 and 14 days after the beginning of the experiment.…”

Use of the Model Organism Caenorhabditis elegans to Elucidate Neurotoxic and Behavioral Effects of Commercial Fungicides

“…Another azole, triadimefon, disrupts dopamine neurotransmission function in rats, with subsequent effects on the nigrostriatal system that governs behaviors like general locomotor activity, as well as stereotyped, repetitive behaviors [15]. One recent study demonstrated edema and necrosis of circular and longitudinal muscle layers in earthworms exposed to tebuconazole for 14 days [16]. Further, epoxiconazole, a commonly applied triazole, acts as a male reproductive toxicant in rats [17] and damaged spermatogenesis in C. elegans [18].…”

“…A number of pesticide and fungicide toxicology studies utilize the earthworm (e.g., Eisenia fetida) because of the importance of earthworms in soil health [16]. However, this organism lacks the ease of cultivation and powerful genetics of the model organism, C. elegans.…”