Assessing lethal and sub-lethal effects of trichlorfon on different trophic levels

Trichlorfon (TCF) is one of the most used veterinary pharmaceuticals not only to fight infestations but also as a preventive measure worldwide. The high concentrations used generate concerns about environmental and human health. In this work we assessed the acute toxicity of this compound to non-target organisms belonging to different trophic levels: Danio rerio (early life stages and adults), Daphnia magna and algae (Pseudokirchneriella subcapitata and Chlorella vulgaris), and studied the potential of the biomarkers cholinesterase (ChE), glutathione-S-transferase (GST), lactate dehydrogenase (LDH) and catalase (CAT) to assess sub-lethal effects of trichlorfon in zebrafish and daphnids. The fish embryo test followed the OECD draft guideline FET and was based on the exposure of newly fertilized eggs to 0, 2.5, 5.0, 10, 20, 40, 80 and 160 mg/L of TCF for 5 days; the fish acute test followed the OECD guideline 203 and was based on the exposure of adult fish to 0, 2.5, 5, 10, 20, 40, 60 and 80 mg/L of TCF for 4 days; Daphnia sp. immobilization assay followed the OECD guideline 202 and was based on the exposure of juvenile daphnids to 0, 0.1, 0.3, 0.5, 0.7, 0.9, 1 and 2 μg/L of TCF for 2 days and the algae growth inhibition assay followed the OECD guideline 201 and was based on the exposure of the two species to 0, 1, 3.2, 10, 32, 100 and 300 mg/L of TCF for 4 days. Biomarker levels were measured after 96 h exposure to TCF in zebrafish early life stages and adults and after 48 h exposure in D. magna. Tested organisms seem to have dissimilar sensitivities towards TCF exposure. D. magna (48 h-LC50 = 0.29 μg/L) was the most sensitive organism, followed by early life stages and adults of zebrafish (96 h-LC50 = 25.4 and 28.8 mg/L, respectively) and finally by the algae P. subcapitata (96 h-LC50 = 274.5 mg/L) and C. vulgaris (no effect observed). As daphnids are a source of food for organisms of higher trophic levels, the impairment on its population is prone to have consequences in the entire ecosystem. The biomarker activities measured in daphnids and fish seemed to be useful tools in the assessment of trichlorfon effects, especially ChE activity which was the most sensitive biomarker tested for all organisms. Trichlorfon was teratogenic for zebrafish embryos leading to anomalies in the absorption of the yolk sac, spine bending and pericardial oedemas. The present research suggests that further work is urgently needed in order to monitor environmental concentrations of trichlorfon and to test the long term effects of environmentally realistic concentrations of this compound.