An evaluation of the effect of four herbicides on some aquatic organisms

Abstract

Studies were carried out on the effect of four commonly used herbicides (2,4-D atrazine, atrazine + metolachlor and paraquat) on some aquatic organisms in simulated aquatic ecosystem at 100 ppm, 150 ppm and 200 ppm of the herbicides active ingredients (ai). The effects of the herbicides on pH, blue-green alga – Aphanocapsa sp, aquatic weed –Lemna sp, tadpole (Bufo regularis) and bacterial species were investigated. While 2,4-D resulted in significant decreases in pH value; paraquat resulted in significant increases (p < 0.05). Atrazine and atrazine + metolachlor treatments impacted the most on the lysis of Aphanocapsa sp as all the cells were lysed at 2 days after application. Paraquat treatments at all concentrations resulted in the death of all (20) tadpoles at 2 days after application. Complete tadpole death in atrazine + metolachlor was observed at 8 days after application at 150 ppm and at 12 days after application at 100 ppm. A general decrease in bacterial counts relative to concentrations and days of treatment was observed with paraquat impacting the most on decreases in bacterial counts. Bacterial species isolated from untreated water samples (control) included- Proteus sp, Enterobacter aerogenes, E. coli, Bacillus sp, Pseudomanas sp, Citrobacter sp, Staphylococcus aureus and Flavobacterium sp; while Bacillus (41.2%) and Pseudomonas (56.3%) species were the most frequently isolated bacteria from herbicide treated water samples after 14 days of treatment. Conclusively, herbicides from agricultural run-offs can impair the normal balance of the flora and fauna of the aquatic ecosystem.

Keywords: Herbicides, aquatic ecosystem, pH, bacteria