Ecotoxicity of Herbicides on Nitrosomonas sp and Nitrobacter sp in Soil

Abstract

Aim: This study aimed to predict the toxic effects of herbicides on non-target organisms within the ecosystem, employing soil microflora (Nitrosomonas sp and Nitrobacter sp) as indicators to monitor ecosystem responses to these substances. Place of Study: Soil samples were collected from the Rivers State University Agricultural Farm in Port Harcourt, using sterile plastic containers, and transported to the Microbiology Laboratory at Rivers State University. These samples were processed within one hour of collection for the isolation of Nitrosomonas sp. and Nitrobacter sp. The herbicides (Veeset-glyphosate and Dragon-paraquat) were procured from a chemical shop in Mile 1 Market, Port Harcourt, Rivers State, and transported to the laboratory for toxicity testing. Test species were selected based on their ease of laboratory culture, availability of relevant background information including physiology, genetics, behavior, and sensitivity to a wide range of toxicants. Methodology: The Winogradsky agar (modified) medium was used, consisting of agar agar (15.09 g/L), King's agar B base (3 g/L), KNO2 (0.1 g/L), Na2CO3 (0.5 g/L), FeSO4·7H2O, NaCl (0.5 g/L), and distilled water (1000 ml). Samples were resuscitated in sterile normal saline (90 ml as diluent), and a ten-fold serial dilution was performed. This modified medium reduced the incubation period to 2 to 3 days, compared to the standard 5 days. Results: The study found that Dragon-paraquat herbicide exhibited higher toxicity towards the test organisms, with a mean LC50 value of 18.98%, compared to Veeset-glyphosate, which had a mean LC50 value of 27.42%. Conclusion: In modern agriculture, herbicide applications have become a routine practice. Given the rapid growth of the global human population, extensive herbicide use is employed to maximize crop yields. These findings underscore the importance of monitoring and understanding the toxicological effects of herbicides on non-target organisms to ensure sustainable and responsible agricultural practices.