Antagonistic Effect on the Lethality of Earthworm (Eisenia Fetid L.) Being Exposed to Binary Mixtures of Metribuzin, Halosulfuron, and Flumioxazin

Frequent use of herbicides might impose a risk for nontarget species, such as earthworms. The objective was to test the combined toxic effect of binary herbicide mixtures: metribuzin:halosulfuron and metribuzin: flumioxazin on a nontarget earthworm in two test systems. Two experiments on filter paper and two on artificial soil determined lethality and chronic toxicity on the earthworm. Results showed the flumioxazin had no high toxicity in contact filter paper test, with the lethal concentration (LC 50 ) of 153.10 µg a.i cm -2 at 48 h. In the artificial soil test, flumioxazin LC 10 was 0.65 mg a.i kg -1 on day 14. Metribuzin showed high toxicity to earthworms in the filter paper test with LC 50 17.17 µg a.i cm -2 at 48 h but LC 10 of metribuzin. Halosulfuron and metribuzin were highly toxic with LC 10 value 0.24 and 0.47 mg a.i kg -1 on day 14. The herbicides' mixed effect showed in both test systems antagonistic effect, meaning that the mixtures retracted the herbicides' action in the earthworms relative to a Concentration Addition reference model. A chronic toxicity test showed that earthworm catalase was stimulated by metribuzin:halosulfuron (50:50%) and metribuzin (100%).