Effects of terbuthylazine on soil fauna and decomposition processes.

Acute lethal and sublethal effects of terbuthylazine and the commercial herbicide preparation Gardoprim [terbuthylazine is the active ingredient (a.i.)] on soil organisms (microbes, oppioid mites, two gamasid mite species, enchytraeids, and nematodes) were studied. In the humus soil terbuthylazine had no toxic effects on soil animals tested. However, the herbicide preparation had acute toxic effects on enchytraeids [no-observed-effect level (NOEL) 1.0 g a.i. /m2] and both gamasid mites (NOEL 2.4 and 5.0 g a.i./m2). According to filter paper test, the LC50 value for oppioid mites was 14.5 g a. i./m2. In the humus soil the commercial preparation caused no dose-related mortality in Oppioidea. The preparation was more toxic to gamasid mites when the herbicide was applied on the soil surface compared to the treatment in which the chemical was mixed into the humus. Application method of the chemical did not affect the mortality of enchytraeids. In the multispecies experiment, the number of nematodes was higher in the highest concentration of the commercial preparation (50 g a.i./m2) compared to the lowest concentration (1 g a.i./m2) and the clean soil. The amount of NH+4-N in the humus tended to increase with increasing herbicide concentration. The herbicide did not affect soil respiration, microbial biomass, or water content of the humus. These results indicated that herbicides can have direct effects on soil fauna. Due to species-specific foraging strategies or different exposure routes and rates to animals, effects of herbicides on soil animals varied considerably. Single-species toxicity tests performed in humus soil were more sensitive to the effects of herbicide than ecologically relatively short-term multispecies test.