Quaternary ammonium salts (QAS) are successfully used on a large scale in agriculture, medicine and pharmacy, in production of cosmetics, detergents and inhibitors of iron corrosion, as well as in oil mining, hydrometallurgy and nanotechnology. A large amount of these substances, introduced to circulation on a yearly basis, causes a real threat of polluting soil ecosystems, especially that many of these compounds exhibit proven bactericidal, algaecidal or fungicidal properties [1, 2]. In the present work, the influence of bis(isoquinolinium) 2,2’-thiodiacetate (disalt), isoquinolinium 2,2’-thiodiacetate (monosalt), introduced to the soil on germination and early stages of growth and development of terrestrial plants has been investigated using the plant growth test based on OECD/OCDE 208/2006 [3]. In this test, the seeds of selected species of terrestrial plants – spring barley (Hordeum vulgare) and common radish (Raphanus sativus L. subvar. radicula Pers.) were planted in pots containing soil to which a test chemical compound was added and in pots with control soil. The impact of QAS on luminescent bacteria Vibrio fischeri (Microtox®) and crustaceans Heterocypris incongruens (OstracodtoxkitFTM) has been determined and compared. More potent toxic to V. fischeri and H. incongruencs was bis(isoquinolinium) thiodiacetate (disalt), while for plants isoquinolinium thiodiacetate (monosalt).