Active substances in herbicides, just like in other pesticides, are chemical compounds synthesized in order to kill organisms which are harmful for cultivated plants. Therefore, they are toxins introduced on purpose by man into the environment. From the perspective of environmental protection, it is very significant that herbicides are most often applied directly into the soil to manage weeds. Since DDT and chloro-organic herbicides such as 2,4,5-T were withdrawn (in the 1970s) and since the EU regulations were unified for all its member countries, plant protection techniques have advanced considerably. Yet, pesticides, thus herbicides as well, continue to be a big group of xenobiotics periodically occurring at high levels in agroecosystems. These compounds infiltrate into related biocenoses from air, soil, water and food (Allinson & Morita, 1995; Kolpin et al., 1998; Adomas at al., 2008). Soil may become a reservoir of various pollutants, including herbicides. Herbicides remain active in soil for different periods. Paraquat has a relatively long half-life in soil (estimated at about 1000 days). The half-life of glyphosate in soil is only 10 to 100 days, and according to Monsanto the average half-life of this herbicide is 32 days (Hornsby et al., 1996; Monsanto, 2005). Remainders of persistent herbicides (e.g. atrazine, metribusin, and trifluralin) can stay in soil and destroy subsequent plantations a year or more after herbicides had been used. Herbicides from soil leach into surface water and ground water. The assessment of herbicides content in the aquifers in Iowa shows that 75% of herbicides (Kolpin et al., 1998), despite degradation, are still detected. From soil, water or air, herbicides get into crops (Adomas et al., 2008). When pesticides are applied, acceptable remainders of active substances (MRL) can often be detected in cultivated plants. Depending on physicochemical properties of the active substances of pesticides and the ways of their detoxification, some of these pollutants tend to increase concentration while passing through organisms of higher trophic levels. It can lead to a significant bioaccumulation of toxins in the food chains (Allinson & Morita, 1995; Dinis-Oliveira et al., 2006). No doubt therefore, monitoring of herbicide (including desiccant) residues in cultivated plants is needed, so that people and environment can be safe. Moreover, application of herbicide desiccants modifies physiological properties of seeds and may thus lead to delayed problems, becoming evident long after the treatment.