Recovery potential of aquatic macrophyte species Lemna minor Linnaeus (Lemnaceae, 1753) and Myriophyllum aquaticum (Vellosco) Verdcourt (Haloragaceae, c. 1880), from toxic stress after exposure to individual herbicides and their mixtures | Potencijal oporavka akvatičnih vrsta makrofita Lemna minor Linneus (Lamnaceae, 1753) i Myriophyllum aquaticum (Vellosco) Verdcourt (Haloragaceae, c. 1880), od toksičnog stresa nakon izlaganja odabranim herbicidima i njihovim smešama

Aquatic ecosystems are exposed to a simultaneous effect of a large number of potentially toxic substances in a temporally and spatially variable conditions in the environment. In this doctoral thesis, the effect of the individual herbicides atrazine,isoproturon, and trifluralin was compared with the effect of their mixtures, in the test with Lemna minor. Mixtures with a similar (binary mixture of atrazine/isoproturon) and dissimilar (binary mixtures with atrazine/trifluralin, soproturon/trifluralin, and ternary mixture) mode of action were selected. There is a clear need to take into account not only the differences in toxicological sensitivity of the exposed individuals/populations, but also the differences in their recovery efficiency.Therefore, in this thesis, L. minor recovery potential was assessed after the exposure to the individual herbicides/mixtures. It was tested whether a natural organic matter (NOM), which was, in these tests, simulated through the humic matter (HM) used in real concentrations in surface waters, modulated the toxicity of atrazine, 2.4 D, and their binary mixture, in tests with L. minor, and disoproturon, dicamba and their binary mixture, in tests with Myriophyllum aquaticum. The deviation between the empirical toxicity of the herbicidal mixtures and the predicted toxicity based on the concentration addition (CA) model was determined. It was also examined whether the current CA model can be used to predict mixture oxic effects by taking into account the information about the plant recovery potential as well. The results showed that by modifying laboratory protocols, where the recovery of aquatic macrophytes was followed for additional five/seven days after the seven day exposure, environmentally relevant data on delayed toxic effects of the individual substances/mixtures can be obtained. In the tests with atrazine and isoproturon as individual substances, the efficient recovery of L. minor was observed. On the other hand, in the case of trifluralin and 2,4 D, delayed toxic effects were recorded during the recovery period.In the test with trifluralin and 2.4 D, it was shown that standard toxicity tests may underestimate the real risk of pesticides by not considering data on recovery. In the case of another synthetic auxin, dicamba, toxic effect on L. minor was not reported in the selected concentration series. The response of L. minor after the exposure tobinary mixtures of atrazine and isoproturon was similar to the one recorded in the tests with these herbicides as the individual substances. Efficient plant recovery was recorded, regardless of the applied herbicide concentration in the mixture. On the other hand, the recovery of L. minor after exposure to binary and ternary mixtures with trifluralin depended on the applied herbicide concentration in the mixture, and was recorded only in the type of mixtures where the concentrations of the individual herbicides were close to the possible concentration of these herbicides in the environment. The toxicity increase of the individual substances/mixtures, influenced by the presence of HM was observed in the case of atrazine, 2,4 D, and their binary mixture, in the test with L. minor, that is, dicamba, in the test with M. aquaticum. In the test with M. aquaticum, the opposite effect was observed in the case ofisoproturon and binary mixture of isoproturon and dicamba, due to lower toxicity being recorded in the presence of HM. Even though some differences in toxicity between the test treatments in the presence and absence of HM were recorded, the differences were not statistically significant. The recovery of macrophytes after the exposure to the binary mixtures, in the presence/absence of HM, depended on the applied herbicide concentration in the mixture. The exception was noticed in the test with L. minor in the binary mixture with atrazine and 2,4 D, where no recovery was recorded in any type of the mixture in the presence of HM. Generally, there was a good agreement between the empirical toxicity and the predicted one based on the CA model, regardless of the mode of action of the toxic substances present in the mixture, or presence/absence of HM. The deviation from additivity was recorded only in the test with L. minor in the case of the binary mixture with trifluralin (atrazine/trifluralin and isoproturon/trifluralin), which meant that the CA model underestimated the mixture effect to a certain extent, suggesting that synergistic interaction between the substances might have appeared. It was also shown that the CA model may alternatively be used for the assessment of toxicity of the selected mixture, based on the integrated knowledge of both sensitivity and recovery potential of the exposed species/populations, providing that such information about individual substances in the mixture exists.