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

Abstract

<p>Akvatični ekosistemi su izloženi simultanom delovanju velikog broja potencijalno<br />toksičnih supstanci u vremenski i prostorno promenljivim uslovima u životnoj sredini.<br />U ovoj disertaciji je poređen&nbsp; efekat pojedinačnih herbicida&nbsp; &ndash;&nbsp; atrazina, izoproturona i<br />trifluralina&nbsp; &ndash;&nbsp; sa efektima njihovih sme&scaron;a u testu sa&nbsp;<em> Lemna minor</em>. Odabrane su sme&scaron;e sa sličnim (dvo-komponentna sme&scaron;a atrazina/izoproturona) i različitim (dvo-komponentna sme&scaron;a atrazina/trifluralina i izoproturona/trifluralina, kao i tro-komponenta sme&scaron;a)&nbsp; mehanizmom toksičnog dejstva. Kako se sve če&scaron;će ističe<br />neophodnost sagledavanja ne samo&nbsp; potencijalnih&nbsp; razlika&nbsp; u&nbsp; toksikolo&scaron;koj&nbsp; osetljivosti jedinki/populacija, već i&nbsp; razlika&nbsp; u&nbsp; efikasnosti&nbsp; njihovog oporavka, u ovoj disertaciji, je određen&nbsp; potencijal oporavka&nbsp; vrste&nbsp;<em> L. minor&nbsp;</em> nakon izloženosti navedenim pojedinačnim herbicidima/sme&scaron;ama. Ispitano je da li prirodna&nbsp; organska&nbsp; materija (POM),&nbsp; koja&nbsp; je&nbsp; u testovima na akvatičnim makrofitama&nbsp; simulirana&nbsp; preko huminskih materija (HM) u realnim koncentracijama u povr&scaron;inskim vodama, modulira toksičnost atrazina i 2,4 D, i njihove dvo-komponentne sme&scaron;e,&nbsp; u&nbsp; testu sa&nbsp;<em> L. minor</em>, odnosno izoproturona, dikambe i njihove dvo-komponentne sme&scaron;e, u testu sa&nbsp; <em>Myriophyllum aquaticum</em>.&nbsp; Utvrđen je stepen&nbsp; odstupanja između empirijske&nbsp; toksičnosti svih navedenih sme&scaron;a herbicida, sa teorijski očekivanim vrednostima na osnovu modela adicije koncentracija (CA), u testovima na obe vrste akvatičnih makrofita.&nbsp; Ispitano je da li se postojeći CA model može koristiti i za procenu toksičnog dejstva sme&scaron;a uzimajući u obzir integralno i podatke o oporavku eksponiranih&nbsp; vrsta akvatičnih makrofita.&nbsp; Rezultati u ovoj disertaciju su pokazali da&nbsp; modifikacijom laboratorijskog protokola gde se oporavak akvatičnih makrofita pratio tokom dodatnih pet/sedam dana testa nakon sedmodnevne ekspozicije se mogu dobiti ekolo&scaron;ki relevantni podaci o odloženom toksičnom dejstvu pojedinačnih supstanci/sme&scaron;a.&nbsp; U testu sa atrazinom i izoproturonom, kao pojedinačnim supstancama, je uočen efikasan oporavak vrste&nbsp;<em> L.minor</em>. Sa druge strane, u slučaju trifluralina i 2,4 D u periodu oporavka je zabeleženo odloženo toksično dejstvo. Na primeru trifluralina i 2,4 D se pokazalo da standardnitestovi toksičnosti, zanemarujući podatke o potencijalu oporavka, mogu potceniti realan rizik od pesticida. U slučaju drugog sintetičkog auksina, dikambe, pri izabranoj seriji koncentracija nije zabeleženo toksično dejstvo na vrstu&nbsp;<em> L. minor</em>.&nbsp; Odgovor vrste<em> L. minor</em>&nbsp; na dejstvo dvo-komponentne sme&scaron;e atrazina i izoproturona je sličan onom zabeleženom u testu sa navedenim herbicidima, kao pojedinačnim supstancama. Zabeležen je efikasan oporavak biljne kulture, nezavisno od primenjene koncentracije herbicida u sme&scaron;i. Sa druge strane, oporavak vrste&nbsp; <em>L. minor</em>&nbsp; nakon izloženosti dvo-&nbsp; i tro-komponentnim sme&scaron;ma sa trifluralinom zavisi od primenjene koncentracije herbicida u sme&scaron;i i zabeležen je jedino u&nbsp; tipu sme&scaron;a gde su koncentracije pojedinačnih herbicida bliske relativno bliske mogućim koncentracijama herbicida u životnoj sredini.&nbsp; Povećanje toksičnosti pojedinačnih supstanci/sme&scaron;a uslovljeno prisustvom HM je primećena u slučaju atrazina, 2,4 D i njihove dvo-komponentne sme&scaron;e, u testu na vrsti&nbsp;<em> L. minor,</em> odnosno&nbsp; dikambe u testu sa<em> M. aquaticum</em>. Suprotan efekat HM je primećen u testu sa&nbsp; <em>M. aquaticum</em>&nbsp; u slučaju&nbsp; izoproturona i dvo-komponentne sme&scaron;e izoproturona i dikambe, jer je zabeležena&nbsp; niža&nbsp; toksičnost u prisustvu HM.&nbsp; Iako određene razlike u toksičnosti između ispitivanih test tretmana u prisustvu i odsustvu HM postoje, one nisu bile statistički značajne.&nbsp; Oporavak akvatičnih makrofita od efekta dvo-komponentnih sme&scaron;a, u prisustvu/odsustvu HM, zavisi od primenjene koncentracije herbicida u sme&scaron;i. Izuzetak čini dvo-komponentna sme&scaron;a atrazina i 2,4&nbsp; D, u testu sa <em>L. minor,</em> gde nije do&scaron;lo do oporavka biljne kulture ni u jednom od tipova sme&scaron;a u prisustvu HM. Generalno, uočena je dobra saglasnost između empirijske i predviđene toksičnosti,&nbsp; na osnovu&nbsp; CA modela, nezavisno od mehanizma toksičnog dejstva supstanci prisutnih u sme&scaron;i ili&nbsp; prisustva odnosno odsustva HM.&nbsp; Odstupanje od adivnosti je zabeleženo jedino u testu sa&nbsp;<em> L. minor&nbsp;</em> u slučaju dvo-komponentnih sme&scaron;a sa trifluralinom&nbsp; (atrazin+trifluralin i izoproturon+trifluralin), gde se ispostavilo da&nbsp; CA model u određenoj meri potcenjuje dejstvo navedenih sme&scaron;a, &scaron;to&nbsp; upućuje na pojavu sinergističkih interakcija između supstanci.&nbsp; Pokazano je i&nbsp; da se CA model može alternativno koristiti za procenu toksičnosti odabranih sme&scaron;a, na osnovu integralnih saznanja o osetljivosti i potencijalu oporavka eksponiranih&nbsp; jedinki/populacija, pod uslovom da su dostupni takvi podaci za pojedinačne susptance koje ulaze u sastav sme&scaron;e.</p>

<p>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&nbsp; atrazine,isoproturon, and trifluralin was compared with the effect of their mixtures, in the test with&nbsp;<em> Lemna minor.</em> Mixtures with a similar (binary mixture of&nbsp; 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&nbsp; thesis,&nbsp; L<em>. minor&nbsp;</em> recovery potential was assessed after &nbsp; 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&nbsp; in surface waters, modulated the toxicity of atrazine, 2.4 D, and their binary mixture, in tests with&nbsp; L.<em> minor,</em> 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&nbsp; 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&nbsp; L.<em> minor</em>&nbsp; was observed. On the other hand, in the case of trifluralin and 2,4 D, delayed toxic effects&nbsp; 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&nbsp; L.<em> minor</em>&nbsp; was&nbsp; not reported in the selected concentration series. The response of&nbsp; L. <em>minor</em>&nbsp; after the exposure tobinary mixtures of atrazine and isoproturon was similar to the one recorded in the tests with these herbicides as the individual&nbsp; substances. Efficient plant recovery was recorded, regardless of the applied herbicide concentration in the mixture. On the other hand, the recovery of&nbsp; L.<em> minor</em>&nbsp; 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&nbsp; 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. <em>minor</em>, that is,&nbsp; dicamba, in the test with&nbsp; M.<em> aquaticum</em>. In the test with&nbsp; M.<em> aquaticum</em>, the opposite effect was observed in the case ofisoproturon and binary mixture of isoproturon and &nbsp; dicamba, due to&nbsp; lower&nbsp; 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&nbsp; 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&nbsp; L<em>. minor</em>&nbsp; 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.<em> minor</em> in the case of the binary mixture&nbsp; 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&nbsp; used for the assessment of toxicity of&nbsp; 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&nbsp; the mixture exists.</p>