Bioindicators for monitoring the pesticides degradation in biobeds

LAMMERTYN, S.; MAGNI, F.V.; DURÁN, A.; GODOY, J.L.; REPETTI. M.R.; C.S. ZALAZAR

Workshop; Workshop Latinoamericano de Residuos de Plaguicidas (LAPRW); 2021

Biological beds are efficient, low-cost and straightforward systems developed for the good management of pesticides on-farms. To prevent pollution during filling and cleaning equipment and accidental spillages, these systems are used to retain and degrade pesticides by the action of microorganisms. The design consists of a waterproofed hole in the ground filled with a biologically active matrix (biomixture). In these systems, the degradation of pesticides is evaluated using complex analytical techniques. However, it is necessary to introduce bioassays in order to obtain more information on the environmental matrix. In this sense, earthworms, such as Eisenia fetida, are used as sentinel organisms to evaluate risks of polluted soil or substrates. And seeds of terrestrial plants, such as Lactuca sativa, are used to assess phytotoxicity.In this work, the sensitivity and efficacy of the proposed bioindicators were evaluated to monitor a biobed composed of wheat stubble, river waste and soil (50:25:25% in volume), in relation to the monitoring of pesticides degradation by chromatography-mass spectrometry (UHPLC-MS/MS). The pesticides used were atrazine, prometryn, clethodim, haloxyfop and dicamba. Also, the enzymatic activity (hydrolysis of fluorescein diacetate, FDA and phenoloxidase) was evaluated. Samples were taken on the initial day (after pesticide application) and days 10, 15, 30, 60 and 90.The results showed a high percentage of degradation of all pesticides for day 90 (99% for atrazine, prometryn, clethodim, dicamba and 90% for haloxyfop), while the test with seeds shows a recovery trend with to the initial day (the germination index values were from zero to 46%). Regarding the avoidance test, 98% of the earthworms choose the control biomixture (without pesticide application), that is, the bioassay showed the high sensitivity of this species at very low concentrations of pesticides and/or metabolites present. On the other hand, an increase in the enzymatic activity was registered by phenoloxidases after the addition of pesticides, while the activity by FDA was practically not altered.This work shows the need for integrated monitoring taking into account the pesticides analyses and the application of bioassays. The avoidance test´s high sensitivity suggests incorporating an alternative test that evaluates effects on earthworms when they are directly exposed to polluted biomixtures. The different levels of injuries could be quantified through a photographic record.