Changed degradation behavior of pesticides when present in mixtures.

Soil microorganisms are indispensable for a healthy soil environment, where the fate of pesticides is contingent on microbial activity. Conversely, soil ecosystems can be distorted by all kinds of variables, such as agrochemicals. These crop protection products have been universally in use for decades in agriculture. In modern crop cultivation, fungicides are increasingly applied because of their high and broad effectivity on plant pathogens. While their use can enhance harvest yields, fungicides, particularly broad-spectrum ones, are responsible for the alteration of the soil microflora. Furthermore, successive and combined application of pesticides is an agronomic routine, which aggravates the concurrent existence of synthetic chemicals in the soil and marine environments. Mutual interactions of such different molecules, or their effects on soil life, can negatively impact the dissipation of biodegradable pesticides from the ecosystems. The direct effects of individual agrochemicals on microbial soil parameters, as well as agronomic efficiency and interactions of mixtures have been thoroughly studied over the past 80 years. The indirect impacts of mixtures on soil and aquatic ecosystems, however, may be overlooked. Moreover, the current regulatory risk assessment of agrochemicals is based on fate investigations of individual substances to derive predicted environmental concentrations, which does not reflect real agricultural scenarios and needs to be updated. In this article, we summarized the results from our own experiments and previous studies, demonstrating that the degradation of pesticides is impacted by the co-existence of fungicides by their effects on microbial and enzymatic activities in soil.

Effects of algae and fungicides on the fate of a sulfonylurea herbicide in a water-sediment system.

The impact of pesticide mixtures on various soil parameters has been extensively studied, whereas research on effects in the aquatic environment is scarce. Furthermore, investigations on the consequences of chemical mixtures on the biodegradation kinetics of parent compounds remain deficient. Our research intended to evaluate potential effects by combined application of an agriculturally employed tank mixture to aquatic sediment systems under controlled laboratory conditions. The mixture contained two fungicides and one radiolabeled herbicide of which the route and rate of degradation was followed. One set of aquatic sediment vessels was incubated in the dark. A second set of vessels was controlled under identical conditions, except for being continuously irradiated to promote algal growth. In addition, the algal biomass in irradiated aquatic sediment was monitored to determine its effects and a potential role in the biodegradation of iodosulfuron-methyl-sodium. The study results showed that the herbicide, although hydro- and photolytically stable throughout the study, metabolized faster (DT50 1.1-1.2-fold and DT90 2.8-4.5-fold) when continuously irradiated in comparison to dark aquatic sediment. Both fungicides had a significant prolonging effect on the biodegradation rate of the herbicide. In the presence of fungicides, DT90 values increased 1.5-fold in the irradiated, and 2.5-fold in the dark systems. Additionally, algae may have influenced the metabolization of the herbicide in the irradiated systems, where shorter DT90 values were evaluated. Even so, the algal influence was concluded to be indirect.

Metabolism of the14C-labeled herbicide clodinafop-propargyl in plant cell cultures of wheat and tobacco.

The metabolism of 14C-clodinafop-propargyl (CfP) was examined in cell cultures of wheat (Triticum aestivum L. cv. 'Heines Koga II') and tobacco (Nicotiana tabacum L.). Besides the non-transgenic tobacco culture, cultures transformed separately with cDNA of human cytochrome P450-monooxygenases (P450s) CYP1A1, CYP1A2, CYP3A4, CYP2B6 and CYP2C19 were examined. Experiments with wheat were executed in the presence and absence of safener cloquintocet-mexyl (CqM). After 48 h of incubation, only about 10% of applied 14C was found in media (both tobacco and wheat). Non-extractable residues of 14C-CfP in wheat cells were 16.54% (without CqM) and 30.87% (with CqM). In all tobacco cultures, 82.41-92.46% of applied radioactivity was recovered in cell extracts. In contrast to wheat, non-extractable residues amounted only to 1.50-2.82%. As determined by radio-thin layer chromatography (TLC) and -high-performance liquid chromatography (HPLC), the parent CfP was not found in the cell extracts of wheat; in tobacco cell extracts, only traces of CfP were detected. After a hydrolysis of assumed carbohydrate conjugates of CfP derived polar 14C-labeled compounds, TLC and HPLC analysis showed that in wheat, a more complex pattern of metabolites of CfP were observed as compared to all tobacco cultures. In hydrolysates resulting from wheat, the identity of three primary products was confirmed by means of GC-EI-MS: free acid clodinafop (Cf), hydroxy-Cf hydroxylated at the pyridinyl moiety, and 4-(5-chloro-3-fluoropyridin-2-yloxy)phenol. In hydrolysates derived from all tobacco cultures, main metabolite was Cf besides only traces of further unidentified products. Differences among the different tobacco cultures (non-transgenic, transgenic) did not emerge. According to kinetics of disappearance of primary metabolite Cf as well as formation of polar soluble products and non-extractable residues, metabolization of CfP proceeded at a noticeably higher rate in wheat cells treated with safener CqM than in cells without CqM treatment. Thus, these results indicated a stimulation of CfP's metabolism by CqM, although metabolic profiles observed in CqM treated and non-treated cells (after hydrolysis) were qualitatively similar. The findings obtained from all tobacco cultures suggested that with the exception of ester cleavage to Cf, CfP cannot be metabolized by tobacco itself or by the human P450s examined.