Land Spreading of Wastewaters from the Fruit-Packaging Industry and Potential Effects on Soil Microbes: Effects of the Antioxidant Ethoxyquin and Its Metabolites on Ammonia Oxidizers

Abstract

c Thiabendazole (TBZ), imazalil (IMZ), ortho-phenylphenol (OPP), diphenylamine (DPA), and ethoxyquin (EQ) are used in fruitpackaging plants (FPP) with the stipulation that wastewaters produced by their application would be depurated on site. However, no such treatment systems are currently in place, leading FPP to dispose of their effluents in agricultural land. We investigated the dissipation of those pesticides and their impact on soil microbes known to have a key role on ecosystem functioning. OPP and DPA showed limited persistence (50% dissipation time [DT 50 ], 0.6 and 1.3 days) compared to TBZ and IMZ (DT 50 , 47.0 and 150.8 days). EQ was rapidly transformed to the short-lived quinone imine (QI) (major metabolite) and the more persistent 2,4-dimethyl-6-ethoxyquinoline (EQNL) (minor metabolite). EQ and OPP exerted significant inhibition of potential nitrification, with the effect of the former being more persistent. This was not reflected in the abundance (determined by quantitative PCR [qPCR]) of the amoA gene of ammonia-oxidizing bacteria (AOB) and archaea (AOA). Considering the above discrepancy and the metabolic pattern of EQ, we further investigated the hypothesis that its metabolites and not only EQ were toxic to ammonia oxidizers. Potential nitrification, amoA gene abundance, and amoA gene transcripts of AOB and AOA showed that QI was probably responsible for the inhibition of nitrification. Our findings have serious ecological and practical implications for soil productivity and N conservation in agriculturally impacted ecosystems and stress the need to include metabolites and RNAbased methods when the soil microbial toxicity of pesticides is assessed. During postharvest handling, fruits are subjected to treatments with fungicides like thiabendazole (TBZ), imazalil (IMZ), and ortho-phenyl phenol (OPP) (1, 2) and antioxidants like diphenylamine (DPA) and ethoxyquin (EQ) (3), resulting in the production of large volumes of pesticide-contaminated wastewaters. The direct environmental discharge of those effluents without prior depuration entails a serious risk for the integrity of receiving ecosystems, considering the high aquatic toxicity of the pesticides (4, 5). This concern has been addressed by the European Commission (EC), and authorization for those pesticides was given with the stipulation "that an efficient treatment of the produced wastewaters should be operative at a local scale" (6, 7).Various processes and systems have been tested for the treatment of wastewaters produced by fruit-packaging plants (FPP) including adsorption onto activated carbon (8), photocatalytic degradation (9, 10), and biological degradation (11, 12). However, their high cost, their elevated technological requirements, and the frequent production of oxidized metabolites which are of unknown toxicity compared to the parent compound have hampered their full-scale implementation. Thus, to date effluents from FPP are either discharged in municipal wastewater treatment systems or they are disposed via land-spreading on the s...

Comparison of thein vitroactivity of novel and established nitrification inhibitors applied in agriculture: challenging the effectiveness of the currently available compounds

“…Considering that in the cultures inhibited by EQ (i) EQNL was formed at concentrations substantially lower than those expected to result in an inhibitory effect on the AO tested, and (ii) QI was formed at concentrations equal or higher than those expected to induce an inhibitory effect on the AO tested, we suggest that QI is the main determinant of the persistent inhibitory effect of EQ on AO and NOB. This is consistent with our previous soil studies where EQ, but mostly QI when applied alone, induced a significant inhibition of potential nitrification and transcription of both bacterial and archaeal amoA genes (32). Unlike our previous soil studies where QI showed equivalent inhibitory effects against AOB and AOA, we observed a difference in the inhibition potential of QI between these two AO groups.…”

“…animals, plants, and soils) (46). In this study, EQ was rapidly transformed to QI and EQNL, with the former being the major but least persistent transformation product, while the latter being a minor but more persistent product, in line with previous studies in soil (32, 33). We observed a different inhibition potential for AOB and AOA.…”

“…In previous soil microcosm studies we showed that ethoxyquin (EQ) (1,2-dihydro-6-ethoxy-2,2,4-trimethylquinoline), an antioxidant used as preservative in fruit-packaging plants, and its derivative 2,6-dihydro-2,2,4-trimethyl-6-quinone imine (QI), strongly inhibited the activity of AOB and AOA (32). EQ in soil is rapidly transformed to QI and 2,4-dimethyl-6-ethoxyquinoline (EQNL), with the former being the major metabolite (33).…”

Blame It on the Metabolite: 3,5-Dichloroaniline Rather than the Parent Compound Is Responsible for the Decreasing Diversity and Function of Soil Microorganisms

“…Recently, Karas et al (9) demonstrated the major role of TPs of chlorpyrifos and isoproturon on the inhibition of soil microbial functions. Similarly, Papadopoulou et al (10) showed that quinone imine, the oxidized TP of ethoxyquin (an antioxidant used in the fruit-packaging industry) was equally as toxic as, or more toxic than, the parent compound to ammonia-oxidizing microorganisms (AOM). This group has been shown to be particularly sensitive to environmental perturbations (11) including pesticide exposure (6,9).…”

Nutritional inter-dependencies and a carbazole-dioxygenase are key elements of a bacterial consortium relying on aSphingomonasfor the degradation of the fungicide thiabendazole

“…NOEC fish = 12 μg L −1 ) [8]. We recently reported TBZ concentration levels in soils adjacent to fruit packaging plants of up to 12,000 mg kg −1 resulting in a depleted bacterial diversity [9]. The extensive environmental contamination by TBZ is the result of its high persistence (DT50 (soil - aerobic)> 365 days) [10] and the lack of implemented methods for the treatment of TBZ-contaminated agro-industrial effluents (despite the implementation of relevant EC legislation) [11].…”