Evangelos Karanasios

Degradation and Adsorption of Pesticides in Compost-Based Biomixtures as Potential Substrates for Biobeds in Southern Europe

Biobeds have been used in northern Europe for minimizing point source contamination of water resources by pesticides. However, little is known regarding their use in southern Europe where edaphoclimatic conditions and agriculture practices significantly differ. A first step toward their adaptation in southern Europe is the use of low-cost and easily available substrates as biomixture components. This study investigated the possibility of replacing peat with agricultural composts in the biomixture. Five composts from local substrates including olive leaves, cotton crop residues, cotton seeds, spent mushroom substrate, and commercial sea wrack were mixed with topsoil and straw (1:1:2). Degradation of a mixture of pesticides (dimethoate, indoxacarb, buprofezin, terbuthylazine, metribuzin, metalaxyl-M, iprodione, azoxystrobin) at two dose rates was tested in the compost biomixtures (BX), in corresponding peat biomixtures (OBX), and in soil. Adsorption-desorption of selected pesticides were also studied. Pesticide residues were determined by gas chromatography with nitrogen-phosphorus detector, except indoxacarb, which was determined with a microelectron capture detector. Overall, BX degraded the studied pesticides at rates markedly higher than those observed in soil and OBX, in which the slowest degradation rates were evident. Overall, the olive leaf compost biomixture showed the highest degradation capacity. Adsorption studies showed that OBX and BX had higher adsorption affinity compared to soil. Desorption experiments revealed that pesticide adsorption in biomixtures was not entirely reversible. The results suggest that substitution of peat with local composts will lead to optimization of the biobed system for use in Mediterranean countries.

On-farm biopurification systems for the depuration of pesticide wastewaters: recent biotechnological advances and future perspectives.

Point source contamination of natural water resources by pesticides constitutes a serious problem and on-farm biopurification systems (BPS) were introduced to resolve it. This paper reviews the processes and parameters controlling BPS depuration efficiency and reports on recent biotechnological advances which have been used for enhancing BPS performance. Biomixture composition and water management are the two factors which either individually or through their interactions control the depuration performance of BPS. Which process (biodegradation or adsorption) will dominate pesticides dissipation in BPS depends on biomixture composition and the physicochemical properties of the pesticides. Biotechnological interventions such as augmentation with pesticide-degrading microbes or pesticide-primed matrices have resulted in enhanced biodegradation performance of BPS. Despite all these advancement in BPS research, there are still several issues which should be resolved to facilitate their full implementation. Safe handling and disposal of the spent biomixture is a key practical issue which needs further research. The use of BPS for the depuration of wastewaters from post-farm activities such as postharvest treatment of fruits should be a priority research issue considering the lack of alternative treatment systems. However, the key point hampering optimization of BPS is the lack of fundamental knowledge on BPS microbiology. The use of advanced molecular and biochemical methods in BPS would shed light into this issue in the future.

Novel biomixtures based on local Mediterranean lignocellulosic materials: evaluation for use in biobed systems.

The composition of biomixtures strongly affect the efficacy of biobeds. Typically, biomixture consists of peat (or compost), straw (STR) and topsoil (1:2:1 by volume). Straw guarantees a continuous supply of nutrients and high microbial activity. However, in south Europe other lignocellulosic materials including sunflower crop residues (SFR), olive leaves, grape stalks (GS), orange peels, corn cobs (CC) and spent mushroom substrate (SMS) are also readily available at no cost. Their potential utilization in biomixtures instead of STR was tested in pesticide degradation and adsorption studies. The microbial activity in these biomixtures was also assessed. The GS-biomixture was the most efficient in pesticide degradation, while CC- and SFR-biomixtures showed comparable degrading efficacy with the STR-biomixture. The SMS-biomixture was also highly efficient in degrading the pesticide mixture with degradation rates being correlated with the proportion of SMS in the biomixture. Microbial respiration was positively correlated with the degradation rates of metalaxyl, azoxystrobin and chlorpyrifos, compared to phenoloxidase which showed no correlation. Biomixtures containing alternative lignocellulosic materials showed a higher adsorption affinity for terbuthylazine and metribuzin compared to the STR-biomixture. We provide first evidence that STR can be substituted in biomixtures by other lignocellulosic materials which are readily available in south Europe.

Isolation of soil bacteria able to hydrolyze both organophosphate and carbamate pesticides.

Two bacteria identified as Pseudomonas putida and Acinetobacter rhizosphaerae able to rapidly degrade the organophosphate (OP) fenamiphos (FEN) were isolated. Denaturating gradient gel electrophoresis analysis revealed that the two isolates were dominant members of the enrichment culture. Clone libraries further showed that bacteria belonging to α-, β-, γ-proteobacteria and Bacteroidetes were also present in the final enrichment but were not isolated. Both strains hydrolyzed FEN to fenamiphos phenol which was further transformed, only by P. putida. The two strains were using FEN as C and N source. Cross-feeding studies with other pesticides showed that P. putida degraded OPs with a P-O-C linkage and unexpectedly degraded the carbamates oxamyl and carbofuran being the first wild-type bacterial strain able to degrade both OPs and carbamates. The same isolate exhibited high bioremediation potential against spillage-level concentrations of aged residues of FEN and its oxidized derivatives.

Quantitative and qualitative differences in the metabolism of pesticides in biobed substrates and soil

Biobed substrates commonly exhibit high degradation capacity. However, degradation does not always lead to detoxification and information on the metabolic pathways of pesticides in biobeds is scarce. We studied the degradation and metabolism of three pesticides in selected biomixtures and soil. Biomixtures stimulated degradation of terbuthylazine and metribuzin, whereas chlorpyrifos degraded faster in soil. The latter was attributed to the lipophilicity of chlorpyrifos which increased adsorption and limited biodegradation in organic-rich biomixtures. Although the same metabolites were detected in all substrates, qualitative and quantitative differences in the metabolic routes of pesticides in the various substrates were observed. Chlorpyrifos was hydrolyzed to 3,5,6-tricholorpyridinol (TCP) which was further degraded only in compost-biomixture CBX1. Metabolism of terbuthylazine in compost biomixtures (BX) and soil resulted in the formation of desethyl-terbuthylazine (DES) which was fully degraded only in the compost-biomixture CBX2, whereas peat-based biomixture (OBX) promoted the hydroxylation of terbuthylazine. Desamino- (DA) (dominant) and diketo- (DK) metribuzin appear as intermediate metabolites in all substrates and were further transformed to desamino-diketo-metribuzin (DADK) which was fully degraded only in compost-biomixture GSBX. Overall, lower amounts of metabolites were accumulated in biomixtures compared to soil stressing the higher depuration efficiency of biobeds.

Key parameters and practices controlling pesticide degradation efficiency of biobed substrates

We studied the contribution of each of the components of a compost-based biomixture (BX), commonly used in Europe, on pesticide degradation. The impact of other key parameters including pesticide dose, temperature and repeated applications on the degradation of eight pesticides, applied as a mixture, in a BX and a peat-based biomixture (OBX) was compared and contrasted to their degradation in soil. Incubation studies showed that straw was essential in maintaining a high pesticide degradation capacity of the biomixture, whereas compost, when mixed with soil, retarded pesticide degradation. The highest rates of degradation were shown in the biomixture composed of soil/compost/straw suggesting that all three components are essential for maximum biobed performance. Increasing doses prolonged the persistence of most pesticides with biomixtures showing a higher tolerance to high pesticide dose levels compared to soil. Increasing the incubation temperature from 15°C to 25°C resulted in lower t1/2 values, with biomixtures performing better than soil at the lower temperature. Repeated applications led to a decrease in the degradation rates of most pesticides in all the substrates, with the exception of iprodione and metalaxyl. Overall, our results stress the ability of biomixtures to perform better than soil under unfavorable conditions and extreme pesticide dose levels.

Integrated biodepuration of pesticide-contaminated wastewaters from the fruit-packaging industry using biobeds: Bioaugmentation, risk assessment and optimized management

Wastewaters from fruit-packaging plants contain high loads of toxic and persistent pesticides and should be treated on site. We evaluated the depuration performance of five pilot biobeds against those effluents. In addition we tested bioaugmentation with bacterial inocula as a strategy for optimization of their depuration capacity. Finally we determined the composition and functional dynamics of the microbial community via q-PCR. Practical issues were also addressed including the risk associated with the direct environmental disposal of biobed-treated effluents and decontamination methods for the spent packing material. Biobeds showed high depuration capacity (>99.5%) against all pesticides with bioaugmentation maximizing their depuration performance against the persistent fungicide thiabendazole (TBZ). This was followed by a significant increase in the abundance of bacteria, fungi and of catabolic genes of aromatic compounds catA and pcaH. Bioaugmentation was the most potent decontamination method for spent packing material with composting being an effective alternative. Risk assessment based on practical scenarios (pome and citrus fruit-packaging plants) and the depuration performance of the pilot biobeds showed that discharge of the treated effluents into an 0.1-ha disposal site did not entail an environmental risk, except for TBZ-containing effluents where a larger disposal area (0.2ha) or bioaugmentation alleviated the risk.

Optimization of biomixture composition and water management for maximum pesticide dissipation in peat-free biobeds.

Biomixture composition and water management are key factors controlling biobeds performance. Although compost-biomixtures (BXs) possess high degradation efficiency, their low water-holding capacity compared with peat-biomixtures (OBX) limits their use. Thus, appropriate water management is required to optimize their performance. The dissipation capacity of selected BXs compared with OBXs was assessed in a column study under two water managements not differing in their total water load but in the intensity and frequency of water addition. Results showed that the less frequent application of large water volumes (water management scenario I) facilitated pesticide leaching (0.001-10.4% of initially applied), compared with the frequent application of low water volumes (water management scenario II) where leaching losses were always <1%. Water management affected differently the dissipation performance of substrates: OBX outperformed BXs under water management scenario I, whereas the grape marc compost-biomixture (BX1) was superior at water management scenario II. Substitution of grape marc compost (C1) with olive leaves compost (C2) or of straw with corn cobs or grape stalks reduced the dissipation capacity of BX1. Mass balance analysis revealed that the high dissipation capacity of OBX was mostly attributable to its high ability to retain rather than degrade pesticides, whereas the exact opposite was seen for BX1. Overall, our findings suggest that BXs-biobeds could treat large wastewater volumes under appropriate water management that extends the contact period between pesticides and BXs, thus exploiting their high biodegradation capacity.

Distribution and function of carbamate hydrolase genes cehA and mcd in soils: the distinct role of soil pH

ABSTRACT Synthetic carbamates constitute a significant pesticide group with oxamyl being a leading compound in the nematicide market. Oxamyl degradation in soil is mainly microbially mediated. However, the distribution and function of carbamate hydrolase genes (cehA, mcd, cahA) associated with the soil biodegradation of carbamates is not yet clear. We studied oxamyl degradation in 16 soils from a potato monoculture area in Greece where oxamyl is regularly used. Oxamyl showed low persistence (DT50 2.4‐26.7 days). q‐PCR detected the cehA and mcd genes in 10 and three soils, respectively. The abundance of the cehA gene was positively correlated with pH, while both cehA abundance and pH were negatively correlated with oxamyl DT50. Amongst the carbamates used in the study region, oxamyl stimulated the abundance and expression only of the cehA gene, while carbofuran stimulated the abundance and expression of both genes. The cehA gene was also detected in pristine soils upon repeated treatments with oxamyl and carbofuran and only in soils with pH ≥7.2, where the most rapid degradation of oxamyl was observed. These results have major implications regarding the maintenance of carbamate hydrolase genes in soils, have practical implications regarding the agricultural use of carbamates, and provide insights into the evolution of cehA. &NA; Graphical Abstract Figure. Carbamate hydrolase gene cehA is ubiquitous in soils modulating the rapid hydrolysis of oxamyl and carbofuran and its abundance is positively correlated with soil pH.