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A laboratory experiment was carried out to determine the organic carbon content and quality of different organic residues (urban and green compost, moist olive oil husks) and soils of different origin (forest and agricultural) to be used as biofilter in the biodepuration of pesticide contaminated water. An adsorption/desorption experiment was also performed to assess the retention capacity of substrates tested against fungicide metalaxyl. The goal of the work was to determine the extent of the adsorption/desorption of the mobile fungicide metalaxyl in substrates containing different amounts and quality of organic carbon and to characterize the relationship between the carbon fractions and the adsorption/desorption parameters determined. The Kads values found in the organic substrates turned out to be higher than those reported for soils, indicating the highest sorption capability of these materials and their suitability to be used as bio-filters for decontaminating water. The quality of organic carbon strongly influenced the entity and the reversibility of bonds between substrates and fungicide. The influence of different organic fractions on the adsorption of metalaxyl can be summarized in the order of humic acids carbon > total humified extractable carbon > total organic carbon > total carbon, leading to the conclusion that the presence of the humified fraction in the organic substrates is essential for a good performance of biofilters. Indeed, the desorption experiment evidenced that metalaxyl is less desorbed in the most humified substrates. Therefore, in bio-depuration systems such as biobed it is convenient to use mature substrates, which have to undergo a composting process, leading to high humus content and quality, responsible for irreversible bonds with pesticides.

Biopurification systems (BPS) have been introduced to minimise the risk for point source contamination of natural water resources by pesticides. Their depuration efficiency relies mostly on the high biodegradation of their packing substrate (biomixture). Despite that, little is known regarding the interactions between biomixture microflora and pesticides, especially fungicides which are expected to have a higher impact on the microbial community. This study reports the dissipation of the fungicides azoxystrobin (AZX), fludioxonil (FL) and penconazole (PC), commonly used in vineyards, in a biomixture composed of pruning residues and straw used in vineyard BPS. The impact of fungicides on the microbial community was also studied via microbial biomass carbon, basal respiration and phospholipid fatty acid analysis. AZX dissipated faster (t 1/2 = 30.1 days) than PC (t 1/2 = 99.0 days) and FL (t 1/2 = 115.5 days). Fungicides differently affected the microbial community. PC showed the highest adverse effect on both the size and the activity of the biomixture microflora. A significant change in the structure of the microbial community was noted for PC and FL, and it was attributed to a rapid inhibition of the fungal fraction while bacteria showed a delayed response which was attributed to indirect effects by the late proliferation of fungi. All effects observed were transitory and a full recovery of microbial indices was observed 60 days post-application. Overall, no clear link between pesticide persistence and microbial responses was observed stressing the complex nature of interactions between pesticides in microflora in BPS.

BiomassBed is an indirect system designed to collect accidental pesticide spills as well as water remnants of tank sprayers. This system was installed in a vineyard and tested in bio-cleaning water that was contaminated by fungicides in a two-year-field experiment. At the end of each treatment, wastewater of sprayer tanks containing mixtures of cymoxanil, dimethomorph, metalaxyl M, folpet, penconazole, cyprodinil, fludioxonil, azoxystrobin, mandipropamid, pyraclostrobin at different concentrations were discharged into the BiomassBed and repeatedly circulated through an organic biofilter of pruning residues and straw for fungicide adsorption and biodegradation. Water collected was sampled and analysed for fungicide residues, and organic biofilter was analysed to assess fungicide dissipation. Fungicides were removed from water in a range of 92.4–100% of the initial concentration. Metalaxyl M was the least retained and probably desorbed during recirculation of water. However, metalaxyl M residues dissipated in 70 days in collected stagnant water. Abiotic and biotic factors contributing to the disappearance of metalaxyl M in water was hypothesised. Fungicide dissipation in the organic biofilter occurred in a 90-day period with the exception of penconazole that remained at 63.6% and 42.0% in 2008 and 2009, respectively. Owing to the advantageous combination of depuration and bio-degradation processes, fungicides were removed from water in a range of 92.4 to 100%. However more effort is needed to enhance adsorption of mobile fungicides and to achieve a faster degradation of more persistent active ingredients.

Biobeds developed in Sweden bind and degrade pesticides from point sources. The objective of this work was to adapt the biobed to Italian operating conditions, for example, to identify organic materials as effective as those in the original Swedish composition. The capacity of urban and garden composts alone or mixed with citrus peel or straw to degrade chlorpyrifos and its metabolite TCP was compared to the typical Swedish biomix consisting of straw, peat, and soil. A tendency for higher 14C-chlorpyrifos mineralization and lower TCP levels was observed in the biomixes with garden compost alone or amended with straw. In a second trial, a high correlation of lower TCP with increasing levels of straw in typical Swedish biomixes was observed. Straw stimulates production of lignin-degrading enzymes such as manganese peroxidase (MnP), and further trials with pure MnP showed that this enzyme degrades TCP. Materials with an active lignin-degrading microflora are a prerequisite for effective dissipation of chlorpyrifos and non-accumulation of TCP. Thus, lignocellulosic materials as straw and garden composts should be present in biomixes to be used under Italian conditions.

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