Maria del Pilar Castillo

Biobeds for environmental protection from pesticide use--a review.

Biobeds originated in Sweden in response to the need for simple and effective methods to minimize environmental contamination from pesticide use, especially when filling spraying equipment, a typical point source of contamination. The biobed system has attracted attention in several countries, where work is being conducted to adapt it to local conditions and applications. As a consequence, the biobed system has been more or less modified and sometimes renamed, for example, as biomassbed in Italy, biofilter in Belgium, and Phytobac and biobac in France. The effectiveness and simplicity of the biobed also make it suitable for use in developing countries, and different adaptations of the biobed concept now exist in, for instance, Peru, Guatemala, and Ecuador. When the modification of the biobed includes an intention to use it for retention and degradation of pesticides in sprayer washings, the construction has to be adapted to, for example, lined biobeds to ensure that no pesticide leaching will occur. Replacement of some of the original materials in the Swedish biomixture (straw, peat, and soil) can also change the performance of the system, for instance, the amount, activity, and composition of the microbial community that develops. This review presents the state of the art of biobeds and similar systems in Sweden and worldwide and identifies future research needs. Factors affecting the efficiency of biobeds in terms of degradation and retention of pesticides are discussed, with particular emphasis on the microbial processes involved.

Degradation of glyphosate and other pesticides by ligninolytic enzymes

The ability of pure manganese peroxidase (MnP), laccase, lignin peroxidase (LiP) and horseradish peroxidase (HRP) to degrade the widely used herbicide glyphosate and other pesticides was studied in separate in vitro assays with addition of different mediators. Complete degradation of glyphosate was obtained with MnP, MnSO4 and Tween 80, with or without H2O2. In the presence of MnSO4, with or without H2O2, MnP also transformed the herbicide, but to a lower rate. Laccase degraded glyphosate in the presence of (a) 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS), (b) MnSO4 and Tween 80 and (c) ABTS, MnSO4 and Tween 80. The metabolite AMPA was detected in all cases where degradation of glyphosate occurred and was not degraded. The LiP was tested alone or with MnSO4, Tween 80, veratryl alcohol or H2O2 and in the HRP assay the enzyme was added alone or with H2O2 in the reaction mixture. However, these enzymes did not degrade glyphosate. Further experiments using MnP together with MnSO4 and Tween 80 showed that the enzyme was also able to degrade glyphosate in its commercial formulation Roundup® Bio. The same enzyme mixture was tested for degradation of 22 other pesticides and degradation products present in a mixture and all the compounds were transformed, with degradation percentages ranging between 20 and 100%. Our results highlight the potential of ligninolytic enzymes to degrade pesticides. Moreover, they suggest that the formation of AMPA, the main metabolite of glyphosate degradation found in soils, can be a result of the activity of lignin-degrading enzymes.

Establishment of the white rot fungus Phanerochaete chrysosporium on unsterile straw in solid substrate fermentation systems intended for degradation of pesticides

The effects of different inoculum-loading rates and pre-treatment of wheat straw with formic acid and hot water (50 °C) on the establishment of Phanerochaete chrysosporium on unsterile straw were studied in laboratory scale and in a 1.5-m3 bioreactor. The establishment of P. chrysosporium on unsterile straw was satisfactory. Phanerochaete chrysosporium and other fungi, which developed simultaneously, were able to produce the activity necessary to degrade two herbicides, bentazon and MCPA (4-chloro-2-methylphenoxyacetic acid) in 20 days (65 and 75%, respectively). The decrease of both herbicides coincided with the presence of the activity of the lignin-degrading enzymes lignin peroxidase and manganese peroxidase/laccase. Extensive growth of P. chrysosporium or other lignin-degrading fungi on unsterile straw would be excellent for inexpensive solid substrate systems intended for degradation of pesticides.

Degradation of isoproturon and bentazone in peat- and compost-based biomixtures

BACKGROUND The composition and properties of a biomixture used in a biobed are decisive for pesticide sorption and degradation. This study was performed to investigate the capability of compost-based substrates in mixtures with citrus peel and vine branch straw and peat-based substrates in mixtures with soil and vine branch straw at different levels in order to degrade isoproturon and bentazone. RESULTS Dissipation and mineralisation rates of both pesticides were determined, and metabolic activity was followed as respiration. Compost-based substrates showed faster pesticide dissipation in the presence of lignocellulosic materials, as in garden compost and vine branch straw. The increasing content of vine branch straw in peat-based substrates does not seem to affect dissipation of the parent compounds. Low mineralisation rate was observed in all treatments. CONCLUSION Higher pesticide degradation was observed in the lignocellulosic substrates, probably because of the development of lignin-degrading microorganisms which have shown to be robust and are able to degrade recalcitrant pesticides. Copyright

Microbial impact of the pesticide chlorpyrifos on Swedish and Italian biobeds

Biobeds provide a simple and cheap solution to reducing point-source contamination by pesticides from farm activities. In its original design, the Swedish biobed is a clay-lined pit in the ground filled with a biomixture of topsoil, peat and straw and covered with a grass layer. The straw stimulates the growth of lignin-degrading fungi and the formation and activity of ligninolytic enzymes which can degrade many different pesticides. Here we compared the behaviour of the chlorpyrifos pesticide in two biobeds of different composition: a Swedish biobed composed of 50%v vine straw, 25%v peat and 25%v Swedish soil; and an Italian biobed composed of 40%v vine straw, 40%v green compost and 20%v Italian soil. Microbial biomass was measured in the Italian biomix by the fumigation-extraction method. The microbial activity was estimated by measuring mineralisation of a synthetic lignin, 14C-de-hydrogenative polymerisate (14C-DHP) in the Swedish biomix. Microbial respiration was followed over time in both biomixes. Our results show that the chlorpyrifos half-lives were similar in both biomixes. The microbial biomass content was reduced by 25 and 50% with, respectively, 10 and 50 mg kg−1 chlorpyrifos in the Italian biomix. The respiration activity was affected only at 50 mg kg−1 chlorpyrifos in the Italian biomix. No effect was observed in the Swedish biomix despite the higher chlorpyrifos concentration of 100 mg kg−1. The mineralisation of 14C-DHP was not affected by the presence of chlorpyrifos in the Swedish biomix. These findings could be explained by the presence of chlorpyrifos-sensitive microorganisms in the Italian biomix and chlorpyrifos-resitant microorganisms in the Swedish biomix. The more robust microftora developed in the Swedish biomix may be explained by its lower nitrogen content, higher C/N ratio and lower pH, all of which are favourable for the development of lignin-degrading fungi and their activity. In Sweden more than 1000 biobeds are in practical use on farms and they have been shown to be efficient at reducing pesticide water-body contamination. The present study compares the capability of an Italian biomix for degrading pesticides to that shown by the Swedish original biomix in order to introduce this biological system for a sustainable Italian agriculture.

Degradation of PAH in a Creosote-Contaminated Soil. A Comparison Between the Effects of Willows (Salix Viminalis), Wheat Straw and A Nonionic Surfactant

The degradation of polyaromatic hydrocarbons (PAH) in an aged creosote-contaminated soil in the presence of Salix viminalis was investigated in a greenhouse experiment. Phenanthrene and pyrene were degraded 100% and 80%, respectively, in the presence of plants but only 68% and 63% without plants. The effects of the nonionic surfactant Triton X-100 or the addition of straw, without plants, were also studied. The addition of straw had no effect on PAH degradation compared to the control. Pyrene degradation with Triton X-100 at low concentrations (0.06 μl g−1 DW) was comparable to that with plants but was less for anthracene and phenanthrene. The treatments with plants were, according to SIR measurements, dominated by active microorganisms (98.8% of the biomass), whereas all treatments without plants contained mostly dormant or non-growing microorganisms (1.7–2.0% active). Viable counts and active biomass were highly correlated in all treatments and demonstrated that S. viminalis greatly increased microbial populations. Dominant bacteria were grouped according to Gram, fluorescence and oxidase tests and revealed differences between treatments. The presence of S. viminalis or the surfactant enhanced PAH degradation, primarily by a rhizosphere effect on the microbial activity in the former case and by increased bioavailability in the latter case.

A practical culture technique for enhanced production of manganese peroxidase by Anthracophyllum discolor Sp4

In this study, different growth conditions of Anthracophyllum discolor Sp4 including the effect of agitation, additions of lignocellulosic support, inducer and surfactant were evaluated on the MnP production in Kirk medium using a culture system made up of the tubes containing the glass bead . The highest MnP production (1,354 U/L on day 13) was obtained when the medium was supplemented with wheat grain and 0.25 mM MnSO4 as inducer, under static conditions at 30°C. Two isoenzymes were purified (35 and 38 kDa respectively). MnP presented a maximal activity in the pH range between 4.5 and 5.5, a relatively high temperature tolerance (50oC) and a high catalytic activity for 2,6-dimethoxyphenol and hydrogen peroxide.

Biobeds - Biotechnology for Environmental Protection from Pesticide Pollution

Point sources of pesticides, for instance frequently occurring at the filling of spraying equipment, are one of the most dominant reasons for pesti- cide pollution of surface and ground waters today. This contaminant risk can be minimized by using biobeds. Biobeds are facilities intended to retain and degrade pesticide spills. In its original design they consist of a biomixture, a clay layer at the bottom and a grass cover on the surface. The typical Swedish stimulates the growth of lignin-degrading fungi and the formation of ligninolytic enzymes (such as manganese and lignin peroxidases), which can degrade many different pesticides. The soil provides sorption capacity and other degrading microorganisms and the peat contributes to high sorption capacity and also helps to regulate the humidity of the system. A grass layer covering the biobed also helps to keep the correct humidity and can be used as an indicator revealing pesticide spills. The clay acts as an impermeable layer at the bottom. More than 1500 biobeds are in use in Sweden today and this concept has proven to be an effective and inexpensive solution to mitigate the release of pesticides to the environment.