John Stenström

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.

Potential denitrification activity assay in soil—With or without chloramphenicol?

Abstract A common way to characterize denitrification in soil is to determine the potential denitrifying activity (PDA). Our objectives were to compare different techniques of mathematically describing experimental data obtained in the PDA assay, both with and without use of chloramphenicol (CAP), and to quantify the effect of CAP on the process. The PDA assay was carried out in the presence of acetylene in slurries of three agricultural soils containing 1 m m glucose and 1 m m KNO 3 . When CAP was not used in the assay, growth related curves of N 2 O-formation were obtained for all three soils. These data were used to calculate the initial rate by: (1) assuming the initial phase to be linear and using the four first data points for linear regression; and by (2) using a growth-assciated product formation equation. The good fit to the data that was obtained with the latter method suggests that PDA is a continuous process without distinct phases. Moreover, our results clearly show that denitrifying activity is inhibited by CAP even at the lowest concentration tested, 20 mg 1 −1 . The inhibiting effect increased with increasing concentrations of CAP. The PDA was 17–42% lower at 1 g CAP 1 −1 compared with assays without CAP. This shows that not only synthesis of new enzymes is affected but also that the activity of already existing enzymes is decreased. Results from our study strongly suggest that single concentrations of CAP must not be used in PDA assays. An alternative strategy could be to use multiple CAP concentrations and then extrapolate to the rate at 0 g CAP 1 −1 . However, we recommend assays without CAP and that data should be fitted to the growth-associated product formation equation. By using this method, values of the PDA and the growth rate of the denitrifying bacterial population are objectively obtained.

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.

Pesticide leaching data to validate simulation models for registration purposes

Abstract A data set originating from three pesticide leaching experiments conducted in undisturbed soil monoliths is described. Leaching of the herbicides dichlorprop and bentazon was measured in five different soils, ranging from loamy sand/sand through sandy loam to silty clay. Information on degradation and adsorption of the herbicides and soil physical and hydraulic properties is also included in the paper. This data was used for a model validation exercise, aimed at comparing and evaluating existing pesticide leaching models from the point of view of regulatory purposes. Larger amounts of dichlorprop were leached than bentazon reaching an average amount of 3.22 g a.i./ha (0.20% of applied dichlorprop) during the eight month study period. The largest leaching loss was found in a clay soil, which was explained in terms of macropore flow.

Degradation of mixtures of phenolic compounds by Arthrobacter chlorophenolicus A6.

In this study the chlorophenol-degrading actinobacterium, Arthrobacter chlorophenolicus A6, was tested for its ability to grow on mixtures of phenolic compounds. During the experiments depletion of the compounds was monitored, as were cell growth and activity. Activity assays were based on bioluminescence output from a luciferase-tagged strain. When the cells were grown on a mixture of 4-chlorophenol, 4-nitrophenol and phenol, 4-chlorophenol degradation apparently was delayed until 4-nitrophenol was almost completely depleted. Phenol was degraded more slowly than the other compounds and not until 4-nitrophenol and 4-chlorophenol were depleted, despite this being the least toxic compound of the three. A similar order of degradation was observed in non-sterile soil slurries inoculated with A. chlorophenolicus. The kinetics of degradation of the substituted phenols suggest that the preferential order of their depletion could be due to their respective pKa values and that the dissociated phenolate ions are the substrates. A mutant strain (T99), with a disrupted hydroxyquinol dioxygenase gene in the previously described 4-chlorophenol degradation gene cluster, was also studied for its ability to grow on the different phenols. The mutant strain was able to grow on phenol, but not on either of the substituted phenols, suggesting a different catabolic pathway for the degradation of phenol by this microorganism.

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 the herbicide bentazon as related to enzyme production by Phanerochaete chrysosporium in two solid substrate fermentation systems

Enzyme production and degradation of the herbicide bentazon by Phanerochaete chrysosporium growing on straw (solid substrate fermentation, SSF) and the effect of nitrogen and the hydraulic retention time (HRT) were studied using a small bioreactor and batch cultures. The best degradation of bentazon was obtained in the low nitrogen treatments, indicating participation of the ligninolytic system of the fungus. The treatments that degraded bentazon also had manganese peroxidase (MnP) activity, which seemed to be necessary for degradation. Pure MnP (with Mn(II) and H2O2) did not oxidize bentazon. However, in the presence of MnP, Mn(II) and Tween 80, bentazon was slowly oxidized in a H2O2-independent reaction. Bentazon was a substrate of pure lignin peroxidase (LiP) and was oxidized significantly faster (22,000–29,000 times) as compared to the MnP-Tween 80 system. Although LiP was a better enzyme for bentazon oxidation in vitro, its role in the SSF systems remains unclear since it was detected only in treatments with high nitrogen and high HRT where no degradation of bentazon occurred. Inhibition of LiP activity may be due to phenols and extractives present in the straw.

Modeling spatial variation in microbial degradation of pesticides in soil.

Currently, no general guidance is available on suitable approaches for dealing with spatial variation in the first-order pesticide degradation rate constant k even though it is a very sensitive parameter and often highly variable at the field, catchment, and regional scales. Supported by some mechanistic reasoning, we propose a simple general modeling approach to predict k from the sorption constant, which reflects bioavailability, and easily measurable surrogate variables for microbial biomass/activity (organic carbon and clay contents). The soil depth was also explicitly included as an additional predictor variable. This approach was tested in a meta-analysis of available literature data using bootstrapped partial least-squares regression. It explained 73% of the variation in k for the 19 pesticide-study combinations (n = 212) in the database. When 4 of the 19 pesticide-study combinations were excluded (n = 169), the approach explained 80% of the variation in the degradation rate constant. We conclude that the approach shows promise as an effective way to account for the effects of bioavailability and microbial activity on microbial pesticide degradation in large-scale model applications.

Environmental problems with the use of diuron on Swedish railways

Lennart Torstensson, Harald Cederlund, Elisabet Borjesson and John Stenstrom, of the Swedish University of Agricultural Sciences in Uppsala, outline the problems caused by using diuron along railway tracks in Sweden.

Soil Functional Operating Range Linked to Microbial Biodiversity and Community Composition Using Denitrifiers as Model Guild

Soil microorganisms are key players in biogeochemical cycles. Yet, there is no consistent view on the significance of microbial biodiversity for soil ecosystem functioning. According to the insurance hypothesis, declines in ecosystem functioning due to reduced biodiversity are more likely to occur under fluctuating, extreme or rapidly changing environmental conditions. Here, we compare the functional operating range, a new concept defined as the complete range of environmental conditions under which soil microbial communities are able to maintain their functions, between four naturally assembled soil communities from a long-term fertilization experiment. A functional trait approach was adopted with denitrifiers involved in nitrogen cycling as our model soil community. Using short-term temperature and salt gradients, we show that the functional operating range was broader and process rates were higher when the soil community was phylogenetically more diverse. However, key bacterial genotypes played an important role for maintaining denitrification as an ecosystem functioning under certain conditions.