Lennart Torstensson

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.

New methods for determination of glyphosate and (aminomethyl)phosphonic acid in water and soil.

New methods were developed to determine glyphosate, N-(phosphonomethyl)glycine, and its major metabolite, (aminomethyl)phosphonic acid in groundwater and soil. The methods involve ligand-exchange, anion-exchange and derivatisation and final identification and quantification by GC-MS. The limits of quantification in this experiment were 0.1 microg l(-1) for both compounds in water and 0.006 microg g(-1) for both compounds in soil. Decomposition in soil and occurrence in groundwater of the herbicide glyphosate was studied after its application for weed control on a Swedish railway embankment.

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.

Microbiological and chemical changes in two arable soils after long-term sludge amendments

Abstract Sludge amendments increase the input of carbon and nutrients to the soil. However, the soil concentrations of heavy metals and xenobiotica can also increase due to sludge amendments, with possible effects on soil microorganisms and soil fertility. Therefore, we studied the effects on soil microorganisms and soil chemistry in two arable soils after 12 and 16 years of sewage sludge amendment (0, 1 and 3 dry matter ha–1 year–1). The sludge amendments were combined with nitrogen addition at three rates according to crop requirements, and all combinations were replicated 4 times, giving a total number of 36 parcels at each experimental site in a non-randomised block design. Univariate data evaluation as well as principal component analysis and discriminant function analysis (DFA) were used to identify differences between treatments in microbial and chemical parameters. The DFA showed that acid and alkaline phosphatase, potential ammonium oxidation and total nitrogen were the most important parameters to discriminate between a priori defined groups of sludge treatments. Among the heavy metals, copper showed the highest increase in soil concentration with sludge amendments, but this increase was still not high enough to have a significant influence on the measured parameters. None of the xenobiotica investigated was found in high soil concentrations. In conclusion, the present study showed that the sewage sludge affected several of the biological and chemical parameters investigated. However, no severe negative effects on soil microorganisms were detected at these moderate levels of sludge amendment.

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.

Interactions between the fungicide benomyl and soil microorganisms

Abstract Decomposition of benomyl and carbendazim was studied in field experiments following repeated applications during autumn to winter cereals. Effects of the fungicides on straw decomposition, balance of straw fungal flora and mineralization of nitrogen in the soils were investigated in field and in laboratory experiments. Persistence in the field of the fungicides at doses of 0.1–0.2 kg ha −1 was 9–12 months in clay soils and 12 months or longer in sand soil. Decomposition of straw in the field was not affected in clay soils by doses up to 2 kg ha −1 . In sand soil, doses up to 0.5 kg ha −1 gave no effect but in one case at 2 kg ha −1 the initial stages of straw decomposition were slightly inhibited. All doses tested in both clay and sand soils caused changes in composition of the straw fungal flora. In a laboratory experiment with benomyl in sand soil an increase in rate of nitrate accumulation was observed at a dose corresponding to 2 kg ha −1 .

Monitoring sewage sludge using heterotrophic nitrogen fixing microorganisms

Abstract Sewage sludge was studied using free-living N 2 -fixing bacteria in two types of soil amended with six types of municipal sewage sludges and cow and pig manures, respectively. Sludge and manure treatments were as follows: no addition, Swedish recommended rates of 5 t dry wt ha −1 , twice the standard rate of addition (2RR), and 10 times the standard rate (10RR). The N 2 -fixing activities of the soils were unaffected by additions of sludge with elevated concentrations of Cd, Co, Pb, Zn and naphthalene, corresponding to the recommended rate and 2RR and 10RR. Addition of a sludge with low contents of heavy metals and organic pollutants reduced N 2 -fixation activities at all concentrations in the Galbo soil. Additions of a sludge with an elevated content of Pb and PCBs reduced the N 2 -fixation when added at 10RR. The Ulleraker soil, which had higher contents of organic carbon and clay than the Galbo soil, showed reduced N 2 -fixation when treated with these sludges at 10RR. Addition of a sludge with elevated concentrations of Ag, Cr, Hg and naphthalene reduced N 2 -fixation when applied at 10RR in both soils. Sludge with the highest concentration of Cu together with elevated concentrations of Ag, nonylphenol and PCBs reduced the N 2 -fixation when applied at the standard rate and 10RR in both soils. The sludge with a moderate concentration of all studied heavy metals except Ag, but with elevated concentrations of nonylphenol and toluene, reduced N 2 -fixation when applied at 2RR in both soils. Additions of cow manure with high concentrations of ammonium and nonylphenol did not affect N 2 -fixation in the Galbo soil at the recommended rate, but reduced it at all concentrations in the Ulleraker soil. Additions of pig manure, with elevated concentrations of ammonium, phenols and toluene, strongly reduced N 2 -fixation at all rates in both soils. The adverse effects of sludges or manures on potential N 2 -fixing activities could partly be explained by the increasing concentrations of ammonium present in soil. Above a certain concentration of added ammonium, which varied between the soils, N 2 -fixation was inhibited. In some sludge-soil combinations, however, adverse effects on N 2 -fixation were observed that could not be explained by elevated ammonium rates. In these combinations, elevated concentrations of Ag, Cu and nonylphenol were observed. Adverse effects of these substances on heterotrophic N 2 -fixation were also observed in pure culture studies where Azotobacter sp. isolated from the Galbo soil were found to be sensitive to Ag, Cd, Co, Cu, Hg, Ni, Zn and nonylphenol at maximum concentrations present in the soils after additions of the sludges. Our findings indicate that particular elements or substances, such as Ag, Cu and nonylphenol present in the sludges or manures, are particularly toxic and deserve attention and that measurement of N 2 -fixation in sludge or manure treated soils is a useful method for predicting the biological quality of a particular organic slurry.

Microbial decomposition of herbicides in the soil

The fate of herbicides applied to the soil is a matter of great practical importance. If they disappear rapidly, for example, they may prove ineffective: if they persist unduly there may be environmental problems. Many factors contributed to the disappearance of herbicides: this article reviews the important role of soil micro-organisms.

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.