Meetgegevens en modelberekeningen zijn gebruikt om de belasting van de Afgedamde Maas door nutrië... more Meetgegevens en modelberekeningen zijn gebruikt om de belasting van de Afgedamde Maas door nutriënten en bestrijdingsmiddelen in beeld te brengen. Naast emissies zijn voor de bestrijdingsmiddelen ook de potentiële ecologische effecten gekwantificeerd. Voor zowel de emissies als de mogelijke effecten blijken de uiteenlopende fysisch-chemische en toxicologische eigenschappen van de afzonderlijke stoffen van groot belang. Er zijn probleemstoffen benoemd waarbij is aangegeven via welke emissieroutes deze stoffen in het oppervlaktewater terechtkomen. Daarnaast zijn de doelgroepen benoemd die verantwoordelijk zijn voor de beschreven emissies en ecologische effecten.
... Titre du document / Document title. Effects of nutrient loading and insecticide application o... more ... Titre du document / Document title. Effects of nutrient loading and insecticide application on the ecology of Elodea-dominated freshwater microcosms. I: Responses of plankton and zooplanktivorous insects. Auteur(s) / Author(s). ...
In this study, we propose a novel approach for the determination of total dissolved nitrogen (TDN... more In this study, we propose a novel approach for the determination of total dissolved nitrogen (TDN) in seawater combining high-precision isotope dilution GC-MS with persulfate digestion. A 2 mL sample aliquot was digested with an alkaline solution of persulfate to convert nitrogen containing compounds to nitrate. Digested samples were spiked with 15 NO 3 − internal standard and treated with aqueous triethyloxonium to convert the analyte into volatile EtONO 2. This derivative was readily separated from the matrix under gaseous form and could be sampled from the headspace before GC-MS analysis. The resulting chromatograms showed a stable flat baseline with EtONO 2 as the only eluting peak (retention time 2.75 min on a DB 5.625 column). Such an approach provides specificity and obviates the shortcomings of current detection methods employed to analyze seawater samples after digestion with persulfate. In negative chemical ionization mode, the method reached a detection limit of 0.5 mol/kg TDN (7 ng/g N) and could be applied to quantify seawater samples with 1-25 mol/kg TDN. On the upper end of the range, quantitation could be repeated within 1%, whereas on a 6 mol/kg TDN sample repeatability was 2.3% on eight measurements. The method was employed in two proficiency testing exercises providing results in agreement with consensus values. We investigated the impact of reagent blank and we implemented a blank-matching optimal design to account for such contribution. Finally, we performed a study on the yield of persulfate oxidation for organic and inorganic nitrogen compounds typically present in seawater. Whilst nitrite and ammonium are fully converted to nitrate, more complex organic molecules showed recoveries varying from 70% to 100%.
ISO/TC190/Soil Quality has developed a standard to enable measurement of water content in soil an... more ISO/TC190/Soil Quality has developed a standard to enable measurement of water content in soil and soil-like materials using a screening method ISO/DIS 20244. To become a full standard, the screening method required validation to show the applicability and comparability of the method in different laboratories (repeatability and reproducibility). This validation was organised by WEPAL, (Wageningen Evaluating Programs for Analytical Laboratories), which is part of Wageningen University in the Netherlands. 11 laboratories participated in the validation. Samples with comparable and known water content were distributed. Repeatability and reproducibility were calculated according ISO 5725. The measured water contents were lower than measured with ISO 11465. Probably the sucrose solution is not able to extract all water. Correction of the result using clay content and or organic matter content may be possible, but needs further investigation. The responsible ISO Working Group has to decide if and how the results can be added to ISO/DIS 20244 to become a full standard.
Use of the insecticide lambda‐cyhalothrin in agriculture may result in the contamination of water... more Use of the insecticide lambda‐cyhalothrin in agriculture may result in the contamination of water bodies, for example by spray drift. Therefore, the possible exposure of aquatic organisms to this insecticide needs to be evaluated. The exposure of the organisms may be reduced by the strong sorption of the insecticide to organic materials and its susceptibility to hydrolysis at the high pH values in the natural range. In experiments done in May and August, formulated lambda‐cyhalothrin was mixed with the water body of enclosures in experimental ditches containing a bottom layer and macrophytes (at different densities) or phytoplankton. Concentrations of lambda‐cyhalothrin in the water body and in the sediment layer, and contents in the plant compartment, were measured by gas‐liquid chromatography at various times up to 1 week after application. Various water quality parameters were also measured. Concentrations of lambda‐cyhalothrin decreased rapidly in the water column: 1 day after a...
The effects of a pesticide mixture (asulam, fluazinam, lambda-cyhalothrin, and metamitron) on aqu... more The effects of a pesticide mixture (asulam, fluazinam, lambda-cyhalothrin, and metamitron) on aquatic ecosystems were investigated in 20 outdoor aquatic microcosms. Ten of the microcosms simulated mesotrophic aquatic ecosystems dominated by submerged macrophytes (Elodea). The others simulated eutrophic ecosystems with a high Lemna surface coverage (Lemna). This paper describes the fate of the chemicals as well as their effects on the growth of Myriophyllum spicatum and the periphytic algal community. In the Elodea-dominated microcosms significant increase in the biomass and alterations of species composition of the periphytic algae were observed, but no effect on M. spicatum growth could be recorded in response to the treatment. The opposite was found in the Lemna-dominated microcosms, in which decreased growth of M. spicatum was observed but no alterations could be found in the periphytic community. In the Elodea-dominated microcosms the species composition of the periphytic algae diverged from that of the control following treatment with 0.5% spray drift emission of the label-recommended rate (5% for lambda-cyhalothrin), while reduced growth of M. spicatum in the Lemna-dominated microcosms was recorded at 2% drift (20% for lambda-cyhalothrin). This study shows that the structure of the ecosystem influences the final effect of pesticide exposure.
Floodplain lakes in the Rhine-Meuse delta of the Netherlands vary considerably in levels of sedim... more Floodplain lakes in the Rhine-Meuse delta of the Netherlands vary considerably in levels of sedimentbound toxicants. Microcosm experiments were done to compare the ecological impact of the fungicide triphenyltin acetate (TPT) between test systems with clean or polluted sediments (10 microcosms each). Differences in sediment quality affected the structure of the aquatic communities that developed in the microcosms. Initially, a faster growth of the macrophyte Elodea nuttallii was observed on the polluted sediments, which contained not only toxicants but also higher organic matter and nutrient levels. Dynamics of TPT concentrations in the overlying water were very similar between the two types of test system. Higher levels of TPT, however, were found in the sediment compartment of the clean sediment systems containing a smaller macrophyte biomass. TPT was very persistent in the sediments. In both test systems representatives of several taxonomic groups showed clear responses to a single application of TPT, although benthic Nematoda were not affected. Although a few differences in the intensity and/or duration of TPT-related population responses were observed between the two types of test system, the background pollutants in the polluted sediment hardly affected the overall sensitivity of the aquatic community to the additional chemical stressor TPT.
The fungicide fluazinam, the insecticide lambda-cyhalothrin, and the herbicides asulam and metami... more The fungicide fluazinam, the insecticide lambda-cyhalothrin, and the herbicides asulam and metamitron were applied to indoor freshwater microcosms (water volume approximately 0.6 m3). The treatment regime was based on a realistic application scenario in tulip cultivation. Concentrations of each pesticide were equal to 0%, 0.2%, 0.5%, 2%, and 5% spray drift emission of label-recommended rates. Contribution of compounds to the toxicity of the pesticide package was established by expressing their concentrations as fractions of toxic units. The fate of the compounds in the water, and responses of phytoplankton, zooplankton, periphyton, macroinvertebrates, macrophytes, decomposition, and water quality were followed for 13 weeks. The half-lives of lambda-cyhalothrin, metamitron, and fluazinam were 1 to 2 d; that of asulam was >30 d. No consistent effects could be demonstrated for the 0.2% treatment regime that was therefore considered the no-observed-effect concentration community (NOEC). The macroinvertebrate populations of Gammarus pulex, Asellus aquaticus, and Proasellus meridianus were the most sensitive end points, followed by species of copepods and cladocerans. Responses mainly were due to lambda-cyhalothrin. The 0.5% treatment regime resulted in short-term effects. Pronounced effects were observed at the 2% and 5% treatment levels. At the end of the experiment, the macrophyte biomass that consisted of Elodea nuttallii, showed a decline at the two highest treatment levels, asulam being the causal factor (NOEC: 0.5% treatment level). Primary production was reduced at the 5% treatment level only. In our experiment, the first-tier risk assessment procedure for individual compounds was adequate for protecting sensitive populations exposed to realistic combinations of pesticides. Spray drift reduction measures seem to be efficient in protecting aquatic ecosystems in agricultural areas.
Analytical and bioanalytical chemistry, Jan 2, 2018
Certification of trace metals in seawater certified reference materials (CRMs) NASS-7 and CASS-6 ... more Certification of trace metals in seawater certified reference materials (CRMs) NASS-7 and CASS-6 is described. At the National Research Council Canada (NRC), column separation was performed to remove the seawater matrix prior to the determination of Cd, Cr, Cu, Fe, Pb, Mn, Mo, Ni, U, V, and Zn, whereas As was directly measured in 10-fold diluted seawater samples, and B was directly measured in 200-fold diluted seawater samples. High-resolution inductively coupled plasma mass spectrometry (HR-ICPMS) was used for elemental analyses, with double isotope dilution for the accurate determination of B, Cd, Cr, Cu, Fe, Pb, Mo, Ni, U, and Zn in seawater NASS-7 and CASS-6, and standard addition calibration for As, Co, Mn, and V. In addition, all analytes were measured using standard addition calibration with triple quadrupole (QQQ)-ICPMS to provide a second set of data at NRC. Expert laboratories worldwide were invited to contribute data to the certification of trace metals in NASS-7 and CASS...
Two laboratory performance studies with 21 and 11 participants were carried out for passive sampl... more Two laboratory performance studies with 21 and 11 participants were carried out for passive sampling of nonpolar chemicals in water, using silicone samplers that were deployed for 7 and 13 weeks at 2 river sites in the Netherlands. Target analytes were polychlorinated biphenyls, polycyclic aromatic hydrocarbons, polybrominated diphenyl ethers, hexachlorobutadiene, hexachlorobenzene, and a number of performance reference compounds (PRCs). Calculation of aqueous concentrations based on prescribed input values and a prescribed uptake model was also included. Between laboratory coefficients of variation (CV) in the analysis of target compounds were approximately 20% at concentrations of 100 ng g-1 and approximately 100% at concentrations of 0.01 ng g-1 , which was similar to previous results for the analysis of biota samples. The analysis of PRCs yielded water sampling rates with a between laboratory CV of 18 to 30%. The sampling rate model showed a near perfect match with the consensus values of retained PRCs. The implications of the present study for future interlaboratory exercises are discussed.
Effects of chronic application of a herbicide-insecticide mixture were studied in indoor freshwat... more Effects of chronic application of a herbicide-insecticide mixture were studied in indoor freshwater plankton-dominated microcosms. Effects could well be explained by the effects of the individual chemicals alone, no synergetic effects were reported.
Greenhouse soils are regularly treated with metham-sodium, which in soil is quickly transformed t... more Greenhouse soils are regularly treated with metham-sodium, which in soil is quickly transformed to the fumigant methyl isothiocyanate. An experimental fumigation was carried out in a greenhouse with sandy soil. Data were collected on the behavior of methyl isothiocyanate in soil and its permeation through a film of low-density polyethene (LDPE) covering the soil. This cover was found to be
An increasing number of reports confirm the worldwide presence of the perfluoroalkyl substances (... more An increasing number of reports confirm the worldwide presence of the perfluoroalkyl substances (PFASs). As a consequence, the demand for qualitative and quantitative environmental occurrence data requires accurate risk assessments. To improve the analytical quality of the determination of PFASs in food and environmental samples, a 4 th international interlaboratory study (ILS) was conducted in 2011. A total of 31 partners participated, and, depending on the sample matrix, up to 29 data sets were submitted. The ILS focused on food samples, as it was organized by the PERFOOD consortium in collaboration with QUASI-MEME. The results showed that the cumulative experience of the participants has improved their analytical quality over four international ILSs. Several sources of errors were identified and methods to avoid them are suggested.
Behaviour of some pesticides in a nutrient-film and in a rock-wool system. Scientia Hortic., 25: ... more Behaviour of some pesticides in a nutrient-film and in a rock-wool system. Scientia Hortic., 25: 1-9. Adsorption of ethoprophos, tetrachlorvinphos and etridiazole onto rock-wool was found to be much weaker than adsorption onto soils. The rates of transformation in water and in water plus rock-wool at 20°C were low. The concentration of etridiazole was measured in a nutrient-film system with recirculating nutrient solution. The decrease was rapid in the first few hours but was more gradual afterwards, to low values at 8 days after application. Etridiazole penetrated poorly into the lower part of a rockwool system when the solution was trickled near the stem-base of the tomato plants.
Meetgegevens en modelberekeningen zijn gebruikt om de belasting van de Afgedamde Maas door nutrië... more Meetgegevens en modelberekeningen zijn gebruikt om de belasting van de Afgedamde Maas door nutriënten en bestrijdingsmiddelen in beeld te brengen. Naast emissies zijn voor de bestrijdingsmiddelen ook de potentiële ecologische effecten gekwantificeerd. Voor zowel de emissies als de mogelijke effecten blijken de uiteenlopende fysisch-chemische en toxicologische eigenschappen van de afzonderlijke stoffen van groot belang. Er zijn probleemstoffen benoemd waarbij is aangegeven via welke emissieroutes deze stoffen in het oppervlaktewater terechtkomen. Daarnaast zijn de doelgroepen benoemd die verantwoordelijk zijn voor de beschreven emissies en ecologische effecten.
... Titre du document / Document title. Effects of nutrient loading and insecticide application o... more ... Titre du document / Document title. Effects of nutrient loading and insecticide application on the ecology of Elodea-dominated freshwater microcosms. I: Responses of plankton and zooplanktivorous insects. Auteur(s) / Author(s). ...
In this study, we propose a novel approach for the determination of total dissolved nitrogen (TDN... more In this study, we propose a novel approach for the determination of total dissolved nitrogen (TDN) in seawater combining high-precision isotope dilution GC-MS with persulfate digestion. A 2 mL sample aliquot was digested with an alkaline solution of persulfate to convert nitrogen containing compounds to nitrate. Digested samples were spiked with 15 NO 3 − internal standard and treated with aqueous triethyloxonium to convert the analyte into volatile EtONO 2. This derivative was readily separated from the matrix under gaseous form and could be sampled from the headspace before GC-MS analysis. The resulting chromatograms showed a stable flat baseline with EtONO 2 as the only eluting peak (retention time 2.75 min on a DB 5.625 column). Such an approach provides specificity and obviates the shortcomings of current detection methods employed to analyze seawater samples after digestion with persulfate. In negative chemical ionization mode, the method reached a detection limit of 0.5 mol/kg TDN (7 ng/g N) and could be applied to quantify seawater samples with 1-25 mol/kg TDN. On the upper end of the range, quantitation could be repeated within 1%, whereas on a 6 mol/kg TDN sample repeatability was 2.3% on eight measurements. The method was employed in two proficiency testing exercises providing results in agreement with consensus values. We investigated the impact of reagent blank and we implemented a blank-matching optimal design to account for such contribution. Finally, we performed a study on the yield of persulfate oxidation for organic and inorganic nitrogen compounds typically present in seawater. Whilst nitrite and ammonium are fully converted to nitrate, more complex organic molecules showed recoveries varying from 70% to 100%.
ISO/TC190/Soil Quality has developed a standard to enable measurement of water content in soil an... more ISO/TC190/Soil Quality has developed a standard to enable measurement of water content in soil and soil-like materials using a screening method ISO/DIS 20244. To become a full standard, the screening method required validation to show the applicability and comparability of the method in different laboratories (repeatability and reproducibility). This validation was organised by WEPAL, (Wageningen Evaluating Programs for Analytical Laboratories), which is part of Wageningen University in the Netherlands. 11 laboratories participated in the validation. Samples with comparable and known water content were distributed. Repeatability and reproducibility were calculated according ISO 5725. The measured water contents were lower than measured with ISO 11465. Probably the sucrose solution is not able to extract all water. Correction of the result using clay content and or organic matter content may be possible, but needs further investigation. The responsible ISO Working Group has to decide if and how the results can be added to ISO/DIS 20244 to become a full standard.
Use of the insecticide lambda‐cyhalothrin in agriculture may result in the contamination of water... more Use of the insecticide lambda‐cyhalothrin in agriculture may result in the contamination of water bodies, for example by spray drift. Therefore, the possible exposure of aquatic organisms to this insecticide needs to be evaluated. The exposure of the organisms may be reduced by the strong sorption of the insecticide to organic materials and its susceptibility to hydrolysis at the high pH values in the natural range. In experiments done in May and August, formulated lambda‐cyhalothrin was mixed with the water body of enclosures in experimental ditches containing a bottom layer and macrophytes (at different densities) or phytoplankton. Concentrations of lambda‐cyhalothrin in the water body and in the sediment layer, and contents in the plant compartment, were measured by gas‐liquid chromatography at various times up to 1 week after application. Various water quality parameters were also measured. Concentrations of lambda‐cyhalothrin decreased rapidly in the water column: 1 day after a...
The effects of a pesticide mixture (asulam, fluazinam, lambda-cyhalothrin, and metamitron) on aqu... more The effects of a pesticide mixture (asulam, fluazinam, lambda-cyhalothrin, and metamitron) on aquatic ecosystems were investigated in 20 outdoor aquatic microcosms. Ten of the microcosms simulated mesotrophic aquatic ecosystems dominated by submerged macrophytes (Elodea). The others simulated eutrophic ecosystems with a high Lemna surface coverage (Lemna). This paper describes the fate of the chemicals as well as their effects on the growth of Myriophyllum spicatum and the periphytic algal community. In the Elodea-dominated microcosms significant increase in the biomass and alterations of species composition of the periphytic algae were observed, but no effect on M. spicatum growth could be recorded in response to the treatment. The opposite was found in the Lemna-dominated microcosms, in which decreased growth of M. spicatum was observed but no alterations could be found in the periphytic community. In the Elodea-dominated microcosms the species composition of the periphytic algae diverged from that of the control following treatment with 0.5% spray drift emission of the label-recommended rate (5% for lambda-cyhalothrin), while reduced growth of M. spicatum in the Lemna-dominated microcosms was recorded at 2% drift (20% for lambda-cyhalothrin). This study shows that the structure of the ecosystem influences the final effect of pesticide exposure.
Floodplain lakes in the Rhine-Meuse delta of the Netherlands vary considerably in levels of sedim... more Floodplain lakes in the Rhine-Meuse delta of the Netherlands vary considerably in levels of sedimentbound toxicants. Microcosm experiments were done to compare the ecological impact of the fungicide triphenyltin acetate (TPT) between test systems with clean or polluted sediments (10 microcosms each). Differences in sediment quality affected the structure of the aquatic communities that developed in the microcosms. Initially, a faster growth of the macrophyte Elodea nuttallii was observed on the polluted sediments, which contained not only toxicants but also higher organic matter and nutrient levels. Dynamics of TPT concentrations in the overlying water were very similar between the two types of test system. Higher levels of TPT, however, were found in the sediment compartment of the clean sediment systems containing a smaller macrophyte biomass. TPT was very persistent in the sediments. In both test systems representatives of several taxonomic groups showed clear responses to a single application of TPT, although benthic Nematoda were not affected. Although a few differences in the intensity and/or duration of TPT-related population responses were observed between the two types of test system, the background pollutants in the polluted sediment hardly affected the overall sensitivity of the aquatic community to the additional chemical stressor TPT.
The fungicide fluazinam, the insecticide lambda-cyhalothrin, and the herbicides asulam and metami... more The fungicide fluazinam, the insecticide lambda-cyhalothrin, and the herbicides asulam and metamitron were applied to indoor freshwater microcosms (water volume approximately 0.6 m3). The treatment regime was based on a realistic application scenario in tulip cultivation. Concentrations of each pesticide were equal to 0%, 0.2%, 0.5%, 2%, and 5% spray drift emission of label-recommended rates. Contribution of compounds to the toxicity of the pesticide package was established by expressing their concentrations as fractions of toxic units. The fate of the compounds in the water, and responses of phytoplankton, zooplankton, periphyton, macroinvertebrates, macrophytes, decomposition, and water quality were followed for 13 weeks. The half-lives of lambda-cyhalothrin, metamitron, and fluazinam were 1 to 2 d; that of asulam was >30 d. No consistent effects could be demonstrated for the 0.2% treatment regime that was therefore considered the no-observed-effect concentration community (NOEC). The macroinvertebrate populations of Gammarus pulex, Asellus aquaticus, and Proasellus meridianus were the most sensitive end points, followed by species of copepods and cladocerans. Responses mainly were due to lambda-cyhalothrin. The 0.5% treatment regime resulted in short-term effects. Pronounced effects were observed at the 2% and 5% treatment levels. At the end of the experiment, the macrophyte biomass that consisted of Elodea nuttallii, showed a decline at the two highest treatment levels, asulam being the causal factor (NOEC: 0.5% treatment level). Primary production was reduced at the 5% treatment level only. In our experiment, the first-tier risk assessment procedure for individual compounds was adequate for protecting sensitive populations exposed to realistic combinations of pesticides. Spray drift reduction measures seem to be efficient in protecting aquatic ecosystems in agricultural areas.
Analytical and bioanalytical chemistry, Jan 2, 2018
Certification of trace metals in seawater certified reference materials (CRMs) NASS-7 and CASS-6 ... more Certification of trace metals in seawater certified reference materials (CRMs) NASS-7 and CASS-6 is described. At the National Research Council Canada (NRC), column separation was performed to remove the seawater matrix prior to the determination of Cd, Cr, Cu, Fe, Pb, Mn, Mo, Ni, U, V, and Zn, whereas As was directly measured in 10-fold diluted seawater samples, and B was directly measured in 200-fold diluted seawater samples. High-resolution inductively coupled plasma mass spectrometry (HR-ICPMS) was used for elemental analyses, with double isotope dilution for the accurate determination of B, Cd, Cr, Cu, Fe, Pb, Mo, Ni, U, and Zn in seawater NASS-7 and CASS-6, and standard addition calibration for As, Co, Mn, and V. In addition, all analytes were measured using standard addition calibration with triple quadrupole (QQQ)-ICPMS to provide a second set of data at NRC. Expert laboratories worldwide were invited to contribute data to the certification of trace metals in NASS-7 and CASS...
Two laboratory performance studies with 21 and 11 participants were carried out for passive sampl... more Two laboratory performance studies with 21 and 11 participants were carried out for passive sampling of nonpolar chemicals in water, using silicone samplers that were deployed for 7 and 13 weeks at 2 river sites in the Netherlands. Target analytes were polychlorinated biphenyls, polycyclic aromatic hydrocarbons, polybrominated diphenyl ethers, hexachlorobutadiene, hexachlorobenzene, and a number of performance reference compounds (PRCs). Calculation of aqueous concentrations based on prescribed input values and a prescribed uptake model was also included. Between laboratory coefficients of variation (CV) in the analysis of target compounds were approximately 20% at concentrations of 100 ng g-1 and approximately 100% at concentrations of 0.01 ng g-1 , which was similar to previous results for the analysis of biota samples. The analysis of PRCs yielded water sampling rates with a between laboratory CV of 18 to 30%. The sampling rate model showed a near perfect match with the consensus values of retained PRCs. The implications of the present study for future interlaboratory exercises are discussed.
Effects of chronic application of a herbicide-insecticide mixture were studied in indoor freshwat... more Effects of chronic application of a herbicide-insecticide mixture were studied in indoor freshwater plankton-dominated microcosms. Effects could well be explained by the effects of the individual chemicals alone, no synergetic effects were reported.
Greenhouse soils are regularly treated with metham-sodium, which in soil is quickly transformed t... more Greenhouse soils are regularly treated with metham-sodium, which in soil is quickly transformed to the fumigant methyl isothiocyanate. An experimental fumigation was carried out in a greenhouse with sandy soil. Data were collected on the behavior of methyl isothiocyanate in soil and its permeation through a film of low-density polyethene (LDPE) covering the soil. This cover was found to be
An increasing number of reports confirm the worldwide presence of the perfluoroalkyl substances (... more An increasing number of reports confirm the worldwide presence of the perfluoroalkyl substances (PFASs). As a consequence, the demand for qualitative and quantitative environmental occurrence data requires accurate risk assessments. To improve the analytical quality of the determination of PFASs in food and environmental samples, a 4 th international interlaboratory study (ILS) was conducted in 2011. A total of 31 partners participated, and, depending on the sample matrix, up to 29 data sets were submitted. The ILS focused on food samples, as it was organized by the PERFOOD consortium in collaboration with QUASI-MEME. The results showed that the cumulative experience of the participants has improved their analytical quality over four international ILSs. Several sources of errors were identified and methods to avoid them are suggested.
Behaviour of some pesticides in a nutrient-film and in a rock-wool system. Scientia Hortic., 25: ... more Behaviour of some pesticides in a nutrient-film and in a rock-wool system. Scientia Hortic., 25: 1-9. Adsorption of ethoprophos, tetrachlorvinphos and etridiazole onto rock-wool was found to be much weaker than adsorption onto soils. The rates of transformation in water and in water plus rock-wool at 20°C were low. The concentration of etridiazole was measured in a nutrient-film system with recirculating nutrient solution. The decrease was rapid in the first few hours but was more gradual afterwards, to low values at 8 days after application. Etridiazole penetrated poorly into the lower part of a rockwool system when the solution was trickled near the stem-base of the tomato plants.
Uploads
Papers by Steven Crum