Summary A total of 74 independently run bioassays with soil incorporated metsulfuron‐methyl from 12 different laboratories was analysed by a logistic dose‐response curve to assess the precision of regression parameters and relate ED50 to soil properties. The potency in terms of ED50 of metsulfuron‐methyl in Brassica rapa L., which was used by all laboratories, varied between 0.05 and 3.9 g a.i. ha‐1. ED50 was negatively correlated with pH and positively correlated with organic matter. The majority of laboratories had ED50 within the interval 0.1‐1.0 g a.i. ha‐1. At one laboratory using three test species, the most sensitive species was Beta vulgaris L. followed by Brassica rapa L. and Lepidium sativum L. The coefficients of variation were smallest for the ED50 and ED90 response levels and largest for the ED10. The slope of the response curves had considerably lower coefficients of variation than the EDs. The results are discussed in relation to a previous collaborative bioassay study. Finally it is suggested that standardization of bioassays with herbicides could be achieved in the same way as standardization of chemical analyses.

Summary A bioassay procedure for quantitative determination of sulphonylurea herbicides is described. Turnips (Brassica rapa) were found very suitable as test plants and gave results within 10 days. Six sulphonylurea compounds were investigated for their activity in three widely differing soils. The potential availability to plants was calculated from the dose‐response curves of vermiculite (non‐sorptive substrate) and the corresponding ED50‐values of the soils. The dose‐response relationship (logistic curve) was described by a computer model by a position parameter, the slope of the curve and the minimum and maximum fresh weights of plants. The limit of quantitative detection in the range of ED30 in vermiculite was 0·06 μg 1−1 for sulfometuron and 1·03 μg 1−1 for DPX‐L5300, methy12‐([4‐methoxy‐6‐methyl‐1,3,5‐triazin‐2‐yl (methyl)carbamoyl]‐sulphamoyl) benzoate. Results with turnips showed that sulfometuron was the most active compound in all substrates (ED50 in vermiculite 0·12 μg 1−1) followed by chlorsulfuron, metsulfuron‐methyl, triasulfuron, DPX‐M6316, methyl 3‐([(4‐methoxy‐6‐methyl‐1,3,5‐triazin‐2‐yl)aminocarbamoyl]‐aminosulphaphamoyl)‐2‐thiophenecarboxylate, and DPX‐L5300 which had ED50 or 1·98 μg 1−1, The Horotiu sandy loam soil showed the highest ED50‐values and the lowest plant availability for all compounds compared to the other soils. Probit and logistic evaluation methods for deriving dose‐response relationships are compared and their applicability is discussed.

Summary: Résumé: Zusammenfassung A bioassay procedure is described for quantitative determination of sulfonylurea herbicides in water and for studying their leaching behaviour in soils. Sunflower (Helianthus annuus L.) was found a more susceptible bioassay species than turnip (Brassica rapa L.) or lentil (Lens culinaris Medic.). The limit of quantitative detection (EC30) in soil leachates was 0.12 μg 1−1 for triasulfuron and 0.15 μg 1−1 for metsulfuron‐methyl. Leaching experiments were carried out by uniformly packing the soil in glass columns corresponding to its natural bulk density and applying simulated irrigation of 50 mm day−1 with leachate water from untreated soil columns. Results obtained by measuring fresh weights of the true leaves of sunflowers in soil leachates showed that metsulfuron‐methyl was much more mobile than triasulfuron in two soils with different sorption capacity. The BBA soil with low sorptive capacity showed very little retardation of both herbicides in the columns. The Horotiu soil with high sorptive capacity retarded triasulfuron for a long period, even under high flow conditions. Une technique d'essai biologique pour étudier l'aptitu.de au lessivage des herbicides sul‐fony‐lurées dans des différents sols Un protocole d'essai biologique est décrit pour la détermination quantitative des herbicides sulfonylurées dans l'eau, et pour l'étude de leur lessivage dans les sols. Le tournesol (Helianthus annuus) a été reconnu comme une espèce pour l'essai biologique plus sensible que le navet (Brassica rapa) ou la lentille (Lens culinaris). La limite de détection quantitative (EC30) dans le lessivat du sol a été 0,12 μg 1−1 pour le triasulfuron et 0,15 μg 1−1 pour le metsulfuron methyl. Des études de lessivage ont été con‐duites en mettant unifomément du sol dans des colonnes de verre de façon équivalente à la densité naturelle dans le sol et en appliquant une irrigation simulée de 50 mm jour−1 avec de l'eau d'un lessivat de sol non traité. Les résult ats obtenus en mesurant le poids frais des feuilles vraies de tournesol dans les lessivats de sol ont montré que le metsulfuron‐methyl était beau‐coup plus mobile que le triasulfuron dans les 2 sols de capacités d'adsorption différentes. Le sol BBA avec une capacité d'adsorption faible a entraiîné un faible ralentissement des 2 herbicides dans les colonnes. Le sol Horotiu avec une capacité d'adsorption élevée a retardé le triasulfuron pendant une longue période, même sous des conditions de fortes précipitations. Biotestmethode zur Bestimmung des Ein‐waschungsverhaltens von Sulfonyl‐Harnstoff‐herbiziden in unterschiedlich sorptiven Böden Eine Biotestmethode zum quantitativen Nach‐weis von Sulfonyl‐Harnstoffherbiziden in Was‐serproben zur Bestimmung des Einwaschungs‐verhaltens wurde entwickelt. Sonnenblume (Helianthus annuus L.) war unter den geprüf‐ten Testpflanzen wesentlich empfindlicher als Herbstrübe (Brassica rapa L.) oder Linse (Lens culinaris Medic.). Als empfindlichste Meßgröße erwiesen sich die Echten Laubblätter der Sonnenblume. Die N...

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