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Afgelopen woensdag (3 november 2010) was er een rondetafelgesprek over gif - of gewasbescherming zoals de sector het zelf graag noemt - in de Tweede Kamer. Dr. Henk Tennekes, die onderzoek doet naar de relatie tussen neonicotinoiden – een heel giftige insecticide - en bijensterfte, was daar ook aanwezig als deskundige. Dr. Tennekes is lang bezig geweest met onderzoek naar kanker. Hij vertelde mij dat hij betrokken raakte bij het onderzoek naar bijensterfte, toen hij ontdekte dat insecticiden zoals imidacloprid op een vergelijkbare manier werken als kankerverwekkende stoffen. Toen hij zich realiseerde wat dit betekent voor het milieu en de biodiversiteit, heeft hij besloten hier werk van te maken. Om zijn zorgen over de effecten van neonicotinoiden met een wijder publiek te delen, heeft Dr. Tennekes ook een boek geschreven over dit onderwerp: The systemic insecticides: a disaster in the making. Voorafgaand aan het rondetafelgesprek bood Henk mij zijn nieuwe boek aan. Hij wilde mij daarmee bedanken voor het feit dat ik al in 2007 Kamervragen heb gesteld over dit onderwerp.

Am 1. November 2010 erschien das Buch „A disaster in the making“ des holländischen Toxikologen Dr. Henk Tennekes über die Ursachen des europaweiten Bienen- und Vogelsterbens. Das Buch wird mit ganzseitigen Bildern des Künstlers Ami-Bernard Zillweger illustriert. Dr. Tennekes legt darin dar, dass der drastische Rückgang zahlreicher Vogelpopulationen, unter anderem Spatzen Bachstelzen, Stare, Kiebitze oder Feldlerchen, mit der Dezimierung von Insekten in Zusammenhang steht. Käfer, Fliegen, Schmetterlinge und Motten, die den Vögeln als Nahrung, werden vor allem durch die Anwendung von Pestiziden, sogenannten Neonicotinoiden, reduziert.

A 72-page 2010 publication raises new and troubling questions about a widely used insecticide's potential for harm to bees, beneficial insects, and bird populations. Using imidacloprid as an example, Dutch toxicologist Dr. Henk Tennekes reports on the hazards of imidacloprid to insects and birds. Imidacloprid is a neonicotinoid chemical, and has systemic action in plants. Other European researchers have linked this insecticide to significant risks for honey bee populations, including possible links to Colony Collapse Disorder.

Dr. Tennekes' findings indicate that imidacloprid (and possibly other neonicotinoid-type insecticides) can bind irreversibly to critical receptors in an insect's nervous system. If these receptors are permanently blocked, the insecticide would not follow a typical dose-response curve. He provides evidence that long term low level to imidacloprid exposure can lead to neurological problems and eventual death of insects.

Studies have shown imidacloprid to be highly persistent in the environment (RCC Compendium of Pesticide Information). In his book, Tennekes presents data showing that imidacloprid has contaminated most of the waterways in the Netherlands.

Systemic activity in plants combined with long-term persistence in the environment and toxicity at low concentrations can be a dangerous combination. Many vulnerable species over large areas could be exposed to this insecticide on land, in surface water following runoff from treated areas and in groundwater due to its potential for leaching through certain soil types.

Several previous studies have shown that imidacloprid is highly toxic to various forms of wildlife, including honey bees, certain beneficial insects, upland game birds, and crustaceans

Tennekes further suggests that imidacloprid has led to a general decline in the insect populations in the Netherlands, and this lack of food in turn has been responsible for declines in bird populations.

Présentation, Christian Pacteau.
Vicky KINDEMBA, pour le compte de Buglife, The Invertebrate Conservation Trust soutenu par Bumblebee Conservation Trust, Edimburg Entomological Club, Soil Association, The Grassland Trust, Plantlife et Pesticides Action Network, a réalisé une vaste méta-analyse de l'état des connaissances en matière d'effets létaux et sublétaux sur les abeilles et les autres invertébrés des insecticides systémiques néonicotinoïdes et des phénylpyrazoles. Cela lui a permis de se rendre compte que le "Rapport d'Evaluation Préliminaire" (DAR) fourni par la firme productrice du pesticide en vue d'obtenir l'AMM, (Autoristaion de Mise sur le Marché) opérait un "tri", entre les recherches témoignant de l'innocuité de la substance, et celles émettant des doutes. Elle a également pu montrer que les recherches indépendantes conduisent des recherches plus approfondies en contradiction avec celles du DAR.

For many years environmental groups and beekeepers´ organizations have been pushing for a ban on neonicotinoid pesticides which are linked to bee decline across the world. In a recent study, The toxicity of neonicotinoid insecticides to arthropods is reinforced by exposure time, the Dutch toxicologist Henk Tennekes demonstrates that the long-term risks associated with the insecticides imidacloprid and thiacloprid are far greater than hitherto thought. Honeybees, bumblebees and many other insects are being slowly poisoned to death by these persistent insecticides. Small doses accumulate over time, meaning that there is no safe level of exposure. The study was published on the 23rd of July 2010 in the journal Toxicology (online).

Der Toxikologe Dr. Henk Tennekes weist in einer aktuellen Studie nach, dass die Langzeitrisiken der Insektizide Imidacloprid und Thiacloprid weitaus größer sind, als bislang angenommen. In der Studie "The significance of the Druckrey-Küpfmüller equation for risk assessment - The toxicity of neonicotinoid insecticides to arthropods is reinforced by exposure", erklärt Tennekes das gängige Verfahren zur Bestimmung der Auswirkungen von bestimmten Dosen eines Wirkstoffs auf einen ausgewählten Organismus. Er belegt, dass die Expositionsdauer einen wesentlichen Einfluss darauf hat, wie hoch eine Dosis sein muss, um einen schädigenden Effekt auf den Testorganismus auszuüben. Setzt man beispielsweise Honigbienen über einen längeren Zeitraum einer niedrigen Konzentration von Imidacloprid aus, so kommt es zu letalen Effekten obgleich die Gesamtbelastung 60-6000mal unterhalb der Dosis liegt, die den gleichen Effekt in Testverfahren zur Ermittlung der akuten Toxizität hat.

Das Risiko von Pestiziden wie Imidacloprid und Thiacloprid wird demnach erheblich unterschätzt. Dies gilt besonders für Wasserlebewesen, Bodenorganismen und Bienen. Die bislang gültigen Grenzwerte wurden weitgehend aus Kurzzeit-Tests abgeleitet. Würde man Langzeit-Versuche durchführen, könnten schon bei wesentlich geringeren Konzentrationen verheerende Schäden auftreten.

Tennekes kommt in seiner Studie zu dem Schluss, dass die Belastung mit niedrigen Neonicotinoid-Dosen einen negativen Einfluss auf das Sammelverhalten und das Lernvermögen von Honigbienen haben können und somit in Folge subletale Imidacloprid-Konzentrationen sich schädigend auf die Bienenkolonie auswirken und dadurch den Zusammenbruch einer Kolonie verursachen können.

Le texte ci-dessous est une traduction de : "The Significance of the Druckrey-Küpfmüller Equation for Risk Assessment - The Toxicity of Neonicotinoid Insecticides to Arthropods is Reinforced by Exposure Time" à paraître in "Toxicology". Le texte complet en français est joint en PDF.

Dans cet article théorique, puisant aux sources de la toxicologie et des mathématiques, Henk TENNEKES s'intéresse à un domaine, ô combien crucial en toxicologie, celui des relations "doses - effets".

There is a very important shift in our understanding of the risk of neonicotinoid insecticides. Their risk may increase exponentially over time, rendering even very small amounts of neonicotinoids much more toxic than previously realized. Dutch researcher Dr. Henk Tennekes, with Dr. Francisco Sanchez-Bayo of Australia, have recently published a review article in the Journal of Environmental & Analytical Toxicology: "Time-Dependent Toxicity of Neonicotinoids and Other Toxicants: Implications for a New Approach to Risk Assessment" (attached). Their starting point is the Druckrey–Küpfmüller equation dt^n = constant (where d = daily dose and t = exposure time-to-effect, with n>1) for chemical carcinogens. The Druckrey–Küpfmüller equation established in the early 1960s explains why toxicity may occur after prolonged exposure to very low toxicant levels. In essence, this equation states that the total dose required to produce the same effect decreases with decreasing exposure levels, even though the exposure times required to produce the same effect increase with decreasing exposure levels. Druckrey and Küpfmüller inferred in the late 1940s that if both receptor binding and the effect are irreversible, exposure time would reinforce the effect. Recently, similar dose–response characteristics have been established for the toxicity of the neonicotinoid insecticides imidacloprid and thiacloprid to arthropods. Imidacloprid was the first highly effective insecticide whose mode of action has been found to derive from almost complete and virtually irreversible blockage of postsynaptic nicotinic acetylcholine receptors (nAChRs) in the central nervous system of insects. Imidacloprid mimics the action of acetylcholine, but unlike acetylcholine, imidacloprid is not deactivated by acetylcholinesterase and thus persistently activates nAChRs. Chronic exposure of insects to imidacloprid therefore leads to cumulative and virtually irreversible blockage of nAChRs in their central nervous system, which play roles in many cognitive processes.
An example of the consequences for insects in the case of imidacloprid is given in Table 5 (attached). Since imidacloprid and other neonicotinoid insecticides have time-dependent effects on arthropods, the risk of foraging worker bees feeding on tiny levels of residues becomes an issue that cannot and should not be ignored. In the example shown here, 50% of worker bees would die within 7-12 days if feeding on a field where 11% of plants have residues of imidacloprid in the specified range (Table 5). By contrast, standard hazard quotients (HQ) for dietary NOEL of 20 microgram per Litre are misleading because they suggest that imidacloprid poses no danger to honey bees. Given that honey bee workers can live up to a few months in winter time the NEC (No Effect Concentration) for imidacloprid is estimated as close to zero, which means that any residue concentration found in pollen will have a lethal effect provided there is sufficient time of exposure.

Despite widespread concern about declines in pollination services, little is known about the patterns of change in most pollinator assemblages. By studying bee and hoverfly assemblages in Britain and the Netherlands, we found evidence of declines (pre-versus post-1980) in local bee diversity in both countries; however, divergent trends were observed in hoverflies. Depending on the assemblage and location, pollinator declines were most frequent in habitat and flower specialists, in univoltine species, and/or in nonmigrants. In conjunction with this evidence, outcrossing plant species that are reliant on the declining pollinators have themselves declined relative to other plant species. Taken together, these findings strongly suggest a causal connection between local extinctions of functionally linked plant and pollinator species.

The evidence provided by the Dutch Water Boards on imidacloprid contamination of surface water (attached) indicates that, in any case in the western part of the Netherlands, high concentrations of imidacloprid are diffused through the environment, which may kill or debilitate insects and possibly other arthropods. Attached is a map of Holland showing the agricultural areas where the use of imidacloprid is permitted.