Untersuchungen zur Arbeitssicherheit des Imkers bei der Anwendung von Oxalsäure zur Bekämpfung der Varroatose

Abstract

Ziel der Studie Die Varroatose ist eine Bienenkrankheit verursacht durch die Milbe Varroa destructor. Seit Anfang der 1990er Jahre werden Bienenvölker erfolgreich mit Oxalsäure-Aerosolen gegen Varroatose behandelt. Es bestehen jedoch Bedenken hinsichtlich der Anwendersicherheit der Behandlungsverfahren. Ziel der vorliegenden Studie war es, die inhalative Belastung von Imkern durch Oxalsäure-Aerosole während der Varroatose-Bekämpfung zu ermitteln und zu bewerten.

Methodik An der Untersuchung beteiligten sich 20 Imker. Eine Gruppe (n=10) versprühte eine 3%-ige wässrige Oxalsäure-Lösung mit einem Zerstäuber direkt auf die Waben (Sprühverfahren). Eine zweite Gruppe (n=10) sublimierte 1 bis 2g Oxalsäure-Dihydrat mit Hilfe eines beheizten Metallpfännchens über das Flugloch in den Bienenkasten (Verdampfungsverfahren). Pro Imker wurden 10 bis 21 Bienenvölker behandelt. In Atemnähe des Imkers wurden Proben der einatembaren und der alveolengängigen Fraktion luftgetragener Partikel nach der Membranfiltermethode gewonnen. Es wurde dabei auf bewährte Probenahmeverfahren des Berufsgenossenschaftlichen Instituts für Arbeitssicherheit (BIA) und der US-amerikanischen Occupational Safety and Health Administration (OSHA) zurückgegriffen. Die Oxalsäure-Belegung der Membranfilter wurde anschließend im Labor mittels HPLC bestimmt.

Ergebnisse Der mittlere Anteil einatembarer Oxalsäure-Aerosole betrug beim Sprühverfahren 0,22 mg/m³ (Spannweite 0,07-0,41 mg/m³), beim Verdampfungsverfahren 0,23 mg/m³ (Spannweite 0,01-0,36 mg/m³). Der mittlere Anteil alveolengängiger Oxalsäure-Aerosole betrug beim Sprühverfahren 0,15 mg/m³ (Spannweite 0,03-0,67 mg/m³), beim Verdampfungsverfahren 0,07 mg/m³ (Spannweite 0,01-0,36 mg/m³). Zwischen den beiden Behandlungsverfahren zeigte sich kein signifikanter Unterschied.

Schlußfolgerungen Alle gemessenen Einzelbelastungen lagen unter dem derzeitigen Luftgrenzwert (MAK) von 1 mg/m³ (einatembarer Staub) nach TRGS 900. Die Tagesexpositionszeiten waren deutlich geringer als der Bezugszeitraum von 8 Stunden. Da sich zudem die Varroatose-Behandlung auf wenige Tage im Jahr beschränkt, besteht gegen die Anwendung von Oxalsäure zur Varroatose-Bekämpfung unter den untersuchten Bedingungen kein prinzipieller Einwand.

The use of oxalic acid for treatment against varroatosis by evaporation or spraying procedure is considered as highly effective and well tolerated by bees. However there exists doubt among beekeepers regarding user-security, in particular with regard to the evaporation procedure. So far no studies were present for this. The presented study shows that the existing exposure-limit for oxalic acid in the air at working places is clearly fallen below by both procedures. By appropriate use there is no risk to the health of the apiarist.

At the Institute of Occupational and Social Medicine (Institut für Arbeits- und Sozialmedizin), University of Tübingen, Germany, user-security for evaporation and spraying procedure was examined the first time systematically. 20 beekeepers in southern Germany participated in October 2001 in the study. During the respective oxalic acid treatments air samples in breath proximity of the beekeepers were taken. These samples were analysed afterwards in the chemical-analytic laboratory for their oxalic acid content. The results were compared to the existing exposure-limit (MAK-Wert) for oxalic acid. The technical rule for hazardous substances „TRGS 900“ of German „Bundesministerium für Wirtschaft und Arbeit“ limits the concentration of oxalic acid in the air at working places to 1.0 mg/m³.

Methods In October 2001 in the context of the presented study 20 beekeepers were accompanied along their oxalic acid treatments. 10 beekeepers used the Varrox-evaporator of Andermatt Biocontrol AG according to the operating instructions. 10 beekeepers applied the spraying procedure with a 3%-solution of oxalic acid following a proven method. Each beekeeper treated 10 to 21 of his hives, 244 hives altogether. The beekeepers needed for their works an average of 100 minutes (8 minutes per hive) applying the evaporation procedure, an average of 111 minutes (9 minutes per hive) applying the spraying procedure. During this entire work-time the sampling device was filtering oxalic acid particles from the air surrounding the working place.

In the presented study standard methods were implemented in order to ensure conformity to „DIN EN 401“, defining the so-called breathable fraction of airbourne particles. The used sampling equipment is a developement of the German „Berufsgenossenschaftliches Institut für Arbeitssicherheit“ (BIA). The oxalic acid particles were filtered by mixed cellulose ester membranes of 0.8 microns according to a method of US-American „Occupational Safety and Health Administration“ (OSHA). The membrane filters were inserted into a standardized air sampler which was connected to a power-stabilized air collecting pump and to a volume gauge. The air-sampler built onto a stand was put as close to the place that the oxalic-acid emerged as possible, without interfering with the beekeeper’s work. This was for the evaporation procedure within an area of 1m and a something above the hive‘s entrance by which the Varrox-evaporator was introduced. For the spraying procedure this was within an area of 1m from the place of spraying, approximately at shoulder height of the beekeeper. After completion of the sampling the oxalic acid carrying membrane filters were brought to the laboratory of the Institute of Occupational and Social Medicine, University of Tübingen, where further analyses took place. Oxalic acid was washed from filters by double-distilled water and was measured according to a proven method by high pressure liquid chromatography (HPLC).

Results Evaluation of data led to a clear result: None of the 20 participating beekeepers reached even half the exposure-limit of 1.0 mg/m³. The average value of the 10 measurements on evaporation procedure was 0.23 mg/m³, the average value of the 10 measurements on spraying procedure was 0.22 mg/m³. There was no significant difference between both methods. To better comprehend these results we must briefly concern ourselves with the definition of the exposure-limit (MAK-Wert): The exposure-limit is in such a way selected that for an employee no health damage is to be expected if he stays 8 hours a day during a working life-time at working places at which the air concentration of the respective hazardous substance doesn‘t exceed the exposure-limit. Thus, based upon the presented data, a commercial apiarist could use oxalic acid treatments during the whole year 40 hours a week without damaging his health.

Conclusions With evaporation- and spraying-procedure of oxalic acid, beekeepers have possibilities of treatment against varroatosis whose effectiveness and beecompatibility have already convincingly been proven. The presented study dispelled reservations against both procedures concerning possible health risks, appropriate application presupposed.