Biologische Bundesanstalt für Land- und Forstwirtschaft (BBA)

1. conc. [%] temp. [°C] A B C D E day D. SCHENKE*, H. GEMMEKE** THE BEHAVIOUR OF O,O - DIETHYLPHOSPHATE AND O,O - DIETHYLTHIOPHOSPHATE IN FAECAL SAMPLES UNDER FIELD CONDITIONS Federal Biological Research Centre for Agriculture and Forestry, * Institute for Ecotoxicology in Plant Protection, Stahnsdorfer Damm 81, Kleinmachnow D-14532, **Institute for Nematology and Vertebrate Research, Toppheideweg 88, Münster D-48161 Introduction Sampling of faeces in field studies is a non-invasive method to evaluate wildlife exposure to pesticides. Organophosphorus insecticides are degraded in animals to dialkylphosphate metabolites which are excreted in faeces. Knowledge about the stability of the metabolites under real field conditions is necessary to decide on the suitable sampling time. Methods FIELD STUDY Faecal samples contaminated with O,O-diethylphosphate (DEP) and O,O-diethylthio-phosphate (DETP) were obtained from a parathion feeding study with rabbits. The five samples for one trial originated from faeces of one rabbit and one day. Samples (~ 5 g) for two trials were dropped simultaneously in a meadow 5 times between May to October 1998. Temperature and relative humidity were measured continuously. Rain was collected daily. Samples were picked up 1, 2, 4 and 8 days after release. RESIDUE ANALYSES O,O-diethylphosphate and O,O-diethylthiophosphate were analysed via an extractive derivatisation with pentafluorobenzyl bromide using a phase transfer reaction, cleaned up with florisil and detected with GC-NPD and -FPD [1]. Parathion and paraoxon were extracted with methanol, cleaned up through a florisil column and detected with GC-NPD and -FPD. Mean recovery rates for DEP (50 %), DETP (100 %) and parathion (85 %) were used for correction of FPD-results. Results Fig. 1 A-E: Decline of summarised concentrations of DEP and DETP in rabbit faeces which lay in the meadow for up to 8 days. Mean concentrations of the two trials each refer to their own initial concentration (100 %). Standard deviation of . Daily mean temperature. Dew point difference: daily mean temperature minus daily mean dew point temperature (high values mean less air humidity). Daily rain (in mm until sampling time). Tab. 1: Initial concentrations (day 0) of DEP, DETP (calculated as parathion equivalents) and parathion in faecal samples (µg/g). Initial concentration DEP DETP parathion in relation to Fig. 1 [µg/g] A 1,85 0,79 not measured B 0,81 1,54 0,031 2,49 1,49 0,069 C 2,27 2,43 0,020 0,98 1,04 0,033 D 1,76 1,15 0,025 2,06 1,01 0,020 E 1,70 1,85 0,021 1,97 1,47 0,018 Probably DEP andDETP excreted with rabbit faeces decline further through hydrolysis. Temperature, humidity (expressed as the dew point difference) and rain (Fig. 1) characterise the micro-climatic conditions. The mean temperature tends to lower values from A to E. In the same way the decrease of the dew point difference shows a higher humidity in the air. The clear differences in mean temperatures and dew point differences between scenarioAand E, both without rain until the second day, suggest no important influence of these parameters on the decomposition of the metabolites. Without rain the summarised concentrations of DEP andDETP in faeces decrease up to 20 % over 8 days, also at high temperature (A). With little rainfall between excretion and sampling the concentrations can slowly decrease (B). Strong rainfall leads to fast decline of metabolites (C, D, E). Obviously rain is necessary to soak the pieces of rabbit faeces. Parathion residues after 2 days are in the same range as the initial concentrations (Tab. 1). Paraoxon was not found. Conclusion In view of decrease of DEP andDETP, the optimum period between excretion and sampling of rabbit faeces in the field should be 2 days without strong rain. Reference: [1] Schenke, D. 2000. Analytical method for the determination of O,O-diethyl phosphate and O,O-diethyl thiophosphate in faecal samples. Chemosphere 41, 1313-1320. Biologische Bundesanstalt für Land- und Forstwirtschaft (BBA)