Abstract:
Proc. Aust. Soc. Anim. Prod. Vol. 18 SPATIAL DISTRIBUTION OF SOIL DIELDRIN LEVELS WITHIN DIELDRIN CONTAMINATED PADDOCKS IN SOUTHERN VICTORIA K.L. BUTLER*, H. SIMPFENDORER*, J. STEWART* and G. ROBERTS* SUMMARY Soil dieldrin levels were measured at random locations within dieldrin affected It was found that most paddocks had contiguous regions of similar paddocks. This shows that to obtain reasonable estimates of dieldrin concentrations. average soil dieldrin concentration it is necessary to sample the whole paddock as representatively as possible. INTRODUCTION Until 1987, the organochlorine, dieldrin was used by potato farmers in several areas of southern Victoria to control insect pests such as wire worm (Gonocephalum pterohelaeus) and white fringed weevil (Graphognathus leucoloma). The traditional management system for these farmers is to rotate paddocks The sown pasture is between potato cropping and sown grass/clover pasture. usually used for grazing beef cattle over a period of. several years, before When the dieldrin sampling at abattoirs returning to potato cropping. intensified after the 1987 'dieldrin crisis', many cattle from these farms were found to have fat dieldrin levels exceeding the Maximum Residue Level (MRL) of Further investigation found that the soil from 0.2 parts per million (ppm). many of the paddocks which these cattle grazed, was contaminated with measurable amounts of dieldrin. This study reports the pattern of soil dieldrin concentrations, from random locations within some of these paddocks, in three potato growing areas of This is important from an animal production viewpoint, southern Victoria. because many dieldrin contaminated paddocks are likely to remain used for grazing and/or hay production in the foreseeable future. The spatial distribution of soil dieldrin has previously been investigated on small plots under controlled application conditions (Taylor et al. 1971; Car0 However, to our knowledge no investigation has been made on et al. 1976). larger paddocks which have been contaminated under commercial conditions. MATERIALS As part of a hay to potatoes and districts around in soil type and AND XETEIODS survey nine separate paddocks, which were previously cropped were known to be dieldrin contaminated, from three separate Melbourne were studied. The three districts differed widely topography (Table 1). In eight of the paddocks ten random locations were chosen for soil dieldrin sampling, using random co-ordinates with fenceposts. At each location five 10 cm cores were sampled within a two metre radius. The first core was sampled at the centre with the four other cores sampled about two metres away at the 'four points of a compass'. The ninth paddock was similarly sampled, but with 10 locations taken on each of two separate days. All sampling occurred within the period November 1988 to February 1989, at a time when hay was being cut. Department of Agriculture and Rural Affairs, Werribee, Vic. 303O.- ---a 160 Proc. Aust. Soc. Anim. Prod. Vol. 18 Table 1 Details of location, topography and soil for districts in which paddocks were sampled Composite core samples (of the 5 cores within a location) were air dried, ground to pass a 2 mm sieve in a roll mill, and thoroughly mixed. A representative sub-sample was moistened with water and then extracted with hexane/acetone (80/20) on a wrist-action shaker for 30 minutes. The supernatant extract was analysed by gas-liquid chromatography using electron capture detection. The identification and quantitation of residues were confirmed on two different chromatographic systems. The limit of detection of the method was 0.01 mg/kg dieldrin. Maps showing measured dieldrin concentrations at each sampling location within each paddock are presented. Contiguous regions within a paddock, which have similar measured soil dieldrin concentrations, are marked. These marked regions are presented only to emphasise main features of these maps. The maps are only approximately to scale, since all distances were calculated using number of fenceposts as units. RESULTS Figures 1 through 9 show that contiguous regions of similar soil dieldrin concentrations exist in most, but not all, of the paddocks sampled. The differences in soil dieldrin between different parts of the paddock are sometimes dramatic (Fig. 2, 4 and 8). 161 Proc. Aust. Soc. Anim. Prod. Vol. 18 detected, 162 Proc.. Aust- Soc. Anim. Prod. Vol. 18 DISCUSSION It can be concluded that within many dieldrin contaminated growing areas of southern Victoria, there are some regions It much greater soil dieldrin concentrations than others. that this effect is related to sampling variability within the paddocks, since such sampling variability would observation of any regional effect. paddocks in potato of the paddock with is highly unlikely chosen locations in simply dilute the The main implication of this conclusion is that to obtain reasonable estimates of mean soil dieldrin concentrations for paddocks it is essential to use a These sampling scheme which intentionally samples all sections of a paddock. samples can then be bulked, as desired, and subsampled for dieldrin analysis. Random sampling, or sampling based on taking zig-zag or circular paths will often be very inefficient, and may be biased. These methods of sampling do not adequately cover the whole paddock, for a given intensity of sampling (number of cores). The Department of Agriculture and Rural Affairs in Victoria has issued practical guidelines to its scientific staff on sampling procedures for These guidelines are estimating soil chemical residue levels in paddocks. consistent with the requirements of intentionally sampling the whole paddock. They state that a paddock should be divided into equal areas or 'zones', using fenceposts or shelter-belt trees as a guide, Then, one or two cores, chosen on The cores from each paddock an ad-hoc basis, should be taken from each zone. are then bulked and subsampled. These results also open the possibility for farmers to use different agricultural management on different regions of some paddocks, depending on This approach is soil dieldrin concentrations obtained in these regions. likely to be most useful when there are clearly identifiable topographical features in the paddock, due to the large cost of each dieldrin assay (around $60) - Presented results are for three districts around Melbourne. However, these districts had major differences in soil type and topography. Thus there is good reason to believe similar phenomena might occur in other districts with paddocks which are dieldrin contaminated from previous cropping management. In this study soil DDT was also measured. Although we have not presented the results for soil DDT, we can report that similar phenomena of regions of high and low DDT did occur. However, the DDT and dieldrin regions did not usually This would suggest that we might expect similar high and low correspond. regions to occur for soil residues from other organochlorine pesticides. The message of this work is that when organochlorine residues in paddocks which needs to be taken to soil core the paddock way. Unreliable results may be produced if estimating the concentrations of have been previously cropped, care in a purposeful and representative this message is ignored. ACKNOWLEDGEMENTS We thank the farmers who allowed their paddocks to be sampled. Stan Winterton and Alan McDonald, Martin Harrison, Gabrielle Nowara and Frank Barkla are thanked for assisting with this study. CARO, J.H., TAYLOR, A-W. and FREEMAN, H.P. (1976). Environ. Arch. Contam. Toxicol. 3: 437. TAYLOR, A.W., FREEMAN, H.P. and EDWARDS, W.M. (1971). J. Agr. Food Chem. 19: 832. 163