Abstract:
Proc, Aust, Soc. Anim, Prod, Vol. 18 INVITED REVIEW ORGANOCHLORINE RESIDUES IN PASTURE AND LIVESTOCK K.W, MCDOUGALL* SUMMARY A summary of National Residue Survey data from 1983-1989 for organochlorines (OC) in livestock cattle, sheep and pastures grown in soil ingestion and fat is given. Low levels of violative OC residues occur in pig fat. The main source of residues is from soil and Grazing animals become contaminated by direct that soil. by consuming contaminated plants. The occurrence and persistence of OC residues in both animal fat and in soil is These chemicals have caused problems in production of pasture and reviewed. Management strategies to give short term guidelines to grain for livestock. graziers are described. Attempts to increase the rate of breakdown in the soil under Australian conditions by varying frequency of cultivation, by addition of lime or nitram, by weekly irrigation or by combinations of these have been Deep ploughing to 500 mm has reduced residues of heptachlor and unsuccessful. chlordane by 35-52% in soil. Other Australian work has examined the uptake of OCs by pasture plants in the field and in the glasshouse, for both summer and winter species. It was found that the seedling stage of plant growth contains Species the highest residues with almost nothing present at maturity. selection could be utilized to minimise residues. INTRODUCTION A lot of publicity has been given in recent years to pesticide residues in meat and other foods. The sensitivity of some nations to residues in meat led in 1987 to shipments of beef being rejected from the USA, Japan and Canada for residues of dieldrin, DDT and heptachlor. In response, Australia increased the level of monitoring substantially and geared up to identify and remove from the food chain animals which contained excessive residues. Thousands of properties Australia-wide were identified as having residue problems, most resulting from past use of the persistent organochlorine pesticides, To date much publicity has been gained by looking at the end effect of residues occurring in the meat and meat fat, Much time has also been spent looking for answers to the questions - How do these residues get into the animals? Why do Are there ways of reducing residues in the feed they persist? and soil to keep residues in livestock to a minimum? In this review the m&y aspects of residues as reported in Australian and overseas literature, including current work not yet published, are discussed, RESIDUES IN THE FEED OF LIVESTOCK The production and storage of feed for livestock involves the use of chemicals such as fertilizers, herbicides and insecticides to meet the nutritional needs of the plants, for pest control and for storage of the product. Residues of these chemicals can occur in pasture and can accumulate in the animal. They are considered undesirable in food for human consumption but the presence of residues in the animal will not necessarily affect animal health or production. Some of the most commonly encountered chemicals in feed production are:-- * Chemical Residue Laboratories, N.S.W. Agriculture and Fisheries, tismore, N.S.W. 2480. 19 Proc. Aust. Soc. Anim. Prod. Vol. 18 Heavy metals, found naturally in our environment. They are indestructible in soil and tend to accumulate in the liver and kidneys of animals. Cadmium is the one of most interest currently. Orqanochlorine pesticides, highly toxic to insects, persistent, able to be translocated in the plant, generally have low volatility and are adsorbed onto sediments very easily. They are lipophilic and hence accumulate in body fat. Residues of these can cause considerable problems in livestock. Orqanophosphorus and carbamate pesticides, both classes of cholinesterase inhibitors. They are also highly toxic to their persistence, accumulate only slightly in the body. in the feed of livestock or in the fat of livestock are no compounds which are insects, limited in Generally, residues problem. Synthetic pyrethroids, the most recently developed class of insecticides. They are extremely toxic to insects, have limited persistence, and can biomagnify. They are used at very low concentrations and residues are difficult to see. Again residues in the feed or meat of animals are no problem. Herbicides, including triazines, substituted thioureas, phenoxy acids and others are highly toxic to plants. Below this level they can still remain in soil and be be translocated into plants. There have been very few residue problems in livestock. RESIDUES IN AUSTRALIAN LIVESTOCK Heavy metals, pesticides and other substances have been monitored in Australian meat for a number of years by laboratories from both the Commonwealth Government through the Bureau of Rural Resources and some State Governments. The National Residue Survey (NRS) has been examining residue data for all major species of livestock and a summary of data is shown in Table 1, where only those residues which exceed the Maximum Residue Limit (MRL), as set by the National ealth and Medical Research Council, are shown. Table 1 The incidence (% of total samples) of violative residues of organochlorine pesticides in Australian meat as shown in the National Residue Survey reports for the period 1983-1989* This data shows the overall violative rate for organochlorine (OCs) in Australian meat is quite low. Data for N.S.W. cattle (McDougall unpublished data) is shown in Table 2, indicating trends for individual OCs. This data shows that DDT and dieldrin violations have decreased significantly in the 14 years. This decrease in DDT residues has occurred since use on cotton was banned in 1981. The N.S.W. survey was set up in 1975 by AMRC in response to HCB problems occurring in animals and was continued by N.S.W. Agriculture and 20 Proc. Aust. Soc. Anim. Prod. Vol. 18 Australia-wide, the picture is generally the same, with dieldrin residues being the main problem although in Western Australia heptachlor is also a problem. Knowing that these OC residues do occur in Australian livestock, then how do they occur? Table 2 The incidence (% of total samples) of violative OC residues in the fat of N.S.W. cattle SOURCES OF RESIDUES Work undertaken by. most states in tracing residue sources on properties has identified the following as the main sources of residues inanimals: * * * * Crop/pasture production Soil/pasture contamination Feed storage Termite treatment In a study of data by Dr. G.B. Neumann (S.A. Department of Agriculture personal communication) crop and pasture production accounted for 47% of all contamination in animals and feed storage 10%. Allender (1989) tested 1200 grain storages throughout N.S.W. and found 20.4% were over the acceptable limit for Oc residues, the main ones found being DDT, dieldrin and lindane. A survey of OC residues in N.S.W. agricultural soils showed significant levels of dieldrin and/or heptachlor were found in caneland soils, banana soils and dairy grazing soils (McDougall et al. 1987; Wan et al. 1989). In all these situations the OC had been used to control a soil pest, leaving a persistent residue. Animals obtain residues both through the pasture and through soil ingestion. The movement and uptake of pesticides into pasture has been extensively studied overseas (e.g. King et al. 1966; Hughes and Fenemore 1967; Wingo 1966; Voerman 197S), demonstrating the ability of pasture and forage plants to take up OCs following soil application under northern hemisphere temperate conditions. There has been no work published which specifically looks at this under Australian conditions although some researchers have looked at -the soil/plant/animal relationship both here and in New Zealand (Hudson et al. 1964;. Harrison et al. 1965; Sally 1967; Sally et al. 1968; Gilbert and It has been well established in Lewis 1982; Harradine and McDougall 1986). this work that animals exposed to OC contaminated soils accumulate residues in their fat. 21 Proc. Aust. Soc. Anim. Prod. Vol. 18 Soil ingestion by grazing animals, both cattle and sheep, has in the literature (Arnold et al. 1966; Healy 1968; Harrison et Dairy cattle ingest on average between 0.5 kg and 1.8 1973). and sheep up to 200 g per day. Therefore, livestock exposed soils increase the risk of residues in the animal. PERSISTENCE OF ORGANOCHIDRINES Extensive have been chemicals summarised Table 3 studies into the persistence of OCs in soils and in meat and milk fat undertaken both overseas iand in Australia. Half-lives of the (time taken for the chemical concentration to be reduced by half) are in Table 3. The half-life (weeks) and maximum residue (mg/kg) of OCs in both body fat and butter fat of cattle been documented al. 1970; Healy kg soil per day to contaminated The assumption of first order reaction kinetics used to calculate half-lives in the above examples is not necessarily relevant. Several authors have -identified a 'two compartmental' model to examine the rate of decline of OCs in cattle. In the results quoted above of McCully et al. (1966), Dingle et al, (1985) and Dingle and Palmer (1977) there is a distinct point in the data where the rate of dissipation is reduced. As many of the CC pesticides are microsomal enzyme inducers (Street lS67), it could be that there is a 'critical' concentration of OC above which the enzyme activity is enhanced and hence a greater rate of decline of the CC residue. Therefore, at residue levels approaching MRL, the actual half-lives of the OCs listed in Table 3 could be substantially greater for at least some of the pesticides, including dieldrin, HCB and the DDTs. Work carried out by Fries et al. (1971), Harr et al (1974) and Dobson and Baugh (1976) found significant increases in the rate of dieldrin elimination after administration of a microsomal enzyme inducing drug. Other work (Street et al. 1966; Street and Chadwick 1967) showed that injections of DDT increased the rate of dieldrin elimination, possibly by induced mirosomal activity. With all pesticides, the rate of decline in the butter fat is greatef than the rate in the body fat of non-lactating animals. 22 Proc. Aust. Soc. Anim. Prod. Vol. 18 There is little information on the persistence of OCs in sheep available in the Hunnego and Harrison (1971) looked at the metabolism of DDTs in literature. sheep and found the half-lives of DDE, TDE and DDT to be 10.5, 3 and S weeks In a trial where dieldrin was fed to penned sheep (McDougall and respectively. Heath 1990) the half life in the body fat was 8 weeks. There is the added complexity in sheep that OC residues can also accumulate in the wool, a fact It appears that for the same which was shown by McDougall and Heath. concentration of a pesticide in the diet the level of contamination in the body fat of sheep is significantly less than expected for non-lactating cattle. Organochlorine pesticides are known to be persistent in soils, with half-lives quoted by Brooks (1974) being (in years) DDT (3 to lo), dieldrin (1 to 7), Edwards (1966) in a separate chlordane (2 to 4) and heptachlor (7 to 12). review of the literature showed DDT and dieldrin to be most persistent. All of this work has been carried out in the temperate climates of the northern hemisphere. In work carried out in the subtropical soils of Taiwan half lives for DDT and dieldrin were estimated at less than 1 year (Talekar et al 1977). It appears that gamma-chlordane and heptachlor epoxide have a half life of 1.5 to 2.5 years but dieldrin has a half life of 4 - 7 years in the subtropical acid soils of northern N.S.W. (McDougall unpublished work). In separate work done in north-western and central western N.S.W. on soils of neutral pH the In the initial 12 persistence of DDT seems to be similar to that of dieldrin. month period of study there appeared to be no conversion of the DDT to DDE, The acidity of the north-coast which would be the expected change to occur. soils and the dryness of the western soils of NSW seem to reduce the rate of breakdown of OCs. RESIDUES OF ORGANOCHI0 RINES IN SOIL AND PASTURE In order to produce feed for livestock which is basically free of pesticide residues there is a need to reduce or bind up soil residues, select crops that take up less chemical than others or use chemicals that produce no residue problems. Most chemicals currently registered for use in the production of feed for livestock have no residue problems so our discussion will be limited to organochlorines from past usage and investigations into the management of these in grazing livestock. Residues in soil Manaqement strateqies are important in the short term if affected farmers are to continue as a viable entity. N.S.W. Agriculture and Fisheries set up management strategies which would minimise residue risk to grazing stock, including: * * * * * * Do not convert contaminated land to pasture. Avoid grazing bare paddocks to reduce soil intake. Provide dense pasture to reduce soil intake. Do not heavily graze pastures. Graze contaminated paddocks intermittently. Cut maize silage at least 300 mm above the soil. Most of these strategies were designed to reduce contaminated soil intake but the only way of reducing contaminated pasture intake was to graze 'clean' pastures. In practice these strategies have helped a number of dairy farmers through difficult times. Residues of OCs have not been eliminated in the milk but have remained below MRL for a number of years. Reduction of Soil Residues was seen to be a possible way out for producers. Studies have revolved around factors which affect breakdown of pesticides in soil, namely pH, soil temperatures and moisture, aeration, activity of soil microflora and dilution. Some work had already been carried out overseas to assess the influence on these things on the rate of breakdown (Lichtenstein and 23 Proc. Aust. Soc. Anim. Prod. Vol. 18 Schultz 1961; Lichtenstein et al. 1971; Guenzi and Beard 1976), including investigations of soil moisture and temperature, cover crops and cultivation but none of this was practical for the field situation. Trials were set up in coastal northern N.S.W. under sponsorship, initially of the Rural Credit Development Fund and lately by AMLRDC, to examine the following to determine if any enhanced breakdown of heptachlor epoxide, dieldrin or gamma chlordane in soil occurred. 1. 2. Frequency of cultivation, where plots were cultivated with a chisel plough either monthly, quarterly or annually. Addition of-hydrated lime to raise the pH of the soil from 4.5 to a value of 6.0. Microbial activity is limited at acid pH8 and this was undertaken to increase microbial activity. Addition of nitram as a source of nitrate which acts as an external electron acceptor in anaerobic metabolic respiration in bacteria (Sokatch 1969) and hence could enhance breakdown of the OCs. Combinations of the above, as well as an uncultivated control, which was sown to pasture. 3. 4. As well as the above, a 7Ocm mouldboard plough was used to deep plough and bury the. residues to remove them from access to cattle and pasture. This was possible only in two out of three trials as the soil in the third trial was unsuitable. The results from these treatments showed no significant increase in two years in the rate of breakdown of heptachlor epoxide, gamma chlordane and dieldrin in the soils examined. The half life of these pesticides over that period were 2 - 2.5 years, 1.5 - 2 years and 7 years respectively. Breakdown of heptachlor and chlordane for the first year occurred during the summer months. In the deep ploughing experiment residues were reduced significantly (Table 4) and then decreased at the normal rate. Table 4 The effect of deep ploughing (cm) on the reduction (% of initial) of heptachlor epoxide (HE) and gamma-chlordane (GCL) residues (mg/kg) in soil From all this work deep ploughing is the only possibility for reducing soil CC residues and it is only applicable where soil type and depth allow it to be used. Conditions for ploughing need to be right to allow maximum depth to be achieved. In separate studies in Western Australia the AMLRDC funded work where Barker ziXd co-workers looked at a number of other treatments to enhance breakdown of the Ocs. The temperature of the soil was raised by repeated burnings on the surface, soils were cultivated at weekly intervals and weekly irrigation was, applied. To quote a media release, 'All three treatments had no effect on reducing soil pesticide levels'. In all studies so far no way has been found 24 Proc. Aust. Soc. Anim. Prod. Vol. 18 to enhance the breakdown of OCs in soil, either attempts at other methods of enhancement, been using wood rot fungii but nothing is currently Therefore the main approach has to be through ploughing can be used. in N.S.W. or W.A. There have including microbial breakdown able to be used in the field. the pastures used unless deep Residues in pasture Uptake by pasture plants in Australia has been examined at Sydney and Kempsey. Glasshouse studies and field studies respectively were undertaken to determine uptake of heptachlor and chlordane in both summer and winter species. This work (Singh et al. 1990a, b) showed that residues were taken up into pastures in varying amounts-and generally these residues decreased with age. Highest residues of heptachlor epoxide occurred in plants at the seedling stage, with variation between species. Up.take in the glasshouse by plants was proportionally greater than in the field studies. Legumes still contained significant residues at the haying-off stage r both in summer and winter species, for soil heptachlor levels ranging 0.19-0.24 mg/kg. In a separate assessment of this and other work (Gilbert and Lewis 1982) Dr. C.R. Harris (personal communication) calculated that for soil residues in excess of 0.1 mg/kg heptachlor, pastures could contain residues which would cause grazing cattle to exceed MRL. Residues of gamma-chlordane appeared in most pastures in the glasshouse trial but species in the field trial took up proportionally less. The reason for this is uncertain although the field soil was generally much drier and it appears from observations of the data that soil moisture can effect both the total uptake of residues into plants and the individual chemical uptake such that the ratio in the plant is different to that in the soil, as can be seen by the following observations from the above two trials plus a second field trial. Table 5 The effect of soil moisture on the ratio of heptachlor epoxide to gamma-chlordane in soil and pasture Soil moisture seems to have significant effects on the uptake of pesticides into plants. For e&mple, a moisture effect was observed in growing lucerne and berseem clover where heptachlor residues decreased with growth of the plants only to rapidly increase following sustained heavy rain. There is obviously increasedspossibility of higher residues occurring in pasture plants from wet soils and the consequent increased risk of residues in grazing animals exceeding MRL. Distribution of residues within the plant has been examined by King et al. (1966) where it was shown that the highest residue occurs in the crown and roots of alfalfa. The risk of excessive residues to grazing animals would again be increased where pasture plants can be pulled out and eaten, roots, soil and all. 2s Proc. Aust, Soc, Anim. Prod. Vol. 18 CONCLUSIONS Organochlorine pesticides have been found in Australian livestock in violative A major proportion of violations of OCs in cattle were due to soil quantities. ingested and to pasture production. Livestock can be contaminated from either pasture or direct soil ingestion. There have been no means found to reduce soil residues to acceptable levels to allow continued use of those soils for grazing and pasture production apart from deep ploughing. Short term management strategies have been identified which maintain residue contamination of-livestock at a minimum. Selection of specific pasture species can al0 keep OC residues to a minimum. It is imperative that any chemical used for pasture production be carefully checked for its ability to persist in the soil and animal and its ability to be taken up by plants. ALLENDER, W.J. (1989). Bull. Environ. Contam. Toxicol. 42:603. Aust. J. Exp. Agric. Anim. ARNOLD, G-W., McMANUS, W.R. and BUSH, 1-G. (1966). Hush. 6:lOl. BERRY, C.R. (1986). Arkan. Farm Res. Nov-Dec:9. BLUNT, C.G. and SAUNDERS, P.J. (1978). Aust. J. Exp. Agric. Anim. Hush. 18:33S. BROOKS, G.T. (1974). 'Chlorinated Insecticides', Vol. II p.68. (CRC Press: Ohio). DINGLE, J.H.P. and PALMER, W.A. (1977). Aust. J. Exp. Agric. Anim. Hush. 17:712. DINGLE, J.H.P., PALMER, W.A. and BLACK, R-R. (1989). Aust. J. Exp. Agric. 29:497. DOBSON, R.C. and BAUGH, E.R. (1976). Bull. Environ. Contam. Toxicol. 16:567. EDWARDS, CA. (1966). Res. Rev. 13:83. FRIES, G-F., MARROW, G.S., LESTER,J.W. and GORDON, C.H. (1971). J. Dairy Sci. S4:364. FRIES, G.F., MARROW, G.S. (1976). J. Dairy Sci. SS:47S. GILBERT, W.S. and LEWIS, C.E. (1982). Aust. J. Exp. Agric. Anim. Hush. 22:106. GUENZI, W.D. and BEARD, W-E. (1976). J. Environ. Qual. S:243. HARR, J-R., GILLET, J-W., EXON, J.H. and CLARK, D.E. (1974). Bull. Envir. Cont. Toxicol. 12:433. HARRADINE, I.R. and MCDOUGALL, K.W. (1986). Aust. Vet. J. 63:419. HARRISON, D.L. and COLLET, 3-N. (1965). N.Z. J. Agric. Res. 8:223. HARRISON, D-L., MOL, J.C.M. and HEALY, W.B. (1970). N.Z. J. Agric. Res. 13:664. HEALY, W-B. (1968) N.Z. J. Agric. Res. 11:487. HEALY, W.B. (1973). Ir? Chemistry and Biochemistry of Herbage', Vol.1, p.567, editors G.W. Butler and R.W. Bailey. (Academic PresstLondon). HUDSON, W.J., GILBERT, W.S. SWAIN,F.G., BRAITHWAITE, B.M. and JANE, A. (1964). Aust. J. Exp. Agric. Anim. Husb. 4:107. HUGHES, J.T. and FENEMORE, P.G. (1967). N.Z. J. Agric. Res. 10:261. HUNNEGO, J.N. and HARRISON, D.L. (1971) N.Z. J. Agric. Res. 14:400. KING, R.L., CLARK, N.A. and HEMKEN, R.W. (1966) J. Agric. Food Chem. 14:62. LICHTENSTEIN, E.P. and SCHULTZ, K.R. (1961). J. Econ. Entomol. S4:517. LICHTENSTEIN, E-P., SCHULTZ, K.R. and FUHREMANN, T.W. (1971) Pest. Monit. J. S:218. McCULLY, K.A., VILLENEUVE, DC., MC KINLEY, W.P., PHILLIPS, W.E.J. and HIDIROGLOU, M. (1966). J.A.O.A.C. 49:966. McDOUGALL, K.W., SINGH, G., HARRIS, C.R. and HIGGINSON, F-R. (1987). Bull. Environ. Contam. Toxicol. 39:286. MCDOUGALL, K.W. and HEATH, A.B. (1990). Aust. Vet. J. (in press). PETTERSON, D.S., CASEY, R.H. EBELL, G.F. and MCINTYRE, B.L. (1988). Aust. Vet. J. 65:50. Proc. Aust. Soc. Anim. Prod. Vol. 18 SINGH, G., HIGGINSON, F.R., FENTON, G. and DOWMAN, T. (1990a). J. Environ. Sci. Health B. (in press). FENTON, G. (1990b). HIGGINSON, F-R., and DOWMAN, T . SINGH, G., J. Environ. Sci. Health B (in press). SOKATCH, J.R. (1969). In 'Bacterial Physiology and Metabolism', p-198, (Academic Press: New York). SOLLY, S.R.B. (1967). Proc. 20th N.Z. Weed Pest Cont. Conf. p-167. SOLLY, S-R., HARRISON, D.L. and SHANKS, V. (1968). N.Z. J. Agric. Res. 11:371. STREET, J.C. (1967). N.Y. Acad. Sci. Conf. Proc. (May). STREET, J.C. and CHADWICK, R.W. (1967). Toxicol. Applied Pharmacol. 11:68. STREET, J-C., WANG, M. and BLAU, A.D. (1966). Bull. Environ. Contam. Toxicol. 1:6. TALEKAR, N-S., SUN, L-T., LEE, E-M. and CHEN, J-S. (1977). J. Agric. Food Chem. 25:348. VOERMAN, S. and BESEMER, A.F.H. (1975). Bull. Environ. Contam. Toxicol. 13:SOl. (1989). WAN, H., HIGGINSON, F.R., HARRIS, C.R. and MC DOUGALL, K-W. Bull. Environ. Contam. Toxicol. 42:177. WINGO, C.W. (1966). Univ. Missouri Res. Bull. 914:l. 27