EI-01693; No of Pages 21 Available online at Environment International xx (2007) xxx – xxx Chemical contaminants in feedlot wastes: Concentrations, effects and attenuation S.J. Khan a,⁎, D.J. Roser a, C.M. Davies a, G.M. Peters a, R.M. Stuetz a, R. Tucker b, N.J. Ashbolt a a Centre for Water and Waste Technology, School of Civil and Environmental Engineering, University of New South Wales, NSW 2054, Australia b Feedlot Services Australia, Toowoomba, QLD 4350, Australia Received 15 February 2007; accepted 29 October 2007 Commercial feedlots for beef cattle finishing are potential sources of a range of trace chemicals which have human health or environmental significance. To ensure adequate protection of human and environmental health from exposure to these chemicals, the application of effectivemanure and effluent management practices is warranted. The Australian meat and livestock industry has adopted a proactive approach to theidentification of best management practices. Accordingly, this review was undertaken to identify key chemical species that may requireconsideration in the development of guidelines for feedlot manure and effluent management practices in Australia. Important classes of tracechemicals identified include steroidal hormones, antibiotics, ectoparasiticides, mycotoxins, heavy metals and dioxins. These are described in termsof their likely sources, expected concentrations and public health or environmental significance based on international data and research.
Androgenic hormones such as testosterone and trenbolone are significantly active in feedlot wastes, but they are poorly understood in terms of fateand environmental implications. The careful management of residues of antibiotics including virginiamycin, tylosin and oxytetracycline appearsprudent in terms of minimising the risk of potential public health impacts from resistant strains of bacteria. Good management of ectoparasiticidesincluding synthetic pyrethroids, macrocyclic lactones, fluazuron, and amitraz is important for the prevention of potential ecological implications,particularly towards dung beetles. Very few of these individual chemical contaminants have been thoroughly investigated in terms ofconcentrations, effects and attenuation in Australian feedlot wastes.
2007 Elsevier Ltd. All rights reserved.
Keywords: Feedlots; Hormones; Antibiotics; Ectoparasiticides; Waste management Polyether ionophores (lasalocid, monensin, narasin, and salinomycin) . . . . . . . . . . . . . . . 0 ⁎ Corresponding author. Tel.: +61 2 93855082; fax: +61 2 93138624.
E-mail address: (S.J. Khan).
0160-4120/$ - see front matter 2007 Elsevier Ltd. All rights reserved.
Please cite this article as: Khan SJ, et al, Chemical contaminants in feedlot wastes: Concentrations, effects and attenuation, Environ Int (2007), doi: S.J. Khan et al. / Environment International xx (2007) xxx–xxx Environmental fate of ectoparasiticides . . . . . . . . . . . . . . . . . . . . . . .
36 kg manure per day for a heavy finished animal (600 kg).
Fresh manure, which comprises of faeces and urine, is normally The Australian meat and livestock industry has adopted a composed of around 90% water and 10% solids.
proactive stance towards the implementation of best practices Good feedlot pad management requires a balance between for the management of chemical contaminants that may be environmental and animal health considerations and the eco- present in manure and effluent from commercial feedlot nomic cost of pen cleaning. However, the period of time bet- operations. While numerous activities will be necessary to ween pen cleanings generally means that there is some achieve this, the first requirement is the identification of decomposition of pad manure before it is removed from the pen.
chemicals likely to warrant closest scrutiny. This review of Depending on variations in management and weather, ma- primarily international data and research was undertaken to nure harvesting rates have been reported to vary between 0.41– identify key chemicals for which local analytical efforts appear 1.05 t dry weight per head per year ( most justified.
While manure harvesting from pens occurs at regular Commercial feedlots are a major method of finishing beef intervals, manure spreading or dispatch offsite depends upon cattle in preparation for slaughter in Australia. Cattle entering management methods, weather conditions and cropping cycles feedlots are typically 12–24 months of age. Depending on the which influence when manure can be spread or sold. Accor- intended market for the cattle, they may be fed for 60 days to up dingly, manure is often stockpiled at feedlots for periods of to 400 days while gaining about 100–350 kg in weight.
months or occasionally years. During stockpiling, manure The main by-products from cattle feedlots are the manure undergoes partial decomposition and drying which can lead to harvested from the surface of the pens and liquid effluent significant mass decrease. If stockpiles are carefully managed collected during rainfall runoff events. A typical animal ensuring aeration as well as optimal water content and carbon to entering a feedlot (e.g. 340 kg for heavier markets) produces nitrogen ratios, manure may be composted in the process. Much approximately 20 kg of manure per day, increasing to up to of the organic matter can be mineralised or volatilised during Fig. 1. Molecular structures of endogenous estrogenic steroidal hormones.
Please cite this article as: Khan SJ, et al, Chemical contaminants in feedlot wastes: Concentrations, effects and attenuation, Environ Int (2007), d S.J. Khan et al. / Environment International xx (2007) xxx–xxx ous hormones are commonly identified in animal excretionsincluding manure and urine (). The levelsof these residues vary considerably with sex, age, breed,castration, and pregnancy.
Both natural and synthetic steroidal hormones are used in many countries as hormonal growth promotants (HGPs) incattle Fig. 2. Molecular structure of zeranol (α-zearalanol).
). They are used to improve feed efficiency, rates ofweight gain and relative proportions of muscle and fat ( composting leading to mass reductions of a further 50% of the Such HGPs have been widely used in some sectors original bulk.
of the beef cattle industry in mainland Australia since 1979 From the point of manure deposition on the pad, through ) and are registered by the Australian stockpiling, to eventual removal from the feedlot site, Pesticides and Veterinary Medicines Authority ( opportunities exist for the transport or transformation of ). HGPs are also used throughout the USA and Canada.
chemical components or contaminants. The major transport However their use is currently prohibited within member routes may include runoff from impermeable surfaces and countries of the European Commission ).
leaching through soil to groundwater. Additional routes may The use of HGPs may increase both the range and involve human intervention such as manure stockpiling or concentration of steroids present in livestock wastes ( application to agricultural fields. Likely chemical transforma- ). HGPs are normally administered via a subcutaneous tions include oxidative or reductive degradations, which may be implant in the animal's ear. All such compounds are known to photochemically or biochemically mediated. The degree of such be present in animal tissue as well as in urinary and faecal transformations and/or transport is important when assessing excretions. At slaughter, the ear, along with any residual drug in the probability of human exposure. This in turn is necessary for the implant is discarded ( the task of identifying best practices for the management of Commercially available hormonal products are also used to feedlot manure and effluent to ensure the full protection of improve the reproductive performance of dairy cattle ( human health.
). Natural and synthetic hormonal steroids, including Chemicals of concern in cattle feedlot manure and effluent progestins and estrogens, are used in Australia for a range of may include endogenous chemicals such as hormones, as well purposes such as the synchronisation of heifer ovulation cycles as non-endogenous natural and synthetic chemicals used to and improvement of fertility maintain the health and optimum growing conditions for the ). However, unlike many other countries, it is animals. Furthermore, there is potential for animals (and hence not common practice to lot feed dairy cows in Australia and thus manure and effluent) to be unintentionally exposed to chemicals products applied for these uses are unlikely to be significant in the environment or via contaminated feed products. To contaminants in Australian feedlots.
reduce the likelihood of this occurring, all feedstuff purchases in Subcutaneous implant devices containing active steroidal Australia require a Commodity Vendor Declaration stating the hormones are registered under a number of trade names in fodder type and any chemicals such as pesticides applied during Australia including Elanco Compudose, Revalor, Coopers Ralgro, Crestar, Synovex and Progro The Veterinary chemicals may be administered to animals while active hormones in these products include 17β-estradiol, estradiol at the feedlot or, alternatively residues of such chemicals valerate, estradiol benzoate, trenbolone acetate, zeranol, proges- applied at a previous location may be (wittingly or otherwise) terone, and testosterone propionate.
transported to the feedlot with incoming animals. Again,management practices to minimise this in Australia include the requirement that all feedlot animals are subject to a NationalVendor Declaration, which serves as a travel document and 17β-Estradiol is the most active of the natural estrogens.
describes all chemicals used in the production of that animal.
During metabolism, 17β-estradiol is primarily converted to After consideration of the international scientific literature estrone and further to estriol ). A variety of sulphate and on this subject, steroidal hormones, antibiotics, ectoparasiti- glucuronide conjugates are also excreted ( cides, mycotoxins, heavy metals and dioxins were identified as ). The relative potencies of the being most worthwhile for further analysis in the Australian steroidal estrogens appear to be somewhat dependant on the assay context. Each of these categories of chemicals is addressed in used and the endpoint targeted. However it seems clear that 17α- the following sections.
estradiol, estriol and estrone are generally less potent than 17β-estradiol (Total estrogen 2. Steroidal hormones production can vary significantly for dairy cows depending onpregnancy stage While estradiol is an Steroidal hormones potentially present in feedlot manure and endogenous hormone, animals may be treated with further effluent include endogenous (naturally occurring) hormones supplements to promote growth. Commercial implants in and some synthetic hormones applied in agriculture. Endogen- Australia contain 12–400 mg estradiol ( Please cite this article as: Khan SJ, et al, Chemical contaminants in feedlot wastes: Concentrations, effects and attenuation, Environ Int (2007), doi: S.J. Khan et al. / Environment International xx (2007) xxx–xxx Fig. 3. Molecular structures of androgenic steroids.
Zeranol (α-zearalanol) ) is a synthetic beta resorcylic beef cattle. Trenbolone is administered to feedlot cattle as tren- acid lactone administered as an anabolic growth promoter in bolone acetate, which is hydrolysed to form the potent androgen beef cattle (While zeranol is not truly a receptor agonist 17β-trenbolone. The major metabolic route of steroidal compound, it is used as a hormonal growth promotant 17β-trenbolone is oxidation to trendione, followed by reduction in parenteral implant devices due to its estrogenic nature. It is to the less potent epimer, 17α-trenbolone structurally and metabolically related to the myco-estrogen 17β-trenbolone has an anabolic activity several times above that zearalanone (see Section 5). Zeranol has been demonstrated to of testosterone. Commercial implants in Australia contain 60– be estrogenic, with potencies similar to 17β-oestradiol in a range 200 mg trenbolone acetate ).
of bioassays ).
Once administered, zeranol is predominantly metabolised to its diastereoisomer β-zearalanol (taleranol) and to a lesser extent,further to zearalanone (). Commercial Secretion of progesterone ) is most prevalent during implants in Australia contain 36 mg zeranol ( the second half of the female estrous cycle. Progesterone ismetabolised to hydroxylated metabolites and their sulphate and glucuronide conjugates which are eliminated in the urine). Progesterone is further used, in Testosterone secreted by the testes is the main androgen in combination with estrogenic hormones, as a HGP, as well as to males, along with its similarly active metabolite dihydrotestoster- suppress estrus in feedlot heifers. Commercial implants in one (see These natural androgens are metabolised and Australia contain 100–200 mg progesterone ().
excreted in urine as both free steroids and water-soluble con- Melengestrol acetate is an orally applied synthetic jugates ). The major urinary metabolites are steroidal progestin widely used as a HGP as well as for estrus etiocholanolone and androsterone, both of which are physiologi- synchronisation and estrus suppression in feedlot heifers in the cally weak or inactive ). In addition to endogenous USA. However, it is not currently approved for use in Australia.
testosterone, further testosterone or testosterone propionate maybe used as a HGP in bovines. Commercial implants in Australia 2.4. Environmental and public health concerns contain 200 mg testosterone propionate Trenbolone () is a synthetic androgenic steroid. It is used During the last few decades, reports of hormonally related to promote growth and enhance the efficiency of feed utilisation in abnormalities in a wide range of species have accumulated Fig. 4. Molecular structures of progestinal steroids.
Please cite this article as: Khan SJ, et al, Chemical contaminants in feedlot wastes: Concentrations, effects and attenuation, Environ Int (2007), d S.J. Khan et al. / Environment International xx (2007) xxx–xxx (Chemical contaminants are believed to be trenbolone to 17β-trenbolone by the fish ).
responsible for many of these abnormalities, acting via This observation demonstrates the importance of considering mechanisms leading to alteration in endocrine function. This both epimers when assessing potential ecological risk of an- phenomenon, known generally as ‘endocrine disruption', has drogens associated with beef feedlot effluents.
been identified by the World Health Organization as an issue ofglobal concern The chemicals implicated 2.5. Steroid hormones in animal excretions have been collectively termed ‘endocrine disrupting chemicals'(EDCs), or simply ‘endocrine disruptors'.
Steroidal hormones are excreted by mammals in free form, or A particular form of this endocrine disruption has been the as sulphate or glucuronide conjugates which may be readily inducement of biochemical hormonal responses in freshwater hydrolysed to the corresponding free steroid under appropriate fish (A growing number of natural and conditions ). Cattle excretions contain con- synthetic environmental chemicals have been implicated as siderable quantities of steroidal hormones, depending largely on causative agents of these observed disruptions. However, in age, sex and stage of the female oestrus cycle ( terms of potency, the most significant have been natural and synthetic steroidal hormones ( The banning of hormonal growth promotants for use in cattle ). Some steroidal hormones have been observed to production in the European Union has led to the rapid develop- cause disruption of the endocrine system of fish at ambient ment of sensitive analytical methods to determine illegal use concentrations less than 1 ng L− 1 ( targeting bovine excretions ( Environmental exposure to estrogenic hormones has been shown to cause feminisation of male fish In some cases, this has facilitated improved un- ). More recently, exposure to derstanding of expected excretion patterns of some compounds androgens has been implicated in the masculinisation of fish under specific conditions.
17α-estradiol, 17β-estradiol and estrone account for more ). Furthermore, scientists suspect that anthropogenic than 90% of the estrogens excreted by cattle as free and con- estrogens, androgens and progestins may act as reproductive jugated steroids (). However, endogen- pheromones in fish, thus adversely affecting reproduction ous loads of estrogens excreted in dairy cow faeces and urine is highly variable depending on pregnancy stage Much attention has focused on the discharge of hormonal steroids from municipal sewage treatment plants ( Furthermore, the urine of heifers implanted with 2 × 25 mg However, livestock wastes have zeranol pellets has been reported to contain 2–5 μg L− 1 zeranol been identified as a further potentially important but poorly and equivalent concentrations of its diastereoisomer taleranol understood source of these compounds in the environment It has been estimated that calves excrete approximately 16 mg of natural estrogenic hormones per year and that male Municipal sewage effluents have been generally charac- calves excrete around 120 mg of natural androgens per year terised as being ‘estrogenic' in nature, due largely to trace Similarly, bulls were estimated to excrete concentrations of estrogenic steroidal hormones as well as some 200 mg of estrogens and 390 mg of androgens per year.
other natural and synthetic chemicals. Similarly, dairy wastes Both trenbolone and melengestrol acetate have been appear to be strongly estrogenic due to the presence of a number identified in effluent and solid manure from treated cattle in of the same estrogenic steroidal hormones Germany (Initial concentrations of trenbolone were reported at 1700 ng/kg in effluent and 5– Conversely, discharges from a beef cattle feedlot in the USA 75 μg/kg in solid manure. After 4.5–5.5 months storage, have been shown to be significantly androgenic in nature residues of 1100 ng/kg in effluent and up to 10 μg/kg in solid (). Consistent with this, studies also manure were measured. Melengestrol acetate was reported in the undertaken in the USA have demonstrated adverse effects to solid manure at 0.3–8 μg/kg and remaining at up to 6 μg/kg after the endocrine and reproductive systems of exposed wild fish 4.5 months storage.
populations ().
17α-trenbolone predominates over 17β-trenbolone in man- The androgenic nature of feedlot discharges may be in part due ure excreted by treated livestock by a ratio of about 10 to 1.
to numerous steroidal hormones such testosterone. However, in Both metabolites are relatively stable in effluent, with half-lives recent years, particular attention has been focused on trenbolone.
of about 260 days having been previously reported ( Beef cattle feedlot effluents have been shown to contain detectable concentrations of both 17α-trenbolone to 17β-trenobalone ). 17β-trenbolone is a potent 2.6. Environmental fate of steroidal hormones androgenic agent to fish ), aswell as to some exposed mammals (). More The fate of any excretion-borne hormones depends upon a surprisingly, 17α-trenbolone also appears to have a high potency number of possible transport pathways and transformation to some fish, which may arise from substantial conversion of 17α- mechanisms. Hormones may be retained in soil or transported Please cite this article as: Khan SJ, et al, Chemical contaminants in feedlot wastes: Concentrations, effects and attenuation, Environ Int (2007), doi: S.J. Khan et al. / Environment International xx (2007) xxx–xxx by surface run-off or groundwater to surface waters. Manure Estrogenic, androgenic and progestinal steroidal hormones containing hormones may be stabilised through storage or have been shown to leach into groundwater from dairy waste composting before being spread on paddocks. The available lagoons However, they appear to be information suggests that steroid hormones slowly degrade in strongly absorbed or degraded over distances of 10–100 m in manure, soil and water, but the exact mechanisms or factors subsurface waters controlling the rates are not yet fully understood.
The use of non-chemical-specific screening assays has Unconjugated steroidal hormones are chemically very stable, revealed that feedlot retention ponds and some feedlot effluents non-volatile, have low water solubility and are moderately in the USA also contain significant concentrations of both hydrophobic ).
estrogenic and androgenic substances and that these may Their environmental fate from livestock manure depends upon contaminate local watercourses Indeed, one both storage conditions and management ().
study of ponds receiving runoff from US beef cattle farms The degradation of estrogens in separated dairy manure waste identified elevated 17β-estradiol concentrations similar to what solids (press cake) has reportedly been characterised by first- has been reported in streams receiving sewage treatment plant order decay kinetics The reported decay effluents. The concentrations measured by a radioimmunoassay constant (K) ranged from 0.029 day− 1 to 0.12 day− 1, increasing (ELISA) were 0.05 to 1.80 ng L− 1 ( with incubation temperature.
It has been proposed that overland flow of steroidal Manure and effluent application rates to soils are typically hormones during rain events may be a much more significant macronutrient-based. The hormone-to-macronutrient ratios means of transport to surface waters compared to seepage effectively determine the rates at which hormones will be through soils (In a few cases, steroidal applied to soils from manure and effluent. One approach that hormone have been identified in USA regional groundwaters has been used to predict hormone loading rates in fields ) and external surface waters ( receiving dairy wastes has been to determine the mass ratios of ) where livestock farming has been suspected as the specific hormones to the macronutrients nitrogen, phosphorus, predominant source. However, all Australian cattle feedlots and potassium in dairy wastes applied ( with a capacity of 1000 head or more (and many of the smaller Once released to soils, the environmental fate of steroid ones) are required to catch and store runoff in effluent holding hormones depends upon the nature of the soil ponds, preventing direct transport of contaminants in runoff to ). In particular, particle size and organic components strongly affect adsorption and migration in soils. 17β-estradiol Few studies have been undertaken to trace the fate of zeranol and estrone have high sorption affinities to soils ( in the environment. However, interestingly, this compound has been observed at low ng L− 1 concentrations in municipal affinity has been well correlated with mineral particle size and sewage effluents and in a river receiving sewage discharges organic matter content. Furthermore, there is an apparent ). Nonetheless, given that these relationship with surface area and/or cation-exchange capacity studies were undertaken in Europe, transformation of the related of the soil (). Testosterone appears to behave myco-estrogen zearalenone would seem a more likely source differently, with lower soil sorption affinity only weakly than residues from growth promotant use.
correlating with soil particle size, organic matter and specific While data is lacking, it has been suggested that steroidal surface area ().
hormones are biodegraded in the environment by many types of Degradation/transformation of 17β-estradiol occurs in the organisms ). In soils, estradiol is sorbed phase in soil and is rapid (Although converted, biotically or abiotically, to estrone, which is slowly it was found that testosterone degraded more readily than 17β- further degraded or mineralised ( estradiol, it appeared to have a greater potential to migrate in the soil because it was not as strongly sorbed ().
These results are consistent with field observations where testosterone was shown to reach groundwater, while estrogenremained bound to the upper crust of the soil ( Antibiotics include naturally-occurring, semi-synthetic and Both testosterone and estradiol have been synthetic chemical compounds with antimicrobial activity. They measured in surface run-off from soils amended with animal are used in veterinary medicine to treat and prevent disease, and for other purposes including growth promotion in food animals Synthetic hormones, trenbolone and melengestrol acetate Depending on their chemical nature, they appear to behave similarly to testosterone, having a significant can be administered orally, parenterally or topically. Antibiotics affinity to the organic fraction of soils, leading to a high are commonly administered to livestock in the USA and retardation, but remaining nonetheless mobile in agricultural Australia via feed or water or via a slow-release implant ( soils ). In a study undertaken in Germany, traces of trenbolone remained measurable in soil up to eight Antibiotics used to treat and prevent disease may be weeks after application of pre-stored manure and effluent of undertaken as therapy (for animals exhibiting clinical disease), treated cattle, while melengestrol remained detectable even after control (administration to a herd to control the spread of cultivation of a maize crop ).
disease) or prevention (administration to healthy animals to Please cite this article as: Khan SJ, et al, Chemical contaminants in feedlot wastes: Concentrations, effects and attenuation, Environ Int (2007), d S.J. Khan et al. / Environment International xx (2007) xxx–xxx prevent onset of disease) ( A wide range of antibiotic agents are registered for thera- peutic use on cattle in Australia. Some of the most important Antibiotic use for growth promotion involves the adminis- include benzathine penicillin, procaine penicillin, ampicillin, tration of an antibiotic agent, usually as a feed additive over a amoxycillin, cloxacillin, cefuroxime, cephalonium dihydrate, period of time, which results in improved physiological per- cefuroxime, ceftiofur, erythromycin, oxytetracycline, sulfadia- formance. Many antibiotics are known to improve average daily zine, sulfadimidine, sulfadoxine, dihydrostreptomycin, novo- weight gain and feed efficiency in livestock in a variety of biocin, trimethoprim, florfenicol, neomycin, tylosin and flunixin ). By virtue of their use, all of these compounds ). Some growth-promoting have some potential to be present in livestock wastes.
effects involve the alteration of the normal intestinal microbiota, However, the agents that are used ‘enterically' as feed resulting in more efficient feed digestion and metabolism additives are likely to be significantly more important feedlot (Others are the result contaminants than the agents used only intermittently to treat of pathogen and disease suppression and immune system illness. There are more than 30 antibiotic products registered for such ‘enteric' uses in Australia Of these, Feedlot cattle are highly susceptible to rumenitis and hepatic monensin is the most common active ingredient, but others abscessation as a result of high carbohydrate diets ( include salinomycin, tylosin, lasalocid, oxytetracycline, nar- asin, and neomycin. Virginiamycin is also registered, but Continuous inclusion of antibiotics in the diet can significantly growth promotant claims have been voluntarily withdrawn by reduce these afflictions the manufacturer, limiting its use to therapeutic applications.
Fig. 5. Molecular structures of polyether ionophores.
Please cite this article as: Khan SJ, et al, Chemical contaminants in feedlot wastes: Concentrations, effects and attenuation, Environ Int (2007), doi: S.J. Khan et al. / Environment International xx (2007) xxx–xxx Fig. 6. Molecular structure of tylosin.
3.1. Polyether ionophores (lasalocid, monensin, narasin, and ions, such as potassium and sodium, from the cell. This osmotic interference often leads to cell death. Ionophores are notcurrently used in human medicine since they are absorbed and Polyether ionophores (lasalocid, monensin, narasin, and salinomycin) are used to improve feed conversion efficiency infeedlot beef cattle (). Salinomycin is also known to increase the rate of weight gain, thus enhancing productivity.
Lasalocid and Monensin are further used to improve milk Tylosin () is a macrolide antibiotic agent produced production in dairy cows. Approved polyether ionophores are from Streptomyces spp. bacteria. Tylosin is used in Australia for typically included in cattle diets at rates of 5–33 g per tonne of the reduction of incidences of liver abscess in beef cattle ( feed Molecular structures are provided in .
and has been shown to be around 40–70% effective for The polyether ionophores are toxic to many bacteria, doing so Tylosin is typically protozoa, fungi and higher organisms. Their three-dimensional given to Australian beef cattle at a rate of 11 g per tonne of feed conformation creates a highly hydrophobic exterior and a hydrophilic interior, enabling the binding of one or more cations.
Macrolides are able to penetrate host cells, and their The lipophilic nature allows ready penetration of cell mem- therapeutic action is, to some extent, a reflection of their branes, enabling uncontrolled influx and/or efflux of selected intracellular concentration. Typically, they accumulate rapidly Fig. 7. Molecular structure of virginiamycin.
Please cite this article as: Khan SJ, et al, Chemical contaminants in feedlot wastes: Concentrations, effects and attenuation, Environ Int (2007), d S.J. Khan et al. / Environment International xx (2007) xxx–xxx Fig. 8. Molecular structure of neomycin.
to a saturation point both in the cytoplasm and in the intracellular 3.6. Environmental and public health concerns granules. As a group the macrolides are particularly valuable forthe treatment of cell-associated pathogens such as mycoplasmas.
There are a number of concerns regarding residual antibiotics for livestock production. The primary concern 3.3. Virginiamycin is the contribution that livestock antibiotic use may maketo the increasing incidence of antibiotics resistance among Virginiamycin ) belongs to the streptogramin class of a wide variety of pathogenic bacteria ( antibiotic agents. Commercial formulations consist of a mixture A second concern regards potential deleterious effects that of virginiamycin S and virginiamycin M which together are these compounds may have on natural soil bacterial bactericidal. Virginiamycin acts in the 50 S bacterial ribosome at a position very close to the site of action of macrolide Antibiotic resistance is a major problem facing modern antibiotics. It is used in Australia to reduce the risk of lactic medicine. Microorganisms with increasing rates of resistance acidosis in cattle that are fed a high grain diet. Virginiamycin is to commonly used antibiotics include enteric Gram-negative currently approved for use in beef and dairy cattle at a rate of bacilli (Klebsiella and Enterobacter species) resistant to 20 g per tonne of feed (however the approved uses extended-spectrum β-lactams, Streptococcus pneumoniae are subject to on-going review in Australia ).
resistant to penicillins, methicillin-resistant Staphylococcusaureus, vancomycin-resistant enterococci, and Shigella and Salmonella species resistant to multiple antibiotics (). Bacterial isolates, recovered from Neomycin () is an aminoglycoside antibiotic. It is humans, cattle, pigs and food show widespread resistance to available in Australia as a feed additive only for the treatment of tetracycline, sulfamethoxazole, cephalothin and ampicillin bacterial enteritus (scours). It is not registered for use as a Cattle isolates show common growth promotant and treatment via feed is restricted to 3– resistance to numerous antibiotics including sulfamethoxazole, tetracycline, ampicillin and neomycin ( 3.5. Oxytetracycline Numerous studies published in the medical literature have suggested a relationship between clinical antibiotic-resistant Oxytetracycline is not registered as a growth infections and the use of antibiotics in agriculture ( promoting agent in Australia, however it is occasionally used as a feed-additive to control infectious cattle diseases caused by evidence of such a relationship remains controversial ( the effects of transport ( ). Furthermore, within Australia, most of the entericantibiotics used in cattle production are not closely related toimportant antibiotics for human health. This applies to thepolyether ionophores (lasalocid, monensin, narasin and salino-mycin) and neomycin.
Tylosin belongs to the macrolide class of antibiotics, which also includes some important drugs used widely for human healthin Australia (erythromycin, roxithromycin, clarithromycin, clin-damycin, azithromycin, and lincomycin) However, mole-cularly, tylosin is a somewhat ‘aberrant' macrolide in that theusual 14-membered ring has been widened to a 16-membered Fig. 9. Molecular structure of oxytetracycline.
Please cite this article as: Khan SJ, et al, Chemical contaminants in feedlot wastes: Concentrations, effects and attenuation, Environ Int (2007), doi: S.J. Khan et al. / Environment International xx (2007) xxx–xxx Virginiamycin is a streptogramin antibiotic. It is not used for health or that could create cross-resistance to them human health, although it is very close to another streptogramin ). Largely in response to this, the known as quinupristin–dalfopristin, which is of great signifi- European Union has imposed bans on the use of avoparcin, cance. Quinupristin–dalfopristin is not widely used in Australia bacitracin, spiramycin, tylosin and virginiamycin for growth but is kept as a last-defence for the treatment of Methicillin Resistant Staphylococcus aureus or Vancomycin Resistant En- In addition to the potential influence that these compounds terococcus faecium infections. The veterinary use of virginia- may have on the development of bacterial resistance, there is mycin has been subject to close scrutiny in Australia because of also concern regarding their toxicity toward aquatic organisms strong concerns regarding the relationship between virginiamy- ). In terms of toxicity, a particular cin resistance and conferred quinupristin–dalfopristin resistance complication for antibiotics is that standardised tests, such as as well as vancomycin resistance ).
the OECD respiration inhibition test, may not be suitable to Oxytetracycline is a member of the chemically homologous assess the effects of these agents on environmental bacteria group of antibacterial drugs known as tetracyclines. Oxyte- ). Alternatively, manometric respiration tracycline is not used for human health in Australia, however tests have been proposed to assess the effects of veterinary some other very closely related tetracyclines are. These include antibiotics in soil (). Such tests provide doxycycline, tetracycline, minocycline and demeclocycline details of relative antimicrobial potency towards soil micro- organisms and can be used to rank compounds.
). The potential for overexposure of somebacteria to oxytetracycline is of some concern since bacterial 3.7. Environmental fate of antibiotics acquisition of resistance to this drug may provide resistance tothe entire class of tetracycline antimicrobials ( Many antibiotic compounds are only partially degraded during metabolism by humans and other animals, and thus are Bacterial populations intrinsically resistant to antibiotics excreted largely unchanged. Accordingly, animal excrements exist in the environment. Exposure to antibiotic drugs may following antibiotic use for treatment or growth promotion are provide a selective pressure for these organisms to increase in considered to be important sources of these compounds to some dominance Furthermore, exposure to affected environments ( antibiotics may induce genes coded for resistance that are subsequently transferred to other members of the microbial Some antibiotics, such as tylosin and oxytetracycline sorb relatively strongly to manure particles ( The storage of liquid manure prior to use as a fertiliser can Considerable increases in antimicrobial resistance have been enhance the degradation of some antibiotic agents, although reported in faecal samples excreted by lot fed beef cattle in some others are more persistent (). In a Canada (). Importantly, substantial increases in 180-day study, degradation half-lives were determined for the prevalence of resistance to the human-health antibiotics, erythromycin (41 days), roxithromycin (130 days) and salino- tetracycline and doxycycline were reported in this study for mycin (6 days). However the concentration of one compound, animals administered chlortetracycline and oxytetracycline in tiamulin (which is not administered to Australian cattle), feed and/or long-acting injection. Some increased resistance to remained unchanged during the entire storage period.
erythromycin was also observed. Dairy farm manure has also Where contaminated manure and effluent are used to fertilise been shown to contain significant concentrations of multiple agricultural soils, loads of up to kilograms of antibiotic per antibiotic-resistant bacteria hectare may be reached ). Considerable variation exists, but some antibiotic agents appear to be very Tetracycline resistance levels in soil are temporarily persistent in soils ( influenced by the increasing addition of pig-manure slurry For example, tetracyclines have been identified on (). Similarly, chorotetracycline and tylosin manure-fertilised fields in Germany at soil depths of up to resistance levels in soils have been shown to temporarily increase after amendment with manure The different classes of antibiotic drugs vary considerably in ). For streptomycin and erythromycin, only minor varia- their molecular structures, and thus in their physical, chemical tions in resistance levels have been reported ( and biochemical properties. Some substances are very hydro- phobic, while others are completely water soluble ( Microbial profiles collected from surface waters in the USA, Accordingly, distribution coeffi- Europe and Asia also show significant levels of resistance to cients to describe the adsorption of antibiotics to soils or diverse antibacterial agents ( dissolution in water can vary across at least five orders of This may be, in part, due to run off from magnitude (). For this reason, it manure-fertilised agricultural soils, but other sources such as is not possible to provide a widely generalised description of sewage treatment plants may also be of significance.
antibiotic fates in soils.
The World Health Organisation discourages the enteric use For some antibacterial agents estimation of the partitioning of antibacterial agents that belong to classes used for human coefficients cannot be made from measures of hydrophobicity Please cite this article as: Khan SJ, et al, Chemical contaminants in feedlot wastes: Concentrations, effects and attenuation, Environ Int (2007), d S.J. Khan et al. / Environment International xx (2007) xxx–xxx (e.g. log Kow) alone (For example, sorption of antibiotic resistance genes ( oxytetracycline appears to be strongly influenced by ionic binding to divalent metal ions as such Mg2+ and Ca2+ as well as The primary route of genetic transfer between different other charged compounds in the matrix ). Soil genera of bacteria (ie: horizontal transfer) is believed to be via a texture, cation exchange capacity and iron oxide content appear process known as conjugation ( to be among the most significant factors determining oxyte- ). Many examples have been reported of horizontal gene tracycline binding (). The adsorption of some transfer between bacterial species, genera or families and even compounds is also significantly influenced by soil pH ( between bacteria and eukaryotes ( ) and overall ionic strength Some antibiotic compounds have the potential to leach An alternative pathway for gene transfer is believed to be via through soil or with surface run-off during rain events and natural transformation involving the uptake of DNA present in contaminate local groundwater and surface waterways. For the environment (). Released into the aquatic example, multiple classes of antibacterial compounds have been environment, DNA is rapidly degraded. However, when bound reported in surface and groundwater samples collected proximal to soils, it may persist for up to a period of months ( to pig and poultry farms in the USA ( Agriculturally-derived antibiotics have also been identified in It is believed that bacterial natural transformation may be a surface waters in Colorado, USA ( significant gene transfer process in nature, at least under some A US Geological Survey study on the occur- rence of pharmaceuticals in surface waters identified a number ). However, little is known about the of antibiotics that are not used for human therapy in the US relative importance of gene transfer via transformation as the (). The relatively high frequency of detection frequency of such occurrences is yet to be properly validated of these agricultural antibiotics may be indicative of the potential for surface water contamination by these chemicals.
Recent attention has turned to the role that cattle rumen Antibacterial agents are susceptible to biotic degradation by protozoa may play in the gene transfer between microorganisms microbial organisms present in manure and soil ). Rumen protozoa are predators of However, biodegradation rates (or bacteria and thus can harbour antibiotic resistance genes. Evi- half lives) vary between different classes of compounds and are dence has been reported for the involvement of rumen protozoa in also influenced by environmental conditions including available the antibacterial-resistance gene transfer between two bacterial oxygen and the specific nature of the microbial community species, Salmonella and Klebsiella ( (Dissipation half-lives vary with soil Animal manure is also considered to be a likely environment type and have been estimated for chlorotetracycline (25– to favour the horizontal transfer of genes ( 34 days) tylosin (49–67 days) ). This is because of the combination Other examples of degradation rates of antibiotics in manure of high bacterial survival and activity, coupled with the selective and soils have been compiled from the literature by pressure resulting from the presence of antibiotics in animal faeces. report that before the use of thestreptothricin antibiotic ‘nourseothricin' as a feed additive in 3.8. Antibiotic resistance genes some countries, resistance quotients for coliforms in manurewere approximately 0.1–1%. However, after the inclusion of In addition to the influence of antibiotic agents themselves, nourseothricin, resistance quotients of up to 80% were microbial resistance to antibiotics can also be disseminated by observed. Furthermore, plasmid-borne resistance of this drug the spread of resistant organisms and the resistance genes that was detected among strains isolated from pigs, and subse- they carry (). Antibiotic resistance to quently in isolates from manure, river water, food and human many agents is widespread in some environments and much of this resistance is the result of genetic coding that may be In soil environments, gene transfer frequencies are thought to transferred between organisms ).
be low, limited mainly by nutrient availability which in turn For example, among sixteen US rivers, over 40% of bacteria limits bacterial density and activity ). Transfer resistant to one or more antibiotics had at least one plasmid that is also affected by other factors such as soil moisture, pH and coded for resistance and genes resistant to ampicillin were temperature ). However, the areas detected in 70% of the isolated plasmids around plant roots are often very high in the amount and Similarly, 24% of surface water Salmonella strains tested in diversity of nutrients and thus these sites can be ‘hot spots' for Greece exhibited resistance to at least one of 20 antimicrobials and 26% were able to transfer resistance to E. coli ().
4. Ectoparasiticides Furthermore, evidence is mounting to support the hypothesis that intestinal bacteria not only exchange resistant genes among Externally used parasiticides, known as ‘ectoparasitides' are themselves, but might also interact with bacteria that are passing chemical formulations used to control external parasites (ectopar- through the colon, causing these bacteria to acquire and transmit asites) such as ticks, flies and lice on livestock including cattle Please cite this article as: Khan SJ, et al, Chemical contaminants in feedlot wastes: Concentrations, effects and attenuation, Environ Int (2007), doi: S.J. Khan et al. / Environment International xx (2007) xxx–xxx (A number of application methods are and toxaphene) were common cattle ectoparasiticides in used including dips, sprays, pour-on solutions, ear tags and back Australia from the mid 1940s However, rubbers Back rubbers are provided their use was banned in 1962 due to their accumulation in for self-treatment by cattle.
animal tissue (particularly the fat), and the need to comply with Many ectoparasitic infections are seasonal and therefore pesticide residue standards set by countries importing Austra- predictable. Accordingly, they can be countered by prophylactic lian meat ).
use of the ectoparasiticides The available Since chlorinated hydrocarbons have not been registered for chemicals may act either systemically, following dermal uptake ectoparasiticidal use in Australia now for more than 40 years, by the host, or simply by direct contact with the target parasites they are not reviewed in detail here. Although these compounds are notoriously environmentally resilient, it is very unlikely that The regulatory framework for the management of ectopar- feedlot sites would be contaminated with them since almost all asiticides in Australia is administered by Australian Pesticides Australian feedlots were constructed since the ban. Further- and Veterinary Medicines Authority ). Product more, regular testing for these chemicals is undertaken at the registration involves rigorous scientific assessment aimed at time of animal processing and any detection above half the ensuring effective and safe use, as well as efforts to make sure maximum residue limit is investigated.
that environmental risks can be controlled ().
4.2. Organophosphates and carbamates There are currently more than 170 registered cattle ectoparasiticide products in Australia (These The use of chlorinated hydrocarbons was predominantly contain a range of chemical compounds including chlorinated replaced by the then newly available organophosphate com- hydrocarbons (now discontinued), organophosphates, carba- pounds (e.g.: diazinon, dioxathion, carbophenothion, couma- mates, synthetic pyrethroids, amidines, macrocyclic lactones phos and ethion) and carbamate compounds (e.g.: carbaryl, and tick development inhibitors ( promacyl, and bendiocarb) (). These chemi-cals work by disrupting the function of acetylcholinesterase 4.1. Chlorinated hydrocarbons enzymes, leading to neuromuscular paralysis The use of some organophosphates and carbamates has re- Chlorinated hydrocarbons (e.g.: DDT, benzene hexachloride ceded during the last few decades due to the widespread devel- (BHC), chlordane, heptachlor, dieldrin, aldrin, methoxychlor opment of resistance by many ectoparasites. However, many Fig. 10. Molecular structures of organophosphates and carbamates.
Please cite this article as: Khan SJ, et al, Chemical contaminants in feedlot wastes: Concentrations, effects and attenuation, Environ Int (2007), d S.J. Khan et al. / Environment International xx (2007) xxx–xxx Fig. 11. Molecular structures of synthetic pyrethroids.
continue to be used and administered through back-rubbers, ear- 4.5. Macrocyclic lactones tags, dips, pour-on preparations, and sprays Registered organophosphate and carbamate cattle Macrocyclic lactones have been employed as ectoparasiti- ectoparasiticides in Australia include fenthion, fenvalerate, cides in Australia since 1985 (). The phosmet, maldison, chlorfenvinphos, diazinon, ethion, carbaryl macrocyclic lactones registered for use on cattle include and bendiocarb ).
abamectin, doramectin, ivermectin, eprinomectin (andmoxidectin. These compounds are produced as fermentation 4.3. Synthetic pyrethroids products of the soil microorganisms Streptomyces avermilitisand Streptomyces cyanogriseus Synthetic pyrethroids are a relatively recent class of ). Most are supplied as pour-on treatments for ectoparasiticide, having first been registered for use in Australia cattle ticks, buffalo flies, lice and mites. However, some are also in 1980 They are used on Australian cattle approved for subcutaneous injection for the control of lice, to control buffalo flies, lice and ticks via sprays, dips, pour-on mites, mange and ticks. Macrocyclic lactones are highly formulations and ear tags. Synthetic pyrethroids are synthesised lipophilic and, following administration, are stored in animal chemicals modelled on the natural insecticide, pyrethrin fat tissue from where they are slowly released, metabolised and (). They are lipophilic molecules and undergo excreted, primarily in the faeces ( rapid adsorption, distribution and excretion. Their effectivenessis believed to be due to their ability to interfere with sodium 4.6. Benzylphenyl ureas channels of insect nerve axons resulting in eventual paralysis(Registered synthetic pyrethroids for use as cattle Benzylphenyl ureas inhibit the production of chitin, a ectoparasiticides in Australia include deltamethrin, cyperme- complex aminopolysaccharide and a major component of insect thrin and flumethrin ().
cuticles ). They are highly lipophilic moleculesand accumulate in body fat from where they are slowly released into the bloodstream and excreted largely unchanged.
Amidines (e.g.: chlorphenamide, clenpyrin, cymiazole and amitraz) have been used in Australia to treat lice and ticks byplunge dipping and spraying (). However,amitraz () is the major amidine currently used, primarilyto kill ticks on beef and dairy cattle. It acts at octopaminereceptor sites, resulting in hyperexcitability and death of theorganism (Amitraz is usually applied in dips,sprays and pour-on solutions.
Fig. 12. Molecular structure of amitraz.
Please cite this article as: Khan SJ, et al, Chemical contaminants in feedlot wastes: Concentrations, effects and attenuation, Environ Int (2007), doi: S.J. Khan et al. / Environment International xx (2007) xxx–xxx Fig. 13. Molecular structures of some macrocyclic lactones.
Fluazuron (is a benzylphenyl urea tick-development ). Some, such as organophosphates and carba- inhibitor used as a pour-on solution to control cattle ticks in mates, are anticholinestrases and due to their wide agricultural Australia. It acts systemically on all developmental stages of application have frequently been associated with toxicity to ticks as they feed and breed on cattle ).
wildlife ().
Furthermore, some ectoparasiticides have been associated 4.7. Environmental and public health concerns with concerns regarding human health (Oralreference doses for a number of important ectoparasiticides have Due to their chemical diversity, ectoparasiticides vary been allocated by the US EPA Integrated Risk Information considerably in their metabolism and excretion behaviour by System (IRIS) or the US EPA Health Effects Assessment cattle. Some organophosphate and carbamate compounds may Summary Tables (HEAST) as shown in be expected to be efficiently metabolised, while other classes ). Furthermore, a cancer slope factor of including the synthetic pyrethroids, benzylphenyl ureas, 2.4 × 10− 2 mg kg− 1 day− 1 has been allocated for the organopho- macrocyclic lactones and fluazuron are known to be passed sphate, tetrachlorvinphos by IRIS (Numerous into manure largely unchanged cases have been reported where farmers' health has been affected by organophosphate exposure through animal dipping and spraying of fields On the other hand, a Ectoparasiticides are, by design, highly toxic to numerous variety of in vitro and in vivo studies have indicated minimal organisms and are typically selected to target the arthropod acute toxicity of the macrocyclic lactones ivermectin and nervous system. There are significant concerns regarding the abamecton towards humans ( potential impacts of some compounds on non-target biota The vast majority of ectoparasiticides are neurotoxins, work- ing by disrupting parasite nervous systems ( Fig. 14. Molecular structure of fluazuron.
Please cite this article as: Khan SJ, et al, Chemical contaminants in feedlot wastes: Concentrations, effects and attenuation, Environ Int (2007), d S.J. Khan et al. / Environment International xx (2007) xxx–xxx reductive mechanisms or by hydrolysis or photolysis under Oral references doses (RfDo) for parasiticides suitable conditions ().
RfDo (mg kg− 1 day− 1) Synthetic pyrethroids are non-polar compounds and sorb strongly to soil (They are considered to be very easily degraded in the environment, primarily by photochemical and biochemical mechanisms Nonetheless, persistence in soils can be quite variable depending upon soil type as well as ambient conditions . Furthermore, synthetic pyrethroids contain a number of chiral centres and the consequent stereoisomers have been shown to be variably degraded by biological transformations ( Macrocyclic lactones tend to have very high organic carbon sorption coefficients and thus are highly sorbed to soils and Chemical contaminants in feedlot wastes: concentrations, effects and have limited water solubility ).
As a consequence of their characteristically tight binding tosoils, the macrocyclic lactones are highly immobile and Accordingly, they are generally very non-specific in their considered to be unlikely to pose a significant threat to activeness. Others work by the inhibition of important insect enzyme functions or by disrupting moulting processes ( While high concentrations of abamectin and doramectin have been reported in sheep manure for numerous weeks Particular concern has arisen for the unintended effects of following treatment, impacted soil concentrations were deter- ectoparasiticides on manure fauna mined to be much lower and effectively dissipated after a few ). Manure fauna play a vital role in the days, indicating that field conditions have an important role in processes of manure degradation, nutrient cycling and pasture the degradation of these agents ).
hygiene. Macrocyclic lactones, in particular, are believed to Macrocyclic lactones such as abamectin and ivermectin pose a broad threat to the survival of manure-dependant appear to be rapidly degraded upon exposure to sunlight ( organisms with reported impacts including larval mortality, These chemicals have mortality of immature adults, reduced egg production, and also been shown to be susceptible to aerobic biodegradation in delayed reproductive development soils under suitable conditions (However ivermectin appears to be quite persistent in manure under towards manure-dwelling insects has also been reported after suitable conditions ().
topical treatment of cattle with various synthetic pyrethroids( As a consequence of reduced insectactivity, animal manure degradation has been shown to have Mycotoxins are toxic chemicals produced by fungi such as been retarded in numerous studies ( mould Thousands of mycotoxins exist and infestation of cereal grains is common (). It Faecal residues or metabolites may be highly toxic to soil- is generally assumed that mycotoxins are of greatest concern in dwelling organisms developing countries where climatic conditions, and agricul- The potential contamination of surface waters by ecto- tural and storage practices, are considered conductive to fungal parasiticides may also be a significant concern since many growth and toxin production aquatic organisms are sensitive to relatively low concentrations ). However, mycotoxin contamination of forages and feeds is reported to be common on European farms ). Many mycotoxins possess acute and chronic toxicity at Exposure of some organisms to low (non lethal) concentra- low concentrations and some are mutagenic, carcinogenic or tions of ectoparasiticides is believed to have significant potential teratogenic to a wide range of organisms causing hepatic to promote the development of resistance to these agents carcinoma even in humans ().
(This may be expected to have implications for Ingestion of contaminated feed has been associated with a future feedlot management.
range of animal disease incidences internationally ). The 4.8. Environmental fate of ectoparasiticides effects of mycotoxins in dairy cattle are reported to result insymptoms that are often non-specific or similar to other diseases Organophosphate chemicals are relatively water soluble and and nutritional disorders and, as such, are often unrecognised are transported readily through soils and into groundwater or surface waters Chemical and biochem- Ochratoxin is a mycotoxin produced by several strains of ical degradation of organophosphates may occur by oxidative or Penicillium and Aspergillus spp. Ochratoxin A (is the Please cite this article as: Khan SJ, et al, Chemical contaminants in feedlot wastes: Concentrations, effects and attenuation, Environ Int (2007), doi: S.J. Khan et al. / Environment International xx (2007) xxx–xxx Fig. 15. Molecular structures of some common mycotoxins.
main toxin in this group. It is found in infected wheat, corn, and However, heavy metals are more likely to be derived from oats, and cheese and meat products of animals consuming the ingestion of contaminated soil by the animal. For example, ochratoxin-contaminated grains soil can be a significant source of Cd ingestion by Australian Although the toxin is reported to occur in foods cattle grazing on fields amended with phosphate fertilisers around the world, the main regions of concern are Europe and, containing high Cd concentrations ( for some foods, Africa ( Dairy cattle manure has exhibited contamination with Pb and Ba Zearalenone (is an estrogenic mycotoxin or via soil ingestion (). Practices such as "mycoestrogen" for which, genotoxicity is also a reported using composted municipal waste as feedlot bedding also have concern ). Occasional outbreaks of the potential to contribute to the presence of heavy metals in zearalenone mycotoxicosis in livestock around the world are contaminated manure However, this is known to cause infertility ( unlikely to be an issue for Australian beef feedlots since bedding This toxin is found almost entirely in grains, in is not used in outdoor feedlots and there are only a few indoor highly variable amounts ranging from a few ng/g up to μg/g feedlots that generally use sawdust or rice hulls as bedding.
concentrations. Deoxynivalenol (is a mycotoxin Unlike organic pollutants, metals persist indefinitely, chan- associated with reduced performance and immune function in ging only in their speciation and thus, mobility, partitioning and livestock The kinetics, biotrans- phytotoxicity In manure, most of the Cd is formation and carry over of zearalenone and deoxynivalenol, as present in an organically complexed form, while other metals well as the effects of on ruminants, have recently been reviewed may be present more commonly in a ‘free' state Biological processing (such as during anaerobic biogas A number of toxinogenic fungal species, particularly production) does not significantly alter the concentrations of producers of tremorgenic mycotoxins, have been isolated most metals in manure but may change its chemical form from traditional fermented meats. Tremorgenic mycotoxins are a group of fungal metabolites known to act on the central Soil properties such as organic matter content, mineralogy, nervous system, causing sustained tremors, convulsions, and salinity and pH can all have major effects on the mobility of death in animals ). Recent investiga- specific heavy metals (). Sudden tions indicate that many of these mycotoxins also exhibit a addition of cations such as Ca2+ to soils can result in cation- degree of genotoxicity (However, it exchange processes, leading to significant leaching of some is not known whether mycotoxin contamination of feedlot heavy metals from some soils wastes may pose a risk to humans or the environment.
In one study based on nutrient loading rates, it was estimated that land application of manures such as beef effluent, dairy slurry or composted cattle manure produced in England andWales could result in typical field concentrations of approxi- The accumulation of heavy metals such as Cd, Pb and Hg in mately 0.002 kg/ha Cd and around 0.04 kg/ha Pb ( soils is a potential concern for Australian agriculture due to the capacity for these elements to adversely affect food quality, cropgrowth and environmental health ).
Livestock manure is a possible source of low concentrations ofsome heavy metals. For example, Pb concentrations of 1.6– Dioxins are halogenated organic compounds derived from 8.6 mg/kg and Cd concentrations of 0.1–0.7 have been reported industrial processes. Many of this group of 210 chemicals are in cattle manure in some countries ().
persistent and have become ubiquitous in the environment Some metals in livestock excreta may be derived from the animal diet, either intentionally or as a result of contamination.
). Dioxins include chlorinated dibenzo-p-dioxins For example, some lighter metallic elements (such as As, Co, (CDDs), chlorinated dibenzofurans (CDFs) and certain poly- Cu, Mn, Se and Zn) may be added to livestock feeds as essential chlorinated biphenyls (PCBs). The term ‘dioxin' is commonly nutrients or to improve feed conversion efficiencies used to refer to the most studied and one of the most toxic Please cite this article as: Khan SJ, et al, Chemical contaminants in feedlot wastes: Concentrations, effects and attenuation, Environ Int (2007), d S.J. Khan et al. / Environment International xx (2007) xxx–xxx Fig. 16. Molecular structures of some dioxins.
dioxins, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) organisms and genes. If poorly managed, manure and effluent The US EPA has assigned an oral cancer slope containing residues of these chemicals may have implications factor of 1.5 × 105 mg kg− 1 day− 1 for TCDD for public health in Australia. Management practices involving Molecular structures of some important dioxins are presented in virginiamycin, tylosin and oxytetracycline should be monitored.
Ectoparasiticides applied for the control of ticks, buffalo If animals are exposed, dioxins accumulate in fat tissue and flies, lice and mites are toxic to a wide range of insect species this is among the most predominant exposure routes for most and may be hazardous to important manure-borne insects such as dung beetles. Ectoparasiticides of greatest (potential) ). Livestock are exposed to dioxins by the deposition significance include synthetic pyrethroids, fluazuron, macro- of airborne dioxins onto plant and soil surfaces, and subsequent cyclic lactones and amitraz.
ingestion of this contaminated vegetation and soil Mycotoxins, heavy metals and dioxins were also considered ). Consumption of vegetation or roughages is considered in this review. These include numerous toxic compounds, for the most important exposure factor (). Consump- which the potential for deleterious implications to animal wel- tion of grass, hay, silage or grain can explain over 90% of dioxin fare and public health is not understood. However, there is less concentrations in cattle ). Lot feeding is available evidence to suggest that they ought to be prioritised thought to significantly reduce dioxin concentrations in beef for research in feedlot manure and effluent.
since the cattle are fed a predominantly grain based diet for The vast majority of the available information has been several months before slaughter (). Grains obtained from international research and may not be represen- contain lower concentrations of dioxins since the seed is not tative of conditions in Australia. Very few of the individual directly exposed to the air while growing. Livestock may also chemical contaminants have been thoroughly investigated in be exposed to dioxins if pentachlorophenol (PCP) treated wood Australian feedlot manure and effluent. The identification of is used on production facilities (). Feedlot best management practices for Australian feedlots will therefore waste production is not known to increase nor concentrate require a comprehensive survey of the presence and fate of dioxins in the environment.
representative chemicals combined with investigations of theirpersistence and transport when manure and effluent are subjected to various management practices.
While a large number of natural and synthetic chemicals are present in feedlot cattle manure and effluent, if any animalwelfare, environmental or public health risks exist, they are The authors are grateful for funding for this research provided expected to be associated with trace concentrations of some key by Meat and Livestock Australia (MLA) and the matching funds biologically significant compounds.
provided by the Australian Government via MLA. Furthermore, Steroidal hormones (both natural and synthetic) have the the authors appreciate the helpful comments provided by Prof.
potential to be significant environmental pollutants that may David Sedlak and Dr. Pat Blackall.
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