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Chemical Residues in Animal Fibers |  |
| From an economic standpoint, the major animal fibers are wool and mohair. Although the primary focus of this section is pesticide residues in wool, many of the concepts discussed apply equally to mohair. |
| Flies, lice, keds, and mites adversely affect wool production and have animal welfare implications for the sheep industry. Ectoparasiticides have been the mainstay for managing infestations of these parasites in sheep flocks for many years. Two important manifestations of chemical application to sheep are the emergence of strains of parasites resistant to chemicals and the contamination of wool with pesticide residues. A particular concern is the application of pesticides to
resistant strains of flies or lice, which increases the likelihood of treatment failure and the need to re-treat later in the wool-growing season. Higher residues in both the wool on treated sheep and in harvested fleeces are possible consequences. Nonetheless, there are some situations in which late-season applications are justified on animal health or economic grounds. In view of community health and safety expectations and changing environmental standards, wool producers are
seeking methods of managing external parasites on sheep that rely less on chemicals. Integrated pest management (IPM) approaches have been adopted to achieve this objective. IPM may involve various husbandry options such as shearing, mulesing, and crutching to combat flystrike; genetic improvements such as selecting against animals susceptible to fleece rot; biologic and environmental controls such as the use of fly traps; and the selective use of chemicals. |
| Pesticide residues in wool are influenced by many factors, including the chemical and formulation used, the method of application, the rate and timing of the chemical application, and the length of wool at the time of application. (See also
dosage forms and delivery systems,
Dosage Forms and Delivery Systems: Overview.) The product types and chemical groups commonly used in the management of flies and lice on sheep include off-shears backline or spray-on products containing insect growth regulators (IGR), organophosphate pesticides (OP), and synthetic pyrethroid pesticides; short-wool plunge or shower dips that use IGR, magnesium fluorosilicate, OP, and spinosad; long-wool backline or spray-on products containing
IGR; and long-wool jetting products containing IGR, macrocyclic lactones, OP, or spinosad. Wool producers must ensure that pesticides are applied in accordance with the label directions. Unacceptably high residues remain in wool to the next shearing when some chemicals are applied to sheep with >6 wk wool growth. Repeat applications of pesticides may also result in higher wool residues at the next shearing, and backline products commonly leave higher residues at the site of
application. Wool producers must be in compliance with stated rehandling periods and wool withholding periods. The rehandling period is the time that must elapse before treated sheep are shorn. It takes precedence over all other applicable standards and ensures the wool meets occupational health and safety standards to protect shearers and other wool handlers. The wool-harvesting interval (or wool withholding period) is the time that must elapse before treated sheep are shorn. It
ensures that harvested wool meets the prescribed environmental residue limits. When determining the wool-harvesting interval, the percentage of the national flock likely to be treated with the product is considered. |
| Pesticide residues in wool have possible implications for public health, occupational health and safety, and environmental safety. Processed wool used in the manufacture of garments is unlikely to pose a human health hazard because any residual pesticide is removed during the scouring process. Of greater concern is residual pesticide that remains associated with the wax component of lanolin, which requires expensive refining techniques to remove. Additional assurance as to the
quality of low pesticide grades of lanolin stems from regulatory standards that apply to the lanolin used in pharmaceuticals and cosmetics for use on human skin and to lanolin used as a nipple emollient by nursing mothers. |
| Another concern relates to possible occupational health and safety implications. Residual pesticide in wool wax poses an occupational hazard to shearers and other wool handlers through dermal absorption. Nervous disorders and dermal irritation have allegedly occurred in shearers after shearing sheep treated with certain OP and synthetic pyrethroid (SP) pesticides, respectively. Long-wool backline applications of SP pesticides can result in residue concentrations at the tips of
backline staples high enough to cause dermal erythema in shearers and wool handlers. To protect workers from unacceptable exposure to chemical residues in wool, it is important that rehandling periods for products are observed. |
| A third major issue is the environmental impact of pesticides that remain in scour effluent. Environmental legislation relating to the discharge of pesticides into aquatic ecosystems has been enacted to protect the environment. For some pesticides, environmental quality standards have been established and represent concentrations that will not harm the most sensitive organisms in aquatic ecosystems. The EU has also included textile products as part of its eco-label requirements,
which labels garments that have been manufactured from low-residue wools and have been processed in accordance with stringent environmental regulations. |
| The depletion of pesticide residues in wool has been mathematically modeled to predict the likely consequences of treatments at different times during the wool-growing season and to determine how late a pesticide may be applied to sheep without creating excessive residues at shearing. Modeling is a useful tool for determining wool-harvesting intervals and for assisting wool growers when choosing a pesticide and method of application. Finally, test kits are available for
establishing the status of pesticide residues in wool. |
