Milk, maximum residue limits

Sulfonylurea herbicides are generally applied to crops as an early post-emergent herbicide. Crops that are tolerant to these herbicides quickly metabolize them to innocuous compounds. At maturity, residues of the parent compound in food and feed commodities are nondetectable. Metabolites are not considered to be of concern, and their levels are usually nondetectable also. For this reason, the residue definition only includes the parent compound. Tolerances [or maximum residue limits (MRLs)] are based on the LOQ of the method submitted for enforcement purposes and usually range from 0.01 to 0.05 mg kg (ppm) for food items and up to O.lmgkg" for feed items. There is no practical need for residue methods for animal tissues or animal-derived products such as milk, meat, and eggs. Sulfonylurea herbicides are not found in animal feed items, as mentioned above. Furthermore, sulfonylurea herbicides intentionally dosed to rats and goats are mostly excreted in the urine and feces, and the traces that are absorbed are rapidly metabolized to nontoxic compounds. For this reason, no descriptions of methods for animal-derived matrices are given here. 

Milk from lactating cows intramuscularly injected with radiolabeled ceftiofur was found to contain 103 and 50 ppb of total residues at 12 and 24 h, respectively, postdosing. No parent ceftiofur could be detected in milk (85). Therefore, use of ceftiofur at the approved dosage and route is not expected to result in ceftiofiir-related residues exceeding maximum residue limit (MRL) at any time postdosing, and no milk withdrawal periods need to be assigned for ceftiofur. In addition, ceftiofur residues are not hazardous to industrial cheese and yogurt starter cultures. 

Under the pressure of an increasing number of drugs with fixed tolerance or maximum residue limits (MRLs), demands on methods to detect antimicrobial residues in edible animal products have changed markedly during recent decades (1). To satisfy these demands and prevent contaminated products from entering the food chain, many microbiological tests with sufficient detection sensitivity of as many analytes as possible in animal tissues, milk, eggs, honey, and fish have been developed or modified. 

Many factors influence the residue profiles of antibiotics in animal-derived edible tissues (meat and offal) and products (milk and eggs), and in fish and honey. Among these factors are the approved uses, which vary markedly between antibiotic classes and to a lesser degree within classes. For instance, in some countries, residues of quinolones in animal tissues, milk, honey, shrimp, and fish are legally permitted (maximum residue limits [MRLs] have been established). By comparison, the approved uses of the macrolides are confined to the treatment of respiratory disease and for growth promotion (in some countries) in meat-producing animals (excluding fish), and to the treatment of American foulbrood disease in honeybees. As a consequence, residues of macrolides... 

Stolker et al. " described an analytical method based on TFC-LC-MS/MS for the direct analysis of 11 veterinary drugs (belonging to seven different classes) in milk. The method was applied to a series of raw milk samples, and the analysis was carried out for albendazole, difloxacin, tetracycline, oxytetracycline, phenylbutazone, salinomycin-Na, spiramycin, and sulfamethazine in milk samples with various fat contents. Even without internal standards, results proved to be linear and quantitative in the concentration range of 50-500 (xg/1, as well as repeatable (RSD<14% sulfamethazine and difloxacin <20%). The limits of detection were between 0.1 and 5.2 xg/l, far below the maximum residue limits for milk set by the EU. While matrix effects, namely, ion suppression or enhancement, were observed for all the analytes, the method proved to be useful for screening purposes because of its detection limits, linearity, and repeatability. A set of blank and fortified raw milk samples was analyzed and no false-positive or falsenegative results were obtained. 

With the extensive use of drugs in animal production, violative residues of the parent drugs and/or metabolites have a high potential to be present in meat, milk, eggs, and honey. The level of residues and the individual drugs they originate from determine the public health significance of such an adulteration of the food supply. The European Union (EU) and the Joint FAO/WHO Expert Committee on Food Additives (JECFA) have established maximum residue limits (MRLs) for several quinolones. 

Mirex was detected (mean detection limit 3 pg/g [ppt])in 62% of 412 breast milk samples collected from women in all Canadian provinces (Mes et al. 1993). The mean, median, and maximum mirex concentrations detected in whole milk were 0.14, 0.08, and 6.56 ng/g (ppb), respectively, and for milk fat were 4.2, 2.3, and 124.5 ng/g, respectively. In previous studies, mirex residues were not detected. None of the 1,436 human milk samples collected in the United States in the late 1970s as part of the National Human Milk Study contained identifiable levels of mirex (Savage et al. 1981). A similar national study of nursing mothers in Canada (Mes et al. 1986) also failed to detect mirex in any human milk samples. The high rate of detection in the Mes et al. (1993) study was a result of improved analytical procedures and lower limits of detection. 

Finally, even if most of the pesticides worldwide are used in fruit and vegetable crops, data on pesticide residues in animal products are also essential, taking into account that livestock can be easily exposed to pesticides directly or through residues in their feed. For instance, the 2009 European Union Report revealed the presence of 34 different pesticides in animal products [115]. Garcfa de Llasera et al. [128] revealed the presence of chlofenvinphos and chlorpyrifos in liver samples, whereas a-endosnlfan, endosulfan sulfate, and dichloran have been reported in pork and lamb samples (<10 pg/kg) [129]. Bolafios et al. [130] studied the occurrence of organochlorine pesticides and polychlorinated biphenyls in chicken eggs. Benzene hexachloride and 28 polychlorinated biphenyl were detected in only one of the 30 samples at concentrations of 15 and 10 ng/g, respectively. However, five samples also contained traces of OC and PCB residues, even if at concentration levels below the limit of quantification. Einally, a-endosulfan and P-endosulfan were found in commercial milk-based infant formulas at concentration levels from 1.18 to 5.03 pg/kg [35]. The same study also showed the presence of fenitrothion, chlorpyrifos ethyl, and bifenthrin at maximum concentrations of 0.23,1.30, and 0.68 pg/kg, respectively. 

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