ROSCOE H. CARTER, H. V. CLABORN, G. T. WOODARD, AND RAY E. ELY.
ANIMAL products intended for food may become contaminated with pesticide chemicals in a number of ways.
DDT and other chlorinated materials are used to control insects on such forage crops as alfalfa, clover, and grass and on peas, beans, corn, and similar crops, of which a part is used as animal feed. Some pest killers, used at recommended dosages and in accordance with good agricultural practices, leave enough residue on forage crops so that some is stored in the animal or excreted in milk if the forage is fed to livestock. Pastures or grain that have had pesticide treatments also may be a source of contamination of animal products.
DDT the common name for the commercial product dichloro-diphenyl-trichloroethane has been found in milk samples from cows stabled in barns sprayed with it, even though the cows were outside when the spraying was done. Enough DDT was picked up from feed troughs, water fountains, and other sources to cause excretion in the milk. Some other pesticides, sprayed directly on the animals, have been excreted in the milk.
Some of the pesticides used in spraying and dipping cattle, sheep, goats, and swine are stored in the animals' bodies. Some materials have caused serious disturbances and even fatalities. Others have little apparent effect. Most of the pesticides used for insect control are soluble in the fat and are stored in the fatty tissues of the animal. Three to four months are required before some of the chemicals are entirely eliminated.
Public Law 518 provides for the establishment of tolerances for pesticide chemicals in or on raw agricultural commodities. The term "pesticide chemical" means any substance which alone, in chemical combination, or in formulation with one or more other substances is an economic poison within the meaning of the Federal Insecticide, Fungicide, and Rodenticide Act. Raw agricultural commodities include fresh fruits and vegetables, grains, nuts, eggs, raw milk, meats, and similar agricultural produce. It does not include foods that have been processed, fabricated, or manufactured by cooking, freezing, dehydrating, or milling.
Detecting and estimating pesticide residues in the biological materials by chemical analysis are complicated procedures. General methods, such as the determination of the organic chlorine content, are used sometimes to determine residues. Specific and spectrophotometric methods are available for certain pesticide chemicals.
The procedures generally require an extraction of the biological product with an organic solvent, such as Skelly-solve B or benzene. These extracts contain fat, glycerides, and other constituents. Because some pesticide materials are stable toward acids and some are stable toward alkali treatments, procedures using those reagents have been developed to break up the glycerides without decomposition of the pesticide. Chromatographic procedures have also been developed to aid in the separation of the pesticide residue from fats, waxes, coloring matter, and such materials.
Methods of analysis capable of detecting minute amounts have been developed so that it is possible to determine residues considerably less than 0.1 part per million (p. p. m.) for some pesticides.
Bioassay procedures capable of determining residues less than 0.1 p. p.m. of some materials have also been developed. They are useful in detecting toxic residues of metabolic products that are not detectable by the specific method for the original toxicant.
EXPERIMENTS in which dairy cows were fed forage that had been treated with insecticides during the growing season and other tests in which the cows were given oil solutions of the insecticides in capsules are briefly described. The insecticides included DDT, BHC (the common name for the technical product benzene hexachloride), lindane, methoxychlor, chlordane, toxaphane, aldrin, dieldrin, heptachlor, and endrin.
Growing alfalfa was sprayed with the insecticides at dosages recommended for insect control. After an interval of 3 to 10 days the crop was cut, field cured, baled, and stored in barns 6 to 8 months until used as feed. Normal, healthy milking cows, generally four to each test, were fed the hay with a supplemental grain ration. The amounts consumed daily and the milk production were recorded.
The tests were generally continued 40 to 90 days, or until it was thought that equilibrium had been established between intake and excretion of the insecticide. After this phase, the cows were given oil solutions of the insecticides in capsules at varying levels of intake considerably above the levels of intake as residue. Milk samples were taken every tenth day for chemical analysis. Since the chlorinated insecticides are fat-soluble and are present only in the butterfat portion of milk, butterfat determinations were made on all samples and the results calculated and adjusted to a uniform butterfat (FCM) content of 4 percent. Composite samples of the hay representing every 10 days of feeding were analyzed for residue. Milk samples were collected in most instances for some time after insecticide intake had been discontinued to obtain information on the persistence of the materials in the animals.
Alfalfa hay that had been treated with 2.4 pounds of DDT on an acre resulted in milk production containing a maximum of 10.1 p. p. m. of DDT; 0.6 pounds of DDT resulted in 0.9 p. p. m. of DDT in the milk.
A comparative study of the effects of dosage level and various methods of administration on the concentration of DDT in milk indicated that increasing intakes of DDT as a residue on hay or in oil solution gave progressive increases in the DDT concentration in the milk in a straight-line relation. This straight line had a greater slope for intake as residue over intake in oil solution.
DDT in oil solution and alfalfa containing various amounts of DDT residue was fed to dairy calves. DDT intake varied from 0.07 to 2.9 milligrams per kilogram of body weight, or 2.2 to 106 p. p. m. of the dry matter consumed. The storage of DDT in tile body and kidney fat ranged from 2 to 345 P. p. m., and the concentration was proportional to the DDT intake.
Residues of methoxychlor on alfalfa ranging from 16 to 109 p. p. m. did not result in detectable amounts in the milk. Crystalline methoxychlor administered orally as a 10-percent solution in soybean oil in daily dosages equivalent to 2,000 P. p. m. of the feed consumed, or approximately 19 mg. per kg. of body weight, resulted in detectable amounts of methoxychlor in the milk.
Four cows were fed hay containing approximately 0.4 P. p. m. of lindane for 100 days and four cows received hay containing approximately 2.6 p. p. m. of lindane for 60 days. The concentrations of lindane in the milk of these cows ranged from 0.13 to 0.27 P. P. m.
Two lots of alfalfa hay, which had been treated with toxaphene emulsion at the rate of 1.5 pounds per acre, were fed to two sets of three cows each for 150 and 100 days. The average insecticide residue on the two lots of hay was 81.8 and 31.8 P. p. m., equivalent to an average daily intake of 1.4 mg. and 0.5 mg. per kg. of body weight, respectively. The average toxaphene con-tent of the milk from the two sets of cows was 0.5 and 0.1 p. P. m., respectively. Increased dosages of toxaphene in soybean oil solution resulted in increased excretion in the milk.
Two lots of alfalfa hay, which had been treated with chlordane emulsion at the rates of 1 and 2 pounds per acre, were fed to two sets of three cows each for 150 and 100 days, respectively. The average chlordane residue on the two lots of hay was 20.4 and 20.8 p. p. m., equivalent to an average daily intake of 0.39 and 0.37 mg. per kg. of body weight, respectively. The average chlordane content of the milk from the two sets of cows was 0.2 and 0 p. p. m., respectively. Increased dosages of chlordane in soybean oil solution resulted in increased excretion in the milk.
Alfalfa hay that had been sprayed with aldrin at the rate of 3.9 ounces per acre was fed to four milk cows for 48 days. The average aldrin content of the hay was 6.6 to 7.1 p. p. m., equivalent to an average daily aldrin intake of 0.10 to 0.15 mg. per kg. of body weight. No aldrin was detected in the milk samples from the hay feeding tests or from increased dosages in soybean oil solution below a daily intake of 0.8 mg. per kg. of body weight.
Two fields of alfalfa were sprayed with dieldrin at the rate of 3.5 ounces and 7.0 ounces per acre and the hay was fed to normal milking cows for 54 and 52 days, respectively. The average dieldrin content of the milk from the cows on the two batches of hay was 0.8 P. P. m. and 1.8 p. p. m., respectively. A daily intake of 50 to 1,000 mg. of dieldrin in soybean oil solution daily for 40 to 50 days resulted in an average dieldrin content in the milk ranging from 1.7 to 13.1 P. P. m.
Alfalfa hay that had been sprayed with 3.8 ounces and 8 ounces of heptachlor contained average residues of 1.2 and 5 P. p. m., respectively. The first lot of hay was fed to four cows for 54 days; following that, the second lot was fed to the same cows for 52 days. The average daily heptachlor intake was 0.03 mg. per kg. of body weight when feeding the hay sprayed with 3.8 ounces per acre; from 0.10 to 0.13 mg. per kg. of body weight from the 8- ounce treatment. After the hay feeding tests, the cows were given increased dosages of heptachlor in a soybean oil solution. No heptachlor was detected in the milk of the cows fed the treated hay or given the oil solutions.
A metabolic product, heptachlorepoxide, was detected in the milk from cows receiving heptachlor at dosages of more than 1.3 mg. per kg. of body weight.
Two lots of alfalfa hay, which had been treated with 2.7 ounces and 6.6 ounces of endrin per acre, were fed to two sets of four cows each for 48 and 44 days, respectively. The average endrin content of the milk was approximately 0.1 p. p. m.-which is below the sensitivity of the method of analysis. When a soybean oil solution of endrin was fed by capsule, an intake of 500 mg., or approximately 1.4 mg. per kg. of body weight, was required before definite indications of excretion in the milk were noted.
Milk samples from cows grazed in pastures that had been treated with DDT and dieldrin contained small amounts of these insecticides.
Samples of fat from swine that had grazed in pastures treated with insecticides contained small amounts of the insecticide. When meat containing DDT residue was fed to pigs, the DDT accumulated in the fat of the pigs.
Dairy cows were sprayed with 0.5-percent concentrations of DDT, methoxychlor, dieldrin, Dilan, Per-thane, and malathion to determine the amounts of insecticides excreted in milk and the duration of milk contamination caused by spraying. This concentration for all the insecticides tested (except dieldrin) is used against the hornfly.