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Biomedical subjects

R L Metcalf

Publications and source records attributed to R L Metcalf.

At least 37 records · Page 2Linked to original sources
PubMed1980

Ecotoxicology of phenylphosphonothioates.

The phenylphosphonothioate insecticides EPN and leptophos, and several analogs, were evaluated with respect to their delayed neurotoxic effects in hens and their environmental behavior in a terrestrial-aquatic model ecosystem. Acute toxicity to insects was highly correlated with sigma sigma of the substituted phenyl group (regression coefficient r = -0.91) while acute toxicity to mammals was slightly less well correlated (regression coefficient r = -0.71), and neurotoxicity was poorly correlated with sigma sigma (regression coefficient r = -0.35). Both EPN and leptophos were markedly more persistent and bioaccumulative in the model ecosystem than parathion. Desbromoleptophos, a contaminant and metabolite of leptophos, was seen to be a highly stable and persistent terminal residue of leptophos.

Animals↗
PubMed1979

Evolution of olfactory receptor in oriental fruit fly Dacus dorsalis.

Male oriental fruit flies (Dacus dorsalis) from colonies in Taiwan and Hawaii were evaluated for limit of response to various analogues of methyl eugenol. The results are interpreted in terms of the geometry and allosteric requirements of the antennal receptor that triggers the characteristic methyl eugenol reflex. This receptor has evolved for complementarity to all portions of the methyl eugenol molecule and responds only to ortho-substituted benzenes with adjacent oxygen atoms or isoelectronic equivalents. Substantial differences in responses of Taiwan and Hawaiian D. dorsalis suggest that perceptible evolution of the receptor protein has occurred during the past 50 years. A plausible scheme for the coevolution of dacini flies with plants containing phenylpropionoid essential oils is outlined.

Journal Article↗
PubMed1977

The Environmental fate of three carcinogens: benzo-(alpha)-pyrene, benzidine, and vinyl chloride evaluated in laboratory model ecosystems.

Radiolabeled benzo-((alpha)-pyrene, benzidine, and vinyl chloride were evaluated in laboratory model ecosystems for environmental fate, degradation pathways, bioconcentration, and food chain accumulation. The comparative effects of microsomal detoxications were evaluated using the inhibitor piperonyl butoxide. The accumulation and bioconcentration of benzo-(alpha)-pyrene and benzidine were closely correlated with their octanol/water partition coefficients and water solubility. Benzo-(alpha)-pyrene as predicted by these parameters was bioaccumulated to substantial levels in several organisms. Vinyl chloride was not accumulated because of its high volatility.

Animals↗
PubMed1977

Tissue distribution of PCB components in swine and sheep fed three different rations containing Aroclors 1242 and 1254.

Growing swine and sheep were fed three dietary variations containing 20 ppm of Aroclors 1242 or 1254 for 13 to 15 weeks. Generally, Aroclor 1254 residues were higher; higher 1242 residues in swine blood, spleen, and ovary are attributed to persistent major components of this Aroclors. Some minor differences in total PCB were observed with varying diets, but peak composition did not vary. Some lower chlorinated components maintained higher levels in the blood relative to other components; other components were selectively accumulated in tissues such as fat and muscle. Blood and fat residues in sheep declined during the last weeks of feeding. Microsomal oxidase levels were elevated in response to PCB and diet in both species, but the response was greater in sheep. Sheep liver microsomes were capable of metabolizing pure analogs and components of Aroclor 1242. Major differences in Aroclor profiles can be demonstrated between swine and sheep residues and total residues can be estimated by measuring selected peaks in blood and backfat. The peaks which provide the most reliable estimate of total PCB residue vary with species and Aroclor.

Animal Feed↗
PubMed1976

Model ecosystem evaluation of the environmental impacts of the veterinary drugs phenothiazine, sulfamethazine, clopidol, and diethylstilbestrol.

Four veterinary drugs of dissimilar chemical structures were evaluated for environmental stability and penchant for bioaccumulation. The techniques used were (1) a model aquatic ecosystem (3 days) and (2) a model feedlot ecosystem (33 days) in which the drugs were introduced via the excreta of chicks or mice. The model feedlot ecosystem was supported by metabolism cage studies to determine the amount and the form of the drug excreted by the chicks or mice. Considerable quantities of all the drugs were excreted intact or as environmentally short-lived conjugates. Diethylstilbestrol (DES) and Clopidol were the most persistent molecules, but only DES bioaccumulated to any appreciable degree. Phenothiazine was very biodegradable; sulfamethazine was relatively biodegradable and only accumulated in the organisms to very low levels. Data from the aquatic model ecosystem demonstrated a good correlation between the partition coefficients of the drugs and their accumulation in the fish.

Animals↗
PubMed1976

Effects of feeding polychlorinated biphenyls to broiler cockerels in three dietary regimes.

Polychlorinated biphenyls (Aroclor 1242 and 1254) were fed at 20 p.p.m. to hybrid broiler cockerels between one and nine weeks of age in three dietary variations. The Aroclors did not affect growth or feed efficiency and no consistent histopathological lesions could be attributed to them. There was a low incidence of hydropericardium in birds receiving Aroclor 1254. Fatty liver was observed in some birds receiving Aroclor 1242 and a single bird receiving this PCB exhibited liver necrosis. Moderate increases in liver weight and mild decreases in the relative weight of the spleen were attributable to PCB.

Adipose Tissue↗
PubMed1976

Laboratory model ecosystem evaluation of the chemical and biological behavior of radiolabeled micropollutants.

A standardized laboratory model ecosystem has been used to evaluate the comparative behavior of radiolabeled micropollutants including organochlorine, organophosphorus, carbamate, and hormone-mimic insecticides; herbicides; important industrial organic compounds including phthalate esters and PCB's; and specific pollutants such as TCBD and hexachlorobenzene. The compounds have been studies for ecological effects over a terrestrial-aquatic interface and through several food chains, especially with regard to the development of quantitative information on ecological magnification and biodegradability index. The pathways of chemical degradation in the various organisms have been evaluated and the ecological effects of degradation products investigated. Illustrations are given of the use of the model ecosystem technology for screening new candidate pesticides for effects on environmental quality; for evaluating the hazards of environmental pollution by industrial waste effluents; and for fundamental studies of the principles fo biodegradability of organic chemicals in a variety of organisms.

Animals↗
PubMed1975

Laboratory model ecosystem studies of the degradation and fate of radiolabeled tri-, tetra-, and pentachlorobiphenyl compared with DDE.

Radiolabeled tri-, tetra-, and pentachlorobiphenyls (PCB) and DDE were studied in a laboratory model ecosystem for degradation pathways, and biomagnification in alga, snail, mosquito, and fish. Trichlorobiphenyl was degraded in all the organisms of the model ecosystem much more rapidly than tetrachloro- and pentachlorobiphenyl. Pentachlorobiphenyl was approximately as persistent as DDE. There was a linear relationship between lipid/water partition and ecological magnification and between water solubility and ecological magnification. No evidence of conversion of DDE to PCB was detected.

Animals↗
PubMed1975

Plasticizers in the environment: the fate of di-N-octyl phthalate (DOP) in two model ecosystems and uptake and metabolism of DOP by aquatic organisms.

The fate of the plasticizer, di-n-octyl phthalate (DOP) has been examined in 33-day terrestrial-aquatic and three-day aquatic model ecosystems. The five organisms of the two systems contained residues of DOP, demonstrating the propensity of this lipoid soluble organic molecule to be concentrated from the water. The residues in the organisms in the three-day system were higher than in the 33-day system with the exception of the fish, indicating perhaps, that DOP can undergo some degradation before the fish is placed in the system on the 30th day. A half-life of five days for DOP disappearance from the water was calculated from water samples taken periodically. Further, effects of mixed function oxidase and esterase inhibitors were investigated on the metabolism of DOP by various selected organisms and tissues of the two ecosystems.

Animals↗
PubMed1975

Attraction of the oriental fruit fly, Dacus dorsalis, to methyl eugenol and related olfactory stimulants.

The attraction of male oriental fruit flies to methyl eugenol and 34 analogues was investigated quantitatively using the characteristic feeding response. Methyl eugenol was the most active compound studied, with a feeding response to 0.01 mug, but saturation of the allyl side chain or replacement of allyl by allyloxy produced compounds almost as effective. Replacement of the methoxy groups by methylenedioxy, methyl, or chloro groups abolished all response. The ring geometry of the methoxy groups was critical, with orthodimethoxy most active and meta-dimethoxy inactive. Replacement of methoxy with hydroxy, methylthio, or amino groups did not abolish the response. The failure of the oriental fruit fly to respond to the methyl and chloro isosteres of methyl eugenol was contrasted with the response of a human odor panel which perceived these compounds as having weak floral odors.

Animals↗
PubMed1975

Environmental fate and biodegradability of benzene derivatives as studied in a model aquatic ecosystem.

A model aquatic ecosystem is devised for studying relatively volatile organic compounds and simulating direct discharge of chemical wastes into aquatic ecosystems. Six simple benzene derivatives (aniline, anisole, benzoic acid, chlorobenzene, nitrobenzene, and phthalic anhydride) and other important specialty chemicals: hexachlorobenzene, pentachlorophenol, 2,6-diethylaniline, and 3,5,6-trichloro-2-pyridinol were also chosen for study of environmental behavior and fate in the model aquatic ecosystem. Quantitative relationships of the intrinsic molecular properties of the environmental micropollutants with biological responses are established, e.g., water solubility, partition coefficient, pi constant, sigma constant, ecological magnification, biodegradability index, and comparative detoxication mechanisms, respectively. Water solubility, pi constant, and sigma constant are the most significant factors and control the biological responses of the food chain members. Water solubility and pi constant control the degree of bioaccumulation, and sigma constant limits the metabolism of the xenobiotics via microsomal detoxication enzymes. These highly significant correlations should be useful for predicting environmental fate of organic chemicals.

Animals↗
PubMed1975

Effect of a polychlorinated biphenyl mixture on swine reproduction and tissue residues.

A commercial polychlorinated biphenyl (PCB) mixture containing 42% chlorine by weight was fed at the dose level of 20 ppm to 3rd-litter sows throughout gestation and nursing. Treated sows differed significantly (0.05% level) from control sows in the number of live pigs they farrowed. Treated sows also had more mummified fetuses. Performance of live-born pigs was not affected by feeding PCB to the sows during nursing. Pathologic changes in the sows included hypertrophy of liver and erosion of stomach. Two treated sows, 1 of which did not conceive, had signs of extensive chronic septicemia. Slight atrophy of spleen and thyroid gland was observed in pigs from treated sows. Blood and tissue residues of PCB were less than 0.5 ppm in both sows and pigs, but the relative amounts of PCB components varied among sows and pigs, as well as among tissues. Fat concentrations of total PCB in sows ranged from 4 to 20 ppm and those of component residues varied from 0 to 60 ppm.

Adipose Tissue↗