Uptake of organic material by aquatic invertebrates. VI. Role of epiflora in apparent uptake of glycine by marine crustaceans

Soft-bodied marine invertebrates from most invertebrate phyla are capable of taking up amino acids from seawater. Marine crustaceans were originally reported not to accumulate amino acids. Artemia salina, Limnoria tripunctata, Tigriopus californicus, and Corophium acherusicum were examined for their ability to accumulate C¹⁴-labelled glycine from dilute solution in seawater. In initial experiments with Artemia and Limnoria the organisms were found to become very radioactive. When animals were preincubated in streptomycin or in a mixture of antibiotics, uptake of the C¹⁴-glycine was drastically reduced. Microorganisms associated with the arthropods and in the culture media were found capable of accumulating C¹⁴-labelled glycine. Efforts to demonstrate removal of amino acids from seawater by colorimeteric determination of material remaining in the medium were unsuccessful. The microorganisms responsible for the uptake are apparently associated with the exoskeleton of the organisms and not the gut. There is probably no substantial contribution to the nutrition of these crustaceans by the epiflora. Preincubation in the antibiotic mixture depressed the uptake of C¹⁴-glucose and C¹⁴-acetate by about an order of magnitude. It is concluded that there is no evidence for accumulation or assimilation of small organic compounds by the small crustaceans examined.     

Culling recolonizing mesopredators increases livestock losses: Evidence from the South African Karoo

Populations of adaptable mesopredators are expanding globally where passive rewilding and natural recolonization are taking place, increasing the risk of conflict with remaining livestock farmers. We analysed data from two social surveys of farmers in the Karoo, South Africa, where black-backed jackals (Canis mesomelas) and caracals (Caracal caracal) have re-emerged as a threat to sheep farms in the context of falling agricultural employment and the expansion of natural areas. We show that irrespective of measurement approach, lethal control of mesopredators in this fragmented socio-economic landscape was associated with increased livestock losses the following year. Terrain ruggedness was positively, and number of farmworkers negatively, associated with livestock losses. Our study provides further evidence that lethal control of mesopredators in this context is probably counter-productive and supports calls to develop, share and financially support a range of non-lethal methods to protect livestock, especially where natural recolonization of mesopredators is occurring. A graphical abstract can be found in Electronic supplementary material.

     

The Production of Pure Peroxyacyl Nitrates

The peroxyacyl nitrates, a series of eye-irritating plant toxicants, are synthesized by gasphase reactions at low concentrations. They are purified by preparative-scale gas chromatography. The preparation and purification of the first member of the series by photolysis of ethyl nitrite vapor (ca 400 ppm) in oxygen is described in some detail. The entire procedure is designed to minimize factors which might cause decomposition of this extremely unstable product. Pure PAN is stored as a vapor diluted with dry nitrogen at about 100 psig and 40°F. Such mixtures (about 1000 ppm) can be analyzed by infrared spectrophotometry using a 10 cm cell. The product is used in studies of its toxicity toward biological materials, in instrument calibration, and for studies of air pollution chemistry.     

The simultaneous modelling of metal ion and humic substance transport in column experiments

Pulsed column experiments using Co, fulvic acid and porous sediment packing, along with up/down-flooding experiments using Eu, humic acid and intact sandstone blocks have been performed. The elution of metal and humic and their distribution along the sandstone columns have been measured. A mixed equilibrium and kinetic coupled chemical transport model has been used to simulate the results. In both cases, one exchangeable and one non-exchangeable component have been used to simulate the interaction of metal and humic substance. For the pulsed experiments, a simple equilibrium approach was used to model humic sorption, while a two component, kinetic model was required for the sandstone columns.     

Distribution of Light Hydrocarbons in Ambient Air

The diversity of hydrocarbons which are present in ambient polluted air provide a potentially rich source of information concerning the nature of this type of pollution. Measurements of the relative amounts of various hydrocarbons can be correlated with the various possible sources. Since hydrocarbon reactivities vary widely it is also possible to estimate the extent to which various individual hydrocarbons have reacted. Except for samples taken deliberately near sources of hydrocarbon pollution these air samples invariably resemble auto exhaust with an addition of natural gas and of C₃–C₅ paraffins which resemble gasoline vapor. Samples taken in industrial areas and near the smoke plume from a brush fire showed distinctive differences in composition. During the smog season in the fall of 1968 good data were obtained of “typical” or “representative” samples of light, medium and heavy smog. These show the expected depletion of more reactive hydrocarbons in a much more convincing way than before. By comparing these distributions with composition in unreacted samples and by making use of data from bottle irradiations, it was possible to estimate the contribution of the various hydrocarbons in terms of “amount reacted.” The amounts of higher hydrocarbons present and reacted were also estimated from gasoline composition.     

Fluorocarbons in the Los Angeles Basin

Ambient air concentrations of fluorocarbon 11 (fluorotrichloromethane) and fluoro-carbon 12 (dichlorodifluoromethane) have been measured using a gas chro-matograph equipped with a pulsed, electron capture detector. Air samples taken on a moderately smoggy day in July 1970, at several locations near Los Angeles gave average readings of fluorocarbon 12, 0.7 ppb and fluorocarbon 11, 0.56 ppb. These readings were contrasted with those taken in early February 1973 when the air was clear and marked with turbulence due to several seasonal rain storms. The readings of both fluorocarbon 1 1 and 12 averaged about 25% less during clear weather than those taken during moderate smog. The effects of weather conditions on the concentration were also dramatically pointed out by the February samples, in that as much as a tenfold change in concentrations of both fluorocarbons from location to location and from day to day at the same location was observed. A concentration versus altitude study clearly revealed that fluorocarbons are trapped by an inversion layer. Examination of air samples taken in the vicinity of factories known to be users of fairly large quantities of fluorocarbons revealed in part how large users contribute to the atmospheric concentrations of fluorocarbons. A comparison of fluorocarbon levels in homes and public buildings with ambient outside air levels revealed that the concentrations in some homes and buildings may be as much as several thousand times as high as levels in outside air. Inside the homes and public buildings, levels were as high as one-half of a part per million. Long term photolysis studies in simulated sunlight of both fluorocarbons 11 and 12 in ambient air samples and in air samples with 1 ppm of hydrocarbon and 1 ppm of nitrogen oxides revealed that the two fluorocarbons are photochemically stable even when photolyzed for several weeks.