Toxicity of the herbicides 2,4-D, DEF, propanil and trifluralin to the Dungeness crab, Cancer magister.

Lethal and sublethal responses to the herbicides 2,4-D, DEF, propanil, and trifluralin of various life history stages of the Dungeness crab, Cancer magister, were examined to estimate maximum acceptable toxicant concentrations (MATC) of each compound for this species. Zoeae were found, in long term tests, to be the most sensitive stage. Based on the experiments with this stage, MATCs were concluded to be greater than 0.95, less than 6.9 microgram/L for DEF, greater than or equal to 26, less than 220 microgram/L for trifluralin, greater than or equal to 1,700 microgram/L for propanil, and less than 1,000 microgram/L for the free acid form of 2,4-D.

Photoelectron microscopy: a new approach to mapping organic and biological surfaces.

A general method of imaging organic and biological surfaces based on the photoelectric effect is reported. For the experiments, a photoelectron emission microscope was constructed. It is an ultrahigh vacuum instrument using electrostatic electron lenses, microchannel plate image intensifier, cold stage, hydrogen excitation source, and magnesium fluoride optics. The organic surfaces examined were grid patterns of acridine orange, fluorescein, and benzo(a)pyrene on a Butvar surface. A biological sample, sectioned rat epididymis, was also imaged by the new photoelectron microscope. Good contrast was obtained in these initial low magnification experiments. These data demonstrate the feasibility of mapping biological surfaces according to differences in ionization potentials of exposed molecules. A number of technical difficulties, such as the intensity of the excitation source, must be solved before high resolution experiments are practical. However, it is probable that this approach can be useful, even at low magnifications, in determination of the properties of organic and biological surfaces.