A method for determining formaldehyde mixing ratios in the atmosphere is presented. Formaldehyde is stripped from ca. 2 m3 of air into an aqueous 2,4-dinitrophenylhydrazine (2,4-DNPH) solution contained in a high-efficiency, highvolume glass sampler. The resulting reaction product, CH20-2,4-DNPH, is separated and determined by HPLC. Possible interference with the reaction by other components present in air is investigated. The lower detection limit of the technique is 0.01 ppbv. At formaldehyde mixing ratios of the order of 0.1 ppbv, the precision of the technique is 10%. The sampler is battery powered and portable and can be easily used to sample atmospheric formaldehyde in remote areas. Typical data from a sampling program at the Irish west coast and from Julich, West Germany, are presented.

Extended screening tests on the cercaricidal activity of various plants from northeast Brazil have shown that the extracts of the leaves and fruits of Piper marginatum, Protium heptaphyllum, and Capsicum annuum show a remarkable effect on the cercaria of Schistosoma mansoni. In the case of the oils of Piper marginatum and Capsicum annuum, 90--96% of the cercaria of Schistosoma mansoni were killed within 15 min. According to the NMR spectra, the active principles of the extracts seem to be water-soluble unsaturated compounds from the oils or their hydrolysis products. Natural substances provide an attractive alternative for preventive actions against schistosomiasis, as the perturbation of the ecological equilibrium of natural waters can be avoided in this manner.

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