In Siena, over a period of 3 yr, atmospheric dust was collected by means of impaction and electrostatic precipitation. The radioactivity of the dust collected was analyzed and analysis was made of the particle size distribution. The relations of particle sizes and associated radioactivity are given and the effect of humidity is discussed.

The absorption of I3'Cs by the Lemma minor was measured in relation to the concentration of the radioisotope in water; the temperature, pH, and luminosity were kept under control. A method for the analysis of the results is illustrated. When applied to the present case, this method evidences the influence on the absorption of the potassiumcesium change, due to chemical affinity, of the natural growth of the organism's colony and of the light effect. The concentration factors have been determined for the above mentioned processes.

In view of the future development of the applications of nuclear energy and the possibility ofsea contamination, it was thought worth while to carry out a systematic study ofthe sorption of the radioelements by marine organisms.In the present work the sorption and the concentration factors of BOSr and 137Cs in Mytilus galloprovincialis are studied Examining the WSr data, it is verified that the equilibrium is maintained after 120 hr, and the concentration factor is 3.6 based on fresh weight (after centrifugation) and 98.3 based on ash weight.In the case of lS7Cs the equilibrium is reached after about 100 hr and the concentration factor, if based on fresh weight (at llO"C), varies from 4.3 for adult organisms to 6.4 for young organism; whereas, if based on ash weight, it varies from 117 for adult organisms to 175 for young organisms.RBsuxnB-En raison des futurs dkveloppements des applications de l'tnergie nucltaire et de la possibilitk de contamination de la mer, on a pensk qu'il serait utile d'ktudier systkmatiquement l'absorption des radiotlkments par les organismes marins. Cet article ttudie l'absorption et les facteurs de concentration du 90Sr et du 137Cs dans le Mytilus galloprovincialis.En ce qui concerne le BOSr on a obtenu l'tquilibre au bout de 120 hr et on a vtrifit que le facteur de concentration est de 3,6 quand il est calculk i partir du poi& de l'tchantillon frais (aprts la centrifugation) et de 98,3 quand il est calcult B partir du poids des cendres. En cce qui concerne le 13'Cs l'tquilibre est atteint au bout de 100 hr environ. Le facteur de concentration bask sur le poids de l'tchantillon frais ( B llO"C), varie de 4,3 pour organismes adultes et 6,4 pour organismes jeunes tandis que le mCme facteur bast sur le poids des cendres varie de 1 17 pour organismes adultes a 175 pour les organismes jeunes.

No abstract

Musca domestica was tagged at each stage of development-larva, pupa and imago-by means of three solutions of I3'Cs of different concentrations. Specific activity was studied throughout the organisms' life-cycle and into the ensuing generation. At each determination of specific activity, the concentration factor was studied in relation to the Contaminated matter. The biological half-life of lS7Cs is calculated. The degree of contamination transmitted to the exposed surfaces by the contaminated organisms was also studied.