Neutron-activation analysis of the elementary composition of the marine phanerogamPosidonia oceanica from a reference area in Port Cros National Park (French Mediterranean)

The marine phanerogamPosidonia oceanica (L.) Delile was collected from a presumably unpolluted reference area in Port Cros National Park, Mediterranean Sea, in November 1985, and its elemental composition was studied by gamma spectrometry after neutron activation and by atomic-absorption spectrophotometry. Neutron-activation analysis revealed 23 elements and atomic-absorption spectrophotometry 4 others. Including all known records by other investigators, this brings the total of elementary components identified inP. oceanica up to 42: antimony, arsenic, barium, bromine, cadmium, cesium, calcium, carbon, cerium, chromium, cobalt, copper, europium, gold, hafnium, hydrogen, iodine, iron, lanthanum, lead, magnesium, manganese, mercury, molybdenum, nickel, nitrogen, phosphorus, potassium, rubidium, samarium, scandium, selenium, silver, sodium, strontium, tantalum, terbium, thorium, uranium, ytterbium, zinc, zirconium. These elements display significant differences in their distribution in the various parts of the plant (roots, rhizomes, and growing and freshly budded leaves).     

Effects of soil moisture and physical-chemical properties of organic pollutants on vapor-phase transport in the vadose zone

Vapor-phase transport of organic pollutants is one of the important pathways in the distribution and attenuation of volatile organic compounds in the vadose zone. In this study, the impact of vapor-phase partitioning and of the physical-chemical properties of organic pollutants on vapor-phase transport was assessed. An experimentally derived relationship to predict vapor sorption for a variety of soil types under varying soil moisture conditions was incorporated into the two-dimensional finite-element model, Vocwaste. The revised model was then used to simulate the transport of volatile organics. Vapor-phase partitioning in the model accounted for vapor uptake by sorption onto moist mineral surfaces as well as sorption at the liquid-solid interface and dissolution into soil water. Under dry conditions, vapor-phase sorption of volatile organic pollutants was shown to have a retarding effect on transport of organic vapors. However, for shallow, contaminated soils, volatilization was controlled by vapor diffusion, even under dry conditions where vapor-phase sorption was high. The influence of Henry's law constant and of the aqueous-phase (solid-liquid) partition coefficient for volatile organic pollutants was considered in the simulations. Volatilization of organic vapors was shown to be favored for contaminants with high Henry's law constants and low aqueous-phase partitioning coefficients. Because of the interdependence of these two physical-chemical properties, individual properties of the contaminant should not be considered in isolation in the evaluation of vapor transport.