International audience

International audience

Competing ions strongly affect heavy metal sorption onto the solid surfaces of soil. This study evaluated competitive sorption of Cd, Cu, Ni, Pb and Zn on three soils: Calcixerollic Xerochrept, Paralithic Xerorthent and Lithic Haplumbrept. Monometal and competitive sorption isotherms were obtained at 25°C. The individual effect of ions on retention of the others was ascertained by a fractional factorial analysis design. Most of the sorption isotherms belonged to type L subtype 2 in the classification of Giles. In competitive sorption the initial linear part was shorter and the knee sharper when compared with monometal sorption isotherms. Parameters related to sorptive capacity, such as Point B, Langmuir monolayer and Freundlich distribution coefficient, were higher in monometal than in competitive sorption, and in basic soils than in acidic soil. Calcium desorbed at different points of the sorption isotherms indicated that cationic exchange with Ca was the main retention mechanism in calcareous soils. For Pb, the ratio Ca desorbed/Pb sorbed was close to one; for Cu, Ni and Zn the ratio ranged from 1.20 to 1.37, probably due to partial dissolution of calcium carbonates by hydrolytic processes during retention. On the other hand, Cd had a ratio around 0.6 reflecting another additional retention mechanism, probably surface complexation. Fractional factorial design confirmed that the presence of the cations investigated reduced the amount of the five metals retained, but the presence of Cu and Pb in the system depressed Ni, Cd and Zn sorption more than the inverse. Cation mobility was enhanced when equilibrium concentration increased and the effect was higher in Ca-saturated soils.

Non-PR | IFPRI4; 2020 | DGO

Discusses the health hazards of indoor air contaminants and includes information on their sources, the illnesses they can cause, the ways of controlling them, and other related topics.

Little is known of the impact of agricultural activity on oysters in Chesapeake Bay tributaries. As a preliminary assessment of pesticide residues in oyster tissues, this study monitored more than 60 pesticides in oysters and overlying water in two tributaries of the Chesapeake Bay. Paired water and oyster samples were collected throughout 1997 from the Patuxent and Choptank Rivers which discharge into opposite shores of the Chesapeake Bay in Maryland. In water, herbicides such as atrazine, simazine, cyanazine, and metolachlor were present throughout the year with individual water concentrations peaking as high as 430 ng/1 in the late spring and summer and subsiding in the fall. These herbicides were not detected in the oysters even when concentrations were highest in the water. Another herbicide, trifluralin, was detected throughout the year at concentrations of less than 0.6 ng/1 and 0.4 ng/g (wet weight) in water and oyster samples, respectively. Several insecticides, such as endosulfans I and II, endosulfan sulfate, chlorpyrifos, α- and γ-HCH, p,p'-DDE, o,p'-DDT, trans-nonachlor, and trans-chlordane were also measured in both oysters and water at low concentrations.