Alberto Lopez Galindo

Trace elements in different marine sediment fractions of the Gulf of Tunis (Central Mediterranean Sea)

Abstract Over several decades, the mouth of the Mejerda River (northern Tunisia) has received large amounts of mining tailings mainly containing Pb, Zn and Ba. We have measured the concentrations of major and trace elements (Al, Ti, P, K, Mg, Na, Ca, S, Fe, Cl, V, Cr, Co, Ni, Cu, Zn, Ga, Br, Rb, Sr, Y, Zr, Nb, I, Ba and Pb) in three different fractions of 45 surficial sediments using wavelength dispersive X-ray fluorescence. The size distribution of fine particles (<2 μm, 2–20 μm, 20–63 μm) revealed that clay and silt compounds were predominant (75–95%) in the deeper estuarine region. These condensed clay phases were mainly dioctahedral smectite, illite and kaolinite. The total organic carbon (TOC) concentration varies from 0.08 to 1.37 %. The C:N ratio varies from 1 to 17 indicating that the organic matter has a mixed marine and continental origin principal component analysis was used to determine the associations of trace elements with organic and/or inorganic phases of the sediment fractions. The correlations of Fe2O3, MnO2 and P2O5 with trace elements showed that amorphous Fe and Mn were the most active scavengers of dissolved metals from the Mejerda River. Cluster analysis clearly distinguished local trace element accumulations according to grain size fractions (< 2 μm and 2–20 μm) near the Ghar el Melh Lagoon and th River.

Adsorption of nutrients on natural Spanish clays for enriching seed coatings

Coating seeds with nutrients remains an effective way of supplying fertilizers for the establishment and development of seedlings. Clays have been proposed, among other coating materials, because of their low price and favorable properties. Nine natural clays (R1-R9), collected in the eastern Andalusian region (south of Spain), were evaluated for the retention of P, Mn and Zn, with the ultimate goal of designing enriched seed coatings. The clays were similar in composition, with high Ca content. Various equations were used for the fitting of kinetic and adsorption data. Adsorption rates of Mn were higher with R2, R6 was the clay in which Zn exhibited the most rapid kinetics, while P was adsorbed on R7 at the highest rate. Slower adsorption rates corresponded in all cases to Zn. The pseudo-second order model adequately explained the experimental kinetic data of Mn, Zn and P on the different sorbents. Adsorption isotherms indicated that the maximum adsorption capacity on the analyzed clays was ranged as Zn > Mn > > P. Clays were able to retain nutrients for long periods of time (up to 96 days) and desorption was inversely related with adsorption. Simultaneous addition on selected clays of Zn and Mn led to significantly higher nutrient desorption. The co-presence in clays of various compounds (nutrients and/or pesticides) affected their release, so this aspect deserves special attention in coating design. Results obtained suggest the feasibility of using these clay materials enriched with nutrients for seed coating.