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In order to evaluate the possible use of hydroxyapatite (HA) as a soil additive for the in situ remediation of metal contaminated soils, the immobilizing capacity of this product was investigated. Three different concentrations of HA (0.5%, 1%, and 5% by weight (w/w)) were applied to a metal (Zn, Pb, Cu, Cd) and As contaminated soil originating from an old zinc smelter site in Belgium. After a three weeks equilibration period, exchangeable metal concentrations of the soils weredetermined using 0.1 M Ca(NO3)2 extraction. Test plants (Zea mays cv. Volga and Phaseolus vulgaris cv. Limburgse vroege) were grown on all soils. Growth parameters were determined and mineral analysis (Cu, Zn, Pb, Cd, Ni, Mn, Mg, Ca, K, As and P) of plants was performed. Exchangeable metal contents in soil decreased withincreasing HA application. Plant growth was partly restored on the 0.5% and 1% HA treated soils. However, at the 5% HA application rate growth was inhibited again. Plant mineral analysis showed that concentrations of 'toxic' metals in the leaves of the test plants decreased after HA application. However, the uptake of essential trace elementsalso decreased and probably led to Mn-deficiency in maize. In bean, addition of 0.5% and 1% HA resulted in a gradual decrease of metal uptake. At the 5% application level an increase of Zn, Cu, and Ni uptake was observed compared to the 0.5% and 1% application rate. In contrast to metal uptake, As uptake was found to increase after HA treatment. The increased PO42- concentration in the soil may be responsible for this. These results illustrate that HA application for the remediation of metal contaminated soils can be effective, but is not self evident. Strong immobilization of essential nutrients may lead to deficiency problems and mobilization of As may leadto an increased transfer to plants and animals and to an increased percolation of this element to the ground water. (c) 1999 Elsevier Science [ABSTRACT FROM AUTHOR]

The aim of this study was to assess thallium (Tl) uptake into the aerial parts of selected crop species grown on French soils with high Tl content of pedogeochemical origin (0.3-40 mg Tl kg-1 on a dry wt (DW) basis). Husked wheat and maize grains contained less than 4 Mu g Tl kg-1 DW, but rape shoots accumulated Tl with a shoot-soil partition coefficient (PC) > 1, and rape seeds had PC> 3. Tl content of rape seed reached 33 mg Tl kg-1 DW and higher concentrations in soil corresponded to increased concentrations in rape seeds. It is argued that parent material of the soil and pedogenesis have a considerable effect on Tl accumulation in rape seeds. These results show enhanced phytoavailability of Tl of pedogeochemicalorigin and prompt questions on the potential for food chain contamination by Tl in rape cattle cakes. [ABSTRACT FROM AUTHOR]

The thallium (Tl) content of the upper horizons of 244 French soils was determined as the first step towards the creation of a reference data bank for total Tl content of arable soils. Forty soil samples were collected in the vicinity of potential anthropogenic sources of Tl, but the remainder came from rural areas. The distribution of Tl concentrations in soils was characterized by a median value of 0.29 mg Tl kg-1 and a 90th percentile value of 1.54 mg Tl kg-1. Very high pedogeochemical contents were found (up to 55 mg Tlkg-1) but none could be attributed to obvious anthropogenic pollution. Areas of very high Tl concentration belong to an epihercynian transgression zone with a contact between a sedimentary basin and a crystalline massif. This contact is associated with stratified mineralizations (Zn, Pb, F, Sb, Ba, Tl and pyrites). High Tl concentrations were common in limestone, marl or granite derived soils, and the Tl in limestones or marls is probably concentrated in the sulfidescontained in these rocks because Tl has a high affinity to S. In granites, Tl may be in the micas and feldspars because Tl+ can replace K+ in these minerals. Silty or clay-silty soils showed the highest concentrations. These granulometric fractions contain the majority of the minerals, which are supposed to be the major hosts of Tl in soils, i.e. clay minerals, oxides and micas. Tl in thesoils was positively correlated with Ba, V, Pb, Fe, Ni, Cd, Zn, Co, As and especially Mn. A significant proportion of Tl may be in the Mnoxides: in oxidizing conditions, Tl(III) could enter the Mn oxides by sorption, or Tl(I) could replace K(I) in the oxide. [ABSTRACT FROM AUTHOR]

Preliminary results from the French ASPITET programme demonstrated that Cd background levels in agricultural soils can vary greatly (0.02--6.9 mg Cd kg{sup}-1{end}) depending on parent material and pedogenic processes (Baize, 1997). However, the total Cd content in soil is often not significantly related to the Cd concentration in edible plant parts. A field case study was undertaken across the southern part of the Yonne district, Burgundy, France. This area has various soil series with either low or high geochemical Cd content in the topsoil. Cd availability in soils sampled at 16 sites belonging to five soil series was investigated using single extractions. In addition, shoots (at stem elongation) and grains (at harvest) of field-grown wheat werecollected at the same sites and analysed for macronutrients and trace elements. Cd concentrations in grain varied from 0.015 to 0.146 mg Cd kg{sup}- 1{end} DM depending on soil characteristics, soil series,and plant mineral composition. Cd grain concentrations did not reflect total Cd content in the surface soil layer; however, they were correlated with Cd extracted by a 0.1 M calcium nitrate unbuffered solution, and to a lesser extent with either soil pH or CEC. These three parameters may be useful guides to predict Cd in wheat grain harvestedin the Yonne district. An inverse relationship was found between Cd and Cu contents in grain. The highest Cd concentrations in wheat grain occurred in plants grown on Aubues soils which had marginal Cu and Zn deficiencies in shoots. In order of Cd accumulation in wheat grain, soil series may be ranked as follows: Domerien < Carixien, Terres Noires < Sols Marron < Aubues. [ABSTRACT FROM AUTHOR]