Pascale Prudent

Total mercury concentrations in an industrialized catchment, the Thur River basin (north-eastern France): geochemical background level and contamination factors

River bottom sediments and soils were collected from the industrialized Thur River basin (north-eastern France) to assess mercury contamination. The regional geochemical background level of total mercury was evaluated to calculate mercury contamination factors (Fc) in soils and river bottom sediments. Our estimate of the mean background mercury levels in river sediments and soils, not affected by human activities, was 232 ng x g(-1) (range: 27-406 ng x g(-1)). Sediments contaminated by the effluent from a chlor-alkali plant yielded the highest contamination factors (Fc=1784). Contamination factors of surficial soils within 1 km of the industrial site range from 6.3 to 43.6. This contamination is attributed to diffuse atmospheric deposition from this local plant. However, even upstream from this industrial area elevated contamination factors were recorded for river bottom sediments (Fc=3.2 to 26.4) and for one alluvial soil profile (Fc=10). This is possibly due to past pollution resulting from waste water discharges. Mercury contamination in the different horizons of alluvial soils is not correlated with soil organic carbon content, but may be the result of occasional accidental pollution arising from the introduction of contaminated suspended particulate matter by the Thur River during periods of flooding.

Characterization of Metal Tolerance and Accumulation in Grevillea Exul VAR Exul

Grevillea exul var exul (Proteaceae), a tree species native to serpentine soils in New Caledonia, is a reported manganese accumulator. Since the metal tolerance of this species remains unknown, its growth and metal accumulation were studied for seven heavy metals under controlled conditions. Brassica juncea, a popular species for metal phytoremediation, was used as a reference. G. exul seedlings were more tolerant to Cr, Zn, Ni, and Cu than B. juncea. There were no differences in Hg, and Cd tolerance between both species. B. juncea seedlings concentrated more Cd, Hg, and Cr in their shoot than G. exul seedlings, while Ni, Zn, and Mn levels were similar for both species. Comparison then focused on tolerance at toxic doses of Ni and Mn using older individuals of both species. No growth inhibition for G. exul plants was observed, whereas the growth of B. juncea was significantly inhibited at the higher metal concentrations. Shoot Mn and Ni concentrations were again lower in G. exul plants as compared to B. juncea, suggesting a mechanism of partial Ni and Mn exclusion in G. exul. In a subsequent study, 1-year-old G. exul plants favored Ni accumulation in roots while Mn accumulated preferentially in shoots.

Effects of agricultural practices on properties and metal content in urban garden soils in a tropical metropolitan area

The appearance of agriculture in urban areas improved the health- iness of the diet of people by enabling their consumption of fresh vegetables and fruits. This study assessed the level of fertility, and the impact of the crop- ping system and of the exploitation time on the physicochemical properties and the pseudo-total and EDTA-extractable metals contents of the vegetable soils of urban garden of in Libreville (Gabon). The results indicated a low fertility of the cultivated soils. The metal contents in the open field cultured soils were generally different from the soils cultured under shelters. Except Al that could be toxic for cultivated vegetables, the soil properties and metal element con- centrations decreased significantly with time in the open field soil, while they did not vary in open shade cultured soils. The pseudo-total cadmium concen- tration was below the detection limit in all soils. Multivariate analysis showed that Al, Fe and Pb were of lithogenic origin, while Cu, Zn and Mn were of anthropogenic origin.