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An inter-comparison exercise was performed between two laboratories on mineralized moss samples. Ten samples, together with three certified reference materials (CRM 61, CRM 62 and CRM 482) and five blanks were mineralized independently in the two laboratories and then analysed by both with different techniques (AAS, ICP-MS, and INAA). The elements analyzed were: Cd, Cr, Cu, Fe, Ni, and Pb. Accuracy tests showed that, for AAS, the relative standard deviations for five repetitions of the same sample were between 0.2 I for Cd and 2.9 % for Cr and that the concentration values found for reference materials were within one standard deviation from the certified values, with the exception of Cr and Cd for CRM 482. The statistical analysis was performed first with a simple linear regression and a Student t-test taking into account the possible influence of the mineralization procedure and ofthe analytical technique, in order to evaluate their reliability. The results showed that more than 78 % of the regressions had a correlation coefficient higher than 0.750, and that 83 % of the slopes were not different from ogre with a level of significance of 0.01. Afterwards, the precision of the measurements were evaluated using maximum likelihood; the normalized errors showed that 1CP-MS had a better performance on most of the elements analysed (with the exception of Fe) aril that both the mineralization procedures gave satisfactory results. The two laboratories were then found to produce reliable results. [ABSTRACT FROM AUTHOR]

In the Mekong River delta and its associated coastal zone trace elements concentrations (Cd, Cu, Ni and Pb) were measured in the dissolved phase (DP) during dry (March 1997) and wet (October 1997) seasons. As, Co, Cr, Ni, Pb, and Al were also measured in suspended matter (SM) and total and organic carbon, trace elements (Cd, Cr, Cu, Hg, Mn, Ni, Pb, Zn) and macro elements in superficial sediments (S). Trace metal concentrations in DP and SM during the contrasting hydrological conditions were generally found within the range observed for uncontaminated environment. The average DP concentrations (nM) in the river for March and October are: Cd 0.03 and 0.09, Cu 15 and 14, Ni 7.8 and 8.4, Pb 0.51 and 0.50, respectively. In general there is no significant difference between the concentrations observed during dry and wet season. The evolution of the DP trace metal concentration in the surface water within the salinity gradient suggests no noticeable exchange between the particulate and dissolved phase. This result is in good agreement with those observed in most plume structures studied so far. The average concentrations in the SM (microg/g) (March, October) at the river end-member are: As (24; 11), Co (17; 9), Cr (49; 29), Ni (32; 18), Pb (42; 19) and Al (113,000; 67,000), respectively. All trace elements show higher concentrations in March than in October, with an average increase of two times. This is essentially related to grain size effect since smaller particles were supplied during dry season. These differences are not reflected in the mixing zone, which integrates the seasonal variations. The concentration of major elements (C total, C organic, Si, Al, Ca, K, Fe, Mg, Ti), trace elements (Pb, Zn, Cu, Ni, Mn, Cr, Cd, Hg) in superficial sediments, show similar values during the two seasons and does not show any important variation with depth, indicating either a very fast sedimentation rate and/or the absence of any significant contamination.

An inter-comparison exercise was performed between two laboratories on mineralised moss samples. Ten samples, together with three certified reference materials (CRM 61, CRM 62 and CRM 482) and five blanks were mineralised independently in the two laboratories and then analysed by both with different techniques (AAS, ICP-MS, and INAA). The elements analysed were: Cd, Cr, Cu, Fe, Ni, and Pb. Accuracy tests showed that, for AAS, the relative standard deviations for five repetitions of the same sample were between 0.2% for Cd and 2.9 % for Cr and that the concentration values found reference materials were withn one standard deviation from the certified values, with the exception of Cr and Cd for CRM 482. The statistical analysis was performed first with a simple linear regression and a Student t-test taking into account the possible influence of the mineralisation procedure and of the analytical technique, in order to evaluate their reliability. The results showed that more than 78% of the regressions had a correlation coefficient higher than 0.750, and that 83% of the slopes were not different from one with a level of significance of 0.01. Afterwards, the precision of the measurements were evaluated using maximum likelihood; the normalised errors showed that ICP-MS had a better performance on most of the elements analysed (with the exception of Fe) and that both the mineralisation procedures gave satisfactory results. The two laboratories were then found to produce reliable results.