Standardized particle size for monitoring, inventory, and assessment of metals and other trace elements in sediments: < 20 mu m or < 2 mu m?

Despite the manifold factors that determine the composition of a river sedi ment (e.g., geology, soil type, rural or highly industrialized and densely populated, as well as forested areas, concentration of carbonates and organ ic matter), the linear regressions between the 9 metals determined in the f ractions <2 mum and < 20 mum have high coefficients (R-2 after Pearson) for Cr and Cu (both 0.94), followed by Pb (0.90), Cd (0.82), Zn (0.81), Ni (0. 76), and Mn (0.72). Low and very low coefficients are found for Hg (0.51) a nd Fe (0.22). In addition, the histograms of the metal ratios <2 mum: < 20 mum (i.e. the slope of a linear regression) show that - with the exception of Cd (1.47) - all median ratios of the other metals fall within a narrow r ange (1.24-1.35). Both "fine" (<2 mum and < 20 mum) fractions are able to fulfil the requirem ents for monitoring, inventory, and assessment of metals in sediments. Pref erence should be given to the rapid, simple, and economic < 20 mum separati on by sieving; this fraction corresponds fairly closely to the former suspe nded load of a riverine transport.